If you're going to be doing focusing tests you have to target more isolated subjects. The AF "cross-hairs" are larger than what you see on the viewfinder. I usually choose newspaper headlines or just write well-spaced lines on a whiteboard. There has to be a clear target that you're going for. If it's too cluttered it may go to the other targets.
Unless you're shooting an object that's completely flat and parallel to the sensor's plane.
How's it using the lens though? I mean, your experience with it. Is the AF fast enough, the feel of the zooming etc
