Originally posted by dude163 How do I base mod the nikkors to a PK mount?
1. Look at the lens base. The lowest structure on the lens body is the aperture ring. If that ring has a 'skirt' all the way around it, just press-fit the lens onto the PK mount. Don't bother trying to modify it.
2. If the aperture ring has a protruding nob on one side and an arc on the other, get out your jeweler's screwdrivers, and a Dremel and Reinforced Cut-Off Wheel #426 (about US$12 for five of them).
3. Unscrew the base plate (3 phillips screws). Pull off the aperture ring. Use the Dremel to cut off the nub and arc, so the bottom of the aperture ring is smooth. You might run a sanding wheel over the ring bottom.
4. Blow away the metallic dust. Replace the aperture ring and lens base plate. If any long tabs are sticking out from the lens base, cut them off. You now have a modded lens. Mount it on your camera. Aim and shoot.
Quote: also: has anyone been able to get a Leica elmar 90mm working on a PK mount or a m42 adapter?
No.
The problem is what's called registry (or register or registration, whatever), the distance from the camera mount to its sensor or film frame. Longer registry lenses can work on shorter registry mounts, but not vice-versa, because they won't focus to infinity. The Nikon registry is 46.5mm. Pentax registry is ~45.5mm. So a Nikon lens can focus to infinity on a Pentax body, but not vice-versa. And the Leica LTM/L39 registry is 28.8mm, much too short for either.
Canon cameras have registers shorter than most SLRs (but longer than Leicas). Canons are "universal recipients". Nikon cameras have registers longer than most SLRs. Nikons are "universal donors".
This webpage lists most camera registers.
There ARE ways a short-register lens like a Leica can be used on a Pentax mount, either PK or M42:
* Major surgery. Cut off about 16.7mm from the Leica lens body. Carefully.
* Use it for macros only. You have three ways to do this:
--- Add a cheap M39-M42 adapter.
--- Use a mount-reversal ring; put the lens on tubes, bellows, or camera body.
--- Use a thread-reversal ring; stack the lens onto a longer lens on the camera.