Canon EF Mount (Electronic Focus)
Direct Answer
The Canon EF Mount (introduced in 1987 for the EOS autofocus SLR system) revolutionized photographic camera design as the first 100% all-electronic lens mount, eliminating all mechanical aperture linkages and autofocus drive shafts. Featuring a 44.0 mm Flange Focal Distance and a large 54.0 mm throat diameter, over 150 million EF lenses were manufactured over 33 years.
Source: Canon Inc. Historical Camera Museum / EF Lens Technical Data
Specs
| Flange Focal Distance (FFD) | 44.00 mm (1.732 in) |
| Inner Throat Diameter | 54.00 mm (2.126 in) |
| Bayonet Tabs | 3 locking tabs with clockwise twist |
| Electronic Interface | 8 gold-plated electronic contacts (expanded to 11 pins on EF super-telephoto lenses for teleconverters) |
| Internal Actuators | Internal USM (Ultrasonic Motor) in lens body + internal electromagnetic aperture diaphragm (EMD) |
| Variants | EF (Full Frame), EF-S (APS-C with rubber bumper back-focus extension), EF-M (discontinued APS-C mirrorless) |
| Camera Systems | Canon EOS-1D X Mark III, EOS 5D Mark IV, EOS 6D II, EOS Rebel series, Cinema EOS C300/C500 |
The 1987 All-Electronic Revolution
When competing SLR makers (Nikon, Minolta, Pentax) kept mechanical motor shafts and aperture spring levers inside the camera body to preserve backward compatibility, Canon boldly abandoned the mechanical FD mount in 1987. By placing dedicated Ultrasonic Motors (USM) and electronic aperture motors directly inside the lens, the EF mount delivered faster, silent autofocus and unmatched telephoto reliability.