Markus Kohlpaintner has produced an exhaustive review of the various autofocus (AF) drive mechanisms that have appeared in Canon cameras since the 1980s.
AF became a standard feature in Canon’s EF lens series in 1987, and since then the company has deployed a range of AF drive systems.
These include the original Arc-Form Drive,Quiet Drive, Micro-USM, Ring USM, USM, STM, MFT, and the latest Voice Coil Motor (VCM), with each variant accompanied by multiple images in the review.
The article also includes an explanation of how USM (ultrasonic motor) AF systems function using a travelling wave across a stator, along with their integrated feedback control systems.
