M42/Nikon Ai adapter problem

[pat2025]

I just tried Mir-1b on my nikon d5100, and everything is alright except focusing ring. Without adapter works perfectly but when I mount adapter works only between 0.7 and 1.7 meter. Anybody knows why, I guess the lens was disassembled and then assembled incorrectly or I bought broken adapter. Any ideas will be appreciated.

[Oldhand]

Hello Pat and welcome.
Any M42 lens on a Nikon will behave in much the same way. It has to do with the registration distance of the various lens systems and the fact that Nikon's is longer than the M42.
So effectively the M42 lens is behaving as if it was attached to a close-up extension tube.
There is probably nothing wrong with your lens.
OH

[pat2025]

Well, I'm sorry I wasn't very precise with question. I've got adapter with glass element so it should work in full range but still it isn't the problem. Ring can't be turn farther the 1.7 meter and without adapter turns smoothly from 0.7 to infinity.

[antico]

Maybe the adapter is pressing the focusing ring, if I'm not mistaken Mir-1b is pretty similar to Helios 44-2 in terms of the body design, and I have known cases that when the adapter is on the lens it made it not capable of turning the focusing ring to a certain distance.
I supose you bought a adapter with corrector glass inside, because if you don't then you have to consider also that the lens never will focus to the indicated distance, because what user Oldhand just said.

[pat2025]

Thanks, I was worried only about adapter. Lens was almost free.

[Oldhand]

As the Mir is focused towards infinity, the rear element moves backwards towards the camera. I am guessing that this rear element of the Mir is hitting the correction element in the adapter at about the 1.7 metre mark and will not rotate any further.
OH

[visualopsins]