The Canon EF-S lens mount is a derivative of the EF lens mount created for some Canon digital single-lens reflex cameras with APS-C sized image sensors. It was released in 2003. Cameras with the EF-S mount are backward compatible with the EF lenses and, as such, have a flange focal distance of 44.0 mm. Such cameras, however, have more clearance, allowing lens elements to be closer to the sensor than in the EF mount. Only Canon cameras released after 2003 with APS-C sized sensors support the EF-S mount.
An example of a plastic EF-S lens mount.
An EF-S compatible body, the Canon EOS 400D, with open lens mount
An EF-S compatible mount close-up, from the Canon 30D. Note the circular indent inside the mount, which corresponds to the raised ring on the lens.
EF lens (left) and EF-S lens (right). Note raised ring on EF-S lens.
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.
The electronic contacts (gold-plated) of an EF mount lens.
The EF mount of a Canon EOS 50
Electronics of an EF-S lens
An EF lens showing its different controls and features
