Triggering optical slave - strobes using Canon 7D flash

LouS · Joined: 07 Oct 2010 Posts: 1 Location: Shrewsbury, MA

NK, love the book. In section11.7.3 it states 7D can use optional all manual control of built-in flash to trigger off camera optical slaves (in my case - Alien Bees)

How do I set this up in the 7D?

I am getting pre-flash triggering.

ghwanner · Joined: 28 Sep 2010 Posts: 6

I'm a Canon 5dMkII user, so I can't give you the exact menu sequence for the 7D, but it should be similar to the following: On the flash control menu for the built-in flash, select the Manual Mode (instead of the default E-TTLII) and select the power level you want the built-in flash to fire at - I use 1/64 power with my 270EX on the 5dMkII. This gives you enough power to trigger an optical slave without contributing light to the subject. You then need to go to the custom functions menu for auto-focus and turn the menu item for flash autofocus assist OFF. The Manual Mode will disable the pre-flash while the autofocus assist OFF will disable the autofocus "infra-red" flash which could spuriously trigger your Alien Bees. Hope this helps!

nkg · Posted: Sat 09 Oct, 2010 11:12 am Subject:

Glad you like the book! ghwanner's answer is basically it. You need to use the camera's menus to set the built-in flash to manual mode. Have a look at page 116 of the manual.

As noted in the previous post you'll probably want to dial down the flash output to 1/64 or 1/128, though some people put little paper or foil reflectors on the front of the flash to direct the light in a different direction. You could also put an infrared-passing light-blocking (ie: black plastic) filter over the flash, since optical slave units can usually receive infrared energy.

Incidentally, I doubt red autofocus assist on a flash unit will trigger an optical slave flash unit. Though in your case the 7D doesn't have a red autofocus assist light.