All, I am using my EOS 40D, with a 300 m lens, to photograph birds at our bird bath. I have the camera on a tripod and am using the EOS utility with a long USB cable as a remote release. My question has to do with the auto focus. Since I know exactly where in the frame the bird will be, and since I have this spot centered in the frame, it seems that I should select only the central AF Point. However, when I was playing with this (just pointing the camera around a room), that with only the central AF Point selected, the camera struggled to focus in many cases. For example, when pointed at a flat wall, it could not focus. When pointed at a tripod leg, about 5 feet away, it would seek into focus, then seek all the back out of focus. This process of seeking to focus, then seeking back out occurred quite often. Given that birds do not pose, I am reluctant to set up and potentially waste a lot of time waiting for the bird, etc., if the focus will misbehave. Can you explain why the camera is behaving this way? More importantly, can you suggest what I might do to minimize out-of-focus risks when trying to take these pictures? Many thanks.