If so, better you buy one with a function called "mirror lockup" (mirror lock-up). This is necessary to reduce vibration of the camera caused by the mirror flip.
This is usually not a problem when using the camera in more average situations, but at high magnifications and long exposure time camera vibration might ruin the photo or at least it'll make it not as sharp as it could be if you were using the mirror lockup function.
So, choose your camera cleverly. To help you with that we've put together a list of Canon cameras that shows which cameras come with mirror lockup in which does not.
MIRROR LOCKUP: YES
Canon EOS-1D Mark IV, EOS-1Ds Mark III, EOS 5D Mark III, EOS 6D, EOS 7D, EOS 30D, EOS 40D, EOS 50D, EOS 60D, EOS 60Da, EOS 70D, EOS 100D, EOS 350D, EOS 450D, EOS 500D, EOS 550D, EOS 600D, EOS 650D, EOS 700D, EOS 1000D
NO MIRROR, so no need for mirror lock-up (o.k., this is not really a dSLR, but shows the new trend an also some Canon users might consider it as a good alternative instead of a dSLR)
Canon EOS M (but be careful with this one, it comes with a special Canon EF-M mount, so it won't be compatible with a "T-ring for Canon EOS". I'm sure there'll be a compatible T-ring soon...)
MIRROR LOCKUP: NO (only for cleaning the sensor)
Canon EOS 300D, EOS 1100D