Carl Zeiss Tessar 80mm f2.8 infinity focus problem

<p>Hi everyone,<br>

I just had a lovely Carl Zeiss Tessar 80mm f2.8 lens (which I understand to be somewhat uncommon) overhauled. As with all my old lenses, the first test I do to make sure that there are no major issues is on a digital body, so that I can get rapid feedback. This lens has an M42 mount, and I used a stack of M42-to-EOS plus EOS-to-Sony E adapters to mount it on my Sony mirrorless camera. But the lens when focused on infinity per the barrel markings, only focuses at around 100 meters.<br>

I then tested the lens on a Pentax MX body, and again, the lens fails to reach focus at infinity. <br>

Is this a problem with the lens helicoid adjustment, or is it possible that this lens is of another mount type that has an M42-like thread but the wrong flange to sensor/film plane distance? (does such a mount exist?)<br>

Thanks in advance for your help,<br />Raj</p>

<p>If the lens was otherwise returned to fully working condition, it might be a good time to ask the repairer to adjust the lens for proper infinity focus.</p>

<p>It is a straightforward adjustment. It is not a helicoid or mount problem at this point.</p>

<p>It has to focus on an M42 mount camera for starters. The rest, if any, will logically follow.</p>

<p><strong>Raj Mohan</strong> Hi!This type of lenses from CZJena have about six entry points for the helical mount to grasp. Only one of them will be the optically correct thread to focus to infinity. I have a hunch that some repairman might have assembled it wrongly from the wrong entry point on the Helical. This is a usual mistake that happens.<br>

Initially, please, try and focus the lens to infinity on a white wall surface without the camera body. If it does not focus then a lens element may have been fixed in the reverse [meaning inside out]. If it does focus then check the register distance and see if it matches the one in the camera body.<br>

Perhaps you have done all this, already. In that case, the only way out is to disassemble and remount the helix. It will take a lot of patience, as it is by trial and error; you have to check the focus for each mounting position. If you are lucky you may get it in the first few tries. Otherwise, it could take days on end. Good luck. SP.</p>

<p>Michael and Subbarayan - thank you very much for your rapid response. I suspect that the repairman did indeed assemble it from the wrong entry point, so I'll ask him to readjust the lens for infinity focus. <br>

Thank you very much,<br>

Raj</p>