Tracking Down Autofocus Issues  Eliminate the obvious and the
solution is unknown*  It seems a lot of folk end up reporting
autofocus problems (very few of which turn out to be real
component failures), so I'm going to provide you a
troubleshooting checklist to run through before you run off
screaming to the manufacturer. Do these steps, in this order:
1. Is it clean? Eliminate dirt and dust. At the bottom of the
mirror box (underneath the mirror) is where the autofocus
sensors live. Get dust balls down there and autofocus will be
problematic. Clean using a Speckgrabber or blower brush. While
you've got your French Maid's outfit on, check the contact nubs
on the lens and the contact areas in the lens mount. The nubs
should all have spring to them and be in the fully extended
position, and both areas should be clean. Clean with a contact
cleaning solution. Does the camera focus every time now?
Yes? Then the problem was your lack of maintenance. Have your
camera and lenses CLA'd regularly by a service c