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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.<ref name="canon">{{cite web▼
▲When the EF mount was introduced in 1987, it had the largest mount diameter (54 mm internal) among all 35 mm SLR cameras.<ref name=canon>{{cite web
|url=http://global.canon/en/c-museum/history/story07.html
|title=History Hall 1987-1991
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Some older USM lenses are identified with a gold ring and the word "Ultrasonic" printed in gold on the lens barrel. L lenses with USM don't have the gold ring, but they still have the word "Ultrasonic" printed on the lens barrel.
=== Stepping motor {{Anchor|Stepper motor|
[[File:Canon EF 40mm STM lens (focus stacked version).jpg|240px|thumb|[[Canon EF 40mm lens|Canon EF 40mm f/2.8 STM]] [[pancake lens]]]]
Canon announced [[Stepper motor|
Canon stated that this technology allows smooth and silent autofocus, and with compatible bodies (the first of which is the 650D) will provide continuous autofocus in live view and video.<ref>{{cite press release|url=http://www.usa.canon.com/cusa/about_canon?pageKeyCode=pressreldetail&docId=0901e0248057dd10 |title=The New EOS Rebel T4i DSLR Camera Puts The Power And Creativity of DSLR Stills And Video at Your Fingertips |publisher=Canon U.S.A., Inc. |date=2012-06-08 |access-date=2012-06-08}}</ref> Unlike USM, STM lenses use focus-by-wire to enable full-time manual mode. Two main disadvantages are linked to focus-by-wire: First, the need to computationally process the input before the intended action is executed leads to a sometimes perceptible lag. Second, using the motor requires power, so when an STM lens is not connected to a camera or the camera is switched off, changing the focus is impossible.
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|archive-date = 18 February 2009}}</ref> L series lenses are compatible with the full range of EF or EF-S mounts and, as they are aimed at the high-end user, most also include environmental or weather sealing and a constant maximum aperture. All L lenses are supplied complete with a hood and a pouch or case, which are not generally included with non-L lenses. Distinctive visual cues include a red ring around the lens and an off-white colour on longer-focal-length models. The latter also helps to reflect light and reduce heat absorption and subsequent internal expansion of lens components that can affect the image quality of long focal length lenses.<ref>{{cite web|title=Lenses: Black or white lenses?|url=http://cpn.canon-europe.com/content/education/infobank/lenses/black_or_white_lenses.do|website=Canon Europe}}</ref>
All L lenses include at least one [[fluorite glass|fluorite]], ultra-low-[[dispersion (optics)|dispersion]] glass element, super ultra-low-[[dispersion (optics)|dispersion]] glass element, and/or certain types of [[aspherical lens|aspherical elements]]. (Note that a number of non-L lenses also use aspherical
==Timeline of innovations==
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| 67 mm
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| [[Canon EF 40mm lens|40 mm STM]]
| {{f/}}2.8
|2012
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| 72 mm
|-
| 85 mm IS<ref>{{cite press release |url=https://www.usa.canon.com/internet/portal/us/home/about/newsroom/press-releases/press-release-details/2017/20170829-Lens/20170829-Lens |title=Canon U.S.A. Expands Its Lens Portfolio with the New EF 85mm F/1.4L IS USM Lens And Their First-Ever Macro Tilt-Shift Lenses |publisher=Canon U.S.A., Inc. |date=29 August 2017 |access-date=30 August 2017 |archive-date=29 August 2017 |archive-url=https://web.archive.org/web/20170829123200/https://www.usa.canon.com/internet/portal/us/home/about/newsroom/press-releases/press-release-details/2017/20170829-Lens/20170829-Lens |url-status=dead }}</ref>
| {{f/}}1.4
|2017
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|{{No}}
|{{No}}
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| 100 mm
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== External links ==
* [http://global.canon/en/c-museum/series_search.html?t=lens&s=ef EF Lenses at the Canon Camera Museum] {{Webarchive|url=https://web.archive.org/web/20170505082457/http://global.canon/en/c-museum/series_search.html?t=lens&s=ef |date=5 May 2017 }}
* [https://docs.google.com/spreadsheets/d/1XHrXeijkKB_ULZxcgJK_v4iPBbxAfOuuo-VuP5ESDvA/edit#gid=0 List of all Canon SLR lenses with technical specifications]
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