I was originally looking to buy something around the Nikon N80 very soon. However a family friend and professional photographer has offered to sell me a used F100. I'm extremely excited as I think it would be fantastic. He's letting me use it for a few days so I can try it out. I love using it however one aspect I am unsure about. The autofocus does not seem to work sharply. I mean that in many of the shots I could easily tell the subject was not in focus and I could get in in sharper focus in manual easily. I'm not sure if i distorted something with the diopter (never fiddled with one before), if the lense is not working properly, if the camera's autofocus is off, or if I'm just making a stupid user error. The camera is still under warranty which is comforting but I'm quite perplexed by this problem. Any advice on this camera or this specific problem?