Canon EOS Beginners FAQ
Copyright © 2002-2007 NK Guy
Version 0.9.6. 6 January, 2007.
Part III - Lenses.
Choosing a lens and basic lens categories.
Why doesnt my camera just come with a lens? Isnt that kind of cheap?
No. Its actually a good thing. First of all, the whole point of a camera with interchangeable lenses is you can attach whatever lens you need. Unlike a simple point and shoot with its non-removable lens you arent limited to whatever the manufacturer builds into the camera. Second, everyone has different needs and budgets. So its usually desirable not to include a lens so you can choose the lens or lenses which are right for you, not some generic lens. Third, what if you were to buy another camera? Then you would have two of the same lenses.
Having said that, Canon do sell many EOS cameras bundled with included lenses. Such lenses are called kit lenses, but frankly not all kit lenses are of a particularly high quality. Youre often best off buying the camera body which suits your needs and finding a good lens to match it.
What are wide-angle, normal and telephoto lenses?
Weve all had the experience before. Youre trying to take a photograph of some friends, but you just cant fit everybody into the picture. You step backwards further, but theres a wall or cliff or something, and it just isnt going to work, so you tell your friends to squeeze in closer. Or you see a bird flying by in the distance, you grab your camera, and you end up with a big photograph of sky with a disappointingly tiny little dot in the middle of the frame.
In each case the field of view provided by the lens isnt appropriate for your subject matter. In the first instance your lens is not wide enough to take in the whole scene, and in the second your lens isnt long enough. There are three rough categories of lenses when it comes to how much of a scene they can take in, and the field of view of each type is defined by an optical property known as the focal length of the lens (a property explained later in this document).
Note one area of potential confusion - there are different measurements expressed here in millimetres, but which refer to two different physical properties. In the case of 35mm film cameras, were talking about the width of the film material. But in the case of, say, an 80mm lens, were talking about its focal length. You can thus put a 28mm lens on a 35mm camera - the measurements are about different things.
These are just broad categories, of course, and there are big variations in each one. You can get an inexpensive 28mm lens, for example, which is only modestly wide. Or you can get a crazy expensive 14mm lens which can take in a huge area of a scene - perfect for shots of ultra-dramatic skies. Similarly you could put an 85mm lens on your camera for portrait photography, or you could sell your car and buy a huge 600mm lens that requires a large suitcase for transportation but which lets you take a closeup of a birds face from a huge distance away.
Whats the difference between a zoom lens and a fixed focal length (prime) lens?
A prime lens is a lens in which the field of view (focal length) cannot be adjusted. The only way to take in more or less of the scene is to walk closer to or further from the subject. (sometimes called zoom with your feet, though this is technically inaccurate since changing camera position is not the same thing as adjusting the focal length) Or you have to carry a selection of lenses of different focal lengths with you and swap them out as required.
A zoom lens is a lens in which the field of view can be adjusted. If you cant fit in all your friends in the picture, for example, you could just rotate the zoom ring on the lens until theyre all in there. Or if that bird is too far away you could rotate it the other way to zoom in closer.
Up until the late 1980s prime lenses were the most common lens sold, because from an optical design standpoint its much easier to design a high quality prime lens that can take nice sharp photographs than a decent quality zoom lens. But a prime is also obviously a lot less convenient, since you have to move around more to fit stuff in. So by the late 80s zoom lenses became more and more popular. Today hardly any low-cost lenses are prime lenses, because everybody wants zooms.
So why buy a prime lens at all? Well, for the same reason as ever - prime lenses are easier to build and offer fewer compromises in design. If you want a really sharp crisp lens, then a good prime will offer sharper pictures than most zooms. Or if you want a lens that can let in lots of light and thus can be used for low-light photography then youll probably want a prime, since its much harder to build a fast (lets in lots of light) zoom lens. And some crusty old photographers also argue that using prime lenses is very important for novice photographers since it forces them to learn about the importance of focal lengths and perspective.
Lens construction is thus always about tradeoffs. You may want a lens thats small, lightweight, has zoom capabilities, lets in lots of light, is really sharp, has high contrast, doesnt distort the image and is cheap. But in real life you can only get some of those properties - its impossible to get all of them, sadly.
Most amateurs on a budget choose the flexibility of low-cost zoom lenses over picture quality as their compromise. Many advanced amateurs choose the higher picture quality of affordable primes and deal with the inconvenience as theirs. And many professionals buy high quality zooms that weigh a ton and cost piles of money as theirs.
Note one common misconception - a lot of people think zoom lenses are used for taking photos of things far away. Thats actually a better description of a telephoto lens, as described above.
Which lens should I buy for my camera?
As with buying a camera there are a lot of things to consider, so this question really cant be asked without asking many more questions first. Here are some of them:
What exactly are you going to be photographing?
Your photographic goals and objectives essentially inform all of the other decisions. Will you being shooting landscapes? Portraits? Your kids or pets? Flowers? Wild birds? Sports? Architecture? Will you be doing travel photography? Will you be hiking with your gear? These sorts of questions are critical to ask yourself first.
How much money do you want to spend?
You can spend huge amounts of money on lenses, so determining your budget, as with cameras, is pretty important.
Do you want to buy a used or a new lens?
The same questions apply as when purchasing a new or used camera.
Do you want a prime (fixed focal length) or a zoom (variable focal length) lens?
Prime lenses generally afford higher optical quality than zooms, except in the case of really expensive pro zoom lenses. However prime lenses mean you have to walk around more - you cant simply adjust the zoom setting to get the framing you need.
What focal length or focal length range do you want to cover?
Id sit down with your photos and think about what focal lengths you tend to use most and where there are gaps. Maybe you want an extreme wide angle, for example. If so theres no point getting another telephoto.
Do you need a fast lens?
Do you want to do low-light photography without a tripod or flash? Do you want to do portrait photos while blurring the background? These applications call for a faster lens which can let in more light.
Do you want to buy Canon-built or third party lenses?
Third party makers build many great lenses, but many are also really poor - you have to do some research. And others have compatibility problems with existing cameras or may have future compatibility problems. Are the price savings worth it for the specific lens youre interested in?
Do you care about the user interface and build quality?
A lens may be slow to focus or inconvenient to use but offers higher optical quality than another lens with a faster motor and a better designed UI. Ring USM motors are fast, silent and offer full-time manual override, but lenses containing such motors tend to cost more than slower, noisier non-FTM arc-form (AFD) motors.
What aspect of optical quality is important to you?
Obviously sharpness and contrast are pretty important to most people, but what about distortion? Many consumer zooms have a lot of distortion, making them unsuitable for architectural photography. They also tend to be more vulnerable to flare (lowering contrast or resulting in bright spots on the picture if a bright light like the sun is in or near the frame) and tend to have very slow maximum apertures.
Which lens should I buy for my EOS digital camera?
There are two things that are important to keep in mind when shopping for lenses for an EOS digital camera, such as the EOS 10D, rather than an EOS film camera.
First, EOS digitals are still not as cheap as film cameras, so dont just try to find the cheapest lens you can. And if youre going to be shelling out this much money for the camera body, buying the cheapest lens you can find is not merely false economy, its downright foolish, if you ask me.
Its like spending massive amounts of money on a high-end CD player and amplifier and then plugging them into a pair of toy loudspeakers. Just as the final sound of your music will be hobbled by the toy loudspeakers the final quality of your pictures will be hobbled by a cheap lens. So avoid lenses in the cheapie category (see below).
Second, with the exception of the cropping factor the selection criteria for buying a lens for a digital camera really dont differ much from the criteria for buying a lens for a film camera. What type of photography do you want to do? Do you need a wide angle for landscapes? A fast-focussing telephoto for sports? A sharp and short telephoto for portraits? How much weight do you want to carry around? These questions are the same regardless of whether you want to shoot film or digital - check the list above.
But as noted, there is one major difference to keep in mind with most digital EOS cameras - the cropping factor, also known as the focal length multiplier. With the exception of the EOS 1Ds, 1Ds mark II and 5D, which have full-size image sensors equivalent in size to a 35mm EOS film camera, most current EOS digital cameras use image sensors smaller than a 35mm film frame. If your camera has a cropping factor of 1.6x it means that, say, a lens with a 50mm focal length will suddenly behave rather like a lens with an 80mm focal length. The focal length of the lens does not change, but its apparent effect does. (since the image sensor is smaller, think of it as simply snipping off all four sides with a pair of scissors, resulting in a smaller picture, and then enlarging the picture on a photocopier)
This issue has two nice advantages. First, you can buy a cheap 50mm lens and use it as a very nice portrait lens. Second, you can attach a telephoto to your camera and itll behave like a much longer telephoto - youll have much more reach. The drawback, of course, is that wide angle pictures are harder to achieve as you need much wider lenses for such photos. This can be a significant problem for many people.
So with such digital cameras you will probably want to get a lens thats a bit wider than you would if you were buying for a 35mm film camera. If you use a 28-105mm lens on your 35mm camera, for example, you might get a 24-85mm lens instead.
The one question related to this is whether the EF-S 18-55 lens (see next section) included with the EOS 300D/Digital Rebel/Kiss Digital kit is worth it. The consensus is that its definitely worth the small increase in price over the body only. The EF-S 18-55 is no L series lens by a long shot, but it offers surprisingly decent optical quality for the incredibly low price, and its the only affordable way to get down to moderately wide angles (roughly the same as a 29mm lens on a 35mm film camera) on the 300D.
One final issue with digital is that some newer lenses have coatings which work a bit better with digital image sensors than those used on older lenses. Generally speaking this is a fairly subtle issue, advertising notwithstanding.
What is an EF-S lens?
From essentially the introduction of the EOS camera system in 1987 through to 2003 Canon standardized on a single lens mount system for all of their SLR cameras - the EF (electrofocus) lens mount. So throughout this time there was no possible source of confusion, since all EF lenses made by Canon and other lensmakers will physically fit all Canon EOS cameras.
However, in 2003 Canon introduced a new digital camera, the consumer-oriented EOS 300D/Digital Rebel/Kiss Digital camera, which sported a new lens mount design dubbed EF-S. All consumer to midrange digital EOS cameras released since have been both EF and EF-S compatible. For reasons explained in a moment, no film camera has ever been EF-S compatible.
So its important to remember that digital camera bodies with EF-S lens mounts are totally compatible with all regular EF lenses. However an EF-S lens can fit only EF-S compatible cameras and no others. (unless the lens is altered - see the section on hacking below).
EF-S bodies have small mirror boxes - roughly 2/3 the size of a regular EOS camera (also known as a 1.6x cropping factor) - because they use image sensors which are smaller in area than 35mm film. They, and APS cameras which similarly used small imaging areas, are thus often called subframe cameras. Cameras which use 35mm film or which use large sensors that are the same size as a frame of 35mm film are commonly called full frame cameras these days.
EF-S cameras thus support lenses with a shorter back focus distance than EF lenses, because the mirror swings further back. This is where the S comes from - EF-S lenses have shorter back focus distances. (ie: the back part of the lens can get physically closer to the image sensor since the mirror is smaller) Having a shorter back focus distance allows Canon to produce cheaper wide-angle lenses that work with the smaller image format of a subframe digital SLR, since its optically very challenging to create a wide angle lens with a long back focus distance.
Canon have a small but growing series of EF-S lenses available, ranging from inexpensive kit lenses to very good high-quality lenses with image stabilization. Theres even a very interesting 60mm macro lens with an EF-S mount. The super wide angle EF-S 10-22mm 3.5-4.5 USM (roughly 16-35mm coverage if it were full frame) is particularly well regarded, as is the EF-S 17-55 2.8 IS USM, which is an L lens in all but build quality and name.
The main issue to be concerned about with EF-S is the future value of the lenses. Right now full-frame image sensors are extremely expensive to make, which is why nearly all digital SLRs out there have image sensors smaller than that of a frame of 35mm film. But in the future its likely that prices on such sensors will drop, at which time full-frame digital SLRs will become more affordable and thus EF-S lenses will no longer be of use except on pre-existing cameras. The two questions are - how long will this take and will you be able to get good use of your investment in EF-S lenses before this occurs? The first nobody knows the answer to, and the second can only be answered by you. For the time being it seems likely that itll be some years before affordable full-frame sensors are ubiquitous, so EF-S lenses arent necessarily a bad idea, assuming you arent planning on upgrading to full-frame as soon as you can.
Can my camera take EF-S lenses?
Any Canon EOS camera with a red dot on the lens mount can take EF lenses. Any Canon EOS camera with both a red dot and a white square on the lens mount can take both EF lenses and EF-S lenses.
What you see is what you get
This whole discussion about focal lengths and EF versus EF-S can be very confusing if youre a beginner. The key thing to remember if youre just starting out is what you see is what you get. When you look through the viewfinder youre going to see pretty well exactly what will be in the photograph - minus a tiny little strip along each edge on consumer cameras. So theres no need to worry about mathematical calculations and whatnot to figure out what will be in your picture and what wont.
The only time the whole cropping factor is really an issue is when youre comparing how much of a scene (coverage angle) is taken in by an EF lens on a full-frame camera, compared to an EF lens on a cropped body, or compared to an EF-S lens on an EF-S compatible camera. For guidance on this, take a look at my Complete EOS Lookup Page. It allows you to compare multiple lenses to see how much of a scene each lens can take in when used on cropped or full frame bodies.
Distinguishing EF from EF-S
Regular EF bodies and lenses use raised red dots for aligning lens and body. EF-S bodies have a white square as well, which must be lined up to the white square on EF-S lenses. Interestingly enough, EF-S lenses also have rubber rings around the end which press up against the interior of the camera body. This is not as sophisticated as the weather seals used in L series lenses, but presumably helps reduce dust levels inside the camera slightly. Also, according to Canon, this ring minimises damage if you were to try and mount an EF-S lens on a EF-only camera.
Full frame equivalent
Youll sometimes see phrases such as full frame equivalent or 35mm equivalent in conjunction with lenses designed for subframe sensors, such as EF-S lenses. Properly speaking these are not equivalent values for a variety of technical reasons, but they are nonetheless useful points of reference. For instance, a 60mm EF-S lens has the same field of view as a 96mm lens on a 35mm film camera. So sometimes 60mm EF-S lenses are said to have a full-frame equivalent field of view of 96mm.
EF-S lenses and film cameras
No EOS 35mm film camera has or is ever going to use an imaging area smaller than 36x24mm, so no EOS 35mm film camera will ever be able to support EF-S lenses. Even if you were to attach one somehow the mirror would collide with the back of the lens when it flipped up, and the lens would vignette severely because EF-S lenses cant image an image circle as large as 35mm film. In theory Canon might be able to build an APS camera with support for EF-S lenses, since APS film uses a surface area smaller than that of 35mm film, but since APS is a commercially moribund format that isnt ever going to happen. So the only cameras youll ever see with EF-S lens mounts are going to be digital.
Hacking EF-S lenses
While EF-S lenses are not designed to fit EF-only cameras, it is possible to saw off or, in some cases, unscrew the back of an EF-S lens and attach the lens to any EOS camera. The problem is that if you put a modified EF-S lens on an EOS camera with a standard sized mirror box then the mirror will flip up and smash into the lens when you try to take a photo. So modified EF-S lenses will only work with older EOS digital cameras with cropping factors of 1.6x that predate the EF-S system: namely the EOS D30, D60 and 10D. Even then there are risks. For example, at its widest position the EF-S 10-22mm lens collides with the mirror in non-EF-S compatible cameras, even those with small mirror boxes. (for this reason its unwise to use a modified EF-S lens on a 1.3x digital camera such as the 1D) Messing around in this fashion is fun - Ive done it myself and it works well - but obviously invalidates your Canon warranty and runs the risk of breaking something.
What are all these numbers printed on my lens?
Lenses have bits of text printed on the barrel or around the front element which convey a lot of important information about their properties. Be really careful when shopping for lenses. Two lenses may have very similar-looking names, but may actually be completely different one from the other.
Here are two examples. Note that all the technical terms used here are described later on in this FAQ.
CANON LENS EF 28-80mm 1:3.5-5.6. Ø58mm.
EF means that the lens is of the Canon EF type. EF lenses fit Canon EOS cameras and virtually no others.
28-80mm refers to the focal length of the lens. In this case there are two values since the lens is a zoom lens which can go from 28mm at its widest to 80mm at its longest. These numeric values in millimetres essentially indicate the coverage area of the lens.
1:3.5-5.6 refers to the widest aperture of which the lens is capable. The 1: is there since f/stops are, technically speaking, ratios. Since the lens is a zoom there are two aperture values - f/3.5 and f/5.6. This particular lens is an inexpensive amateur lens which can be opened up to f/3.5 at the widest end (28mm) but only f/5.6 at the longest end (80mm). This means its a fairly slow lens - it cant let in much light, even when its aperture diaphragm is fully open.
Note that the autofocus motor type is not indicated, which means that the lens uses either an AFD (arc-form drive) or micromotor drive. Both types are slow and noisy compared to ultrasonic (USM) motors.
Ø58mm refers to the filter ring diameter. In other words, screw-on filters 58mm in diameter will fit this lens.
CANON LENS EF 200mm 1:2.8L II USM. Ø72mm.
EF means that the lens is a Canon EF lens for EOS cameras.
200mm refers to the focal length. Since only one value is indicated, this lens is a prime lens (ie: a lens with a fixed focal length).
1:2.8 refers to the widest aperture of which the lens is capable. f/2.8 is reasonably wide, especially for a 200mm telephoto lens, and so this is considered a fast lens.
L indicates that the lens is an L or luxury series Canon lens. Such lenses are generally the best that Canon manufacture. They are marked with a characteristic red stripe around the end of the lens barrel.
II indicates that this is the second version of this lens with these particular numerical specifications that Canon have made.
USM refers to the autofocus motor type used by the lens. In this case it uses an ultrasonic motor - see below. Non-L USM lenses are marked with a characteristic gold stripe around the end of the lens barrel. L lenses usually have USM motors, but have a red stripe instead (ie: the red stripe takes priority and you dont see lenses with two stripes).
Ø72mm refers to the filter ring diameter. In other words, screw-on filters 72mm in diameter will fit this lens, making it a fairly large lens.
What is a Canon L-series lens and why is it a big deal?
Canon sell a number of lenses in a special series they refer to as L for luxury. These are their most expensive and highest-quality lenses, and are readily identifiable by the red stripe painted around the end of the barrel.
L series lenses offer higher optical quality than their non-L equivalents, and have an important technical aspect in common. At least one element in every L lens is either made of fluorite crystal rather than glass, is a ground aspheric lens element (not a moulded/replicated aspheric lens as used in less expensive lenses) or is made from ultra-low dispersion glass. Most L series lenses are also sturdily built - many are encased in metal barrels and are weatherproofed - and most are very fast lenses for their focal lengths. Nearly all telephoto L series lenses are also off-white rather than black.
These lenses are, therefore, marketed as professional camera lenses and are usually priced out of the range of most consumers. They can be used to take great photographs, but the cost, weight and size of these lenses are the tradeoffs.
Of course, a lens doesnt have to be an L series lens to take good pictures. Many EOS lenses offer excellent optical quality - they just dont need and thus dont have exotic fluorite lens elements and so on. Many of Canons prime lenses in the 35mm to 135mm range fit in this category - see below. And some recent EF-S lenses offer near-L image quality but lack the red ring and the tough build quality of contemporary L series lenses.
Note also that the presence of a red ring around the end of a lens barrel only indicates an L series lens if its actually made by Canon. Some other makers happily paint red stripes around the end of their lenses too, but this in no way guarantees that the lens meets the quality standard of a Canon L lens.
What other general categories of Canon EOS-compatible lenses are there?
In addition to the aforementioned L series lenses most other Canon EF lenses fall into a number of broad categories. Note, however, that these are not official Canon-named categories. As far as Canon is concerned, EF lenses come in two categories - L and all the rest. Nonetheless these informal categories are useful to keep in mind when lens shopping.
Category 1 - consumer lenses.
At the bottom of the consumer line are the cheapies - ultra-low cost, low-quality, slow lenses with plastic mounts and no distance scales. Most of the kit lenses - 28-80 and 28-90 lenses with typical aperture ranges of 4.0 to 5.6 - fit into this category. These lenses are built to be sold as inexpensively as possible and dont have very good optical quality. The only exception to this basic rule is the 50mm 1.8 II - plastic lens mount - which has excellent optical quality despite its cheap build quality, because it isnt a zoom lens like all the others. The cheapies are easily recognizable by their all-plastic construction and straight, parallel-sided lens barrels. Most of the late-model cheapies are identified by the silver (chrome) ring around the end.
Am I being a huge snob by calling them cheapies? Maybe, but the point is that Canon optimize these lenses for cheapness. They want products to sell in massive numbers in shopping mall/high street camera shops and department stores. This market does not, it seems, place a great deal of value on image quality - cheap prices for impulse buys are everything. Thats great for Canons balance sheet, but frankly, if Im going to be dealing with the hassle of carrying around an SLR camera I want at least half-decent optical quality for the attached lens. Otherwise I think its a lot easier just to carry around a cheap lightweight point and shoot camera.
Category 2 - midrange zooms.
In the midrange are better lenses with improved optics, sturdier build quality, metal mounts and distance scales. These often have ring USM motors. The 24-85 3.5-4.5 USM, 28-105 3.5-4.5 USM and 100-300 4.5-5.6 USM are typical examples. Theyre decent consumer lenses but dont have the optical clarity of the pro lenses, especially when shooting wide open. However, they generally cost a fraction of the price of the top of the line stuff. These lenses are generally fairly elegantly designed, with slightly rounded and tapered lens barrels, and usually have easy to grip ribbed rubber zoom rings rather than bare plastic.
There are also older low-end zooms with decent optical quality, such as the 28-70 3.5-4.5 II, which dont use modern USM drives but which nonetheless offer good value for money on the used market.
Category 3 - inexpensive primes.
Canon also sell and have sold a number of prime (ie: non zoom) lenses with acceptable optics and average build quality (usually with noisy motor drives, metal mounts and distance scales), such as the 28mm 2.8 and 50mm 1.8 (metal lens mount). Despite their low cost and pretty unremarkable construction they can provide quite good photographic results.
All lenses in this category are mostly normal or near normal lenses - no super wide angles and no long telephotos. The designs generally date back to the early days of the EOS lineup, so they tend to look a bit old-fashioned, style-wise. Canon just havent seen the need to update any of them.
Category 4 - good primes.
This is a group of prime lenses which offer excellent optics and decent build quality, but which dont really need and thus dont use ultra low-dispersion glass or calcium fluorite crystals or other hallmarks of L-class lenses. Remarkably good lenses like the 85mm 1.8 and the 100mm 2.8 macro fit into this category. Most have ring ultrasonic motors. They generally resemble the category 2 lenses - slightly rounded and tapered lens barrels. Optically they are professional lenses in all but the name, though theyre usually not quite as heavy-duty as the fancier L lenses.
Category 5 - specialized lenses.
Canon also make a handful of expensive specialized lenses for unusual applications which Ill just lump into this category for lack of anywhere else to put them. These include their tilt-shift TS-E lenses, the MP-E 65mm super-macro lens and the DO (diffractive optics) lenses.
Which lens falls in which category?
Heres a list of most Canon EOS-compatible lenses - both current and discontinued - sorted according to the categories above. Lenses are EF lenses (all EOS cameras) except those marked EF-S, which fit only EF-S-compatible digital EOS cameras.
The numeric value marked with the Ø symbol is the filter mount diameter. In other words, round screwmount filters of the size indicated can be attached to this lens. A few lenses - the extreme wide-angle lenses and the really long telephotos - use drop-in or gelatine filters inserted into the lens barrel.
Many lenses have the word Macro marked on them but only those identified here as macro are true macro lenses. True macro lenses are defined as those lenses capable of 1:1 focussing or better. The only Canon macro lens which doesnt quite fit this definition is the 50mm 2.5 Compact Macro, which requires the add-on Life-Size adapter to reach 1:1.
Check out Canons Camera Museum site for technical details on all the EF lenses that Canon has ever produced.Category 1 - cheapies.
These inexpensive lenses feature all-plastic barrel construction with plastic lens mounts (the 75-300 series and the 28-200 lenses being exceptions - they have metal mounts) and no distance scales. Those lenses in this category which have ultrasonic motors (USM) use cheaper micromotor USM, not ring USM. USM lenses are marked with a striped gold line around the end. Some of these lenses also have silver (chrome) rings around the end for good looks. Most lenses in this category support optional manual focussing, but their manual focus rings are usually awkward and cumbersome to use.
EF-S 18-55 3.5-5.6, Ø58
Inexpensive EF-S kit lens; reasonable optical quality
EF-S 18-55 3.5-5.6 USM, Ø58
Apparently only sold in Japan
EF-S 18-55 3.5-5.6 II, Ø58
Cosmetic update to the above
22-55mm 4.0-5.6 USM, Ø58
28-105mm 4.0-5.6, Ø58
28-105mm 4.0-5.6 USM, Ø58
28-80mm 3.5-5.6, Ø58
28-200mm 3.5-5.6, Ø72
28-200mm 3.5-5.6 USM, Ø72
28-80mm 3.5-5.6, Ø58
28-80mm 3.5-5.6 II, Ø58
28-80mm 3.5-5.6 II USM, Ø58
28-80mm 3.5-5.6 III, Ø58
28-80mm 3.5-5.6 III USM, Ø58
28-80mm 3.5-5.6 IV USM, Ø58
28-80mm 3.5-5.6 V USM, Ø58
28-90mm 4-5.6, Ø58
28-90mm 4-5.6 USM, Ø58
28-90mm 4-5.6 II, Ø58
28-90mm 4-5.6 USM II, Ø58
35-70mm 3.5-4.5 A, Ø52
Autofocus only - no manual focus ring
35-80mm 4-5.6, Ø52
35-80mm 4-5.6 PZ, Ø52
Powered (motorized) zoom
35-80mm 4-5.6 II, Ø52
35-80mm 4-5.6 III, Ø52
35-80mm 4-5.6 USM, Ø52
35-105mm 4.5-5.6 USM, Ø58
38-76mm 4.5-5.6, Ø52
55-200mm 4.5-5.6 USM, Ø52
55-200mm 4.5-5.6 II USM, Ø52
75-300mm 4-5.6, Ø58
75-300mm 4-5.6, Ø58
75-300mm 4-5.6 II, Ø58
75-300mm 4-5.6 II USM, Ø58
75-300mm 4-5.6 III, Ø58
75-300mm 4-5.6 III USM, Ø58
75-300mm 4-5.6 USM, Ø58
80-200mm 4.5-5.6, Ø52
80-200mm 4.5-5.6 II, Ø52
80-200mm 4.5-5.6 USM, Ø52
90-300mm 4.5-5.6, Ø58
90-300mm 4.5-5.6 USM, Ø58
100-200mm 4.5 A, Ø58
Autofocus only - no manual focus ring
Category 2 - midrange zooms.
All lenses in this category have metal lens mounts, and come in two basic flavours - old-style lens barrel and new style. The old style feature hard textured plastic barrels with narrow focus rings and their AF/MF switches are low and sometimes difficult to adjust. The new style feature slightly more resilient shiny plastic with wider focus and zoom rings, often with lots of easy-grip ribbed rubber. The new style lenses also boast ring USM focus drives and easier to operate AF/MF switches.
EF-S 10-22mm 3.5-4.5 USM, Ø77
Unusually for a lens not marketed as L series, this lens contains a Super UD element and has very good image quality.
EF-S 17-85mm 4-5.6 IS USM, Ø67
EF-S 17-55 2.8 IS USM, Ø77
This is an interesting lens since it actually has L-series image quality thanks in part to the use of UD glass. However, build quality is on par with better consumer lenses and not L series lenses.
20-35mm 3.5-4.5 USM, Ø77
24-85mm 3.5-4.5 USM, Ø67
Available in silver or black
28-70mm 3.5-4.5, Ø52
28-70mm 3.5-4.5 II, Ø52
28-80mm 3.5-5.6 USM, Ø58
(unlike later all-plastic II and higher models, these lenses have a metal mount)
28-105mm 3.5-4.5 Macro USM, Ø58
28-105mm 3.5-4.5 II Macro USM, Ø58
28-135mm 3.5-5.6 IS Macro USM, Ø72
35-70mm 3.5-4.5, Ø52
35-105mm 3.5-4.5 Macro, Ø58
Old-style barrel, push-pull zoom
35-135mm 4-5.6 USM, Ø58
50-200mm 3.5-4.5, Ø58
70-210mm 3.5-4.5 USM, Ø58
70-210mm 4 Macro, Ø58
Old-style barrel, push-pull zoom
70-300mm 4-5.6 IS USM, Ø58
The replacement to the 75-300 4-5.6 IS USM
75-300mm 4-5.6 IS USM, Ø58
Optically a cheapie, but image stabilization moves it up a category
100-300mm 4.5-5.6 USM, Ø58
100-300mm 5.6 Macro, Ø58
Old-style barrel, push-pull zoom
Category 3 - inexpensive primes.
With the exception of the all-plastic (including plastic lens mount) 50mm 1.8 mark II, the inexpensive primes all have old-style lens barrels - hard textured plastic, a narrow focussing ring and distance scale.
28mm 2.8, Ø52
35mm 2, Ø52
50mm 1.8, Ø52
50mm 1.8 II, Ø52
Plastic lens mount, no distance scale but same good optics as the 50mm 1.8
Category 4 - good primes.
As with the midrange zoom lenses, the good primes are available in either old-style lens barrel designs or new-style.
15mm 2.8 fisheye
20mm 2.8 USM, Ø72
24mm 2.8, Ø58
28mm 1.8 USM, Ø58
50mm 1.4 USM, Ø58
50mm 2.5 Compact macro, Ø52
True (1:2; 1:1 with adapter) macro, old-style barrel
EF-S 60mm 2.8 USM macro, Ø52
EF-S only true 1:1 macro lens
85mm 1.8 USM, Ø58
100mm 2 USM, Ø58
New-style barrel - do not confuse with the 100mm 2.8, which is a macro lens
100mm 2.8 Macro, Ø52
True 1:1 macro, old-style barrel
100mm 2.8 Macro USM, Ø58
True 1:1 macro, new-style barrel
135mm 2.8 SF, Ø52
Old-style barrel, adjustable soft focus control
Category 5 - specialized lenses.
Unusual, expensive and specialized lenses.
MP-E 65mm 2.8 1-5x Macro
Powerful macro lens, for closeups only
TS-E 24mm 3.5 L, Ø72
Tilt-shift, manual focus only
TS-E 45mm 2.8, Ø72
Tilt-shift, manual focus only
TS-E 90mm 2.8, 58
Tilt-shift, manual focus only
EF 70-300 4.5-5.6 DO IS USM
Diffractive optics. Marked with a green ring
EF 400mm 4 DO IS USM
Diffractive optics. Marked with a green ring
L series lenses
All L series lenses are easily identifiable by the red ring around the end of the barrel and the letter L at the end of their technical designations.
Most L series lenses are heavy shiny black plastic or white-painted metal. Most newer lenses (since 1999 or so) are weather-sealed though some (the earliest L series) are textured black plastic. The handful of early L series lenses with old-style barrels are not built to the same tough build quality of modern L lenses, though optically theyre fine.
Most L series lenses are large and fast lenses and thus quite expensive. However in the past few years Canon have also released a few more affordable L series zooms. These lenses are optically slower f/4 lenses which are smaller, lighter and cheaper than their f/2.8 counterparts. No L series lens has ever been made with an EF-S lens mount: they are always EF lens mounts only.
14mm 2.8 L USM
24mm 1.4L USM
16-35mm 2.8 L USM, Ø77
16-35mm 2.8 L II USM, Ø82
17-35mm 2.8 L USM, Ø77
17-40mm 4 L USM, Ø77
20-35mm 2.8 L, Ø72
24-70mm 2.8 L USM, Ø77
24-105mm 4 L IS USM, Ø77
28-70mm 2.8 L USM Macro, Ø77
28-80mm 2.8-4 L USM, Ø72
28-300mm 3.5-5.6L IS USM, Ø77
35mm 1.4 L USM, Ø72
35-350mm 3.5-5.6 L USM, Ø72
50mm 1 L USM, Ø72
50mm 1.2 L USM, Ø72
50-200mm 3.5-4.5 L, Ø58
Old-style barrel, push-pull zoom
70-200mm 2.8 L USM, Ø77
70-200mm 2.8 L IS USM, Ø77
70-200mm 4 L USM, Ø67
70-200mm 4 L IS USM, Ø67
Old-style barrel; not compatible with teleconverters
85mm 1.2 L USM, Ø72
85mm 1.2 L USM II, Ø72
100-300mm 5.6 L, Ø58
Old-style barrel, push-pull zoom
100-400mm 4.5-5.6 L IS USM, Ø77
135mm 2 L USM, Ø72
180mm 3.5 Macro L USM, Ø72
True 1:1 macro
200mm 1.8 L USM
200mm 2.8 L USM, Ø72
200mm 2.8 L II USM, Ø72
300mm 2.8 L USM
300mm 2.8 L IS USM
300mm 4 L USM, Ø77
300mm 4 L IS USM, Ø77
400mm 2.8 L USM
400mm 2.8 L II USM
400mm 2.8L L IS USM
400mm 5.6L USM
500mm 4 L IS USM
500mm 4.5 L USM
600mm 4 L USM
600mm 4 L USM II
1200mm 5.6L USM
Whats wrong with the kit lens included with my camera? Why do you call it a cheapie?
Dont take it personally. Canon sell most of their inexpensive consumer cameras either as camera bodies alone with no lenses or as complete kits with a cheap lens, camera strap and perhaps other accessories included. Such kits are usually aggressively priced, and most consumers go for them since theyre convenient and the supplied lenses are so cheap. The included lenses are usually referred to as kit lenses, though they can also be purchased separately if you like.
Unfortunately, kit lenses for low-end cameras are optimized for cheapness, as noted above. They arent engineered to offer the best optical quality you can find. This means theyre usually not terribly sharp and they also tend to produce somewhat low-contrast photos. Kit lenses are also considerably less rugged than more expensive lenses. Finally theyre always very slow lenses and so are not much good in low-light situations. These drawbacks are also the case, to varying degrees, for kit lenses made by every manufacturer, incidentally, not just Canon.
Of course, a cheap kit lens will take better photos than a lens you cant afford and thus dont have. Particularly if you avoid shooting wide open and use an aperture setting like f/8 to maximize sharpness. Nonetheless, you dont have to settle for poor quality if you check out the used market or if youre willing to pay a little extra - see the section after next for details.
Why are quality lenses so expensive?
Lenses are very complex and costly products to design and manufacture. Each component has to be built to incredibly tight tolerances and carefully assembled. The extremely pure optical-grade glass used in making lenses is very expensive to produce. Expensive lenses dont have the volume sales of cheap lenses, making them more expensive still to produce profitably. So, unfortunately, when it comes to lenses you generally get what you pay for.
Lenses going for 200-300 US$ or € may seem very expensive to a novice, but they are in fact considered dirt cheap lenses by professionals. This isnt snobby elitism necessarily - its just how it is. Lenses with high optical quality usually cost a lot of money. Photography is, unfortunately, a fairly expensive endeavour.
Whats a good beginner lens?
This really depends on your photographic goals. Here are some possibilities to consider.
But before you rush out and buy a lens based on these suggestions I strongly recommend trying out the lenses youre interested in before you buy. Most decent stores wont mind if you go in with your camera and roll of film or an empty memory card and take a few shots of the shop using a couple of lenses. (be sure to use a tripod or rest the camera on a sturdy surface and use identical settings for each lens) They might grumble a bit, but how else can you decide whether a given lens is good for you? Certainly you dont want to be trusting the advice of random people on the Internet!
Cheap prime lens.
If your primary objective is to learn more about basic photography skills and take photos of reasonable quality then your first lens should probably be a Canon 50mm 1.8 lens. This is a very fast fixed focal length lens. But since its technically easy to build a 50mm lens, its also astoundingly cheap. New Canon 50mm 1.8 mark II lenses can be bought for as little as $75 US.
Such a lens, while cheap, takes sharp clear photos and can be used in extremely dim environments without the harsh light of a flash because its so fast. So the photos you take with it will look better than those from a typical point and shoot both because theyre sharp and because youre not bathing your photos in ugly glaring light from a cameras built-in flash. Natural light photographs almost always look better than on-camera flash.
Of course, since its a prime lens you will have to walk around more to get a lot of shots framed right. And some wide-angle or telephoto-type shots you wont be able to get at all, so those are the obvious disadvantages.
Note that Canon have made two versions of the 50mm 1.8 lens. The older lens has no Roman numeral designation and has a metal mount, a distance scale and an optional clip-on hood. The mark II version has a plastic mount, no distance scale and a clumsy screw-on optional hood. If you can find an original lens its probably worth going for - it costs as much used as the mark II does new, but is of slightly tougher build quality. Optically the two lenses are basically identical. Canon also sell the 50mm 1.4 USM, which is optically a bit faster and uses a USM drive with FTM, but it costs considerably more than the 50mm 1.8.
However, if you use a digital camera with a cropped sensor (basically any EOS digital camera except for a few top models) then the 50mm might be a less useful choice, since it essentially behaves like a longer telephoto on such models, and wont let you get in much of a scene. In such cases a 28mm 2.8 might be a better option.
Cheap zoom lens.
If you value convenience and image quality is not a priority then an inexpensive zoom lens, such as the kit lenses sold with consumer-level cameras, is fine. However I dont recommend most of these lenses (the cheapies in category 1 above) to anyone whos at all interested in photographic image quality. The one exception is probably the EF-S 18-55 kit lens included with the EOS 300/350/400 and Digital Rebel series cameras. This lens, while incredibly cheap, is actually not too bad if you factor in the low cost. Especially if you stop down to f/8 or so when using it.
So what if youre on a budget but really want the convenience of a zoom? Well, you could pick up a used zoom lens of an older generation, many of which have quite decent optics for the price. For example, you could buy a used metal lens mount 28-70 3.5-4.5 II for nearly the same price as a new 28-80 all-plastic cheapie. If you want a lens with silent-focussing USM you could consider the metal lens mount 28-80 3.5-5.6 USM (not one of the later plastic lens mount models with Roman numerals), which has similar build quality to the 28-105 3.5-4.5 USM. Two other reasonable but discontinued lenses available inexpensively on the used market include the 35-135 4.0-5.6 USM and the older 35-105 3.5-4.5. The main drawback is that these lenses arent really wide enough to be useful on cropped digital SLRs.
In short, you dont have to put up with shopping mall quality just because youre on a tight budget so long as youre willing to consider used lenses.
Mid-priced zoom lens.
If you have a slightly larger budget, a mid-priced zoom (category 2) is worth considering. For example, two popular Canon zoom lenses are the 28-105 3.5-4.5 USM and the 24-85 3.5-4.5 USM. Both are reasonably sturdy lenses with decent though not outstanding optical quality. They feature fast and silent ring USM autofocus motors. Theyre more expensive and heavier than cheap zooms, but most people find the tradeoff worth it.
Of the two lenses the former has a bit more reach and so is good for isolating objects or for doing simple portrait work. The latter has less reach but is considerably wider (theres a surprisingly big difference in coverage area between a 24mm lens and a 28mm lens) and so is popular for travel photos. The 24-85 is also a good match for those digital cameras with less than full frame image sensors, such as the 300D/Digital Rebel/Kiss Digital or 10D.
If youre interested in the 28-105 3.5-4.5 USM see the important note below about its similarly-named low-cost cousin.
What are some popular Canon EF and EF-S lenses?
Here are a number of popular Canon EF and EF-S lenses you might come across.
EF 16-35 2.8L USM and EF 17-35 2.8L USM.
Professional-quality new and old fast wide-angle zoom lenses, used by many photojournalists. Expensive.
EF 17-40 4L USM.
Affordable and optically slower version of the above, popular with advanced amateurs.
EF-S 18-55 3.5-5.6.
Pretty well every 300D/Digital Rebel, 350D/Rebel XT and 400D/Rebel XTi owner out there has one of these, since theyre bundled with most consumer Canon digital SLRs sold. Image quality is OK considering the rock-bottom price.
EF-S 17-85mm 4-5.6 IS USM.
Very popular with users of Canons subframe D-SLRs, this lens combines decent image quality with a useful focal length range and has image stabilizing to boot.
EF 28mm 2.8.
Inexpensive lightweight wide-angle lens, suitable for landscapes and so on.
EF 50mm 1.8 and EF 50mm 1.8 II.
Super-cheap lightweight fast lenses, ideal for beginners and advanced amateurs. Take surprisingly sharp pictures for the price.
EF 50mm 1.4 USM.
Versatile standard lenses, useful in low light. These lenses contain micromotor USM mechanisms that unusually support full-time manual focussing.
EF 24-70 2.8L USM and EF 28-70 2.8L USM.
Large, heavy black L series lenses, noted for their high quality. Expensive and popular with wedding photographers.
EF 24-105 4L IS USM.
Very popular and quite expensive L-series image-stabilized walkaround lens.
EF 28-70 3.5-4.5 II.
Cheap older lenses with a reputation for decent optical quality despite the really low price. Rotating recessed end makes filter use awkward, however.
EF 28-80 3.5-5.6 II-V, 28-90 4-5.6.
Extremely cheap Canon lenses, supplied with many low-end camera bodies as kit lenses. Lousy optics.
EF 24-85 3.5-4.5 USM, 28-105 3.5-4.5 USM and EF 28-105 3.5-4.5 USM II.
Medium-sized, medium-priced and medium-speed lenses popular with many amateur photographers. The 24-85 is particularly popular with APS and subframe digital EOS users owing to its wider short end. Do not confuse the 28-105 3.5-4.5 lenses with their cheaper and slower 4-5.6 cousins.
EF 28-135 3.5-5.6 IS USM.
Popular and versatile midrange lenses equipped with image stabilization for low-light shooting.
EF 85mm 1.8 USM.
Sharp and relatively inexpensive prime lenses, ideally suited for portraiture.
EF 100mm 2.8 Macro and EF 100mm 2.8 Macro USM.
True macro lenses capable of 1:1 closeup photography, yet equally useful as portrait lenses.
EF 70-200 2.8L USM and EF 70-200 2.8L IS USM.
Heavy white L series lenses, favoured by a lot of photojournalists. Expensive.
EF 70-200 4L USM.
Optically slower and less heavy siblings to the 2.8L. Considered a bargain for the price by many photographers, and popular with advanced amateurs.
EF 70-200 4L IS USM.
The image stabilized version of the 4L. Much more expensive, however.
EF 70-300mm 4-5.6 IS USM.
A popular lens for its compromise between size, convenience and image quality. Much sharper than its 75-300 predecessors, and image stabilization is a big plus. Not to be confused with the DO (diffractive optics) lens, which is extremely expensive.
EF 75-300 4-5.6.
Commonly available cheapie-series telephoto lenses (see below). Ubiquitous owing to the low price, but optically poor.
EF 1200mm 5.6L USM.
Okay, so these gigantic and insanely expensive telephoto lenses arent popular as such, but always feature prominently in Canons lens advertising. Canon will gladly custom-build one for you, given a prepaid order. I think they run for roughly the cost of a luxury automobile.
Frankly if you need this sort of focal length youre better off with the 600mm 4L IS USM and a 2x teleconverter, though admittedly youll need an EOS 1V, 1D, 1Ds or 3 to autofocus with it.
Should I buy a non-Canon (third party) lens?
Despite Canons vigorous advertising campaign against third-party lenses a lot of people happily use lenses made by Tamron, Tokina and Sigma (and lenses with other brandnames but probably built by one of those three). And theres one really good reason for this - the third party lenses are almost always much much cheaper than equivalent offerings from Canon.
So. Should you buy a third party lens? Its not a simple yes/no issue, so here are some points to consider.
Types of lenses.
Why doesnt my camera have a motorized zoom lens with wide/tele buttons?
Because its not a point and shoot. Such motorized lenses are fine for simple tiny consumer-oriented cameras, but SLRs with interchangeable lenses are meant for a different market.
All Canon EF zoom lenses but one are manual zooms. That is to say you adjust the focal length either by turning a ring (two touch) or sliding the lens in and out (push-pull). And most people find that adjusting the zoom setting on such lenses is much faster and more precise than a slow and cumbersome motorized point and shoot zoom lens.
Note that Canon did briefly sell a motorized zoom lens for EOS cameras a while back, presumably as a sort of experiment. That lens, the Canon EF 35-80 4-5.6 PZ (Power Zoom), was an all-plastic cheapie with fairly low optical quality. The lens barrel had two pushbuttons that let you adjust the zoom position.
Whats the difference between all the Canon 28-105mm lenses?
Canon sell and have sold a number of different lenses which use the 28-105mm focal range.
28-105mm 3.5-4.5 USM, flower icon.
This is the first version of this popular lens, released in the early 1990s. Its a midrange consumer zoom with decent optics and a fast and silent ring USM motor with FTM. The mark I version with a flower icon on its lens barrel apparently had a 5-blade aperture diaphragm. Marked with a striped gold line since its a USM lens, and has a metal lens mount. Discontinued.
28-105mm 3.5-4.5 USM, MACRO icon.
This is the second version of the lens, though it was never officially identified as such - its still considered to be a mark I. Its identical to the first version but it has the word MACRO printed on the lens barrel in lieu of the flower (closeup) icon. Internally, however, it has a 7-blade aperture diaphragm, which in theory offers slightly better bokeh, or out-of-focus blurring. Marked with a striped gold line since its a USM lens, and has a metal lens mount. Discontinued.
28-105mm 3.5-4.5 USM II.
This is the official second version of the lens, as indicated by the II symbol. According to Canon the original 28-105 and the mark II versions have identical optics, but the mark II version has slightly different external styling, including an allegedly slightly tougher design. According to Canon Malaysia an internal component used in the zoom mechanism has been updated to metal from plastic. Marked with a striped gold line since its a USM lens, and has a metal lens mount. Discontinued.
28-105mm 4-5.6 USM.
This lens is a cheapie lens, released in 2002. It is a completely different and very much inferior lens from all the ones listed above. Its almost entirely made of plastic (including the lens mount) and has vastly worse optics than the faster lenses. It can easily be identified by the silver (chrome) ring around the end of the barrel. Interestingly, while it uses a micromotor USM autofocus system it nonetheless supports full-time manual, according to Canons literature. Its a lens intended for consumers and does not fit the same position in the lineup as the 28-105 3.5-4.5 USM II.
In short, be very careful when shopping for a 28-105 lens. You dont want to buy a lens thinking its the popular midrange lens only to end up with the bottom of the line cheapie instead. Always double-check the listed aperture range before buying.
Should I buy the Canon 28-200 or the Tamron 28-200 or the Sigma 28-300 (or some other lens with a big focal range)?
A popular question back in the late 90s, when such lenses were heavily marketed as the ultimate in consumer convenience since they cover such a huge focal length range. Sadly, the lenses tend to be fairly big and heavy, as consumer lenses go. And most importantly, the optical quality of these lenses leaves a lot to be desired. Its very difficult to build optically sharp zoom lenses, particularly those with a really wide zoom range like these ones. The lenses are pretty slow, with small maximum apertures. They also tend to have a lot of distortion, which makes squares and rectangles in photos appear like theyre bulging in or out slightly - bad for photos of buildings.
If you only take 4"x6" snapshots then these drawbacks are probably fine, but if you ever want to make enlargements beyond that you may find that your photos look disappointingly soft - not very sharply focussed. Since theyre optically so slow youll probably also find that any telephoto photos you take will be badly blurred unless you use a tripod or flash. Finally, using long telephoto lenses requires a certain degree of technique and experience since the focal lengths are so long. You cant easily handhold a slow 300mm lens, for example. Doing so, particularly without high-powered flash, is a surefire recipe for disappointingly blurry photos. And Sigma has regrettably a long history of older lenses turning out to be incompatible with later EOS cameras.
As a beginner youre probably best off getting one or two lenses of a more modest focal length range, no matter what nonsense the salesperson in your camera shop may say about you never needing to buy another lens again. In short, consumer-level 28-200 or 28-300 lenses always suffer from tremendous optical compromises; compromises which render them of limited value, especially at the long (200-300mm) end.
There are really only two lenses with a huge focal length range that are generally accepted as possessing decent optical quality - Canons 35-350 3.5-5.6L and Canons 28-300 3.5-5.6L IS. However both are gigantic and expensive lenses not intended for beginners.
What affordable Canon long telephotos are there?
Canon make telephoto zooms which fall mostly into two basic categories - very cheap slow lenses with mediocre optical quality and very expensive fast lenses with fabulous optical quality. There are few intermediate choices, though the 70-300 4.5-5.6 IS USM is one to consider. Canon have also never built any affordable long EF telephoto prime lenses - all EF telephoto primes longer than 135mm are L series lenses.
There are a number of Canon zoom lenses in the 75mm to 300mm range, however. Heres a bit of basic information about some of them.
75-300 4-5.6 USM
75-300 4-5.6 II
75-300 4-5.6 II USM
75-300 4-5.6 III
75-300 4-5.6 III USM
Canon sell and have sold quite a few different lenses with focal lengths from 75mm to 300mm. All apparently use the same optics - they just have different cosmetic styling of the lens barrel (the mark III version, for example, has a silver ring on the end to impress novice camera buyers) and different autofocus motors. Theyre very inexpensive lenses as telephoto zooms go, but offer fairly mediocre optical quality. At the short (75mm) end theyre not too bad but at 200-300mm they tend to get very soft (slightly blurry). You really need to stop them down to f/8 or f/11 or so for okay optical quality, which of course requires longer shutter speeds.
The 75-300 USM models all have micromotor USM autofocus mechanism which do not support full-time manual (FTM). All other versions of this lens use slow and noisy micromotor or DC motor drives. These lenses, while in the cheapie category of Canon lenses, have metal lens mounts. They do not, however, have distance scales. All versions of this lens have rotating ends when focussing, which makes using a polarizing filter rather inconvenient.
75-300 4-5.6 IS USM
One notable lens in the 75-300 series is the IS model, which offers image stabilization for improved shooting at lower shutter speeds. It was the first IS lens offered by Canon, but the lens sadly has the same unremarkable optics as the other 75-300 lenses.
70-300 4.5-5.6 IS USM
Do not confuse this lens with the cheaper 75-300 crowd or the more expensive DO lens with almost the same name. This lens combines decent optics with image stabilizing and is an excellent compromise for the advanced amateur. Its not quite as sharp as the 100-300 5.6L, but IS makes it a lot more convenient since you end up with a much higher percentage of keepers when used off-tripod.
70-300 4.5-5.6 DO IS USM
This lens is particularly unusual in that its the first zoom lens to use diffractive (DO) lens elements. This Canon technology allows for smaller and lighter lenses. The 70-300 DO is considerably shorter than its 75-300 siblings, and has image stabilization (IS) technology to boot. It isnt cheap, however. Do not confuse it with its non-DO sibling.
90-300 4-5.6 USM
I really dont see the point of this lens. It appears to be pretty well the same as all the cheap 75-300 lenses, only its short end starts at 90mm. Its USM but only micromotor USM and thus has no FTM.
100-300 4.5-5.6 USM
This lens is, in terms of build quality and physical appearance, the telephoto zoom counterpart of the 28-105 3.5-4.5 USM and the 24-85 3.5-4.5 USM. It has reasonably solid construction, a fast and silent ring USM autofocus drive which supports full-time manual (FTM), does not having a rotating end and has a distance scale. Optically the 100-300 USM I had was very slightly sharper than the 75-300 at the long end, but many people report that theres really no difference between their samples of the lenses. Essentially the 100-300 USM gives you improved focussing speed and a more convenient user interface compared to the 75-300s, but not improved optics. You also lose 25mm and half a stop off the short end, for what its worth.
The predecessor to the 100-300 4.5-5.6 USM. Very similar in size and construction, only with a focal range thats shorter at each end. Offers similar optical quality.
An older and now discontinued lens, the 100-300 5.6L is an interesting lens in that, while its technically an L series lens with fluorite and UD lens elements, it doesnt have the tough build quality of a typical L series lens sold today. It uses a slow and noisy AFD autofocus motor and has an awkward (low-profile) and fiddly (hard to slide) MF/AF switch. The manual focus ring is also rather gritty to turn. However, it does offer considerably improved optical quality over the 75-300 series and the 100-300 USM. It's also sharper than the 70-300 IS USM. So if you can deal with the slow optical speed (maximum aperture of only 5.6) and the horribly sluggish autofocus motor its well worth looking into if youre on a tight budget.
Similar to the 100-300 5.6L, in that its a first generation EF-mount L series lens. It has the optics of a modern L series lens - but not the build quality - and has a push-pull zoom design. The 50-200 isnt a bad lens, but for some reason holds its used market value rather well. Personally I think the 70-200 4L USM is a better deal. Its typically not much more money but gives you better build quality and silent focussing USM.
70-200 4L USM
This lens, the smaller and cheaper sibling of the impressive 70-200 2.8L USM professional lens, is considered a bargain by many EOS users. It costs three times as much as the cheapie lenses but its sturdy, focusses quickly with a ring USM system with FTM and, most importantly, it has great optical quality. Its bigger and heavier than the consumer lenses, but if you want something good but cant afford the 2.8L, consider this lens. It doesnt use a huge 77mm filter like the 2.8L - it uses a 67mm filter like the 24-85 3.5-4.5 USM. This is a little unfortunate, has hardly any other Canon lenses have 67mm filters.
70-200 4L IS USM
The image stabilized sibling to the 4L. Visually almost identical, down to the 67mm filter, but much much more expensive than its non-L counterpart. According to some reviewers, one of the sharpest Canon lenses in its whole zoom lens range.
80-200 4.5-5.6 USM
80-200 4.5-5.6 II
Plastic cheapies, basically analogous to the 28-80 plastic cheapies. They are very lightweight and portable, though. If you want something really inexpensive and never enlarge your photos past postcard size then theyre fine.
With pretty well identical build quality to the 100-300 5.6L, this older lens has all the disadvantages of the 5.6L without the sharp optical quality of the L lens.
I want to take photos of wild birds. What lens do I need?
You probably wont want to hear this answer, but nature photography of small and fast-moving wild animals is a difficult field and basically requires really expensive lenses. 500mm and 600mm lenses are commonly used by bird photographers - your typical 100-300mm zoom lens is just not long enough for great photos. And lenses longer than 300mm are both incredibly expensive and really heavy.
So the harsh reality is while you may be able to get nice snapshots of fairly tame birds with a 100-300mm lens you wont be able to get those amazing wildlife book or calendar shots - small birds filling the entire frame - with one. You can always use your lens at 300mm and then crop off the edges of the picture, but then picture quality will suffer.
If you really want to do this type of photography on a tight budget you might want to consider buying used manual focus gear. You can find really quite decent used high-end manual focus telephotos quite inexpensively compared to their autofocus counterparts.
I want to do sports photography. What lens do I need?
Unfortunately, this answer is going to be somewhat like the previous one. The challenges of sports and other action photography are twofold. First, by its very nature, sports photography tends to involve rapid motion - fast-moving players or cars or whatever. Second, usually theres some distance between the action and the camera.
Solving the first problem requires lenses which can let in plenty of light, the use of flash or faster film or high ISO settings on a digital camera. Each of these solutions has drawbacks, however. Fast lenses are large, heavy and expensive. Fast film or high ISO settings result in higher grain or noise and thus lower picture quality. And flash may be inadequate to illuminate the subject effectively, particularly if the subject is some distance away.
Solving the second problem basically requires the use of long telephoto lenses. However, most affordable autofocus telephoto lenses are very slow - they dont let in much light. So this amplifies the first problem.
Now obviously there are some cases where these two issues arent a massive problem. For example, perhaps youre shooting a basketball game and youre in the front row. Basketball courts are of a modest size and so you could probably do okay with flash (assuming youre allowed to use flash - some places wont let you as it can temporarily blind or distract the players) and you wont need an incredibly long lens accordingly. Such a situation is a little less challenging than shooting hockey on a big, poorly lit, rink.
Nonetheless, pro photographers rely on fast lenses, and this is the primary stumbling block for amateur photographers on a budget. Fast telephoto lenses, especially fast telephoto zooms, are really expensive. And theres not much you can do to work around that fact without a lot of compromises. To cover these points further:
Fast lens. Get the fastest (largest aperture) lens you can afford. A 70-200 2.8 lens is great for basketball, for example. A 75-300 4-5.6 is probably not, since even shooting wide open means youll have slow shutter speeds, which will result in unwanted motion blur.
Telephoto lens. Youll need a long telephoto zoom unless youre planning on shooting very close to your subjects. For example, you wont need a long lens to shoot skateboarders in an urban setting, but you will if youre covering a football game.
Cropping. You can always make up for a long lens to a certain extent by cropping the picture - trimming off the edges. The problem with this is that enlarging the picture also enlarges the grain in the case of film and lowers the apparent resolution in the case of digital.
Image stabilization. Useful for reducing blurring caused by camera motion, but of no value whatsoever in freezing subject motion.
Flash. Useful both for illuminating the subject and freezing subject motion. Not every venue permits flash usage, however.
Film/ISO speed. Fast film or high ISO settings are needed to keep shutter speeds to a minimum. Once again this involves tradeoffs with picture quality.
Camera with fast focus. A fast pro camera (such as the EOS 1 series) can lock focus surely and accurately and has minimum lag time when the shutter release is pressed. A consumer camera is not going to be as surefooted and decisive, and will make it harder to nail the perfect shot.
Fast lens motor. A Canon ring USM lens can autofocus rapidly, whereas a Canon AFD (arc form drive) lens cannot. A lens with a rapid motor frequently makes the difference between achieving a shot and getting nothing.
To summarize - if you plan on putting a 75-300 4-5.6 consumer lens onto your camera, dont expect photos like those which grace sports magazines. This isnt to say that you cant get satisfactory photographs with such equipment, just that its challenging to do so. It takes a lot of skill, experience and luck to come up with consistently good results. And you should be operating on the expectation that you will face problems with blurring of the subject and general low sharpness and low contrast if you use an affordable consumer telephoto zoom lens.
What about mirror lenses? I can get a really cheap telephoto that way!
Some third-party lens makers sell mirror or, as theyre more accurately known, catadioptric lenses. Such lenses use a pair of mirrors to fold the light path in half, in addition to containing regular glass elements. The advantages are that mirror lenses can be made fairly cheaply and will also be shorter and lighter than all-glass (refracting) lenses of the same focal length. And mirror lenses with focal lengths of 500mm to 1000mm are not uncommon. Russian makers produce a lot of these lenses.
Unfortunately mirror lenses have a number of drawbacks. First of all, theyre manual-focus only. Second, they are optically really slow lenses - usually around f/8 or so. Third, they dont have aperture diaphragms, so the only way to adjust the exposure is to adjust the shutter speed, the film speed/digital ISO or to put a neutral density (darkening) filter on the lens. Fourth, the smaller of the two internal mirrors blocks the light path somewhat, resulting in rings or doughnuts appearing around bright highlights in out of focus areas. This effect, a form of bokeh, can be visually very distracting. And fifth, they tend optically not to be of the highest quality - youre not going to get National Geographic-quality bird photos using them.
So, while such lenses are attractive if youre on a budget, they do have many limitations associated with them. Youre probably better off buying a used manual-focus refracting (non-mirror) lens and adapting it to your camera, or buying a manual-focus body. As noted above, photography can be a really expensive endeavour.
What is a macro lens? My lens has MACRO written on it.
Macro photography is the somewhat confusing name for closeup photography. Just as the human eye can only focus up to a certain distance (a distance which moves alarmingly further away with age), not all lenses can focus as closely as others. Most lenses are designed to focus up to a metre or two with long telephoto lenses having much longer minimum focussing distances than that.
Now this obviously isnt going to help you if you want to take a super closeup of a small flower - you need a much shorter minimum focussing distance. Basically you want to be able to fill the frame with your small subject. And another concept comes in - the magnification factor. Traditionally, true macro photography refers to 1:1 photography and smaller. In other words, a lens with 1:1 magnification is able to image an area as small as the exact size of the image format in question. In the case of 35mm film this means an area of 24x36mm in size. Sometimes magnification is written as a decimal factor, such as 0.25x or 1.0x.
Unfortunately, lens manufacturers tend to throw around the word macro with cheerful abandon as a marketing gimmick. The fact a lens has MACRO printed on it basically means nothing, and you have to look closely at the lens specs. If a lens can do 1:1 or 1:2 photography then its a real macro lens, optimized for closeup photography. It may also be designed with a flat field so it can be used to take photographs of flat objects like stamps without focus problems. Lenses that can only reach 1:4 or whatever cant take really close-up pictures.
True macro lenses are generally of much higher optical quality than ordinary lenses and usually cost more. They are also usually optimized to take photographs of small flat objects with even focus across the surface - flat field. Theyre still a good buy if you dont do a lot of macro photography, however. You can always use them for regular photography as well - they just have the bonus that they can focus much closer than ordinary lenses can.
What is a portrait lens?
Obviously any lens can be used to take a portrait of someone. However, the results can be very different depending on its focal length.
The distance required between you and your subject, when you take a head and shoulders portrait, depends on the focal length of the lens. If you have a wide angle lens then you need to stand very close to them in order to have their head and shoulders fill the frame. But if you have a telephoto lens then you need to stand a fair distance away from them for the same effect.
This distance results in a change in perspective. Try this experiment with someone in real life without using a camera. If you stand really close to the person and look at their face youll notice that this position tends to emphasize their nose and make their forehead look like its sort of sloping away. But if youre further away from them then their face tends to look flatter. And generally speaking people find that a slightly flatter perspective on a face is usually a bit more flattering in general. Portraits taken with wide-angle lenses can, in fact, have a rather comical or grotesque effect.
So generally photographers like to use lenses of about 85mm to 135mm in length when taking head and shoulders portraits, depending on the look theyre trying to achieve. Some fashion photographers even use 200mm and 300mm telephotos for a particularly flat effect. You can take photos of people with 50mm and shorter lenses, but these lenses tend to distort the face somewhat. Such shorter focal lengths are, however, perfectly fine for waist-up or full body shots.
Canon make a number of of popular lenses used for portrait photography. Two of the more affordable ones include the compact and sharp 85mm 1.8 and the 135mm 2.8 SF which has a soft focus feature which allows you to introduce image-softening at will.
Finally, note that the lens focal lengths I list here are for 35mm film or full-frame EOS SLR. If youre using a camera with a smaller image area - digital or APS - then the ideal focal lengths for portraits are going to be shorter. For example, a 50mm lens is generally considered a bit short for most portraiture with 35mm film, but when mounted on an EOS 10D digital camera it takes photos much like those taken with an 80mm lens on a 35mm film camera.
What is a fisheye lens?
Most lenses are rectilinear, which means theyre designed to project an image onto a flat surface (the film or the image sensor) and render straight parallel lines as straight parallel lines. This is actually a complicated optical trick, since a simple lens really wants to project an image onto a spherical surface (such as the interior of the human eyeball). It also becomes increasingly complicated to do as the field of view of the lens becomes larger, as with wide-angle lenses - one reason why really wide angle lenses are so expensive.
This type of projection onto a flat field is something that different lenses do to varying degrees of success. High quality lenses, particularly those intended for use for macro or architectural photography, do a pretty good job. But cheaper lenses will compromise on this slightly and will either barrel or pincushion somewhat. That is to say, a photograph of a square object may appear to be either bulging outwards or squashed inwards, because parallel lines are being portrayed as curved. In fact, nearly all cheap lenses tend to have barrel distortion - its just that people usually dont realize it because they rarely take photos of square or rectangular objects.
A fisheye lens is a wide angle lens where no effort has been taken to render parallel lines as parallel. Instead, only lines which pass through the centre of the frame are straight. All other lines appear as curves, becoming increasingly curved as you near the edge of the frame. This line curvature has the effect of making near objects seem closer and more distant objects seem further off, as they fall away. If youve ever looked through the glass peephole viewers in a door then you know the effect.
Sometimes people call rectilinear lenses corrected and fisheye lenses distorting, but I dont think thats very useful or accurate. Rectilinear lenses arent necessarily correct - a wide-angle lens has extreme distortion and stretching towards the edges to make the lines straight. That being said, the fisheye effect is very pronounced and extreme, and does render scenes in a characteristic fashion. Portrait photographs of people taken with fisheyes, for example, have cartoon-like bulging noses and so on.
Fisheye lenses are useful for three basic things. First, its a lot easier to make a super wide angle fisheye than it is a super wide angle rectilinear lens, so a fisheye lens is going to be cheaper than its rectilinear equivalent. Second, and this is how fisheyes came about, its possible to build a fisheye lens which covers a full 180° field of view, which is very handy for scientific photography, particularly of the sky. And third, bulgy wide angle effects are fun for taking crazy trippy photographs.
There are two basic types of fisheye lenses. Circular or 180° fisheyes cover a full (or nearly full in most cases) 180 degree field of view across the narrower side of the image rectangle. These lenses make photos that look like bulging circular balls on a black background. The other type are sometimes called full frame or semi fisheyes and basically offer a cropped field of vision so you dont get the black areas at the corner of the picture. As a result they only cover 180 degrees of view on the diagonal.
On 35mm cameras, full frame fisheyes usually have a focal length of 8mm, and semi-fisheyes have a focal length of 15mm or 16mm. In near-circular lenses, Japanese maker Sigma sell an 8mm autofocus fisheye for use with EOS cameras, and Belarus maker Peleng sell an 8mm manual-focus fisheye that can be adapted to EOS cameras. In full frame fisheyes, Canon sell a 15mm autofocus fisheye for EOS, and Russian maker Zenitar sell a 16mm manual-focus fisheye lens which can be adapted. There are also popular screw-on adapters that convert ordinary lenses into fake fisheye lenses. Such adapters are virtually all of extremely low quality, but are definitely fun to play with.
A lot of photographers turn up their noses and dismiss fisheyes altogether as gimmicky remnants of the 1970s. Personally I think fisheye distortion can yield interesting effects if used occasionally, but its obviously not something youre likely to use every day. In nature or underwater photography, where there are few straight lines, fisheyes can be a useful tool as well.
What is the difference between two-touch zoom and push-pull zoom?
There are two basic ways to adjust the focal length of a zoom lens. Some zoom lenses have a zoom ring as well as a focus ring and so are called two-touch. Rotating the zoom ring adjusts the focal length. Other lenses slide in and out like a trombone or telescope; the so-called push-pull design.
The push-pull design is more vulnerable to zoom creep than two-touch. This is the problem of the zoom accidentally adjusting focal length (sliding) when tilted up or down because the friction of the push-pull system isnt enough to counteract the weight of the lens. Push-pulls also tend to suck in a lot of air and therefore dust into the lens when adjusted. However, push-pull lenses can be operated more rapidly, if usually a bit less accurately, than two-touch zooms.
Why are some Canon lenses painted white or silver?
Nearly all large telephoto L series lenses have barrels constructed from solid metal and painted off-white, rather than black plastic or black-painted metal. Canon say they do this since white surfaces absorb less heat than black when used out in the sun, and fluorite crystal lens elements are sensitive to heat - they can expand and contract, altering their optical properties. Of course, the fact that a white-painted Canon lens stands out in the crowd is probably part of the reason as well. Look at any major sports event and youll see rows of hefty white lenses. Though to confuse matters Nikon have also begun to sell some lenses in optional white paint.
A few lenses intended to be sold as kit lenses with silver-painted camera bodies have also been available with silver-painted plastic barrels. These include the 35-135 4-5.6 USM (to match the silver-painted commemorative edition of the EOS 10/10s which was released to mark the sale of 60 million Canon cameras), the 24-85 3.5-4.5 USM (to match the APS IX camera) and the 28-90 4-5.6 USM II (to match the Rebel Ti/EOS 300V/Kiss 5). The silver paint on these midrange and low end lenses is purely for cosmetic reasons.
What is a tripod mount on a lens for?
Normally you put a camera onto a tripod by attaching the camera body right to the tripod head itself. But if you have a really heavy lens this is a bad idea. Large lenses can often weigh far more than the heaviest SLR cameras. So the right way to do it is to attach the lens to the tripod head via a tripod mount. The camera then sort of hangs off the back of the lens unsupported, but this isnt a problem - lens mounts are designed to handle that kind of weight easily.
Lens tripod mounts or collars are mounting rings with built-in clamps. These rings make it easy to rotate the camera from portrait (vertical) to landscape (horizontal) position. If the maker of your lens sell a tripod mount for the lens then its probably wise to get one.
What is a distance or depth of field scale?
Most Canon EF midrange and better lenses have distance scales - clear rectangular plastic windows set into the lens barrel. A series of numbers can be seen through this window indicating the distance, in both metres and feet, from the lens to the point in focus. Inexpensive consumer lenses generally do not have distance scales.
Canon EF prime lenses also have simple depth of field scales marked on the barrel below the window. These marks indicate the acceptable depth of field distances from the current focus distance, usually for a small number of apertures - f/11 and f/22, say, or f/5.6, f/11 and f/16. Canon EF zoom lenses, however, do not have any depth of field scales because of the complexity of indicating depth of field over varying focal lengths.
Youll notice that there is usually a red dot on the distance scale window as well. This is used for determining the focus distance when using infrared film with an infrared filter. Since infrared energy focusses at a different point from visible light this dot is a useful aid. However, if youre using infrared film with an ordinary red filter or no filter at all then you may not need to adjust focus using this dot, since much of your image is going to be visible light anyway. For more information please consult my Infrared Myths document.
What is the issue with a rotating end of a lens?
Some lenses have an outer end which rotates when you adjust either the focus or the zoom setting or both. Others do not.
This matters a lot if youre using a polarizing filter or a graduated neutral density (ND) filter, since the properties of the polarizer vary depending on its angle of rotation and the graduation line runs across the filter in a straight line. It can be very annoying to set a filter to achieve the effect you want, touch up the focus, and find that the polarizing or graduated ND effect has changed because the end of the lens has rotated.
Why does it matter how many blades the aperture diaphragm has?
The adjustable aperture diaphragm in most camera lenses consists of a number of flat wedge-shaped metal blades. As you adjust the lens aperture settings these blades rotate in or out, and the aperture opening changes size in an iris-like fashion.
The shape of the hole made by this adjustable diaphragm depends on the number of blades and the shape of the blades. For example, if you have a 5 blade aperture diaphragm then the aperture will be a pentagon in shape. An 8 blade aperture diaphragm will of course yield an octagon.
There are two areas in which this aperture shape affects the final image. First, the shape of lens flare on a photograph is typically governed by the shape of the aperture. You may have seen photographs with pentagonal or hexagonal lens flare, for example, or star-shaped highlight areas in a photograph taken with a small aperture setting. Second, its generally held that the closer the aperture is to a circle the smoother out of focus areas (bokeh) tends to be, though it isnt the only factor contributing to bokeh. Many lenses have at least 6 or 8 aperture blades, frequently with curved edges, to approximate a circular aperture opening for this reason. Canon have in fact started billing some of their recent lenses as having circular apertures, indicating near-circular openings.
Which lenses are weather-resistant?
Most of Canons new professional (L series) lenses introduced since mid 1999 are equipped with gaskets and rings to keep out dust and moisture. Theyre not waterproof, by any means, so dont go diving with them. But theyre much more resistant to inclement weather than Canons other products.
Of course, a weather-sealed lens isnt much good unless you have a weather-sealed camera to match it. And at present only the top of the line EOS 1V, 1D, 1Ds 1D mark II, 1Ds mark II and 1D mark IIN cameras (but not the 1, 1N or 3, which have lesser sealing systems) have the same level of weather sealing - gaskets and rings around every opening, button and switch, in fact. You can use the sealed lenses with non-sealed cameras, of course, but the gasket around the lens mount will still let in water unless mated to the gasket around a sealed camera. (this rubber ring around the lens mount is, incidentally, an easy way to tell if a lens is weather sealed or not)
At time of writing the weather-resistant Canon lenses are:
16-35mm 2.8L USM
16-35mm 2.8L II USM
17-40mm 4L USM
24-70mm 2.8L USM
24-105mm 4L IS USM
70-200mm 2.8L IS USM
70-200mm 4L IS USM
28-300mm 3.5-5.6L IS USM
50mm 1.2L USM
85mm 1.2L II USM
300mm 2.8L IS USM
400mm 2.8L IS USM
400mm 4 DO IS USM
500mm 4L IS USM
600mm 4L IS USM
The mark II versions of Canons teleconverters, the Extender EF 1.4x II and Extender EF 2x II, also have weatherproofing. None of Canons more affordable lenses or cameras have weather sealing. Note also that weather-resistant zoom lenses do not have sealed glass ends - you need to put a filter on these lenses to seal out the far (non camera) end.
What is the close or minimum focus distance?
Just like a human eye, camera lenses have a near point at which they cannot focus anymore. This focus distance depends on the lens construction, but typically wide angle lenses have nearer close focus distances than telephotos. Many macro lenses, of course, are optimized for near close focus distances.
If youre a human you can adjust this close focus distance by moving the object youre trying to focus on further away. Similarly you can add extension tubes to your lens to move the lens further from the camera and thus bring the close focus distance closer. You will lose the ability to focus on infinity with such a tube, though.
Hey! I can turn the focus ring of my lens past the infinity mark! Why?
Your lens can go to infinity - and beyond! Yes, many lenses can be adjusted past the infinity marking on the lens barrel.
Its not a problem. Such lenses are intentionally designed this way to allow the lens to compensate for the changes in optical characteristics that occur when the lens is subjected to ambient temperature changes. (the focus of lenses can be affected by thermal expansion)
What does a lens hood do?
Aside from making the lens look longer and bigger and thus more impressive to non-photographers, lens hoods (sometimes called shades) serve two basic functions. First, they help reduce the amount of stray light hitting the surface of the lens. This is a good thing, since non-image-forming light coming into the lens at an angle results in lens flare. Lens flare can result in lower-contrast images or, in extreme cases like light from the sun, can result in big glowing blobs in the final photo. Second, lens hoods serve as physical protection for the lens - the plastic or metal tube can absorb blows that might otherwise hit the glass itself.
Lens hoods come in a number of basic forms. The two types sold by Canon today are tube-shaped hoods and petal-shaped (notched) hoods, made of hard black plastic. The petal-shaped type are sometimes called perfect lens hoods and shield the lens more effectively than simple tubes of the same weight. This is because the notches are cut out to match the rectangular shape of the imaging area (think about it).
Some hoods clip onto the lens, some twist on bayonet-style and some screw onto the end. Some are lined with black light-absorbing flocking and some are not. You can also buy flexible adjustable rubber hoods from third party makers, but Canon do not sell any such hoods themselves.
Unfortunately, lens hoods are hugely overpriced. Camera makers somehow feel justified in charging massive sums for simple moulded plastic tubes. Ah well.
How are lens hoods named?
Canon lens hoods are identified by a confusing and cryptical alphanumeric code. There is a system to the hood naming, though its only somewhat informative. Still, if you understand how the hood naming works you can usually figure out which hoods can be interchanged with other lenses.
Some hood naming examples:
E indicates that the hood fits an EF mount lens.
T indicates that the hood fits a telephoto lens.
65 indicates that the hood mount is 65mm in diameter.
III indicates this is the third hood of the ET-65 series, and means in this case that the hood is flocked to reduce reflections.
This particular lens hood fits a number of Canon EF telephoto lenses - the 85 1.8 USM, the 100 2.0 USM, the 135 2.8 SF, the 70-210/3.5-4.5, the 75-300 4-5.6 and the 100-300 4.5-5.6 USM.
E indicates that the hood fits an EF mount lens.
W indicates that the hood is for a wide angle lens.
78 indicates that the hood mount is 78mm in diameter.
B indicates that its a hood of type B.
This particular hood fits the 28-135 3.5-5.6 IS USM.
E indicates that the hood fits an EF mount lens.
T indicates that the hood fits a telephoto lens.
160 indicates that the hood mount is 160mm in diameter.
This gigantic hood fits the 600mm 4L USM IS.
Knowing this system you can figure a few things out. For example, the EW-65, ES-65 and ET-65 can all clip onto the same lenses - the only difference is the length. The EW-65 is the shallowest lens and the ET-65 the deepest, so putting an ET-65 onto a 28mm 2.8 lens is a bad idea as youll get vignetting unless you have a cropped image sensor on a digital camera. But you can put an EW-65 onto a 100-300 4.5-5.6 USM if you like. It wont shield your lens as effectively as the longer hood, but its better than nothing. Or if you cant find the discontinued ES-65 you can always use the EW-65 instead.
General lens questions.
Is it okay to change lenses when theres film in the camera?
Yes. A key advantage of a camera with interchangeable lenses is the ability for you to change lenses whenever you want. The camera body contains a shutter which prevents light from hitting the surface of the film regardless of whether or not the lens is attached.
Of course, you should try not to change lenses when youre outside in the pouring rain or in the middle of a sandstorm or whatever. And dont poke your fingers into the shutter itself as youll damage it.
Are there compatibility problems with any EF lenses made by Canon?
Basically, no. Any Canon EF-mount lens will work with any Canon EOS camera.
Now, there are minor compatibility issues with IS lenses on certain old EOS cameras - the lenses work, but IS control is a bit weird or the image may shake in the viewfinder. Luckily this latter does not affect image quality of the photos at all. And autofocus-only EF lenses (a handful were made) are not much use on the oddball EF-M camera, which was an EOS camera which lacked autofocus circuitry and which can only be used with manual-focus-capable lenses. But these are minor issues on the whole.
Note that this compatibility issue is only slightly complicated by the introduction of EF-S lenses, in that an EF-S lens is not an EF lens. EF-S lenses, marked with small white squares rather than raised red dots, can only fit EF-S bodies.
Are there compatibility problems with any EF lenses made by third party manufacturers?
Sometimes. Unfortunately certain third-party lenses not built by Canon, notably many older Sigma lenses, will not work correctly on some newer EOS camera bodies like the Elan 7/EOS 30/33 and the digital EOS 10D. The most common symptom is the mirror flipping up and then the camera freezing when you try to take a photo. You then have to switch the camera off to unlock it. The only solution to this problem is to see if Sigma will upgrade the lens for you. If they still have inventory of the control chip they apparently will happily do so for free.
The only third-party maker of EF-compatible lenses with no major compatibility problems so far is Tamron. Some people have suggested that this is because Tamron have licensed official lens protocol data from Canon, but Canon USAs Chuck Westfall has stated repeatedly in public fora that Canon have never licensed their lens mount protocol to any other manufacturer. So Tamron have either been very lucky or very clever in their reverse-engineering of the Canon lens system. They seem to be a reasonably safe bet right now for compatibility, given their track record, but its impossible to predict future developments in this regard.
The following Sigma lenses require upgrading for compatibility with newer EOS cameras, according to Sigma:
24-70mm 3.5-5.6 aspherical UC
28-80mm 3.5-5.6 mini zoom macro aspherical
28-80mm 3.5-5.6 mini zoom macro aspherical HF
28-80mm 3.5-5.6 mini zoom macro II aspherical
28-105mm 2.8-4 aspherical
28-105mm 3.8-5.6 UC-III aspherical IF
28-135mm 3.8-5.6 aspherical IF macro
28-200mm 3.5-5.6 DL aspherical IF hyperzoom macro
28-300mm 3.5-6.3 DL aspherical IF hyperzoom
70-210mm 4-5.6 UC-II
70-300mm 4-5.6 APO macro super
70-300mm 4-5.6 DL macro super
100-300mm 4.5-6.7 DL
135-400mm 4.5-5.6 APO aspherical RF
170-500mm 5-6.3 APO aspherical RF
8mm 4 EX circular fisheye
15mm 2.8 EX diagonal fisheye
28mm 1.8 II aspherical
50mm 2.8 EX macro
105mm 2.8 EX macro
300mm 4 APO tele macro
400mm 5.6 APO tele macro
500mm 4.5 APO
500mm 7.2 APO
800mm 5.6 APO
28-70mm 2.8-4 UC
28-105mm 4-5.6 UC
28-105mm 4-5.6 UC-II
70-210mm 3.5-4.5 APO macro
28-200mm 3.8-5.6 aspherical UC
Can you use old Canon manual-focus lenses with EOS cameras?
Not really. In the years before introducing EOS autofocus cameras, Canon sold many manual-focus lenses for their SLR cameras. The majority of these lenses are of the FD type. Sadly, FD lenses cannot be used with EOS cameras. The lens mounts are of incompatible sizes and types. This is in contrast to Nikon - most Nikon manual-focus F-series lenses can be used with most Nikon autofocus cameras.
Now it is possible to use adapter rings to attach FD lenses to EOS cameras. Unfortunately its usually not worth the nuisance, in my opinion. There are just too many drawbacks. I have a separate article on using manual-focus lenses with Canon EOS cameras, if youd like to learn more.
Can you use non-Canon lenses with EOS cameras?
That depends. Many third party lensmakers - Tamron, Sigma and Tokina being the big three - manufacture lenses specifically designed to fit Canon EOS cameras. These lenses will, of course, work fine with EOS cameras. The main caveat is the compatibility with the electronics detailed above.
However, if you have a third-party lens which does not physically fit onto your EOS camera then you can obviously assume that the lens will not work with EOS cameras. Sometimes third party lenses can be adapted to fit EOS cameras by way of metal adapter rings, but its often not worth the bother. Autofocus will not work, and apertures will have to be set manually on the lens. So adapting lenses this way is only worth it if you have a particularly unusual lens or are operating on a particularly tight budget. For more information have a look at my using manual-focus lenses with Canon EOS cameras article.
I have a consumer Canon camera. Can I put a professional L-series lens on it?
Of course. As noted above, any Canon EOS camera works with any Canon EF (or compatible) lens.
The major issue you really have to be concerned about is weight, since a really heavy lens can strain the lens mount. The answer is to support the heavy lens by the lens itself - just let the camera hang off the back of the lens. The weight of the camera is not going to strain the lens mount. This applies to all low to midrange EOS cameras, since even those cameras with metal lens mounts have steel mounts attached to plastic body frames. All larger lenses either come with or have optional tripod mounting brackets (see below), so you can attach the lens to a tripod rather than the camera body.
Now of course an inexpensive low-end camera wont have the manual exposure control, focussing speed (AF speed is determined by both the lens motor and the speed of the cameras computer and AF sensors) and film-winding motordrive speed to make full use of a top of the line lens the way a professional would like it. And a small camera will feel unbalanced and cumbersome on a large lens. But its better to have a great lens on a so-so body than the other way around. Renting professional lenses is a great way to learn and practice when youre on a budget.
This brings up the other issue which might arise - snide looks from camera ignoramuses who think that your little Rebel Ti camera isnt fancy enough for the 70-200 2.8L youve got fastened to it. Ignore them. Theyre probably the sort of wealthy dummy who rushes out and buys an EOS 1V and then sticks a cheap consumer lens on the end.
Whats the big deal about f/8?
Most lenses provide sharpest results when used in the middle part of their aperture range. Lenses usually have performance problems when used wide-open. Stopping down helps a great deal, but once the aperture becomes too small then an optical phenomenon known as diffraction comes into play and the quality deteriorates once again. So most lenses work best at around f/8 or f/11 or so.
Naturally this sharpest point (some people call it the sweet spot) varies from lens to lens, so some testing would be required to find whats actually best with a given lens. And the effect is generally more pronounced with less expensive lenses. Really high-quality lenses are often almost as sharp wide open as they are stopped down.
What is a focal length multiplier (or cropping factor) for digital and APS cameras?
35mm film has an image area of 24mm by 36mm. These are the exact dimensions of the area on the film to which an image is recorded.
Medium to low-end digital cameras sold today have sensor chips smaller than 24x36mm in size, since producing a 24x36mm image chip is still quite expensive to do. Similarly, APS film records to an area of film 16.7x30.2mm in size.
The upshot of this is that if you use such a digital or APS camera youll be taking photos which do not record the same image size as 35mm film. So its like taking a photo using 35mm film and then cropping out (snipping off) the edges. Imagine drawing a smaller rectangle within a given 35mm photo and then cutting it out - youve got a digital or APS photo.
This cropping factor is often confusingly referred to as a focal length multiplier. This is because the cropping makes, say, a 50mm lens on an APS camera behave rather like a 70mm lens on a 35mm camera. Not because the focal length has actually changed - it hasnt - but because of this cropping of the image. The cropping factor is sometimes specified as a numeric value - 1.3x or 1.6x, say.
If you want to use your lens to take photos of things far away then this might actually be to your advantage. But if you want to use a wide-angle lens then this cropping factor can be a problem, since wide-angle lenses yield less dramatic results when you crop out the edges.
Some people object to the term cropping factor as well, arguing quite rightly that the issue is a matter of a change in format of the image recording area and using lenses designed for a different size format. This is true, but people are so used to equating a given 35mm film focal length with a given coverage area (or field of view) that I think the concept of a cropping factor is convenient and easily understood.
To give an example, lets say you have a 100mm lens. When used on a 35mm film camera you get a certain coverage of the scene. But if you were to put the same lens on a digital camera with a 1.6x crop factor (ie: a smaller than full frame sensor) then you would not get the same view of the scene - youd get less. The view you would see on your 1.6x digital camera would be the same as if you had a 160mm lens, were there such a thing, on your 35mm film camera.
Theres dust inside my lens!
Unfortunately thats pretty normal. Only certain expensive L series lenses are sealed to prevent air from entering. All others have a lot of cracks and openings where air - and dust - can easily enter. Zoom lenses which extend in length when you alter the focal length are particularly vulnerable to this problem, since air gets sucked in every time you move the lens barrel.
Luckily a little bit of dust inside a lens isnt going to make much difference, so dont worry about it. It may be alarming to see the dust specks when you hold the lens up to a bright light, but itll cost an awful lot of money to have a camera repairperson dismantle the lens and clean each internal element. And theres no guarantee that the elements will be properly aligned when he or she gives it back to you. So unless the lens is coated with a dusty grey film of dust you shouldnt have any problems.
Theres a scratch on the front glass of my lens!
A tiny scratch or chip on the front glass of a lens, alarming as it may look, wont actually make much difference in image quality under most circumstances since its far enough from the film or image sensor plane not to be in focus. It can, however, affect lens flare, so its usually worth filling in the chip with black pen. Having said that, a large chip (more than a few millimetres long) is obviously undesirable. And chips on the rear glass of a lens are more of a problem.
Ive seen ads for teleconverters or extenders. Can I put one of these onto my, say, 50mm lens and magically turn it into a 100mm lens?
Yes and no. The answer to this is complicated, but leans mainly towards the no side.
Teleconverters, called extenders by Canon, are optical accessories which fit between the camera body and the lens. Theyre essentially tubes with a few glass lens elements inside which multiply the focal length of the lens in use - typically by 1.4x or 2x. So a 50mm lens with a 1.4x teleconverter (TC) would take the same photographs as a 70mm lens, and a 100mm lens with a 2x TC. Think of TCs as magnifying glasses - they enlarge the central portion of the image and cut off the periphery.
Unfortunately you cant get something for nothing. And in the case of TCs there are three major tradeoffs.
First, using a TC cuts the amount of light entering the camera. A 1.4x TC costs you a stop of light and a 2x TC costs you 2 stops. This is particularly problematic if you have a slow lens. Since most Canon cameras (pro cameras notwithstanding) cant autofocus with lenses slower than f/5.6 you may lose autofocus, or at least reliable autofocus, if you use a TC. You can sometimes get around this by taping over the teleconverters extra pins, thereby fooling the camera into thinking there isnt a TC on it at all, but obviously thatll only really work if theres enough light coming into the camera for the autofocus mechanism to function. Manual focussing will also be difficult if the view through the viewfinder is dark, as it will be with slower lenses.
Second, theres the question of compatibility. Canon manufacture two teleconverters - Extender EF 1.4x and Extender EF 2x - but they are specifically designed to work only with the handful of expensive telephoto lenses listed below. These extenders have protruding front elements and so physically cant attach to most EF lenses - the protruding element simply gets in the way. You could work around it by sticking an extension tube between the TC and the lens, but this would cut even more light and would also mean you lose infinity focus.
You can avoid this problem by eschewing Canon and going third-party for your TCs. Tamron and Kenko sell their own TCs which dont have these protruding elements and so can physically mate with any EOS lens (though TCs in general dont work very well optically with lenses which arent telephotos). These third party TCs come in varying levels of optical quality. The better quality (more expensive versions, such as the Kenko Teleplus Pro 300 DG) models are generally held as having decent optics, though not quite as good as the Canon products.
Third, all TCs degrade image quality somewhat. First, youre adding a bunch more glass between you and the scene youre photographing and second, youre using only part of the centre of your lens. 2x TCs enlarge more of the middle of the lens than the 1.4x TCs, which makes 2x converters worse optically. Now, in the case of a fancy Canon L series lens and a Canon Extender, this optical degradation will be fairly minimal. However, if you take your typical cheap consumer zoom lens and slap a third-party TC on it youll find that the results will be less than stellar. In fact, in such cases youre probably better off simply cropping and enlarging part of a photo taken without a TC and leaving it at that. The quality would be higher and youd save money.
So. The answer to this question really depends. If you have a professional lens and a quality TC then, yes, youll be able to increase your focal length at the cost of some light. But if you have your typical consumer lens then theres probably no point buying a TC - youll end up with fairly crummy photos.
Canon extender compatibility list:
The Canon extenders are physically compatible with all prime (fixed focus) Canon EF lenses with a focal length of 135mm or longer except for the 135mm 2.8 SF. They are also compatible with a handful of recent L series zoom lenses. The full official list is:
Consult Canon when checking out newer L series lenses introduced since this list was written, and youre on your own if you use third party lenses. You can also use Canon extenders with Canon TS (tilt-shift) lenses, but it should be noted that the TS lenses cant report to the camera that the extenders are there.
- 70-200mm 2.8L
- 70-200mm 2.8L IS
- 70-200mm 4L
- 100-400mm 4.5-5.6L
- 400mm 4 DO
- 135mm 2L
- 180mm 3.5L Macro
- 200mm 1.8L
- 200mm 2.8L
- 300mm 2.8L IS
- 300mm 4L
- 300mm 4L IS
- 400mm 2.8L IS
- 400mm 5.6L
- 500mm 4L IS
- 600mm 4L IS
- 1200mm f/5.6L
Autofocus is not supported by non-pro EOS cameras when the 1.4x converter is used with 100-400mm 5.6L, 400mm 5.6L, 500mm 4.5L, 1200mm 5.6L, and with the 180mm 3.5 Macro when its focussed closer than 0.8 metres, or when the 2x converter is used with the 70-200mm 4L, 100-400mm 4.5-5.6L, 180mm 3.5L Macro, 300mm 4L IS, 300mm 4L, 400mm 4 DO, 400mm 5.6L, 500mm 4L, 500mm 4.5L, 600mm 4L, and the 1200mm 5.6L.
Note that there are two generations of the Canon Extenders - the original 1.4x and 2x models and the mark II successors, which add improved weatherproofing. The 1.4x II is said to be optically identical to its predecessor but the 2x II has minor optical enhancements.
I want to take closeup (macro) photos. What do I need?
Closeup or macro photography is a lot of work, but it can also be extremely rewarding. Detailed closeup photos of tiny objects can literally introduce you to another world. Here are some reasons why its a very challenging area of photography.
Here are your six basic choices if you want to take a closeup photograph.
1) Buy a true macro lens capable of reaching 1:1 magnification.
(see the previous section for an explanation of 1:1 magnification) This is the most expensive option, since true macro lenses arent cheap. However, its usually the most high-quality option. True macro lenses come in a variety of focal lengths, from 50mm to 90 or 100mm to 180mm. The advantage of the longer lenses is that they give you more working distance from your subject. A 50mm macro lens isnt very useful for shooting, say, dragonflies in the wild since you have to be really close to them. A 180mm macro lens, on the other hand, lets you maintain more distance so youre less likely to frighten them off. Of course, 180mm macros are pretty expensive. A 90/100mm lens is usually the better compromise in terms of working distance and cost.
There are six true macro lenses in the EF lineup which can do 1:1. There is the 50mm f2.5 Macro (which technically only goes to 1:2 or half-size and requires the optional Life Size Converter EF to reach true 1:1), the discontinued 100mm 2.8 Macro, the newer 100mm 2.8 Macro USM, the expensive 180mm 3.5L Macro USM and the EF-S 60mm 2.8 macro, which only fits EF-S-compatible cameras. There is also the unusual MP-E 65mm lens; see below. Another popular macro lens worth considering, though not from Canon, is Tamrons 90mm macro lens.
2) Buy a diopter (macro filter).
These are round screw-on lenses which fit on the end of a lens in exactly the same way as a filter and which act essentially like magnifying glasses. The amount of magnification you get depends on both the strength of the diopter and the focal length of the lens to which you attach it. Diopters cost no light but can degrade the image slightly, depending on the quality of the product. Still, theyre lightweight and portable and, since they cost no light, usually permit autofocus to work. Theyre usually a good approach for beginners looking to explore macro photography.
You can buy both single-element diopters which contain a single piece of glass and two-element diopters which contain two. Two-element diopters are what you want - they cost more but provide vastly better optical quality by correcting certain optical aberrations. Diopters are available in a variety of physical sizes which match popular lens filter sizes, but can be adapted with step rings just like ordinary filters if necessary.
Canon sell two two-element diopters - the 250D and the 500D. The former is intended for shorter focal length lenses, from about 30-135mm. The latter is meant for longer focal length lenses, from about 70-300mm. You can also buy a 500 diopter which, since its a single-element accessory, isnt as good. You dont have to buy Canons diopters, of course - Nikon also sell highly-regarded diopters (the Nikkor 3T, 4T, 5T and 6T closeup attachments) which are actually usually less expensive than Canons. Bob Atkinss Web site has a comprehensive table of magnifications available using different diopters on different lenses.
3) Buy an extension tube.
These are hollow plastic tubes which fit between the lens and the camera body, thereby increasing the distance of the lens to the camera and thus reducing the close focus distance of your lens. (ie: they let you move the lens closer to the subject while retaining focus) Attaching an extension tube means you lose infinity focus but thats obviously not an issue if youre using the tube to take closeup pictures. Tubes also reduce the amount of light reaching the film or image sensor (because moving the lens further from the film or sensor plane causes the light to spread out across a larger area).
Unlike diopters, however, they do not affect image quality at all as no optics are involved. The magnification you get depends on both the length of the tube or tubes used and the focal length of your lens - Bob Atkins table lists some common combinations. Some lenses, particularly wide-angle and specialized lenses such as the 15mm 2.8 fisheye, 14mm 2.8L and MP-E 65mm 2.8, dont work properly with tubes. If you have EF-S lenses for newer EOS digital cameras then youll need the mark II Canon extension tubes (the Extension Tubes EF 12 II and EF 25 II), since the earlier versions dont mate with EF-S lenses - EF-S lenses extend deeper into the camera body than EF lenses.
Canon sell a couple of extension tubes, but theyre pretty expensive. The three-tube set from Kenko is a better deal - its fairly well made and contains a 12mm, a 20mm and a 36mm tube. However, current Kenko tubes are compatible only with EF lenses - they do not physically mate to EF-S lenses.
Adjustable bellows are also used for closeup photography - theyre basically adjustable tubes when you get down to it. Novoflex sell an EOS-compatible bellows or you could buy the old Canon FD bellows and adapt it using the FD to EOS macro adapter. Bellows are typically used with movable rails for precise focussing.
4) Reverse a lens by mounting it onto the camera backwards.
Doing so requires some sort of adapter with a standard EOS lens mount on one end and a filter ring on the other which attaches to the filter ring of the lens. People often make such things at home by gluing a filter ring to a drilled-out body cap. Reversing a lens like this is a very old photographic trick for doing macro photography.
This technique is a problem for EOS lenses, however, since EOS lenses require electrical connectors in order for the aperture diaphragm to operate. There are at least three possible solutions for this. First, you could set the lens aperture to whatever you want it to be, press the depth of field button on your camera to stop down the lens and then detach the lens. The lens diaphragm should stay wherever it was when you removed the lens and you can then reverse the lens and use it. This isnt terribly convenient, of course, since you cant adjust the aperture without remounting the lens. Second, you could use a non-EF lens. Any 35mm lens will do, really, since youre mounting it backwards and not using the normal lens mount. Third, you could buy Novoflexs rather expensive lens reversal adapter, which contains the necessary wires and connectors to let the electromagnetic diaphragm operate correctly.
5) Attach a reversed lens to an existing lens.
Another old macro trick is to attach a 50mm (normal) lens to the end of another lens, but backwards. (ie: the filter threads of the 50mm lens are attached to the filter threads of the camera-mounted lens by means of a special lens-reversing or macro-coupling ring) You wont be able to adjust the aperture of the reversed lens if its an EF-type lens, but theres nothing stopping you from using a non-EOS lens in this way, as above. A 50mm lens reversed on a 100mm lens can give you 2x magnification, for example, albeit with a fair bit of light loss.
6) Buy the Canon MP-E 65mm lens.
This is an unusual and specialized lens thats designed solely with macro photography in mind. It cant be used for normal photography, unlike the other Canon macro lenses, as it starts out at 1:1 magnification. It goes from there to 5:1 magnification. At this magnification an object 5mm x 7mm in size will fill the entire frame of 35mm film.
Though intriguing, it has a number of drawbacks. First, you can use it for super closeup photography and nothing else since it lacks infinity focus. Second, it suffers from the usual problems of macro photography - very narrow depth of field and the difficulty in illuminating objects adequately given the short working range. Third, ambient light metering works only with EOS 1 series cameras - all other EOS cameras can only be used with TTL flash metering. And fourth, the focussing screen of your camera may not be precise enough for accurate focussing.
Can I use the Canon 100mm macro lens for portraits?
Absolutely. The 100mm 2.8 macro and macro USM lenses are both excellent portrait lenses in addition to being great macro lenses. The only problem is that theyre extremely sharp lenses, and some people prefer softer lenses for portraiture, particularly of women. If youre in that camp you could always slap a soft focus filter onto the lens.
What happened to the solid all-metal lens barrels of yesteryear? Why is everything today made of plastic?
Its true that a lot of lens barrels of the 60s and 70s were solid finely-crafted metal masterpieces with smooth focussing spiral-shaped helicals and precisely-machined parts. Whereas today many lens barrels are made largely of plastic. There are a number of reasons for this - the rise of autofocus, rise in labour costs, lower SLR sales, improved plastics technology, a desire to make lighter-weight gear, increased profit margins for manufacturers and so on.
Certainly the rise of autofocus is a major factor. Autofocus lenses with geartrains (ie: ring USM lenses excepted) require a bit more looseness and play in the geartrain system. They also dont usually use long focussing helicals as that would take more battery life and time to focus. Manual focus lenses with helicals, by contrast, can be machined to very tight tolerances.
However, there are advantages to increased use of plastics in lens construction. Quality plastic is fairly resilient and doesnt dent like metal, plastic is obviously much lighter than metal, plastic components are less expensive to produce and can in theory result in lower prices to the consumer and so on.
So, while the old manual-focus lenses may feel great to hold and use and exude that terrific sense of precise quality that plastic lenses simply do not do, its unlikely that less expensive autofocus lenses will ever be made with metal barrels. Note, however, that many Canon L series lenses use solid metal barrels and have reasonably tight-feeling manual focus rings. So if youre willing to spend the money you can still get metal lenses and retain autofocus.
Grades of plastic
Theres also plastic and theres plastic. Canon have used, very roughly speaking, three different grades of plastic shell material for their EF lenses over the years.The first generation of EF lenses used a fairly brittle hard type of plastic, which I call type 1. (though that isnt, of course, an official Canon designation) This material was moulded with a slight rough texture and the lenses had basically parallel lines to their cylindrical barrels, with little if any tapering. Focus and zoom rings often did not have rubberized surfaces. The 50mm 1.8 mark 1 is an example of this late 80s type of design. In my experience, though this purely anecdotal, type 1 plastic is a bit more likely to crack upon impact than later plastics. The second generation, particularly black L lenses and advanced amateur lenses, are made of a more resilient hard black plastic, which I call type 2. These lenses have relatively little texture - theyre either quite smooth or have a subtle hammered finish. These barrels tend to have subtly tapered barrels rather than simple cylinders, and have rubberized zoom and focus rings. The 28-105 3.5-4.5 USM is an example of a midrange zoom of this construction, and the heavier 135mm 2.0L USM is an example of an L lens using this construction, albeit with thicker plastic and a generally sturdier design. Lenses of this type first came out in the early 1990s, and seem to me to be slightly less likely to crack upon impact - the plastic has a tiny bit more inherent flex to it.Finally, inexpensive cheapie lenses over the past few years have been made of lightweight smooth plastic which I characterize as type 3. These lenses often have somewhat exaggerated rubber rings for zoom grips, and later models (late 90s on) have shiny chrome rings around the end to impress less experienced consumers. The EF-S 18-55 3.5-5.6 is a typical example of this type.
Lens-related technical terms and vocabulary.
What is focal length?
The focal length is a basic optical property of any lens, and the most important one to a photographer. The simple way to think of the focal length is to think of it as a numerical value, expressed in millimetres, which represents how much of a given scene (the coverage area) a lens can take in.
Focal lengths for Canon SLR lenses range from ultra-wide (14mm) to incredibly long telephoto (600mm and 1200mm). The typical range of an affordable lens or lenses is from 28mm to 105mm or so.
Why, then, these strange values in millimetres? Why not indicate the angle of view taken in by each lens instead? Well, partly for historical reasons and partly for practical reasons. The technical description of focal lengths is rooted in the mathematics of optics - its the distance between the focal plane and the rear nodal point of the lens, given infinity focus. How this bit of Martian translates to the field of view depends on the size of the imaging area being used, which can be different between 35mm film cameras, APS cameras and some digital cameras. And as for practical reasons, the focal length of a lens is an innate property of the lens, but the actual coverage area of the scene depends on the size of the image format used.
So note that crucial point - all the examples I gave above are for a 35mm film camera or full-frame EOS SLR only. If you were to use a 28mm lens on an APS camera or a digital camera with an image sensor smaller than that of 35mm film (ie: most digital cameras sold today) then you would have a much narrower field of vision than if you were to use the same lens on a 35mm film camera. For more details see the section on focal length multipliers/cropping factors.
The same focal length system is used to describe lenses for other types of cameras as well, such as medium format cameras. But the area taken in by a lens on a medium format camera will be totally different from that of a lens of the same focal length on a 35mm camera, because the area covered by medium format film is considerably larger.
What is a lens aperture or f stop?
The aperture of a lens is its second most important optical property after its focal length. Consider the human eye. It has a coloured iris with a pupil which can dilate or contract in order to let in more or less light, depending on ambient light conditions. When its dark the pupil opens up to let in as much light as possible. And when its sunny the pupil contracts to prevent the bright light from overwhelming the eye. Most camera lenses have a device analogous to the iris - a metal or plastic diaphragm which can be adjusted in size to control the amount of light entering the lens.
The variable-sized hole in the diaphragm is known as the aperture, is analogous to the pupil of the eye, and is indicated numerically by an f-stop or f-number value. This value, the relative aperture of a lens, describes the amount of light that a lens lets in. The value is relative because it is equivalent to the focal length of the lens divided by the size of the lens aperture, not the physical dimensions or anything.
For example, if you were to take a 50mm lens with a 6.25mm diameter aperture youd have a lens set to f/8 (since 50/6.25 = 8). Generally each increase or decrease in f-stop value either doubles or halves the aperture size. Since f-stop values are relative to the focal length, each camera lens should let basically the same amount of light through at the same f-stop value regardless of focal length. (barring complex technical factors such as light loss from large numbers of elements and so on, but we wont get into that here)
The usual f-stop range on 35mm and digital SLR camera bodies is:
1.0 1.4 2 2.8 4 5.6 8 11 16 22 32
though most camera lenses are only optically capable of a subset of that overall range.
The relationship between these values involves halving and doubling the amount of light. Going from f/2.8 to f/4, for example, involves a halving of the aperture size. Each number is approximately 1.4x more than its previous stop since 1.4 is the square root of 2 (to one decimal place), though since the specific numbers derive from tradition they are not always spot on. Lenses for larger camera systems such as large format cameras usually have even smaller apertures - going to f/64, for example.
This series of numbers may look difficult to work with, but in fact theres a fairly simple way to recall it. Just remember that the first two values are 1.0 and 1.4 respectively. Each following value then doubles by every other value. So 1.0 becomes 2, then 4, then 8 and then 16. 1.4 becomes 2.8, then 5.6, 11 and 22. (the only minor glitch, of course, to this handy mnemonic scheme is between 5.6 and 11)
Confusingly enough, when the number is small (eg: f/2.8) then the lens diaphragm is open wider (opened up) and thus more light enters the lens. If the number is large (eg: f/22) then the lens diaphragm is closed smaller (stopped down or closed down) and thus less light enters the lens. In addition to altering exposure times, the aperture setting also affects depth of field.
The letter f is frequently italicized for good looks, and a slash is often placed between the letter f and the numerical f stop value to indicate that the f-stop value is a fraction of the focal length. eg: f/4 means that the aperture is a quarter of the focal length. The letter f stands for focal, factor or focal length depending on who you talk to, and the number is also often stated as a ratio. (eg: 1:2.8)
Note that not all lenses have adjustable diaphragms. Many types of lenses, though not usually those sold for use with EOS cameras, have fixed apertures. Mirror lenses, for example, fall into this category since they lack (adjustable) diaphragms. Really crummy cameras - disposable cameras being one example - also have fixed apertures. These two examples aside, however, nearly all lenses sold for use with EOS cameras have adjustable apertures.
What is a slow lens or a fast lens?
These are colloquial expressions describing the maximum aperture value or values of which the lens is capable. Slow lenses have a very small maximum aperture, which means less light enters the lens and so longer time periods are required to expose the film or image sensor. Fast lenses have a very wide maximum aperture and so shorter time periods are required to expose the film or image sensor.
The larger the maximum aperture of a lens the more light it lets in. And so faster lenses are generally more desirable than slower lenses. First, fast lenses let you take photos in lower light levels using available light rather than blasting the scene with ugly light from a flash unit. Second, you can see through the viewfinder better since fast lenses let in more light and so the view through the finder will be brighter with a fast lens.
As explained above, lens f stops are ratios, and so smaller numbers indicate larger apertures. A lens with a maximum f stop value of 1.4 is, therefore, fast. And a lens with a maximum f stop value of 5.6 is slow by comparison. However, f stop numbers are the ratio between the focal length of the lens and the aperture, which means that its very easy to design a fast 50mm lens (1.8 is a typical maximum aperture value) but very hard to design a long 200mm telephoto lens with a maximum aperture so large.
In fact, designing fast lenses in general is more complex and expensive than designing a lens with a small maximum aperture, so fast lenses tend to cost more than slow ones. Its also harder to design and build a fast zoom lens than it is a fast prime (fixed focal length) lens. Faster lenses are also usually physically larger than slower lenses of equivalent focal lengths. The reasons for all this are tied into the complex mathematics of optics.
Note that autofocus lenses for EOS cameras have the focus motor built into the lens, not the camera. And some lenses focus more rapidly than others. So sometimes you hear people talking about a lens having a fast or slow focus motor speed, which is a separate matter altogether from the optical properties of the lens.
What is depth of field?
When you focus on something, the subject isnt the only thing thats going to be sharply focussed. Certain objects closer to you and further away from that subject will also be in acceptable - though not quite as sharp - focus. The distance range within which these objects appear to be in reasonable focus in your final photograph is known as depth of field. Being able to control depth of field is an important photographic skill since it can affect the appearance of a photograph dramatically.
For example, lets say youre taking a portrait of someone outside. And lets say that the reason youre doing so outside is to get nice natural lighting, but you dont care so much about the background as such. Maybe youre in a park and you dont want to show a cluttered background of trees, grass and bushes. In this case youll want a narrow depth of field and focus on the persons eyes since theyre the key thing you want to have in focus. If you have a narrow depth of field then the background will be thrown nicely out of focus and youll just have a pleasingly blurry green background to your portrait.
But lets say you want to take a nature photograph of a flower in a dramatic mountain landscape with an interesting sky. In this case youll probably want everything from the flower to the sky to be sharply in focus. This would require great depth of field.
There are three factors which control depth of field on a given camera. They are as follows:
The aperture (f stop) to which a lens is set is a very important factor governing depth of field. The larger the aperture (smaller the f stop number) then the smaller the depth of field and vice versa. So if youre shooting something in low light conditions and open your lens up to f/1.8 in order to admit as much light as possible youll find you have a really narrow depth of field, which can be a real problem sometimes, since precise focussing is required. Conversely if youre shooting outdoors on a bright sunny day you may find youll need to stop down a long way to get the shutter speed you want, but this can result in too great a depth of field for some applications.
The focal length of your lens also makes a tremendous difference. Lenses with short focal lengths (wide angle lenses) have wider depths of field available and lenses with long focal lengths (telephoto lenses) have shallower depths of field available. This is generally a good thing. If youre using a really wide lens for landscape shots youll be able to get huge areas of scene in sharp focus. But if youre using a really long telephoto lens for bird photography then your depth of field will be really shallow and youll be able to isolate the bird in the landscape nicely.
Finally, the distance from the lens to the subject also affects depth of field. If youre really close to your subject, such as in macro photography, then depth of field will be shallow. But if youre taking a photo of something thats a long way away then your depth of field will be deeper.
Naturally all three of these factors work together, so you can adjust all three factors to achieve the effect youre looking for.
It should be noted that the size of a cameras image area also dictates the depth of field. A camera with a large image area - say a medium-format or large-format camera - is capable of a much more shallow depth of field than a camera with a smaller image area. This is why consumer digital cameras, which have tiny image sensors, have such deep depth of field. However, you cant change this particular factor without switching cameras. The other three factors above are adjustable on any given EOS camera.
It should also be noted that this is a very non-technical description of what depth of field is all about. To be more accurate about it you need to go into a lot of math and a definition of the circle of confusion and a consideration of the print size and so on. But the simplified stuff above is adequate to get a grasp of how to control depth of field adequately to make your photos look the way you want them to.
What is a bayonet mount?
Canon EF mount lenses are of the bayonet type. This means that the lenses have mounting lugs (three in the case of EOS lenses) which slot into the camera body mount. You then rotate the lens a partial turn to lock it into place with a click.
Most camera makers these days use bayonet-style mounts, though other types were popular in the past. For instance, older Pentax and Leica cameras used screwmount systems - you simply screwed the lens into the camera bodys threaded mount. The lens system used by Canon prior to the introduction of EOS was the FD system, which used a breechlock mount system with a rotating friction ring.
Lens hoods often fasten by means of bayonet mounts. Some filters for certain European lenses also use bayonet mounts, though Japanese makers generally use threaded filter mounts.
Its not clear why the lens mounts are called bayonet mounts. The two theories Ive heard both stem from bayonets, the knives which soldiers fasten to the end of their rifles. One theory, which is probably utterly apocryphal, suggests its a gruesome joke deriving from the instructions given to soldiers on how to use their bayonet - thrust in and twist. The more probable and prosaic theory is that the term derives from the design of bayonet mounts on rifles.
What does a Roman numeral on a lens refer to?
Canon, like most Japanese lens makers, use the optical specifications of a lens to distinguish one model from another. (European makers have traditionally come up with fun names resembling Star Trek planets, like Tessar, Biogon or Super Angulon, to describe their lens designs) But sometimes a maker will produce new models later on which happen to have the same basic specifications as previously-made ones. To distinguish these lenses one from another Canon will add a Roman numeral to the end of the lens specification, starting with II. For this reason you will never see a lens marked with a I, though people often refer to mark I lenses when subsequent models are released. You will, however, see lenses marked with II, III, IV, etc. These are commonly referred to as mark II, mark III, etc, lenses in common parlance.
Sometimes these later lenses are an improvement over the original, sometimes theyre worse and sometimes they are almost identical bar some cosmetic changes. For example, the 50mm 1.8 II is markedly inferior to its predecessor in build quality but has the same great optics, the 28-80 3.5-5.6 USM II is entirely worse in every respect to the mark I edition, but the 28-105 3.5-4.5 and 28-105 3.5-4.5 II lenses are basically the same with slight cosmetic differences. Theres unfortunately no way to tell from the Roman numeral designation itself whether or not a later lens is better or worse. I try to identify these differences between versions in my PhotoNotes lookup page, so thats a good starting point.
Canon also release updated versions of lens hoods using Roman numeral designations, as described above.
What is the difference between the various kinds of lens motors (AFD, MM, USM)?
Unlike most camera makers Canon chose to position the autofocus motor inside the lens barrel rather than in the camera body when they designed the EOS system. This was arguably a wise move, since it means autofocus motor can be tailored to the requirements of each lens. A big telephoto lens can have a large motor and a small normal lens can have a more compact motor. By contrast, systems which rely on the autofocus motor being only in the camera body dont have this flexibility - the motor is always the same regardless of the lens used unless you change camera bodies.
So. Canon employ a number of different motor technologies in their lenses. The first two types are never identified specifically on the exterior of the lens. You have to look up in Canons product literature to see which type of motor a given lens uses.
Traditional electromagnetic motor drives.
Such motors contain tiny wound coils of wire and rely on electromagnetic principles to turn a shaft. Little cogwheels and gears are then used to translate this rotational motion into the movement needed to adjust lens focus.
Arc-form drive (AFD).
Generally used in a number of older lower-cost lenses, AFD motors are simply little electric motors which drive a geartrain. Theyre somewhat noisy - electric buzzing and grinding of gears - and not terribly fast. This isnt a big deal on smaller lenses since the distances the motors must move the focussing elements arent very far. However, telephoto lenses with AFD motors can be quite sluggish.
Micromotor (MM) drive.
Generally used on a few older lower-cost lenses. Similar to AFD - slow and noisy and based around an electric motor driving a geartrain. Some particularly low-cost lenses use micromotor drives with rubber belts.
Ultrasonic motors do not rely on magnetic coils like most electric motors. Instead they use extremely high-frequency vibrations which translate into circular motion. The result is a very fast and pretty well silent (to human ears, anyway) lens motor. There are two basic types employed by Canon.
Ring ultrasonic (USM) drive.
The kind you want. These motors consist of two metal rings which vibrate at a very high frequency. (have a look here for photos of these rings) Ring ultrasonic lenses are great because they focus quickly and silently and also support full-time manual (FTM). There are actually two variants of this design - see the FTM section below.
Micromotor ultrasonic (USM) drive.
This kind is less desirable. Its a form of USM motor that Canon designed for their cheapie lenses so they can bill them as ultrasonic for marketing purposes. An MM lens replaces the standard magnetic motor with an ultrasonic motor but retains the usual geartrain setup. Such lenses are still reasonably quiet, though not as quiet as ring ultrasonic motors, but usually lack FTM - see below.
Note that, while all lenses with USM in the name contain an ultrasonic motor, Canon do not distinguish between ring and micromotor USM drives in the name - you have to look up the specs for the individual lens to find that out. Also, most non-L lenses with USM drives have striped gold lines painted around the end of the barrel. However, all L lenses have red lines painted around the end, whether or not they use USM (ie: Canon never have two painted rings around their lens barrels, and the red L line takes priority over the gold USM line).
What is full-time manual (FTM)?
As noted above, Canon EF lenses with AFD (arc form drives) and MM (micromotor) drives use very simple autofocus mechanisms which rely on electric motors and geartrains - rows of tiny cogwheels. Unfortunately, turning such a focus system by hand can damage the geartrain, so such lenses have a switch mechanism which disengages the cogwheels when you focus manually. There is thus no way for you to focus manually when the lens is switched over to autofocus mode.
However when Canon introduced lenses with USM (ultrasonic motor) autofocus systems they also introduced full-time manual focussing (FTM). Such lenses allow you to adjust focus manually even when the AF/MF switch is set to autofocus. This is very handy, as it lets you adjust or touch up focus without having to flip the switch.
There are a few points to keep in mind here.
The best USM motors are those used in most midrange and L series contemporary lenses - ring USM motors. A ring USM motor consists of two metal rings which vibrate at high frequencies, resulting in rotational energy. Full-time manual on a ring USM lens is easy - theres a simple friction clutch which means youre simply turning the whole motor by hand when you rotate the focus ring. This means you can focus the lens manually at any time, even if the camera is turned off or the lens isnt attached to a camera.
EF 50mm 1.0 L USM
There are a couple of exceptions to confuse matters,
however. The 50mm 1.4 USM and the newer 28-105
4-5.6 USM lenses contain slip clutch mechanisms which let you use FTM in a fashion similar to a ring USM lens.
EF 85mm 1.2 L USM
EF 85mm 1.2 L USM II
EF 28-80mm 2.8-4 L USM
EF 200mm 1.8 L USM
EF 300mm 2.8 L USM
EF 400mm 2.8 L USM
EF 400mm 2.8 L II USM
EF 500mm 4.5 L USM
EF 600mm 4 L USM
EF 1200mm 5.6 L USM
The best USM motors are those used in most midrange and L series contemporary lenses - ring USM motors. A ring USM motor consists of two metal rings which vibrate at high frequencies, resulting in rotational energy. Full-time manual on a ring USM lens is easy - theres a simple friction clutch which means youre simply turning the whole motor by hand when you rotate the focus ring. This means you can focus the lens manually at any time, even if the camera is turned off or the lens isnt attached to a camera.
EF 50mm 1.0 L USM
There are a couple of exceptions to confuse matters, however. The 50mm 1.4 USM and the newer 28-105 4-5.6 USM lenses contain slip clutch mechanisms which let you use FTM in a fashion similar to a ring USM lens.
Do USM lenses take better photos than non USM lenses?
No. USM (ultrasonic motors) are autofocus mechanisms. They in no way affect the optical quality of a lens.
Of course, since USM lenses focus faster and more quietly than non-USM lenses theres the possibility that using one might help you get a photo that you might not have got with a slower or louder autofocus lens. But that again is unrelated to the optical quality itself.
This confusion may come in because Canon only put ring USM drives into their midrange and pro (L series) lenses. You cant buy cheap Canon lenses with ring USM - only micromotor USM (see above). But again this is no guarantee of anything, since there are plenty of Canon lenses - particularly their older prime lenses - which lack USM but which have excellent optical quality.
What is image stabilization?
Image stabilization or IS is a Canon technology that optically corrects for camera motion when you take a photo. Since camera motion - caused by handholding the camera, for example - can result in blurring of the image at slower shutter speeds, IS can result in sharper photographs when fast shutter speeds are not possible.
IS is a fairly complex technology involving motion sensors, microcomputer chips and small motors to move key lens elements. There is, therefore, a price premium for IS-capable lenses. But they can be very convenient - when handholding a camera you can easily gain a stop or two over using a non-IS lens.
However, remember that IS does not increase the maximum aperture of the lens or anything. An IS lens with a maximum aperture of 3.5 still has a maximum aperture of 3.5. IS simply lets you use a slower shutter speed than would otherwise be possible when youre handholding the camera, by compensating for camera motion. So you wont necessarily be able to get that narrow depth of field that you could with a faster lens - which could be a drawback or a benefit depending on your point of view.
IS has a few other drawbacks over faster lenses as well. Earlier IS lenses tended not to perform very well when mounted on a tripod when the IS mechanism was engaged. Consumer IS lenses also do not work very well when panning (tracking a moving object), though pro IS lenses do. IS does not help you if the subject is moving - it compensates only for camera motion. IS doesnt help freeze subject motion and in fact will probably make things worse by letting you use a much slower shutter speed than a fast lens. Some people find the slight swimming motion in the viewfinder when using IS a bit dizzying and IS uses a little more battery power than no stabilization at all. Finally, some earlier film EOS cameras are not entirely compatible with IS lenses and have minor inconveniences, such as viewfinder shake once a photo has been taken (though this does not affect the picture quality).
Nonetheless, these drawbacks aside, most people find IS quite valuable, particularly on long telephoto lenses.
Canon were the first company to include image stabilization technology in SLR lenses, though Nikon actually pioneered the field with a stabilized-lens point and shoot (the Zoom-Touch 105 VR) in 1994. Today Nikon sell a range of VR (vibration reduction) SLR lenses; the main difference being Nikon sell mainly to the high end lens market where Canon sell a variety of IS lenses covering the mid to high end markets. Sigma have also released a number of image-stabilized lenses. Canon IS technology is built into the lens, like the Mega Optical Image Stabilizer (Mega OIS) system used by Panasonic. These both differ from the Minolta-developed Super SteadyShot stabilization technology used by Sony, which is built into the camera body. Building anti-vibration technology into the camera has the advantage of making the feature available to any lens attached to a supported camera, but it has the disadvantage of not being tailored to each focal length range.
What is distance data and which lenses support it?
Many Canon EF lenses have the ability to send distance data to the camera. For example, if youre currently focussed on an object 4 metres from the camera then the lens would send that approximate distance data to the camera body.
Canon have built and sold lenses since 1990 with this data, but it wasnt until 2004, with the advent of E-TTL II flash metering, that Canon really put it to good use. E-TTL II has the ability to factor distance data into flash metering calculations under certain conditions. This distance data can improve the reliability of flash metering when its available and appropriate.
For more information on this topic please consult my EOS flash photography article, which has a section on E-TTL II and a list of Canon EF lenses capable of returning distance data.
What is a lens element?
Theres some confusion of terminology here. The word lens refers both to a single chunk of shaped glass (think of the single lens of a magnifying glass) and the tube-shaped device containing such lenses which you fasten to the end of your camera.
A lens element is a single piece of shaped glass or crystal. Camera lenses these days contain anywhere from 4 lens elements and up. They are frequently arranged in optical groups within the barrel. For that reason you may hear of a given lens having, say, 18 elements in 15 groups.
There are complex tradeoffs made in lens designs, so the number of elements and groups isnt always the most reliable indicator of image quality. Simpler lenses with just a few elements tend to offer good results because they are so simple. Flare in particular (light reflection between elements in this case) is vastly reduced. However, wide angle and telephoto lens designs generally require more elements to correct for various optical aberrations.
What is a lens coating?
As anyone who has looked through a window knows, glass both reflects light and lets light pass through. And reflections can easily happen at oblique angles as well as when you look at a lens straight-on. Camera lenses suffer from the same basic problem of reflections as windows. And excessive reflections within the lens can result in lens flare - either a generalized loss of contrast or bright reflected blobs appearing in the picture.
The invention of lens coatings by German lensmaker Carl Zeiss in the mid 1930s revolutionized lens design. Such coatings are fine layers of transparent material which are applied to the surface of lens glass and which minimize internal reflections within the lens. All modern camera lenses, including Canon EF lenses, are multicoated to reduce reflections. Canon refer to their technology as SSC, or Super Spectral Coating.
You can easily tell a coated glass surface from an uncoated one. An uncoated piece of glass reflects a lot of light, and reflected white light is also white. A coated piece of glass, however, reflects far less light and the light that is reflected is often greenish, purplish or reddish. These apparent colours, it should be noted, are artefacts of the way coatings absorb reflections, and do not mean that photos taken through decent quality coated glass are going to be tinted one colour or another.
Lens coatings have two drawbacks. First, they must be kept scrupulously clean at all times, as oils and dirt interfere with the way they work. Fingerprints are extremely obvious on coated glass. Second, many lens coatings are fairly fragile and are easily scratched, so care is required in handling and cleaning them. Some lens and filters include hardened surfaces over the top of the coatings to protect them, but this is not universal.
What do aspheric or aspherical mean?
The glass elements which make up a traditional camera lens can be thought of as cross-sections of a large sphere. That is to say that the curvature of each surface is even. The problem with spherical lens designs is that light passing through the outer edges of curved camera lenses focus at different points from light passing through the centre. This causes focus errors, or spherical aberration and other forms of optical problems. Spherical lenses work fine if the recording surface is also spherical (eg: the human eyeball), but in the case of cameras its not - the film surface or image chip surface is always flat.
One way to fix the problem is to add additional lens elements to correct for the aberration. A generally more efficient way to fix it is to make a lens element which is not a sphere in cross section. In other words the curvature of the lens varies from the middle to the edges. Such an aspherical lens element can help simplify lens design by minimizing the number of elements required and can result in a sharper image. Aspherical elements are particularly useful for correcting distortion in wide-angle lenses.
There are three basic ways to make an aspherical element. The expensive way is to grind a piece of glass down to the right shape. This is quite difficult owing to the extreme precision required to achieve the complex geometry, and so only some L series lenses use ground aspherical elements in Canons lens lineup. Another way is to mould a glass lens element. Such glass moulded aspherical lens elements are used in a number of Canons less expensive lenses. The cheapest way is to cement a plastic resin aspheric surface to the top of a glass spherical element. Such lenses are known as replicated aspherical elements and are particularly common among point and shoot cameras.
Note that some lensmakers, particularly Sigma, use the terms aspherical or ASPH as marketing labels. However many modern lenses made by other makers such as Canon also employ aspherical elements - they simply dont advertise this fact on the outside of the lens. Its important to remember that lenses with aspherical elements are not automatically and intrinsically better than lenses without. Sometimes they are, though this is usually for a variety of other factors, not merely the fact that they use aspherical elements.
What is low dispersion glass?
Low dispersion glass and its variants - ultra-low dispersion (UD) glass, extra-low dispersion (ED) glass - is expensive optical glass which can reduce unwanted colour fringing and other optical problems in lenses, particularly long telephoto lenses.
Dispersion is the rainbow effect seen with prisms and the like - white light being split up into a rainbow spectrum of its constituent wavelengths. Low dispersion glass does not disperse white light as much as regular glass, thereby reducing the amount of correction required to compensate for the phenomenon.
What is fluorite?
Technically, calcium fluorite isnt glass. Its actually a type of crystal produced synthetically by Canon and used in many of their top of the line L series lenses in place of low dispersion glass. Its an expensive material but is extremely useful for minimizing optical lens aberrations, particularly with telephoto lenses.
What are diffractive optics (DO)?
DO lenses contain a new type of lens element unique to Canons product lineup. Such lens elements, multi-layer diffractive elements, are nearly flat lens elements with extremely fine grooves etched into them. They exploit the principles of optical diffraction rather than optical refraction.
The advantage of such DO elements is that they do a very good job of reducing chromatic aberration (colour fringing), a particularly significant problem in long telephoto lenses. They can also be made much lighter than regular low-dispersion or fluorite lens elements, thereby shortening the length and reducing the weight of a large telephoto lens considerably.
Unfortunately, lenses with DO elements are at present quite expensive, and have some issues with lens flare under some lighting conditions. Canon DO lenses, while professional products, are not sold as L lenses and are marked by a pale green stripe around the end of the lens rather than a red one.
What is rear or internal focussing?
Many lenses become physically longer or shorter when you adjust focus. In other words they have two nested tubes which telescope in and out as you rotate the focus ring. This design, while inexpensive to make, is generally undesirable because when a lens extends or contracts there will always be air and dust sucked inside it. And inevitably this yields a bit of dust buildup over years of use.
Many Canon lenses use rear focussing (RF) or internal focussing (IF) instead. In rear focussing the lens elements closest to the camera move back and forth when you focus but the frontmost elements do not. In internal focussing some glass elements inside the lens move within the lens barrel. In both cases the lens does not change length at all because all lens element motion is contained within the lens barrel.
Another advantage of rear and internal focussing is that the end of the lens does not rotate during focussing. Many lenses which extend when you focus also rotate, which can be a nuisance if you use polarizing filters or graduated neutral density filters.
What is bokeh?
A term borrowed from the Japanese, pronounced with short vowels. (ie: more like French pronunciation - bo-ké - versus long English diphthongs - bow-kay.) Essentially bokeh, which is derived from the Japanese for blurring, refers to the highly subjective quality of the out of focus areas of a picture. Good bokeh is generally held to be smooth and soft, whereas bad bokeh is generally held to be distracting in some way - perhaps clumpy or doubled-up bright spots and so on.
Bokeh can be important for portraiture - you want out of focus areas behind the subject to be smooth and as non-distracting as possible. Highly patterned or sharp-edged areas dont look as good. Mirror lenses are notorious for bad bokeh - they have annular (ring or doughnut shaped) out of focus highlights.
Bokeh is also written without the H, but the H is usually added to remind English speakers that the word has two syllables and not one.
Part II - Cameras.
Part IV - Flash.
- NK Guy, PhotoNotes.org.
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