Auto Focus Mechanism

Definition:

An electro-mechanical system that detects the distance from the camera to the subject and extends the optical system to the point where the sharp image is formed on the imaging surface.

Description:

There are mainly two major types of subject-to-camera distance detection methods. One is so-called "an active system". The camera directly measures the distance received by infrared light beams or ultrasonic sound waves projected by the camera and reflected back by the subject.

The other is so-called a "passive system" which detects the electrical-phase matching point of corresponding paired photo-electric outputs from a pair of line sensors such as the CCD (Charge Coupled Device) placed at the point corresponding to the film plane and receives the image-forming light through the objective lens.