I thought first that I should include this in the "off brand club", but then it appears that the lenses there are mostly lenses that does really mount on K or M42 cameras, focus to infinity etc. So maybe we are ready for a club for lenses that should not work on a Pentax camera?
I have a history with Konica before I went for Pentax, and I still have a soft spot for Konica Hexanon lenses. Today they are dead lenses, since they don't mount on any digital camera without mechanical hacking. And I'm not prepared to trash my fine Hexanons since I still occasionally use them on a Konica T3.
Of course, I have not been able to resist to try to mount them on a Pentax DSLR. There are two problems with this:
1) The bayonett does not fit. However, some Hexanon lenses can with some trial and error mount a little bit on a K-mount. The connection is less solid than the Nikkor lenses, where some also mount (almost) on K mounts.
2) Konica have about 5mm shorter registration distance than Pentax and was one of the shortest SLR registration distances. This combined with that Minolta bought Konica, promissed to carry on the AR mount, gave it up and stopped all use of the AR mount, and then sold out from camera production themself, is why I call these lenses dead in the digital age.
There are primarily two lenses I'd like to be able to use on a Pentax DSLR:
1) Hexanon AR 85mm f1.8. A very nice portrait lens.
2) Hexanon AR 55mm f3.5 macro. A very sharp macro normal comparable to the micro-Nikkors. It reach 1:1 with an automatic tube that was sold together with the lens. My plan is to hack two third party tubes, a Pentax and a Konica, and get a mount with a K mount on the camera side and an AR mount on the lens side. I will lose apperture connection, but should be able to work quite well in M mode. The fact that the macro Hexanon have the same functionality as some micro-Nikkors, with an apperture opening that automatically compensate for the changing lens speed with changin magnification should help.
But first the 85mm. It mounts on the K20D, but I dare not let go of the lens. I loose inifity. In fact, I cannot focus beyond about 2m. But portraits can be taken within 2m distance:
