Canon EF Lenses

Canon EOS SLR and DSLR mount, introduced in 1987 | 35 mm film and full-frame digital, with APS-C EF-S lenses using the same register but a deeper rear envelope

Canon EF was a decisive break from the mechanical FD system. Every aperture and focus command is electronic, and autofocus motors live in the lens rather than the camera body. That architecture let Canon introduce ring-type USM telephotos, image-stabilized lenses, diffractive-optics experiments, and a broad professional DSLR lens family without maintaining older mechanical couplings.

The mount's 54 mm throat and 44 mm SLR flange distance make it a classic full-frame reflex platform: generous enough for fast L-series primes and telephotos, but still constrained by mirror clearance for wide-angle designs. EF-S later used the same register and an EF-derived interface for APS-C cameras, but EF-S lenses could project farther into the mirror box and were mechanically keyed away from full-frame bodies. That distinction matters when a patent formula is EF-compatible in one version and crop-only in another.

EF is also a good example of a camera maker treating the lens as a controlled electromechanical module. Ultrasonic motors, optical stabilization, electronic diaphragms in later lenses, and distance reporting could evolve without changing the basic bayonet. In this catalog, EF lenses represent Canon's mature autofocus SLR era before the shorter-flange RF mirrorless system, and they are especially useful for comparing late reflex optical correction against mirrorless successors that no longer need to preserve the same back-focus envelope.