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12-02-2009, 11:00 AM   #1
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Lens compatibility

Newbie question. Can Nikon or canon lens be used on the Pentax k-x with some kind of adapter?

Thank you

12-02-2009, 11:13 AM   #2
Lowell Goudge's Avatar

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I am not aware of any canon to pentax adaptor, but there is available on E-Bay a nikon to pentax adaptor.

Just to be clear, virtually all camera makers have a different regestration distance, that is, the distance from the face of the lens mount to the focusing plane (i.e. film or sensor). Most are shorter than pentax, and therefore, most lenses, even if you could physically mount them (which you cant) would not focus to infinity.

Nikon however has a slightly larger registration distance, but not so large that you can put a mechanical adaptor (i.e. spacer) in place and maintain infinity focus.

the unit available on E-Bay is "optically corrected" which means it has a lens in it to correct the focusing, this however adds magnification. It has about a 1.25x magnification from tests I did on the one I bought, which makes it undesireable for wide angle, but perhaps practical for telephoto lenses.

The down side of this adaptor is that there is no aperture control. As you stop down the lens the viewfinder darkens, and the magnification costs you 1/2 stop of exposure.

There are other people, on ths forum, who have mechanically modified canon, nikon and a host of other lenses to Pentax K mount or Screw mount, but these modifications are for the brave. In this case, Nikon lenses are easiest because of the registration distance being slightly longer than pentax and this can be accepted as the lens focusing past infinity, or corrected by adding spacers / shims between a K mount and the lens body. Again with this conversion automatic aperture is lost.
12-02-2009, 11:57 AM   #3
Marc Sabatella's Avatar

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Basically, the answer is, with sufficient expertise and tinkering, one could probbly get it to work with some limitations. Just as (sorry to those who are tired of this analogy) one could could probably figure out a way to get a Toyota to use a Honda engine. But basically, no, it's not something one would normally expect to be able to do, except if you had a lot of time and money to spend just to prove it was possible.

Some Nikon lenses will sort of fit on a Pentax without an adapter - browse or search the forums for references to this. But with no exposure or focus automation, of course.

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