Fed Lens repair

Dear Enthousiast,

I have a Fed NKVD (serial 76777), with the following lens problem. The rear optics consist of two elements cemented (glued) together. This glue is separating, causing som kind of blur and spider web like cracks.
It took a long time to search a repair method, but I found one.
I'm planning to separate both elements, using solvents.
And reglueing them with canada balsam (which is used for microscope preparations).
When I succeed, i'll let you know if you are interested. I'm testing this on an old broken I-22 now, but the two lenses won't yet separate.

With kind regards,


Milo Schekkerman

some say that gentle (and slow) heating will help unglue ...
the critical temperature should be around 80°C not more

and that when hot you can press the lenses ttogether and get rid of the problem

but I never tried...

Stephan

Well... I have to say this topic is more than 5 years old now. But I recently fixed the lens, recementing the elements with canada balsem.

It was a hard job. I had to 'open' a seam first before I could carfully take out the two rear elements out of their brass fitting.
I heated the lens in the oven on 180 degrees, and after a while it gently came loose. I re-cemented it after removing the old resin and ultrasonic cleaning of the lens parts.

It's a very hard job...
I know one guy in France working on glasses
He is used to unglue and re-cement lenses
He can also polish glasses, but you will loose the coatings.
It is not really cheap, so it's better to choose high value lenses...

Fred