Canon EF-S lens mount

The Canon EF-S lens mount is a derivative of the <a href="/facts/Canon_EF_lens_mount/YMWYE90s">EF lens mount</a> created for some <a href="/facts/Canon_Inc./qoWp5I04">Canon</a> <a href="/facts/Digital_single-lens_reflex_camera/1gq1Y1qt">digital single-lens reflex cameras</a> with <a href="/facts/APS-C/jefcWjb4">APS-C</a> sized image sensors. It was released in 2003. Cameras with the EF-S mount are <a href="/facts/Backward_compatibility/FbHFBu5y">backward compatible</a> with the EF lenses and, as such, have a <a href="/facts/Flange_focal_distance/c3jenIH0">flange focal distance</a> 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.
The "S" in EF-S has variously been described by Canon as coming from either "Small image circle" (the lens projects a smaller <a href="/facts/Image_circle/oU9QF5vK">image circle</a> than normal EF lenses to match the sensor), or "Short back focus" (the smaller mirror used in APS-C cameras also allows optical elements to protrude further into the camera body, reducing the minimum distance between the sensor and the back element of the lens). The combination of a smaller sensor and shorter <a href="/facts/Focal_length/brGIUkEY">back focal length</a> distance enhances the possibilities for wide angle and very wide angle lenses. Such lenses designed for the EF-S mount can be made smaller, lighter (containing less glass), faster (larger <a href="/facts/Aperture/8PV11GQm">aperture</a>) and less expensive. 
Although not all Canon EF-S lenses use this short back focal length, they cannot be mounted on <a href="/facts/DSLR/1gq1Y1qt">DSLRs</a> with sensors larger than APS-C. However, some lenses produced by third-party manufacturers may feature the standard EF mount if they do not have the shorter back focal length but only have a small image circle. Such lenses will give noticeable <a href="/facts/Vignetting/QMcCmUNw">vignetting</a> or unsharp outer areas if used on a <a href="/facts/35mm_format/5MU6mXr0">35mm film</a> or <a href="/facts/Full-frame_digital_SLR/LsUjIXCH">full frame sensor</a> cameras. To a lesser degree, vignetting also occurs with <a href="/facts/APS-H/jefcWjb4">APS-H</a> sensor sizes, such as several (now discontinued) cameras of the 1D series.

Canon EF-S lens mount open-in-new

Canon EF-S lens mount