There's a couple things at play here and it's all related to how much available light you have to work with.
There are 2 things to worry about
- Using fast enough shutter speed to prevent handshake from affecting your pics. For your XTi + 75-300 combo you want shutter speeds at least 1/120 @75mm and 1/480 @300mm. (Assuming this is not an I.S. lens)
- In addition, using fast enough shutter speed to stop the dance action. This really varies depending on how fast the action is. You can certainly try 1/120, but you would probably get better results at 1/250 or faster. You need to see what works for you and the kind of effects you want. (Freeze the action or capture the motion, etc...)
If you are tight on the budget, you can certainly check out the 50 1.8. However, if you have some cash, then definitely check out the 85 1.8. It has super fast AF and generally regarded as a very nice indoor action lens. In any event, at f1.8, it will allow in more light giving you extra stops of shutter speeds to help you out. You also want to raise the ISO as well. (At the cost of introducing some noise) You'll need to experiment with different combinations of the above.
Remember, a tripod would be practically useless in stopping the action. It's all about using fast enough shutter speeds. And usually that means shooting wide open and raising the ISO. If you still can't stop the action and flash is not allowed, then that means you need to get faster glass...or wave the white flag!

jcramos wrote in post #5374144
Hello,
Can someone help me out. Sorry if this question has been asked.
My daughter is having her dance residal next month on stage and I am going to take some pictures with my Canon Rebel XTI and 75-300mm lens. How do I take a good clear picture in very low light and NO flash.
I took pictures last year and they all came out blurry and not good at all. I’m new to all this and still learning.
My question is what setting should I use to get a good shot?
Jason