What are the best work-arounds out there for dealing with the built-in flash when trying to use the Wireless Flash feature of the 7D?
Is there a Canon version of the SG-3IR? Or do you use a modified version?
Are there camera settings or techniques that eliminate (or almost eliminate) the light from the on-camera pop-up flash?
In my specific situation, a model wearing glasses and looking at the camera gets the built-in flash reflecting off her glasses. I'm using a wide open 50mm f/1.8.
When you use the pop-up flash on the 7D as a ETTL Master, you have the choice of whether the flash is used as a light source or not. If you choose to not use it, it will not fire when the shutter is open. Don't mistake the pre-flashes that are used to communicate with slave flashes, with the actual exposure flash.
Edit and Update:
Based on the request from @Imre, I will update my answer as best I can. Unfortunately, I do not have immediate access to a 7D, as my experience is with another photographer's camera. Therefore I will post evidence of others, until I can produce my own.
My first link is a shooter on FredMiranda.com forums, who posts two pictures, one showing no flash contribution from the 7D pop-up:
http://forums.dpreview.com/forums/read.asp?forum=1019&message=33209810
Further down this same thread, user "Jehuty" reports that they configured the 7D for wireless control, and turned off the external flashes, taking a photo of the 7D in a mirror. The result was no visible flash. Unfortunately, there is no photo evidence of this provided.
Finally, there is information on CPN (Page 2, "EOS 7D: Integrated Speedlite Transmitter uses") that discusses this tangentially. It suggests that you can use the pop up flash as a fourth group, but that its power will be reduced to a GN of 4, due to the power of the flash being first used to signal the other flashes. As Canon suggests, this has little impact other than providing catch lights in eyes.
EOS 7D: Integrated Speedlite Transmitter uses
Thanks to its Integrated Speedlite Transmitter the built-in flash on the EOS 7D can be used as the master in a multi-flash set-up to control wireless slave units, but it can also be used as a fourth lighting group to add a little bit of front light. If you do this though, the power from the built-in flash will only have a maximum guide number of 4 because it will have used the majority of its stored power to trigger the other remote flashguns. However, this may be just enough to add a gentle catch light to a subject’s eyes without a high risk of causing redeye.
Though they do not say it explicitly, this again suggests that unless you enable it as a fourth group, the pop-up flash does not fire and contribute to the image.
Until I, or someone else can contribute a set of images taken in a mirror, I suspect this will always be a contentious issue. However, the 7D manual and CPN both suggest that the flash does not fire at the moment of the shutter being open.
I do not what to make a scene of this, and am happy to be proven wrong, in which case I will gladly withdraw or update my answer, as it would not be contributing to the knowledge of this board. I am not here to be 'right' I am just doing my best to add to the knowledge. Unfortunately, I am not able to test and confirm, and hope that others can to 'illuminate' this topic.
There are instructions in LayerMask's Flickr stream on how to modiy a Nikon SG-31R to be compatible with Canon. Basically, you have to cut off the part of right-hand edge of foot which would click microswithes in a Canon hot-shoe while leaving the rear end intact to provide support.
As a cheap DIY alternative, a dark (overexposed) frame of a developed film negative could be used in front of the pop-up.
From my experience, if shooting in a relatively small space (i.e, a large room, not outdoors), you don't really need the line of sight to control the slave unit. The reflections form the walls/ceiling does the job. You can try making a small deflector that gets on the built-in flash and obscures the light from reflecting in the models glasses, while still communicating with the slave. A few pieces of black cardboard and aluminum foil can do the job.
I have the Canon 60D and a 430EX II which have the same functionality as the 7D. The key thing to remember is that the popup trigger flash is usually going to be a certain power regardless of your settings and as a result, your camera settings will directly affect it's ability to influence the photo.
What I've found is that when I'm using a small aperture, low ISO and high power on my flash units, the effect of the popup flash is negligible since the aperture and ISO are taking that popup flash and reducing it considerably, when it's set to the commander mode power. The problem occurs mainly when you are shooting wide open with a moderately higher ISO. Since the trigger flash is the same power in both situations, it will be much more visible at lower light settings.
This is the limitation of the popup flash as an optical commander since it has only one direction; forward. When you use a swivel-head flash unit such as the 580EX II, the ability to aim the flash off to the side to trigger one or more flashes will reduce the influence it has on your photo almost entirely.
To answer your problem about the light spot in your models glasses.
I recommend making the "catch light" more appealing. If you cover it with a white circle spot and bouncing it off that; it'll make a more appealing reflective shape.
To answer your specific question about alternate equipment to use if you don't want to use the built-in flash as the controller, Canon makes a wireless controller that attaches via the hotshoe - it's the Canon ST-E2.
