Meyer Trioplan 10cm f/2.8 (C-mount) thread issue

[Fabian]

I've bought a nice Trioplan recently. Cosmetically the barrel has some paintloss and light damage, but the glass is pristine and the color combo of the lens and hood is just sexy to my eyes.

Since it was originally intended for 16mm film there was some light blocking ring at the end, which caused vignetting on my MFT camera. To get there I had to remove the back part of the lens, but it was a very very very hard thing to do. After having managed to remove it, I mentioned the culprit: someone messed with the lens while not knowing what he was doing and tightened the screws right on the thread instead of the intended place on the left to it.





While I know what kind of force I had to use to get it loose, I won't even try my best getting it back on again without fix because it has to be in the right position again and I'm not sure I get that far even with damaging the lens. I suppose there are people here with experience on the same issue: what's the best thing to do here? Simply lubing doesn't solve it, and making another hole like the original one on the left to get the damaged thread gone looks a little bit drastic right now.

[kds315*]

nope, that is not too uncommon that grub screws go into pre-drilled holes within a thread - and that looks exactly like that, otherwise the remaining threads aroudn that hole woudl be damaged.

[Fabian]

I'm not sure I understand you. Those pre-drilled holes are there intended for the screws to go into, but on the right of it (on both sides) someone tightened the screws on the thread itself instead of the pre-drilled holes. The thread is damaged enough to give too much friction.

To clarify a 100% crop:

[kds315*]

Yes, it wasn't correctly placed at the right position.

[iangreenhalgh1]

Take a small piece of abrasive paper and sand down the damage, then it should screw on fine. I had the same issue with a Schneider barrel lens.

[luisalegria]

I have fixed this kind of damage often.
I have a sharp jewelers"V" file I use to clean up damaged male threads to remove the dings.
It does not work on female threads of course.

Just run it through the thread a few times. Its worked well on brass and aluminum threads.

[pavko]

I would rather suggest small file so you can "clean" thread without sanding it down.

[iangreenhalgh1]

That's what I meant, clean it up with some very light abrasion.

[Fabian]

I'll take a look tomorrow if I can buy such a jeweler's file somewhere local, looks more precise than sanding paper, I didn't know such small ones existed. Thanks all for help, I'll update when fixed.

[Lloydy]

you can buy thread restoring files,

http://www.ebay.co.uk/itm/Thread-Repair-Restore-Files-for-Imperial-Metric-Internal-External-Use-/111217057975

is the best picture I can find, which shows one in use. The files are multi sided to suit different threads, so you have to know how many 'threads per inch' the damaged thread is. If there's not a full inch, measure 1/8 inch and multiply by 8. Then get the thread file to match the TPI. The problem with getting the right file is determining the right thread on the lens, which could be difficult without precision measuring equipment.

For fine male threads in aluminium or brass I have rolled a sharp knife blade in the thread with great success. Lube the two parts and gently thread them together and if it is still tight repeat the process with the knife.

[luisalegria]

Mine is in no way as precise.

It came in a set like this -

http://www.ebay.com/itm/10-piece-Needle-File-set-jewelers-budget-files-hobby-5-3-8-gunsmith-/261328640781?pt=LH_DefaultDomain_0&hash=item3cd8669b0d

These are very common and cheap. Everybody should have some.

[Lloydy]

You can get sets of diamond dust needle files in just about all hardware shops now, the Chinese are knocking them out for next to nothing. But they are excellent for the price, and the amount we are likely to use them. I have a set in the draw of my desk just in case I need them urgently!

[Fabian]

[Fabian]

This isn't a showcase for sharpness (no tripod, windy, available dull light, and somewhat below shake avoiding shutter speed) but I think it shows how it draws nicely while I didn't want to go to a higher ISO because of added noise. Cropped on right (origally landscape) and a bit on top afterwards, subject is on left outer edge of lens image circle. Standard pp of uncoated lenses: only contrast up and blacks down.

(And now I'll leave this topic to rest, most people aren't interested in C-mount lenses and there's another section for that.)