I have a question after shooting quite a few candids at a birthday party. I had some good photos...actually I shot 135 and I got a good 45 that I am proud enough to show to the other guests...really getting better I think I have some trouble with auto focus. It was slightly low light as it was indoors and not a ton of open windows (I had to use a fairly open aperture). It seemed like I had trouble getting it to focus on some kids. I have noticed this with my son and it also happened alot with one girl. My son has a dark complexion, dark eyes and hair. Often the focus comes out on his hair when I feel quite sure I focused on his eyes. I have it on the center focus thingy, so it isn't that. and I have watched closely, it isn't movement. And then it happened alot with a girl today who is very very light skinned...also most photos seemed to focus on her hair. Is this just an odd coincidence? Or does this have any basis in how auto focus works? What things can throw off the auto focus? All our more advanced shooters, do you use the manual focus much?