I've got a Nikon D300, a Nikon SB600 flash, and a Sigma 18-125 lens. I need to take photos inside a small auditorium of people on stage at the end of a dancing thing. No photos while dancing, but afterwards, take pictures of people accepting awards. They will be on stage, I will down below where the seating is. I'll need to zoom many times maybe 70 to 100mm. I want to make sure people are in focus and that the light looks correct. My question is that I always thought that your shutter speed should double the lens length. So if I'm shooting at 100mm, my shutter speed should be 200. But if I'm using a flash, it's automatically at a 60th. Won't I have blurred shots. What can I do, or what am I missing in my thought process? Also, how can I make sure the color balance is good? Thanks for any help.