EF Mount: Canon's electronic lens mount with 54mm diameter — widely used on cinema cameras due to its extensive lens selection.
Technical Details
The EF Mount utilizes 8 electronic contacts to control aperture, focus, and image stabilization. The bayonet mount has a diameter of 54mm with a flange focal distance of 44.0mm. Canon produces the EF Mount in two variants: EF for full-frame sensors and EF-S for APS-C sensors with a smaller image circle. The purely electronic aperture control is achieved via stepping motors with a precision of 1/8 f-stops. The mount supports lens focal lengths from 8mm fisheye to 1200mm super telephoto.
History & Development
Canon introduced the EF Mount in 1987 with the EOS 650, revolutionizing lens technology through complete electronic integration. In 1993, Canon expanded the system with EF-S for smaller APS-C sensors. With the EOS C300 (2011), the EF Mount became established in professional cinema cameras. In 2018, Canon announced the RF Mount as the successor to the EF Mount, but continues to produce EF lenses for the established market.
Practical Use in Film
Cinema cameras such as the RED Epic, ARRI Alexa Mini, or Canon C500 Mark II use the EF Mount for maximum lens compatibility. "Mad Max: Fury Road" utilized Canon EF lenses on RED Dragon cameras for extreme driving shots. The electronic aperture control allows for seamless exposure ramps during shooting. EF lenses are particularly dominant in the low-budget sector, as photographic lenses are more cost-effective than specialized cine optics.
Comparison & Alternatives
The EF Mount competes with the PL Mount (Positive Lock) for high-end productions and Sony's E-Mount in the mirrorless segment. PL Mount lenses offer more precise mechanical focus markings but cost three to five times as much. Canon's own RF Mount (2018) is gradually replacing the EF system, featuring a 54mm diameter but only a 20mm flange focal distance. Adapters allow EF lenses on RF cameras, but not vice versa. For documentary filmmakers and smaller productions, the EF Mount remains the first choice due to its lens diversity.