Jason Sinclair
Well-known member
As far as i know the autofocus in dslr's is of two types. The second type, contrast detection, probably is used in the canon mount setup. It has to go either side of the contrast to find the sharpest area which "finds" focus. As far as i am aware, on pro dslr's this is second choice to another technique involving sensor in the camera. Contrast detection is not professional enough to use on the move. Great for finding focus.