I was talking with a fellow T2i owner over on my Facebook page and she was wondering which lens is best for dance recitals (action from a distance in low light). I thought it would be beneficial to share our conversation with all of you...
Jennifer's Question: Do you have any recomendations for lenses for dance recitals?
Moose's Answer: In order to capture fast action, from a distance, in low light (in a dance hall or theater), you need the help of a "bright" telephoto lens. When I say "bright", I'm referring to a lens that's capable of achieving an aperture f-number between f/1.4 to f/2.8. Lower f-numbers basically allow more light to enter through the lens giving you faster shutter speeds at lower ISO's, which is critical to "freezing" fast action indoors. I know it's going to seem like a shock, but the most affordable indoor action shooter is the Tamron 70-200mm f/2.8 lens. While this may seem outrageously expensive, the Canon equivalent is double the price. As you might of guessed, low-light (indoor) action photography is probably the most challenging and expensive types of photography.
In regards to settings, I would shoot in Shutter priority (Tv on the mode dial) and select a shutter speed between 1/250 and 1/1000. Make sure your ISO is set to Auto in order to get an accurate exposure. I would also enable burst mode, so that you can rattle off a series of shots in quick succession...usually you can find a few keepers that way. In addition to all of that, try experimenting with AI Servo focusing (just press the AF button the back of your camera). This will allow you to continuously focus on a moving subject by half pressing the shutter button.
If you just don't have the budget right now for the above mentioned lens, the next best option would be the Canon 55-250mm f/4-5.6 lens. Using the settings I mentioned above, you'll probably end up with some underexposed (dark) shots, full of grain (image noise). However, the good news is that you'll be able to zoom in for tight framing from a distance and your shots should be relatively sharp. You can use basic photo editing software (like Picasa) to brighten your shots and for image grain you can use noise reduction software (like Noise Ninja).