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I have a Canon XTi (EF-S lens mount). Can I get an adapter to mount a Pentax M42 lens? If so, do I lose any functionality?

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up vote 4 down vote accepted

You can use an adapter to mount a lot of lenses to a Canon EOS body, due to the short flange distance.

You will lose auto-focus, and the camera cannot set the aperture of the lens when taking the shot.

That means you will have to focus manually, and meter by stopping down.

Here's a good introduction to using non-EF mounts on modern Canon cameras.

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More generally, I've also found the table at helpful. – drewbenn Jan 13 '11 at 19:55

As far as I'm aware, every M42 lens will fit an EF-S camera (i.e. one with a cropped sensor), but a few will not fit a full-frame camera like the 5D or 1Ds ranges because bits of the lens can catch on the (much larger) mirror as it flips up and/or down during an exposure.

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Yes, using a M42 to EF adapter.

You will lose focus confirmation, unless you find an adapter that specifically supports it. has a good article about this. Also, the auto focus systems are incompatible, so you will only be able to use manual focus.

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just to add to the answers - you'll loose all electrical connections from the body to the lens. so you will loose Automatic focus, but it'll be a manual focus lens anyway and automatic aperture control, but it'll be manual anyway.

Everything else (metering for example) will be fine.

not sure about it hitting the mirror on full frame bodies ? the adaptor will move the lens away from the body moving it away from the mirror ?

But I would expect to get vignetting on full frame, that the smaller APS sized sensor will avoid - I know I have 85mm russian lens on my 7D.

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M42 lenses like the Pentax M and Zeiss Jena has a mechanical stick to stop down the lens when shooting. This stick will hit the mirror on fullframe. You can remove or hone down this stick to avoid it. – Michael Nielsen Feb 2 '13 at 20:25
live and learn - thanks for that – Tony Feb 4 '13 at 12:31

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