I recently purchased a Canon 7D, as my previous 450D had become a severely limiting factor in my endeavors to wildlife and bird photography (particularly bird photography, which I LOVE, but for which I have a bare handful of keepers out a few thousand shots.) The AF system of the 450D had a single cross-type point and a total of nine, while the 7D has a much more advanced 19 point system, all of which are cross-type. I've taken the 7D out a few times since I first purchased it, and while I have definitely had better luck photographing wildlife, I am still having trouble photographing birds on the move.
I have read through the 7D manual, however I am still not exactly sure where to start on learning how to use an advanced AF system in the real world for moving subjects. I could really use some insight from photographers who regularly use advanced AF systems for tracking subjects and keeping them in focus. I would also like to know how to take multiple shots of a subject on the move and keep them in focus between shots. While I can often nail one shot in a motion sequence, I regularly seem to fail to get proceeding or trailing shots after the one keeper (and that keeper is often not the most interesting one of the bunch.) The 7D supports a variety of AF modes as well, including AF Expansion and Zone AF, where the camera can supposedly utilize extra points around the selected point in case the subject moves away from the selected points area of sensitivity, or the selected point lands on a low-contrast part of the subject and a neighboring point lands on an area of high contrast (so focus can always be achieved, even if the selected point isn't detecting anything to focus on.) I have also not had much luck using either of these modes, and I think its primarily because I simply don't know how.
From a lens standpoint, I have used the following lenses:
- EF 100-400mm f/4.5-5.6 L
- EF 100mm f/2.8 Macro
- EF 50mm f/1.4
My most frequently used lens is the 100-400, usually at the 400 end, so aperture is only f/5.6. I am not sure if that might be a problem or not (as far as I understand, the 7D supports AF at f/5.6, although I am not sure how many points might be considered "high precision" at that aperture.)