History
The EF mount replaces its predecessor, the FD mount. The standard autofocus lens mounting technology of the time used a motor in the camera body to drive the mechanics of the focus helicoid in the lens by using a transfer lever. The key innovation of the EF series was to use a motor inside the lens itself for focusing. This allowed for autofocusing lenses which did not require mechanical levers in the mount mechanism, only electrical contacts to supply power and instructions to the lens motor. The motors were designed for the particular lens they were installed in.
When the EF mount was introduced in 1987, it had the largest mount diameter (54 mm internal) among all 35 mm SLR cameras.
The EF series includes over sixty lenses. The EF series has encompassed focal lengths from 8 to 1200 mm. The EF-M mount was introduced with two lenses, a 22mm prime and an 18–55mm zoom. Many EF lenses include such features as Canon's ultrasonic motor (USM) drive, an image stabilization system (IS), diffractive optics (DO) and, particularly for L-series lenses, fluorite and aspherical lens elements.
Read more about this topic: Canon EF Lens Mount
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