I've just got into shooting portraits and I've had some difficultly focusing on a subject, then trying to get them in one side of the picture without my lens focusing on the background. Evaluated mode works okay but not perfect. I find myself spot focusing then flicking AF to MF to take a shot. It's not terrible but it sure isn't conveintent. My question, in summary, is what is the best way to auto-focus a non centered subject?