Originally posted by Barnster Sorry Marc,no disrespect,but this comment above,I had to have a chuckle!!But getting back to the subject.Their was a comment about adapters in another post with this similar question.One of the members replied something like"Why would you want to put a Nikon/Canon lens on a Pentax anyway"?Are they that better that you would want to go to all that trouble to buy adapters,unless you already own Nikon/Canon lenses in the first place,and you want to utilise those lenses.
If you have Nikon or Canon lenses, buy a Nikon or Canon body for them. It's not like as if they aren't common and fairly cheap if you go back a couple of generations.
Whether you can adapt a non manufacturers lens to a particular camera has to do with the flange to focal plane distance of the optical design of the lens. If it is longer than the camera, and the throat of the camera is big enough, then it's probably doable. If it's shorter than that of the camera, then you either give up infinity focus, or you put a refractive element into the adapter and kiss any lens quality you might have had good bye.
This is in addition to losing any of the lenses usability features, such as AF or auto aperture.