The EF lens mount is the standard lens mount on the Canon EOS family of SLR film and digital cameras. EF stands for "Electro-Focus": automatic focusing on EF lenses is handled by a dedicated electric motor built into the lens. Mechanically, it is a bayonet-style mount, and all communication between camera and lens takes place through electrical contacts; there are no mechanical levers or plungers. The mount was first introduced in 1987. Canon claims to have produced its 100-millionth EF-series interchangeable lens on 22 April 2014. 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. The EF mount reversed the mechanical logic of the FD mount. The FD mount provided the three-eared bayonet fitting on the camera body, and each FD lens provided a breech-lock receptacle to register and fasten the lens to the bayonet. The EF mount reverses this logic, providing the bayonet on each lens, and a receptacle on the camera body. The EF mount also changed the logical clamping action of the bayonet receptacle to improve the tactical operation. Attaching an FD lens to a camera body required two hands: one to hold the lens in position, and a second to twist the breech-lock ring to rigidly lock the lens to the camera. The EF mount instead provides leaf springs in the receptacle, which hold the registration surfaces of the lens and receptacle together along the optical axis, while the manual twisting action engages a spring-loaded registration pin in the receptacle which drops into a recess provided on the bayonet fitting, locking the rotation. This EF mount feature provided the convenience of attaching EF lenses with one hand (holding the lens and twisting), versus two hands (one to hold the lens, one to twist the breech-lock) required for the FD attachment. An EF lens may also be removed with one hand by gripping the base of the