Can i use my old slr lenses with new dslr rebel T3i camera

Question

I am contemplating buying the Canon Rebel T3i DSLR, but have read varying opinions on whether or not my older lense collection from Rebel Eos SLR will be compatible. Please help

Answer 1

All the Canon EOS lenses from a film SLR will work on any of their digital SLRs.  
The sensor on the T3i is about the same size as a single frame of negative from APS-C film (APS-C = Advanced Photo System - Classic size).  Those were the drop-in cartridge rolls that started to become popular in the 1990s.  It's a little smaller than a single frame of 35mm film.  
Canon also makes DSLR cameras that have "full frame" sensors -- which means the sensor is the same size as 35mm film.  
When you shoot with, say, a 50mm lens on a 35mm film camera you are used to a certain angle of view.  Since the sensor on a Rebel body is a little smaller, it's as if someone cropped in on the negative slightly and decided to make a print using only the middle area of the negative.  This results in a tighter angle of view -- it's almost as though you've zoomed in a bit.
For this reason, the APS-C sensor is referred to as a "crop frame" sensor.
The crop factor is 60% (multiply by 1.6).   In other words, suppose you had a 50mm lens on your film body.  When you put that same lens on a Rebel T3i, you would multiply the focal length by 1.6.  50 X 1.6 = 80.  This means the 50mm lens on the camera with the APS-C size sensor is going to provide an angle of view which is approximately the same as using an 80mm lens on the film (or full-frame sensor) camera.   The Canon 6D, 5D series, and a few of the !D series bodies (such as the current 1D X) have "full frame" sensors ... the same size as a 35mm negative.  (Some 1D bodies used APS-H size sensors which have a 30% crop factor but Canon does not currently make those anymore -- you can certainly find them on the used equipment market.)
Your Canon EOS lenses WILL all work on the T3i body, but you'll notice you get a narrower angle of view (and there's nothing wrong with that -- it just takes a bit of getting used to.)
Canon also makes "EF-S" lenses which reduces the cost to build the lens by using elements that are not designed to completely cover a 35mm negative -- it only project an image circle which is large enough to cover the APS-C sensor.  The up-side is that they cost a little less.  The down-side is that if you ever chose to get a camera that uses a full-frame digital sensor then you would not be able to use those "EF-S" lenses.
But Canon's EOS "EF" lenses work on _every_ EOS camera body, film or digital.
Tim Campbell
5D II, 5D III, 60Da