Why can EF-S lenses damage a full-frame Canon camera, and is it only an image-circle issue?
Asked 2/3/2013
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I’ve heard that Canon EF-S lenses should not be used on full-frame bodies because they may damage the mirror. Is the incompatibility only because EF-S lenses don’t project a large enough image circle for a full-frame sensor, or is there also a real risk of physical interference inside the camera? Does this depend on whether the lens is a prime or a zoom, or on how the lens focuses?
Originally by Photography Stack Exchange contributor. Source · Licensed CC BY-SA 4.0
Photography Stack Exchange contributor
13y ago
2 Answers
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The main problem with using EF-S mount lenses on a FF camera is as you said the risk of damaging the mirror. EF-S lenses can protrude further back into the camera body than EF lenses, which means the mirror might hit the rear of the lense. This is what can cause damage to the mirror itself or the mechanism for flipping the mirror.
For some EF-S mount lenses this might not be a problem, since the lens doesn't extend back far enough to cause the mirror to hit it. Depending on the lens design and if the lens is rear focusing or not. Rear focusing lenses will use the rear group or elements to focus and this can extend the lens backwards into the camera. These lenses can work on a full frame camera at some focus distances, but not others. A zoom lens can also use the same technique when zooming, and cause the same problem.
The answer is really that it depends on the lens if it's safe to use or not.
The image quality will not be as good either, since the EF-s mount lenses will be optimized for smaller image circles than EF mount lenses.
Originally by user7271. Source · Licensed CC BY-SA 4.0
user7271
13y ago
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Generated from our catalog & community — verify before relying on it.
It’s more than just image coverage. Many EF-S lenses are designed for crop-sensor bodies and can sit farther back into the camera than standard EF lenses. On a full-frame DSLR, the larger mirror swings much closer to the rear of the lens, so some EF-S or crop-only lenses can physically interfere with the mirror and potentially damage the mirror, lens, or mirror mechanism.
Canon prevents this with EF-S lenses by making them mechanically incompatible with full-frame EF bodies. Some third-party crop lenses may still mount, but that does not mean they are safe.
Image circle is the other issue: even if a crop lens does not hit the mirror, it often won’t cover the full-frame sensor, causing strong vignetting or requiring cropping.
Whether it is safe depends on the specific lens design, not simply whether it is a prime or zoom. On some lenses, rear elements can move during focusing or zooming, so a lens may seem safe at one setting but not at another. Unless a specific lens is known to clear the mirror on your camera, don’t use crop-only lenses on full-frame DSLRs.
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