[Stefan Jr]

((sorry if I posted this thread in the wrong section))


Maybe there's someone some here that know an easy fix for an issue I got with a CZJ 135/3.5 M42.

The problem is:
When focusing the lens, and when reaching (about) the 1,2 meter mark, the iris close a little bit.

Which effectively makes it a variable aperture lens with about f3.8 at minimum focusing distance. The issue affect all aperture settings.
I'm sure there is "some way" to correct the diaphragm, but don't want to pick the whole lens apart to figure it out.

Anyone know the trick to fix the issue?

Best // Stefan



EDIT!

A temporarily and partial fix was to: release the 3 screws in the mount, focus to MFD, force the aperture ring to the F3,5 direction, and then retighten the 3 screws.

It made a difference. But I'm sure there is a more correct and long term way to adjust the diaphragm? So my initial question remains!

.

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Last edited by Stefan Jr; 03-29-2023 at 10:48 AM.

[kypfer]

What I do notice with my example is that, with the aperture ring set wide open, when the A/M switch is moved to the M position the aperture does close down a bit.
Even with the switch is set to A, when the pin is depressed the aperture does close down a fraction.
Are you using the A/M switch to control the aperture on your lens or have you got the pin permanently depressed, either within the lens or using an adaptor, or, indeed, are you using a screw-mount camera?
For all practical purposes, the difference between f/3.5 and an assumed f/3.8 is likely to be negligible
Excellent lens, by the way … well worth the effort

[Stefan Jr]

What I do notice with my example is that, with the aperture ring set wide open, when the A/M switch is moved to the M position the aperture does close down a bit.
Even with the switch is set to A, when the pin is depressed the aperture does close down a fraction.
Are you using the A/M switch to control the aperture on your lens or have you got the pin permanently depressed, either within the lens or using an adaptor, or, indeed, are you using a screw-mount camera?
For all practical purposes, the difference between f/3.5 and an assumed f/3.8 is likely to be negligible
Excellent lens, by the way … well worth the effort

Mine show an absolute minimal sign of the same behavior. But I hadn't noticed it before I red your answer.
Instead mine close a little bit at around the 1,2m mark.

So we both has the same issue, just showing at different stages.
Indeed - it's not that big of a problem. But f3.5 isn't that fast to start with, so it would be nice to sort it out. Even though it's not worthy a full disassembly. I will settle with the little trick with readjusting the aperture ring and mount.

The aperture mechanism on these is dodgy, so I guess one can be happy that it actually functions. And yes - a lovely lens indeed.