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I have made a silly mistake. I own a Canon 7D and have bought a lens but I didn't realize it was for an EOS M. There are converters for eos lenses on EOS M bodies but are there converters for the EOS EF-M lens to fit the EOS body? Thanks

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It is not possible to convert an EF-M lens to fit EF-S cameras. This has to do with the shorter flange focal distance of the EF-M mount. The flange focal distance (FFD) of the EF-M is 18 mm and for EF-S it's 44 mm. The greater FFD of the EF-S mount is to accommodate the mirror of the DSLR:s that use them. The EOS M is mirrorless and can therefore be made smaller by having a shorter FFD.

Flange focal distance by Shigeru23 (https://commons.wikimedia.org/wiki/User_talk:Shigeru23)

Flange focal distance by Shigeru23 (https://commons.wikimedia.org/wiki/User_talk:Shigeru23)

It's possible to use EF-S and EF lenses on EOS M bodies by using an adapter that only acts as a spacer and an electrical contact interface. An adapter for EF-M lenses on EF-S bodies would unfortunately be required to be of a negative thickness and is therefore not possible to make.

Further answer: it technically possible to adapt lenses with a shorter FFD than the body mount they are adapted to by using adapters with lenses. Unfortunately this makes them act as teleconverters and for the case EF-M lenses on EF-S bodies drastically change the lens characteristics as well as the image quality they produce.

Canon has made an adapter for lenses using the FD mount (FFD 42 mm) for EF mount bodies (44 mm). This is a very small difference in FFD so the change in image quality as well as the teleconverter effect of the adapter was not that significant.

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No You see the EF-M mount has a shorter flange distance than EF-S or EF mounts. So an adapter just makes up for the gap to put an EF-S or EF lens on a EF-M camera. One cannot do the reverse since a lens for EF-M mount must sit closer to the sensor than the EF-S mount on the 7D.

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