Dummy question about M42 to Nikon mounting ring

[norm123]

Hi all
I do photography since 30 years and for the first time I decided to use an old Zeniton 135 mm lens (M42) on a Nikon F90X just because I'm curious about this lens. So, I bought a transfert ring and I was surprised to see a piece of glass in it. What is it? Is it a corrective lens for infinite focus?
Thank you

 

[foveon_m]

M42 flange distance is about 1 mm shorter than Nikon F, so it needs the optical element to reach infinite focus.^^

 

[AgX]

Yes, a pure mechanical adapter would introduce too much extension for still yielding infinity focus.

The Canon R/ FL / FD mount for example has a that short flange to film distance that there still is enough free length a the lens-side to make a pure mechanical such mechanicl adapter work.

M42 flange distance is about 1 mm shorter than Nikon F, so it needs the optical element to reach infinite focus.^^

Even if there would be zero difference that would not mean in general that an adapter would fit.

That all is both a matter of flange-fim distance of a camera body and the design of the respecive bayonet (and how much extension a adapter would add..

 

[vlasta]

What is it? Is it a corrective lens for infinite focus?

Yes.
And you will be not satisfied with results !

 

[Paul Howell]

Yes.
And you will be not satisfied with results !

I found that to be true, I have a pretty good line up of M42 glass, but my working camera was an F, then F2 and 3, I bought an adapter with the corrective balance lens, it worked but acted as a teleconverter, wide angle lens vinyeteded and there was loss of sharpness. I used once or twice and then tossed it out, didn't want to pass on my troubles. Perhaps over the years the corrective lens has been improved. Don't know what you paid, if you can return it, a better option would a cheap M42 body, Ricoh or Chinon can be had for under $20.00.

 

[AgX]

On the other hand one may ask whether one actually needs infinity focus. The yielded focusing range may be sufficient for a given task.
Of course the focusing scale on the barrel will be off too, in case one would need it.