AF systems are of two main types: optical, and infra-red.

Makes me wonder if vibrations from the taps are causing the AF system to make adjustments to compensate.

The AF system was a minor upgrade to the one on the 20D.

There are five exceptions to Canon's recent rule of a 9-point AF system.

Each lens contained a motor to focus, unlike the body-integral AF system pioneered by Minolta.

The speed of the AF system is highly dependent on the maximum aperture offered by the lens.

Active AF systems measure distance to the subject independently of the optical system, and subsequently adjust the optical system for correct focus.

Passive AF systems determine correct focus by performing passive analysis of the image that is entering the optical system.

Another way to assist contrast based AF systems in low light is to beam a laser pattern on to the subject.

Also had active sonar echo-location AF system.