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Oops, my bad. It look like if you adjust things just right you can get infinity focus with APS-C cameras, 1D/1DS series cameras, and the 5D/5D mkII with a shaved mirror. So it sounds like the 5D/5DII with an un-shaved mirror are the only Canon cameras that cause a problem.
After reading the thread again, it's unclear to me if any has had an adapter machined that threads into an M42-EOS adapter, and then allows the rear element to threaded into the adapter. I see mention of M39 to M42 adapters, but it sounds like the rear element is being epoxied...Show more →
As far as i know there has only been one success with infinity focus using a 1 series camera.It would be really great if they all allow this!... but it's not been proven yet
No one makes such an adapter that allows the rear element to be easily screwed into a common M42 adapter.That would be a great thing and would achieve several things at once! :
-it's adjustable! It could be used to modify the lens to any camera from crop frame to the most difficult- the 5D's
-It would eliminate the problem of M39-M42 adapters being abit too thick or 'bulky' .From what i've seen so far these have to be ground down around the outer edge so they dont contact the mirror box surround,though i may be wrong.
-If properly made it would also act as a 'safety stop' by limiting how close the last two elements can come together.This is a very useful feature as it gives complete peace of mind that on cant make mistakes when adjusting it.Mine does this -it allows the elements to come within 1/3mm but not touch
-A rear internal light blocking hood could also easily be built into this part,eliminating the problem of trying to adapt the original
Unfortunately such a part would still not cure all the problems we face in modifying this particular lens.
Other big issues are how to attach the M42 adapter to the lens chassis,and how to make and adjust the parts that will operate the aperture
The 'flange on an M42-EOS adapter being threaded with 0.5mm threads' was mine.
Basically its a very similar idea to the idea above but i started with a stop down flange type M42 adapter and a threaded part i just happened to find from another (different type) lens.
This part had a thread on the inside that accepted the 85/1.2 rear element directly,so it was a reasonable simple matter of having the flanged M42 adapter threaded to accept this part.It was too small and thin to thread into a normal M42 adapter,thats why i started with the flanged M42 adapter -i has a smaller hole.
Overall i wouldnt do it this way again because i dont have another one of those threaded parts