Beroflex 85/1.7 m42 YS aperture fix (was: need advice on lens group distance shimming)

So I'm currently fixing a Polaris / Beroflex / Raynox / Sigma 85mm f/1.7 lens (as pictured).

The lens is with sort of built-in auto-aperture m42 adapter. It actually has a YS mount behind it - someone in the internet believes this is a Sun Opt. made lens, and I agree. Sold under several names.

Issue was oil on aperture blades, as usual, and they were stuck open. Already cleaned that, BUT

now I noted that the rear group is attached with threads to an another thread that also holds the aperture adjustment ring/lever sandwiched between it. This makes the distance of rear group and front group adjustable by about 0.5mm.

I think there are 3 or 4 lenses in the front group and maybe 3 lenses in the rear group - looks a bit like Sonnar design. Aperture blades are of course between the groups.

Question is, how sensitive this kind of design is for errors in the lens group spacing? I know that Jupiter-9 has a shim or two for adjusting it, but the shims seem to be thick compared to this lense's adjustment range.

Whoops, my bad, it seems to be that the rear group does in fact thread into the fixed portion, so there's no adjustment nor shims to worry about.

Let's make this an aperture fix thread then, I will post some pictures and info.

Got to forwarding this project again.

The front lens group had been previously "cleaned" from the rear (at the aperture) - resulting in lots of scratches. I don't know how someone had done it, maybe they used sandpaper when cleaning? There were no other damage, so it might even have been done professionally. Dunno, weird

But I had massive amount of luck, some Ebayer had a front lens group for sale as parts for this already uncommon lens. So I will replace the whole assy!

If anyone will attempt cleaning the aperture blades, to get to them the front lens group has to come off. Then you will have to unscrew the focus helicoid (mark the exit thread position!) because the lock screws for the aperture assembly are in the helicoid threads.




I have heard that people usually do not praise Sun made optics but mechanically this lens seems fine. All parts are quite chunky, especially the screws.

The aperture was very stuck which had resulted in bent aperture pin. I pressed it back straight using drill press. Maybe not exactly mandatory, because the pin will just move the aperture as far it goes (towards the stop limiter)




The lens groups blackening was also deteriorating from the edges, I used permanent marker to "finely" fix the edges and then matte black primer paint to fix larger areas. Doesn't look that great, but looking from the light entering direction thru lens, it's OK.




One (too modern) design peculiarity; the rear lens group seems to be pressed in. Yes, the metal edge looks like it has been pressed shut, like they ultrasonic weld plastic nowadays. Result: the rear lens group cannot be opened for cleaning or re-painting the lens edges. Permanently sealed. My unit has some kind of separation or lines in the lens balsam, I suspect they will not affect anything. And if they did, I cannot do anything about it.

Ha, I was wrong again. The lens manufacturer has been wise and put holes in the barrel to access aperture grub screws without needing to unscrew helicoid

I also tested with m4/3 camera with adapter, ther performance looks really okay. Going to shoot some Fuji color film with this also.