原帖由： Flying Dutchman ,
Most likely, the optical system of the autofocus has been damaged. In most SLRs, including Nikons, the autofocus sensor is in the bottom of the mirrorbox, and requires a secondary mirror which is under/behind the main reflex mirror. Either the secondary mirror, or the autofocus sensor may have been bumped out of alignment, or otherwise damaged. It is possible that the autofocus sensor assembly can be accessed by removing the bottom cover of the camera, but I'm not sure. The secondary mirror can be inspected by removing the lens and ''very gently'' pushing the main mirror upwards with a suitable, preferably non metallic instrument. Take care not to touch the surface of the mirror. The secondary mirror will be visible behind the main mirror and should be positioned in dead center of same. You can check if it's cracked or misaligned, but repairing and/or replacing it is probably best left to an expert repairperson.