I sometimes shoot moving subjects at airshows, birds in flight, etc. I'm less than delighted with the sharpness I get relative to when the subject is still -- i.e. a bird flying compared to after it lands in a tree. It isn't a huge difference, but it is noticeable. I'm on a tripod with ball head loose enough to follow action smoothly, IS is off if applicable, aperture is in the middle of the range, shutter speed is very fast (2-3x 1/focal length).
I think the issue is either focus following or tracking. I have tried both One Shot and AI Servo, and One Shot seems a little better if I don't linger with the shutter button halfway down. (There is usually some component of subject movement toward or away, but not usually a lot.)
But I'm puzzled by CF 17. Should it be on? It sounds like it only works when I am in AI Servo with the center AF point selected. Then it activates some invisible points near the center point that give better tracking. But why is the default to have it off? Wouldn't I want to leave it on all the time, even though it apparently isn't helping in most situations?
I haven't had a good chance to test it -- the 5D is fairly new. Any advice?
