Originally posted by RioRico Slightly tangential: Adapting Exakta to PK isn't difficult nor destructive. Here's how:
* Remove (and save!) the index screw from the lens base
* Glue a cheap M39-M42 adapter ring around the bayonet -- I use contact cement, which is dissolved by thinner, so the mod is reversible (don't lose the screw!)
* Grind away about 0.6mm from the wide side of a cheap M42-PK adapter -- tape rough sandpaper to a very flat time, use d block of wood as a grip while grinding
* After the glue is well dried, screw-on the ground-down adapter -- keep grinding till you get infinity focus
See, this mod chops the adapter, not the lens. And one ground-down adapter can be used on several glued lenses.
RioRico,
I've been reading this how to convert Exacta mount to PK for the umpteenth time trying to figure out how you achieved infinity focus.
PK register distance = 45.46mm
Exacta/Topcon register distance = 44.7mm
Difference of 0.76mm
In the modification you have described, you have mounted an m42 to PK adapter on top of the Exacta mount. If you take a cheap, black m42 to PK adapter and grind away all of the flange so that you are left with only the m42 threaded ring that has 3 PK bayonets, and screw this onto the m39 to m42 adapter that's been glued around the Exacta lens' bayonets, the result is an Exacta lens with unchanged register distance but with a PK mount. Am I correct, so far?
Here comes the big BUT... The lens register distance is the distance between the sensor plane and the lens mount plane on the camera body. You may have an Exacta lens with a PK mount but when you mount this lens on a Pentax DSLR, you have effectively extended the lens by 0.76mm, making infinity focus impossible. I cannot see how you can achieve infinity focus without shortening the Exacta lens by 0.76mm at the back of the lens. If the modification as you have described was to be done to either Olympus or Nikon lenses, it makes perfect sense because either of the two brands have longer register distance than Pentax.
It seems obvious that you have done this modification and achieved infinity focus with an Exacta lens, please enlighten me if I have confused myself in my thought process along the way.
Thanks,