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Canon EOS Beginners’ FAQ DonationsCopyright © 2002-2007 NK Guy

Version 0.9.5. 6 January, 2007.

Part IV - Flash.

Mastering Canon EOS Flash Photography

Which flash should I buy for my camera?

Choosing a flash generally comes down to four things: how much you want to spend, how much weight you want to carry around, how much power (light output) you need and how much control you have over the flash output. There are a number of other permutations as well, such as the type of camera you have, whether you want a dedicated flash (see next section) or not, whether you shoot film or digital or both, and so on.

Please consult the “which flash?” section of my EOS flash photography article for more details. Indeed, please note that this entire section is pretty well a distilled version of that article. It’s a very long read, but it’s also currently the most complete resource on Canon flash photography available anywhere.

What is a “dedicated” flash unit?

A dedicated flash unit is an electronic flash which contains computerized electronics and which is designed to work uniquely with one particular camera system. For example, Canon sell Speedlite E-series flash units. These flash units contain electronics which work only with Canon EOS cameras and which do not, for example, work properly with Minolta or Pentax cameras. Similarly Nikon sell Speedlite SB flash units which work with Nikon SLR cameras but which don’t work properly with Canon EOS cameras.

The advantage of a dedicated flash unit is that it may be able to take advantage of features unique to the system in question. Note that a flash does not need to be made by the same company that made the camera body to be dedicated. The term refers to the capabilities of the device, not its maker. So it’s possible to buy a dedicated flash unit for EOS cameras that is made by a company other than Canon.

I have an off-brand (non-Canon) flash unit. Will it work with my EOS camera?

Maybe. That entirely depends on the flash unit. If the flash unit was designed to work with EOS film cameras - if it’s dedicated to EOS cameras - then it may support TTL (through the lens) metering and may work fine with most EOS film cameras. If the flash unit supports E-TTL metering then it may work fine with newer EOS film cameras and EOS digital cameras. If the flash unit is an older automatic but non-dedicated flash then it may work automatically by itself just fine. If the flash unit is a dedicated unit designed to work with non-EOS cameras then it almost certainly won’t work. The only way to know is to try it or ask the manufacturer if it’ll work.

However, there is one key thing you must check before attaching the flash unit to your camera. Many older flash units, even small battery-powered ones, use high voltages to trigger the flash circuit. Most Canon EOS cameras can use flash units with trigger voltages of 6 volts and no higher. So if your flash uses, say, 135 volts to trigger the flash then you may damage your camera by using it. You’ll literally be frying the camera’s circuits in this case.

So test the flash unit’s hotshoe with a multimeter before using it with your camera. If you find that the unit uses a high voltage for its trigger circuit - or if you can’t or don’t know how to test for it - you can either use an optical slave trigger device or a protective adapter such as the Wein Safesync.

Why does my camera want such long shutter speed times when I’m using flash in Av mode?

This happens because you are trying to take a flash photo in low-light conditions and the camera is in Av (aperture priority) mode or the night PIC (icon) mode if your camera has it.

In Av, night icon and Tv (shutter speed priority) modes the camera meters for ambient (existing) light and fills in the foreground subject using the flash. It does not assume that the primary light source is the flash, and therefore the shutter speed it sets is the same as it would set if you weren’t using flash at all. In low light this results in slow shutter photography. If the shutter speed is very long you will, therefore, need a tripod to avoid motion blur during the exposure.

Alternatively you can switch to full auto (green rectangle) or Program (P) mode, which automatically expose for the flash-illuminated subject and not the background. These modes try to ensure that the shutter speed is high enough to let you handhold the camera without a tripod. The drawback of P and basic modes is that photos taken in dimly lit areas usually end up with black or poorly lit backgrounds, as explained below.

My flash photos look like they were taken in a black hole. Why is the background totally dark?

This is the flip side of the previous question. In P (program) mode and all flash-using PIC (icon) modes except for night mode (if your camera has it) the camera uses the flash as the primary light source for the foreground subject. If the ambient light levels are low, therefore, the background will turn out very dark. This is because the flash is not illuminating the background and the shutter speed is too short to expose adequately for background areas.

Remember that the light from any battery-powered flash is somewhat limited. You can’t expect a small flash unit to light up the Grand Canyon or Eiffel Tower. You can only reasonably expect it to light up people standing in the foreground or close backgrounds such as room interiors.

To avoid this problem of black backgrounds you will need to take a photo in Av, Tv or M modes, as mentioned in the previous question. If the ambient lighting is very low you may need a tripod to avoid motion blur for the time required to expose the background adequately. Using fast film or a high speed setting on a digital camera (eg: ISO 800) and wide lens apertures (the smaller the f stop you can get on your lens) will help bring up the background as well.

What is the difference between TTL, A-TTL, E-TTL and E-TTL II flash?

These four modes are all forms of through-the-lens flash metering used by Canon cameras. Older EOS film cameras support TTL and A-TTL metering only. Newer film models and almost all digital EOS cameras support E-TTL flash metering. E-TTL II is available on most EOS cameras from 2004 on.

Remember that to take advantage of a given flash technology you need a camera and a flash which both support the flash technology you want to use. So if you have, for example, a camera body capable of supporting E-TTL and then you attach it to a flash unit which supports TTL but not E-TTL then you won’t be able to use E-TTL.

For more information on these modes and how they affect your photography please consult my Canon EOS flash photography article.

What is a type A or a type B camera?

When Canon introduced the the first camera with E-TTL flash capabilities (the EOS 50/Elan II/EOS 55 in 1995) they introduced with it a new naming scheme to make it easier to identify whether or not a camera supports E-TTL.

Note a few points here.

What is X-sync?

X-sync or flash sync refers to the highest shutter speed which can safely be used with flash photography on a given camera model. This can be as slow as 1/90 sec on low-end Canon cameras to 1/250 on high end film cameras or even 1/500 sec on the EOS 1D digital camera.

The flash sync problem occurs because of the way focal plane shutters used in most SLR cameras are designed. Such shutters contain two travelling curtains which open briefly to expose the film or image sensor. At slower shutter speeds the entire image area is exposed, but at higher speeds an interesting trick is used. Rather than exposing the entire image area in one go the two curtains form a moving slit which travels the length of the image.

With ambient light exposure this isn’t a problem, since the lighting will remain constant as the slit travels across the frame. However, flash exposure is a problem since the subject-illuminating burst of light from the flash is so brief. If flash is used in conjunction with a high shutter speed like this then only part of the frame will be correctly exposed. The result will be a picture that's properly exposed in one area but which is dark in another - often like a dark bar across part of the frame.

All EOS cameras are programmed so that they cannot use shutter speeds higher than the maximum flash sync speed, so long as you’re using either the internal flash unit or an external shoe-mounted Canon Speedlite flash unit. However, problems can arise if you trigger a non-dedicated flash unit and try to use a high shutter speed.

The X-sync issue usually poses problems when it comes to fill flash outdoors. Let’s say you’re taking a photo of someone on a bright sunny day and you want to use a pop of flash to fill in the shadows a little bit. But you also want to shoot with a wide aperture so as to blur out the background somewhat (narrow the depth of field). The problem is that if it’s a bright sunny day then you will have to use a very high shutter speed in order to do this, or else use fast film or a high ISO setting. But if you need to use a high shutter speed that exceeds the camera’s X-sync then you won’t be able to use flash. Unless, of course, your camera and flash support high speed sync, as described in the next section.

What is FP mode or high-speed sync?

FP mode, also known as focal plane mode or high-speed sync, is a way of circumventing a camera’s X-sync limitation. FP flash lets you take flash photos at any shutter speed you like, and works by pulsing the flash bulb at an extremely high rate - 50 KHz - simulating constant light at the cost of total light output. FP stands for “focal plane,” by analogy to the old FP flash bulbs, though a convenient way to think of it is “fast pulse.”

Only E-TTL capable (type A) EOS cameras support FP mode. (except the EOS 1N, which can partially support FP mode flash via an optional upgrade)

More more information on FP mode, how it’s often used and what its limitations are, please consult my flash photography article.

What is flash exposure lock (FEL)?

Flash exposure lock is a technology contained in all type A (E-TTL capable) EOS cameras and EX series (E-TTL capable) flash units. Think of it as the flash equivalent of auto-exposure locking (AEL).

Consider this example. Let’s say you’re taking a photograph of someone who’s standing to the side of large object - say a white building. Normally you would turn the camera to focus on the person and also set ambient light metering, then recompose the image by turning it to include the large building as well.

The problem is if you’re using flash then flash metering will be done on the large white building, not on your friend, since the camera’s active focus point (to which flash metering is biased) is going to be over the large building. This problem with “focus and recompose” is one of the major reasons for flash metering turning out badly on E-TTL cameras.

What you really want to do is to lock in the flash exposure settings when you’ve got your friend as the main subject in the viewfinder. Then you can turn the camera to move your friend to the side while retaining the correct flash exposure settings. This is what FEL does - it locks in the current flash settings for a number of seconds. It does so by issuing a preflash burst of light when you press the FEL button, and setting the flash meter level based on that information.

FEL is thus technically independent of ambient light exposure locking, but on most EOS cameras the two functions are controlled by the same button. Top of the line EOS cameras, however, have separate FEL and AEL pushbuttons so the two functions can easily be set independently.

More more information on FEL, please consult my flash photography article.

Why do I have blurriness around my subjects in my flash photos?

You’re probably taking a slow sync photo. In other words, your subjects are being illuminated first by light from your flash unit. Then, if you have a slow shutter speed (typically 1/30 sec or slower), your subjects will also be illuminated by ambient light. The result is a kind of double-exposure - a sharp bright image lit by flash and a blurrier secondary image lit by ambient light. Sometimes this is called “dragging the shutter.”

Sometimes slow sync is a desirable effect, since it can add a sense of dynamic motion to a photo. However, it can also tend to look like a blurry mess. If you want to freeze motion with your flash unit you should set a faster shutter speed.

EOS cameras default to slow sync mode when in Av mode or the night icon mode if your camera has it.

What is second-curtain sync?

Normally a camera will fire the flash immediately after the shutter has opened - first-curtain sync. If this flash is combined with a slow shutter speed as above, and you’re photographing a moving object, you’ll get a ghostly light trail showing the motion of the object. Unfortunately, if the flash fires right after the shutter opens then the object will appear to be moving backwards in the photo.

The solution is to fire the flash immediately before the shutter closes. This allows the moving object to record motion onto the film or sensor and then you freeze it with flash just before the exposure ends. This technique is known as second-curtain sync (rear-curtain sync to Nikon), and is an option with certain EOS cameras and flash units.

More more information on second-curtain sync and whether your camera and flash support it, please consult my flash photography article.

What causes the dark crescent-shaped shadows at the bottom of my flash-illuminated photos?

You’re probably using the internal flash on your camera in conjunction with either a large lens or a lens with a large lens hood. The lens or hood is blocking light from the internal flash unit.

Since you can’t raise the internal flash any higher your only choices are to use a shoe-mounted external flash unit, skip flash altogether, remove any lens hoods or adjust the lens (if it’s a zoom lens which gets longer as you zoom) so that you’re shooting at the wide end where the lens may be shorter.

What causes redeye and how does redeye reduction work?

The interior of the human eye is lined with a fine mesh of blood vessels. If you shine a bright light into someone’s eyes then this light can be reflected back and, since it’s reflecting off blood vessels the light is going to be coloured red. Normally you don’t notice this effect in real life for three reasons. First, the light source has to be really bright compared to the ambient lighting. Second, the pupils of the eye have to be fairly dilated for enough reflected red light to be noticeable. And third, the light source has to originate as close as possible to the viewing axis (ie: to your own eye).

Unfortunately these three conditions are often met handily when you do flash photography in dim lighting conditions. Flash units produce a tremendous amount of light for a split second and, since flash units are frequently attached to the camera or built into the camera body, they’re often located very close to the lens axis. The result is the evil glowing red satanic eye effect that’s the bane of snapshot photography. Point and shoot cameras are particularly vulnerable to the problem, partly since they tend to be used in low-light situations like restaurants and living rooms, and partly because their built-in flash units are located very close to the lens.

The best solutions for avoiding redeye are either to abandon flash altogether or, if you have to use it, to move the flash unit as far away as possible from the lens. A good technique for improving flash photos is to tilt the flash unit head so that light bounces off the ceiling or the wall. Unfortunately, neither bounce flash nor moving the flash are possible with a camera’s built-in flash.

So cameramakers have come up with another idea - shine a bright light into the subject’s eyes first. This causes the pupils of the eye to contract, lowering the risk of redeye. So many cameras come equipped with redeye reduction lamps - typically bright white lights or, on some cameras (notably point and shoots) epilepsy-inducing pulses of blinding light from the main flash tube (see also the next section). Unfortunately these redeye reduction systems usually have the effect of making your human subject look dazed and stunned. Stunned and glazed or evil and satanic - with onboard flash photography, the choice is yours!

Yargh! My camera fires blinding pulses of flash in low light! What can I do?

Unfortunately, most non-pro EOS cameras sold today employ the built-in flash as an autofocus assist light when shooting in low light levels. This means that when ambient light is dim the camera will suddenly start firing intermittent blinding pulses of epileptic seizure-inducing light in an attempt to provide enough light for the camera’s autofocus system to work properly. Needless to say this is rather annoying and more or less eliminates any chance you might have of getting candid shots.

If your camera is in a creative zone mode (P, Av, Tv, M) and the internal flash is down then it shouldn’t fire these flashes of light. However, in all icon zone modes except for landscape sports the flash may fire these pulses of light.

There are three options that can help with low-light autofocus. First, low-light sensitivity of lower-end EOS cameras, while regrettably poor to begin with, can be improved by using a faster lens. So if you have a choice between a 50mm 1.8 and a 28-90 4.5-5.6, always go for the 50mm 1.8 if it’s dark. Second, you can attach an external Speedlite flash unit to the hotshoe. All Canon Speedlites for EOS cameras have a red patterned light built in. This red AF assist light is still visible but is considerably less obnoxious than the built-in flash. Third, and this probably isn’t a terribly helpful answer, you could acquire an older EOS model, such as the Elan/100, the Elan II/50 or A2/5, which all have discreet red patterned lights built into the camera body.

Some cameras, such as the EOS 30/33/Elan 7/7E, have the ability to use the Speedlite’s AF assist light while not firing its flash. Other cameras may require you to turn off the flash once focussing has been achieved if you don’t want flash illuminating your picture. For this reason some owners of cameras with poor low-light focussing (eg: the digital D30 and D60 cameras) have bought the ST-E2 wireless flash transmitter. It will fire an AF assist light without bathing the scene in the harsh light of flash.

Note, however, that differing flash unit models have different coverage areas. Not all of them have the ability to illuminate all the focus points of a multiple focus point camera - some will only cover the centre point, for example. Others can cover a 3-point or 5-point camera but not a 7-point one. For details, please consult my EOS flash photography document.

My flash unit doesn’t work with my digital EOS camera.

Of the four types of flash metering technology used by Canon, only E-TTL or E-TTL II are supported by Canon EOS digital cameras. TTL and A-TTL are not supported, since they rely on recording light bouncing off the surface of film, and digital cameras have no film.

Of Canon’s flash lineup only Speedlite EX series flash units support E-TTL. Therefore you must use an EX series flash unit with your digital EOS body if you want automatic metering. Earlier E and EZ series flash units will not fire with a digital camera. Note that if you have a flash unit like the 550EX, which can be switched between TTL-only and E-TTL modes, you must be in E-TTL mode for flash to work with such a camera.

Most third-party flash units which are billed as being EOS compatible only support TTL metering. Sigma and Metz do make flash units and adapter modules respectively which are E-TTL capable, however, so read the specifications carefully.

My flash unit keeps firing off bursts of light randomly.

This problem could indicate a failed unit, or it could simply mean the contacts need cleaning (on both the camera’s hotshoe and the foot of the flash) or the batteries need replacing. Or it could be that your camera is using the flash as an autofocus assist light - see above.

What is a PC connector?

Some cameras, particularly some advanced amateur and most professional cameras, have a small round connector for hooking the camera up to external studio flash units as below. This is a PC connector. The “PC” stands for “Prontor/Compur” (two early camera shutter manufacturers) and not “personal computer.” PC connectors are not data connectors for computers or anything - they have nothing to do with USB or FireWire.

All beginner EOS cameras lack PC connectors since they’re mostly used in professional and semi-professional studio situations. If you really need one you can add a third party hotshoe to PC cord adapter to your camera.

Most Canon Speedlite flash units do not have PC connectors. Those which lack them can be adapted via a hotshoe adapter, but generally do not work reliably when triggered by a PC cable. Even when they do work you lack all forms of automated metering, of course.

What is studio flash?

The term usually refers to large flash units used in indoor studios. These flash units are powered by AC (mains) power and are not portable, like on-camera shoe-mounted flash units. They offer far more light output than small battery-powered units, are usually mounted on telescoping stands and can be attached to various light-modifying devices for considerable flexibility. They’re usually called “studio strobes” in the US.

Studio flash units are not, however, generally automated in any fashion. They can’t interface directly with the camera’s electronics the way Speedlite shoe-mounted flash units can and thus do not meter through the lens. They are typically triggered by simple electrical signals (“fire now!”) from the camera or a slave trigger. Sometimes they connect to the camera by a simple electrical cable with PC connectors as above, and sometimes they are hooked up to optical slaves and trigger in response to a burst of light from a master flash unit.

The photographer dials in a power setting on a controller box and the flash pumps out the amount of light specified when triggered. Metering requires a separate device - a handheld flash meter - to measure flash output and determine the output setting correctly. Predicting the final look can be tricky so professional photographers often install Polaroid instant film backs onto their cameras so they can do some test shots with instant film before loading up the camera with regular film.

Such setups are thus only of value in slow-moving studio situations, not fast-moving situations like photojournalism or candid photography. Canon do not make or sell any studio flash units, and studio flash gear is rarely used by novices because of the complexity and expense.

Why do professional photographers have those great big umbrellas on stands?

Umbrellas in flash photography are simply convenient, collapsible reflectors. Lighting, including light from a flash, can be hard or soft. And the hardness or softness basically comes down to the size of the area emitting the light. The larger the area, the softer the light. So umbrellas are used as reflectors to bounce light onto the subject from a larger area than a small flash head. Softboxes - large rectangle frames with white fabric stretched over them - are used the same way.

Umbrellas in photographic studios are nearly always used in conjunction with large AC-powered flash units as above, not small battery-powered units.

Why do my flash photographs always look so bad?

Mastering flash and making it look as natural as possible is a difficult art to master. For more information on this topic have a look at the flash tips section of my EOS Flash Photography article.

Part III - Lenses.

Part V - Filters.


- NK Guy,

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