My lenses lowest aperture is 3.5. I want a lens that is good for taking pictures of bands. Most of the time it's low light, despite all the lights on them. I don't have a very large budget. It just so happens my favorite band is coming September 8th so I need something pretty fast. My current camera is a Canon Rebel XTI if you want to help me picking a lens. So what specs should I be looking at if I want to photograph bands? If you have some actual suggestions that would be even better. Thanks in advance.