The EF lens mount is the standard lens mount on Canon’s EOS family of 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 electronic contacts, with no mechanical levers or plungers. The EF mount was first introduced in 1987, superseding the FD mount, and bridged Canon’s transition from film to digital camera bodies. Canon announced the production of its 100-millionth EF-series interchangeable lens on April 22, 2014. The last new EF lens design was released in 2018, with Canon’s focus shifting to their new RF lens system. EF lenses can be used via an adapter on RF camera bodies, but RF lenses cannot be used with EF cameras. EF has no interoperability with the FD mount system.
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. 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 eighty lenses, encompassing focal lengths from 8 to 1200 mm. 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.
Versatility
Its large diameter and relatively short flange focal distance of 44.0 mm allows mechanical adaptation of EF camera bodies to many types of non-EF lenses. It is possible to mount lenses using the Nikon F mount, Olympus OM, Leica R and universal M42 lens mounts (among others) by the use of a mechanical adapter without electronic control of the aperture or autofocus. In contrast, parfocal adaptation of EF lenses to non-EF camera bodies is not possible with only a mechanical adapter that does not contain optical elements. EF mount lenses are somewhat compatible with newer Canon bodies, though the reverse is not true:
EF-S lens mount cameras can mount EF lenses without an adapter EF-M lens mount cameras can mount EF lenses with an EF-EOS M adapter RF mount cameras can mount EF lenses with a variety of adapters Lenses for the earlier Canon FD lens mount are not usable for general photography on an EF mount cameras, unless adapters with optical elements are used because they are made for a flange focal distance of only 42.0 mm. Infinity focus would be lost with an adapter which lacks optical elements. The Canon FD-EOS adapter is rare and is only usable with certain FD telephoto lenses. With a manual connection, the aperture and focus controls of the lens cannot be controlled or read from the camera; the lens must be focused manually. Since the only possible metering is through-the-lens, the lens must be manually stopped down to accurately meter at anything less than full aperture. (This is called stop-down metering.)
Third-party lenses Compatible third-party lenses with the EF lens mount are manufactured by Yongnuo, Samyang, Schneider, Sigma, Tamron, Tokina, Cosina and Carl Zeiss. The manufacturers of these lenses have reverse engineered the EOS electronics—except Zeiss, which does not have the rights to use the autofocus or the electronic aperture control of EOS cameras . The use of these third-party lenses is not supported by Canon. Sometimes compatibility problems arise, as no third party has access to Canon's specifications for camera-to-body communication. These compatibility issues mostly occur when using a newer body with an older third-party lens. Over time, most of these issues have been resolved by the major third-party brands.
Third-party cameras Due to the high market penetration of EF-mount lenses, other camera manufacturers began to offer EF-mount cameras. Since the EF-mount was created for SLR cameras with their long focal flange distance, mirrorless interchangeable-lens cameras can use EF lenses with a mechanical adaptor that bridges the distance. Red Digital Cinema Company offers various camera models that can be equipped with an electronic EF-mount. Many Blackmagic Design cameras are sold in EF-mount variants. For Sony E-mount various adaptors enable using EF-mount lenses with full electronic control.
Controls and features
Canon EF lenses typically have a number of controls, switches and physical features, used by the photographer to control the lens. The types and number of the controls can vary from lens to lens. With the most basic lenses having only a few, to the most complex having over a dozen different controls and switches. This is a list of the different controls and switches found on most Canon EF lenses, along with a detailed description on what they are used for. Lens mount index: This raised, round red mark is found on all EF lenses. It is used for matching the EF lens mount to the mount on an EOS body, so one can connect the lens to the body quickly. Focusing ring: This control, found on most EF lenses, is used for focusing the lens. It is usually a ring on the lens body, that can be turned. Zoom ring: This control is found on most EF zoom lenses. It is used for changing the focal length of the lens. The zoom ring usually has certain, common, focal lengths marked on it. To set the zoom ring to any given focal length, one must turn the ring so that the marked focal length matches the zoom index. The zoom index is typically a white, or black, line found next to the zoom ring.
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