Hi, I have a Zeis tessar 2.8/50mm Jena DDR lens mounted on a Pentax spotmatic. There are two problems - 1) I cannot get infinity focus, and there appears to be a tight spot when screwing on or unscrewing the lens.
Any help much appreciated.
Fidgety

As for the infinity focus, it could be the lens needs recalibration. I remember when I bought my Yashica FX-#, it had a Yashinon lens, and it wasn't focusing properly. All the distances were incorrect, and when it focuses to infinity, the lens isn't at its furthest point (I tend to use the distance markers on the top of the lens, and the correlation between the focus and the distances was incorrect.) The problem was easily fixed by screwing a couple of screws.

The tight spot sounds to me as if the teeth of the lens mount are not properly filed. They're not as smooth. Maybe you could get them checked.

OR, it could be the mount on the Pentax itself.

Thanks for the advice, I will get it checked out!