I would like to lock focus on a face or an eye, and have the camera keep re-focusing in the middle of a burst as the subject moves. Can any of the current Rebel series continue re-focusing in the middle of a burst, or is this feature reserved for the 50D or 7D (or higher)? Thanks for your time. BTW, I heard that Nikon was somehow better at predicting movement and maintaing focus on a moving subject, but my friends with whom I share lenses shoot Canon, so that's what I'm using. Any truth to Nikon having superior focusing ability on any of their crop sensor cameras?