Canon FF cameras incompatibility with APS lenses.

Started Oct 3, 2012 | Discussions thread
oss Regular Member • Posts: 270
Re: Canon FF cameras incompatibility with APS lenses.

The 'S' in EF-S stands for short back focus.

It was a design decision taken about 10 years ago to allow them to make smaller lighter lenses.

Canon's EF mount has the largest bore of any DSLR camera range because of decisions taken over twenty five years ago, at the time the extra size gave them room to build the lens AF electronics and motors into the lens body rather than in the camera body like other manufacturers.

The large diameter of the EF mount and longer distance to the focal plane add up to physically larger lenses.

When EF-S was designed it took advantage of the smaller mirror in APS-C camera's to allow optical formulas with a shorter distance from the focal plane to the back of the rear element, this allowed the lenses to be smaller and lighter overall, so it was an advantage at the time even if it means that they now have to deal with a set of incompatible lenses on full frame bodies.

So forget the conspiracy theories, these were engineering decisions, the EF-S range was designed specifically for APS-C camera's for what were no doubt considered to be good reasons at the time, namely for a long time they could offer cheaper, lighter, smaller lenses to the very large market for APS-C cameras.

Some of the EF-S lenses on offer were very high quality, I owned for a number of years the 10-22 and it was every bit as good as its EF equivalents.

Simple reality is that if you want to use a Canon camera with a FF mirror box then EF-S lenses will foul the mirror at some point, the EF-S 10-22 modifications get past this but as been mentioned by others it will still foul the mirror at its widest focal length.

APS-H format was from memory slightly more forgiving, you could get away with the mods to the 10-22 on the 1D.

Ma55l wrote:

gavin wrote:

The EF-S lens are not compatible with FF Canon SLRs. Their image circle is not big enough. I think they may also hit the back mirror.

What camera do I have? I rather you look at my photos

Thanks for the response. In truth I see no problem with a small image circle as you could just crop to an APS size in photoshop and discard the outer image. That is basically what the other cameras do automatically and in camera. But has that changed in the 6D?

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