Damaged threads on lens

[richard_neumann]

Is it possible to repair crossed-threads on a lens? When I twist on

my Cokin P adapter-ring, it doesn't turn smoothly, but I can

ultimately get it fully seated. I do not like the way it feels

however. I recently purchased this lens on e-bay and didn't realize

the problem until now. The adapter-ring turns smoothly onto another

lens I own, so I know the problem doesn't lay there. Is it possible

to "tap" the threads clean?

[andrew pell]

Is it possible you've got two diferent thread pitches and you're forcing the Cokin ring onto an incorrect thread?

 

This may be an assumption but is the Cokin a 1mm pitch thread and the "awkward" lens is 25 or 26TPI - near but not the same?

 

As for getting a thread retapped - I'd have thought it was a specialist lens repairer's job as you're not going to get a tap at the local hardware store and as it's an internal thread, a thread file wouldn't be much use...

 

It might come down to either getting a male / external thread of the correct spec and working it to and fro gently until it corrects the cross-threading (fine grinding paste as well) or have the lens stripped down and get it turned out by someone with a suitable lathe that can thread-cut.

 

Failing this, is it possible to buy / scrounge / make a step-up adaptor to get from your thread to the next size up Cokin ring?

 

Just a few thoughts off the top of my head as it's bedtime here...

[jimvanson]

It is usually possible to clean-up the threads with a thread chaser ($200) or you could talk to <a href="http://www.baldmtn.com/">Ken</a> at "Photography On Bald Mountain". He could probably fix you up.

[ardea]

IMO if you can screw the adapter ring down untill "it is fully seated" and you can unscrew it, it is most likely not cross theading. When it is fully seated is there even clearance/contact between the adapter and lens? If this is so then I would doubt that it is cross threaded. I would look to the adapter as the problem. Aluminun to aluminum as is most likely the case in the lens to adapter, can be quite "sticky" or "gritty" feeling and can sometimes seize and be blamed on "crossthreading" I would try a filter or other adapter of the same thread size and see if they fit better. The best test (other than a hardened and ground steel GO/NOGO thread pitch gage) would be a BRASS bodied filter like B+W. Dissimilar metals don't tend to stick and high quality filter bodies are most likely machined to closer tolerances. But first look at the periphery of the lens by the threaded area and look for dents or dings. These can be squeezed out if thay are present.

Good luck...And let us know. Regards Richard

[tim_curry]

I had a similar problem with a "pristine" 90mm Super Angulon from ebay. I didn't see the small dent in the front lens until I tried to screw on a filter in the field, P.I.T.A. I bought a dent remover from Micro tools and managed to fix it well enough to function properly.