Camera: Nikon D5000 set to single point focus at fast shutter speed (1/500th ish). Subject: Usually runners or cyclists so moving targets. The Nikon viewing software shows a red box that indicates the point of focus but in quite a few cases the point of focus has been out (even though the red box is on my intended target) and the focus point is actually a few feet behind. I am trying to learn some lessons here and need to understand what is going on so is it likely to be: A - The software is not 100% accurate and I actually missed the subject in the 1st place? B - I need to use a different method of focus C - The camera is subject to shifts in focus even though the target square is aimed true D - Something else............. Any help greatly appreciated.