Is it possible to mount a modern EF lens to an old m42 mount camera? I see dozens of adapters for using M42 lenses on modern cameras, but never the other way around. It feels a bit like sacrilege but I'd love to try one of my nice zoom lenses on my old film camera.
Posted Apr 28, 2023, 5:39 AM UTC
EF mount lenses are designed to project their focused image 44mm back from the mount flange. An M42 body puts the film 45.46mm behind the mount flange, and an adapter would add even more space, which would be too far away.
Also you wouldn't have aperture control because that's electronic in EF lenses.
Not really. EOS mount lenses don't have aperture rings on them—all control of aperture is done through electronic communication you won't have with M42, so the lens would have to be wide open all the time (there's a workaround for this, but it ain't pretty: mount it on an EOS body, stop it down, then take it off while stopped down and mount it to the M42 body. And do that every time you want to change the aperture).
And the M42 mount is deeper than the EOS mount; and the throat diameter is smaller on M42 so essentially, the back end of the lens can't enter the camera body at all. This means holding the lens a lot farther from the image plane than it was designed to sit, despite the fact that the actual flange distances are only millimeters apart, the actual distance the lens would have to sit from where it was designed to would probably be >1cm (the whole of the lens's mount+adapting difference requirements).
So a glass element in the adapter probably can't compensate for the the lost focal length range the way it can with, say, a Canon FD/FL to Canon EOS adapter can. If a glass element could compensate, it's basically a teleconverter: increasing focal length, decreasing max. aperture, and if it's cheap, messing up the optical quality.
That's a lot of negatives for one adapter, which is probably why you can't find one.
Due to the build of the lenses, such a thing cannot practically exist. The M42 threads are smaller than the EF mount diameter.
The only way that’s possible, is if you move the EF lens further away from the camera body. These adapters do exist but they work as macro extension tubes and you will not be able to focus on infinity.