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well, do suggest to him. I suggested mine. =)
Do suggest some thing which allows him to have more keepers instead of something theotically sound. =)
We already did, but you are counter-suggesting something which is totally out of the rule-book of many paid photographers here.
I don't see how shooting at 1/20s and f/2.8 for a group shot will allow him to have more keepers. If your definition of keepers means a photograph with a high chance of subject blur and shallow DOF beyond the first row of people in a group shot, I am dumbfounded.
Correct me if I am wrong, Catchlights. According to what I understand from film users, the type of aperture used will affect the coverage of the flash. Therefore at F2.8, the coverage of the flash using E-TTL will be minimal and hence there will be slight vignette at the wide end which may not be noticeable on 4R but obvious to photographer's eye at 8R. This observation is applicable to big group shot.
I personally also adhere to the rule of minimal F5.6 with understanding. And I as a paid photographer will also never shoot at 17mm for group shots. Shooting at 17 mm will cause the faces of the pp at the side to be warped. If forced to shoot at 17mm, must ensure that i am at the correct elevation.
Adding to this fact,I will have to zoom in a bit to prevent distortion of faces at the side and this means that F2.8 becomes pretty unusable for group shots. It will be pretty obvious on 8R and above.
If I'm not mistaken, what you are talking about for coverage is more related to the zoom head of the flash (assuming you are firing direct flash). If firing with a bounce, this is no longer applicable. As a general rule of thumb in flash photography, aperture affects how hard the flash works (in terms of output power), while shutter speed determines how much ambient light you are letting in.
The term "dragging the shutter" means to shoot at a slightly slower (but not too slow) shutter speed to allow more ambient light into your image to balance with the flash's light. However, consider this: if you use a f/5.6 lens, and the flash has to work so hard to come up with enough light, your images generally will look a little less natural than with a f/2.8 lens, at the same shutter speed. I think this is what fabiano is trying to drive at. However, we are not talking so much about general flash photography, but shooting in group, where you are right about both points:
f/5.6 - it is set as such to give sufficient DOF to the whole group. Some photographers will even play it safe and go for f/8 if they can.
17mm - depending on which lens you use, distortion will vary. However, on most that I've used thus far, I have not seen one where there is hardly any perspective distortion (the stretch at the edges) at 17mm. You are right in saying that you should zoom in slightly to avoid perspective distortion, and failing that, ensure that you are more or less level with your subjects. If you are too low or too high, the perspective distortion is made more obvious.
