Don't want to crap on the thread too much, but figured it was worth pointing out that group shots are better with longer lenses from a large distance.
I wouldn't use a 17mm for a big group. That will look weird, as the people in the center will be noticeably bigger than the people on the edges. That sort of focal length also does weird things to parallel lines and things when shooting large flat objects (like a riser full of people). It will be subtle and not immediately apparent, but the photos will feel "off".
Best off using a 200mm lens from the back of the auditorium, to be honest, for pleasing compression and lack of distortion, rather than a 28mm from the front row or a 17mm from the stage.
Unless, of course, such a working distance is impossible... then you just have to settle for what you can do. 🙂
But when I was shooting professionally, I remember a mentor making a really big deal pointing out how a zoom isn't a substitute for moving your feet, it's an artistic tool. Comparing two group shots, one at a very wide angle from close and one from a large distance with a long lens... the difference is subtle on first glance but striking when you compare the two. You won't shoot a group of people with a 17mm lens again after doing that comparison.
