Basics of the EF mount (family)
As of 2022, the Canon EF mount is still a current mount, although Canon has already introduced a newer mount (the Canon RF mount). While Canon’s main focus seems to have shifted to its mirrorless mount (Canon RF), the days of the EF -mount are not yet numbered, especially as the EF mount lately has broadened its spectrum of application from still to video cameras.
The Canon EF-mount is actually a family of mounts composed of:
• the original Canon EF (electronic focus) mount (starting 1987),
• the EF-S mount for crop-sensor dSLR’s (starting 2004) and
• the EF-M mount for the Canon EOS M-series mILC’s (Starting 2012).
All three have physically the same mount, but inter-system compatibility is limited.
EF and EF-S mounts have the same flange focal distance (44 mm), but EF-S lenses are designed with Canon’s APS-C sensors (22.7 mm x 15.1 mm; Crop factor: 1,6x) in mind, and do not cover a full-frame sensor.
EF-M lenses are designed for Canon’s EOS-M series of interchangeable lens mirrorless cameras, and while they use the same APS-C sensor (22.7 mm x 15.1 mm; Crop factor: 1,6x), the flange focal sic with a significantly shorter flange focal distance (18 mm).
While EF-S and EF lenses can be used on EOS-M cameras using a suitable adapter (a smart adapter), EF-M lenses can not be used on EF or EF-S bodies.
Besides Canon, Canon EF lenses have been manufactured by practically all third-party lens manufacturers.
Adapting Canon EF (and EF-S) lenses:
With Canon EF (and EF-S) lenses having a flange focal distance of 44 mm, they can relatively easily be adapted to all mILC’s, with one proviso: As Canon EF lenses are fully electronically controlled, controlling the aperture of Canon EF lenses necessitates a smart adapter (A dumb adapter could be used to mount an EF lens at the correct distance, but the aperture would always remain wide open). Naturally Canon EF lenses can also be used on Canon R -mILC bodies with Canon’s own EF-to-RF adapter.
Identifying the Canon EF mount?
See more here.