Originally posted by MattGunn ... As Dave suggested in the other thread, I have considered mounting a genuine Pentax adapter semi permanently on an M42 lens, removing the locking spring clip, and drilling a hole for the locking pin in the back of the lens.
Coupl'a notes:
Some of the M42 mount lenses aren't wide enough to accommodate the latch pin hole. It's easy enough to check with a lens and camera in hand. Spot drilling works well for those lenses that have a wide enough base. Consider an intentional slight off-set for the hole so the aperture ring is easier to see beneath the flash housing.
The flange on the flanged adapters is about 0.8mm thick. I have removed the flange and shortened the adapter by that much on a lathe so that it works the same as the OEM adapter without the spring clip. When used on those M42 lenses wide enough to drill the latch pin hole you have effectively built an M-mount lens. If you remove the anodizing from the base so as to short out the AE pins you can even provide certain pseudo -A mount lens functions as described elsewhere.
H2