Canon EOS and the electronic lens mount
March 1987 (EOS 650)
Canon dropped its old mount for a fully electronic one, with the focusing motor in each lens. It became the most used SLR system of the film-to-digital era.
How it began
Minolta’s Maxxum 7000 of 1985 brought autofocus to SLRs. Canon answered in 1987 by starting again: the EOS 650 and a new mount, EF, that did not fit its old lenses.
How it works
There are no mechanical links between body and lens, only electrical contacts. Each lens has its own focusing motor, later the fast and quiet ultrasonic USM type, and its own electronic aperture.
Why it mattered
Putting the motor in the lens made autofocus fast and allowed big telephoto lenses to focus quickly. It was a gamble that angered owners of old lenses, but it paid off: Canon became the leading maker for sport, news and, later, digital SLRs.
Limits and what replaced it
The SLR mirror and the long flange distance limited lens design. Canon replaced EF with the RF mirrorless mount in 2018.
Today
EF lenses work on Canon mirrorless cameras through an adapter; the EOS name continues.