I have a Canon T3i. When I go to buy a new lens, do I have to buy a specific size or type for the T3i?
The lenses that will work with your camera will be denoted as EF or EF-s (e.g EF 50mm f/1.8, or EF-s 18-55mm f/3.5-5.6 IS II) if the are Canon or as "For Canon EF" or "For Canon" for other manufacturer's lenses, such as Sigma, Tamron, Zeiss or Samyang. EF-m lenses will not work properly on your camera, or any Canon DSLR. Likewise the EF-s lenses will not work on Canon's full frame bodies (i.e. 1D, 5D and 6D).