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Canon EF-S lens mount

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(Redirected from Short back focus)
An example of a plastic EF-S lens mount.

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.

The "S" in EF-S has variously been described by Canon as coming from either "Small image circle"[1] (the lens projects a smaller image circle than normal EF lenses to match the sensor), or "Short back focus"[2] (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 back focal length 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 aperture) and less expensive.

Although not all Canon EF-S lenses use this short back focal length, they cannot be mounted on DSLRs 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 vignetting or unsharp outer areas if used on a 35mm film or full frame sensor cameras. To a lesser degree, vignetting also occurs with APS-H sensor sizes, such as several (now discontinued) cameras of the 1D series.

Compatibility

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The cameras that can use the EF-S mount are:

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.

By design, it is physically impossible to mount EF-S lenses on EF-only cameras. This is because the increased proximity of the lens to the sensor means that on full-frame sensor or 35mm film EF cameras the lens itself would obstruct the mirror's movement and cause damage to the lens and/or camera. While it is possible to modify the lens such that the physical obstruction is removed, allowing for mounting to EF mount cameras, the rear of the lens would still obstruct the mirror. An additional reason is that the lenses produce a smaller image circle of even illumination (circle of no vignetting). An EF-S lens alignment mark is indicated by a small white rectangle, whereas the EF employs a small red dot. The lens will insert into the body when the alignment marks on each are matched, and the lens can then be rotated and locked into the operating position. EF-S camera bodies have both EF-S and EF alignment marks, while EF bodies have only EF marks. Some have reported success attaching EF-S lenses to full-frame bodies with the use of an extension tube; however, this does not eliminate the vignetting problem, and also removes the lens's ability to achieve infinity focus.[3] Also, attachment of EF-S lenses on EF bodies can often be accomplished by removing the small plastic ring seen in the photo above. Although vignetting is still an issue, photos can be taken, and infinity focus achieved. This modification comes with caveats, one being that on some lenses, like the EF-S 10-22mm, at the 10mm setting, the element protrudes too far back toward EF mount camera bodies.

The 10D, D60, D30, and earlier cameras share the EF-only mount with the full frame EOS camera bodies, and also with the APS-H size EOS camera bodies (1D series prior to the 1D X), despite having a smaller sensor and therefore a smaller mirror.

List of EF-S lenses

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See also: List of EF lenses

The EF-S lens mount is a relatively new offering from Canon, so the selection of available lenses is limited compared to the full EF range, but it is backward compatible with the EF mount, and can therefore still accept all EF lenses. The variety of EF-S prime lenses is very limited in comparison to EF-S zoom lenses, with three primes to nine zooms. EF-S lenses are very popular due to their lower cost and zoom lenses are preferred by amateur photographers. As of April 2017, no EF-S lens has been produced with the "L" designation or with diffractive optics, and only three EF-S prime lenses have been produced.

EF lens (left) and EF-S lens (right). Note raised ring on EF-S lens.
Focal length Equivalent focal length
(×1.6 crop factor) 		Maximum Aperture range Mark Introduced Macro USM STM IS

10–18mm 16–28.8 mm f/4.5–5.6 IS STM 2014 No No Yes Yes
10–22mm 16–35.2 mm f/3.5–4.5 USM 2004 No Yes No No
15–85mm 24–136 mm f/3.5–5.6 IS USM 2009 No Yes No Yes
17–55mm 27.2–88 mm f/2.8 IS USM 2006 No Yes No Yes
17–85mm 27.2–136 mm f/4–5.6 IS USM 2004 No Yes No Yes
18–55mm 28.8–88 mm f/3.5–5.6 I 2003 No No No No
I (Jpn.) 2003 No Yes No No
II 2005 No No No No
II (Jpn.) 2005 No Yes No No
III 2011 No No No No
IS 2007 No No No Yes
IS II 2011 No No No Yes
IS STM 2013 No No Yes Yes
f/4–5.6 IS STM 2017 No No Yes Yes
18–135mm 28.8–216 mm f/3.5–5.6 IS 2009 No No No Yes
IS STM 2012 No No Yes Yes
IS USM 2016 No Yes No Yes
18–200mm 28.8–320 mm f/3.5–5.6 IS 2008 No No No Yes
55–250mm 88–400 mm f/4–5.6 IS 2007 No No No Yes
IS II 2011 No No No Yes
IS STM 2013 No No Yes Yes

24mm 38.4 mm f/2.8 STM 2014 No No Yes No
35mm 56 mm f/2.8 IS STM 2017 Yes No Yes Yes
60mm 96 mm f/2.8 2005 Yes Yes No No

References

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  1. ^ "Technical Hall - Technical report 2004.1". Canon.com. Archived from the original on 2013-06-05. Retrieved 2017-06-04.
  2. ^ "Technical Hall - Technical report 2003.9". Canon.com. Archived from the original on 2013-06-05. Retrieved 2017-06-04.
  3. ^ "Canon EF-S 17-55mm f/2.8 IS USM Lens Review". The-digital-picture.com. Retrieved 2013-06-10.
[edit]
  1. ^ Rumors, Canon (2021-04-08). "Canon officially discontinues a lot more EF lenses". Canon Rumors - Your best source for Canon rumors, leaks and gossip. Retrieved 2021-04-09.
  2. ^ Rumors, Canon. "Recently Discontinued EF lenses". Canon Rumors - Your best source for Canon rumors, leaks and gossip. Retrieved 2021-04-23.
  3. ^ Rumors, Canon (2021-04-08). "Canon officially discontinues a lot more EF lenses". Canon Rumors - Your best source for Canon rumors, leaks and gossip. Retrieved 2021-04-09.
  4. ^ Rumors, Canon (2021-04-08). "Canon officially discontinues a lot more EF lenses". Canon Rumors - Your best source for Canon rumors, leaks and gossip. Retrieved 2021-04-09.
  5. ^ Rumors, Canon. "Recently Discontinued EF lenses". Canon Rumors - Your best source for Canon rumors, leaks and gossip. Retrieved 2021-04-23.
  6. ^ Rumors, Canon. "Recently Discontinued EF lenses". Canon Rumors - Your best source for Canon rumors, leaks and gossip. Retrieved 2021-04-23.
  7. ^ Rumors, Canon (2021-04-08). "Canon officially discontinues a lot more EF lenses". Canon Rumors - Your best source for Canon rumors, leaks and gossip. Retrieved 2021-04-09.
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