Canon EF-S lens mount
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The EF-S lens mount is a derivative of the EF lens mount created for a subset of Canon digital single-lens reflex cameras with APS-C sized image sensors.
The "S" in EF-S stands for "short back focus", which means that the rear element of the lens is closer to the image sensor than on regular 35 mm SLR cameras. The biggest advantage is that it allows for smaller and less expensive wide angle lenses. Lenses designed specifically for APS-C sized sensors are often optically designed to provide a narrower light cone to match the sensor. However, not all such lenses require the shorter back focus, and may feature the standard EF mount. Such lenses will give noticeable vigneting if used on a 35mm film or sensor camera.
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[edit] Compatibility
The cameras that use the EF-S mount are: the Canon EOS 300D, 350D, 400D, 20D, 20Da, and 30D digital SLRs. These cameras can all use both EF and EF-S lenses. EF-S lenses, however, can not be used on EF mount cameras and Canon designers have taken steps to ensure it is physically impossible to mount EF-S lenses in this way. 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. An additional reason is that the lenses produce a smaller image circle of even illumination (circle of no vignetting).
The 10D and earlier cameras share the EF-only mount with the full frame EOS camera bodies, despite having a smaller sensor and therefore a smaller mirror. At least one person has managed to mount the 18–55 EF-S lens on a 10D body by physically modifying the lens itself. This is not recommended for obvious reasons and should an EF-S lens modified in this way be mounted on a full-frame EOS camera, it would almost certainly cause a lot of damage. There are also speculation that these lenses, when modified, might be useful on APS SLRs (the EOS IX and EOS IX Lite), but this is also not recommended for the same reasons.
[edit] List of EF-S 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 backwards compatible with the EF mount, and can therefore still accept all EF lenses.
| Focal length(s) | Aperture range | Macro | Ultrasonic motor | Image stabilization | L-series | Diffractive optics | |
|---|---|---|---|---|---|---|---|
| Article | 10–22 mm | 3.5–4.5 |  No |
 Yes |
No |
No |
No |
| Article | 17–55 mm | 2.8 | No |
Yes |
Yes |
No |
No |
| Article | 17–85 mm | 4–5.6 | No |
Yes |
Yes |
No |
No |
| Article | 18–55 mm II | 3.5–5.6 | No |
No |
No |
No |
No |
| Article | 18–55 mm II | 3.5–5.6 | No |
Yes |
No |
No |
No |
| Article | 60 mm | 2.8 | Yes |
Yes |
No |
No |
No |
† the optional EF-S 18–55 mm I kit lens that comes with the EOS 300D/Digital Rebel and EOS 20D, or EF-S 18–55 mm II with EOS 350D/Digital Rebel XT, does not have a USM; a USM focusing system version of EF-S 18–55 mm can be purchased separately, or with a Silver 350d/Rebel XT as a kit from Jessops (Located in the UK).
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| Preceded by - |
Canon APS-C lens mounts August 2003 – present |
Succeeded by - |
