Repolishing old lenses with fungus, balsam separation

[Jody_S]

Just read through the whole thread, matches my personal experience. Comments:

1. Easiest way of separating any lens group, whether Canada Balsam or any lens cement I've ever encountered, is old furniture stripper (MEK-based). Hard to find, I scour flea markets for old cans.

2. Centering most lens groups is easy with a flat surface and a pair of machining V-blocks.

3. If you can't find UV-cure optical cement (I ordered mine off AliExpress), clear-coat UV-cured nail polish is a good substitute, available at any nail salon.

4. The only reason to polish off surface etching from fungus is if you plan to sell the lens, IMHO, and if it's a coated lens and you polish off the coating to make it look pretty, you might get a better price for your lens but it's a little unethical IMHO. I expect all those 'mint' Leica lenses for sale on FleaBay have had some treatment of this sort. If the etching is bad enough to affect a LF lens, then your grinding might manage to keep the exact curvature of the lens, if you follow the proper pitch lap technique, but changing the thickness of the lens by polishing off a huge amount of glass might affect the lens' performance anyway. Even more so if it's a modern coated lens. I don't mind doing this to polish off a huge number of cleaning marks.

[kfed1984]

The only reason to polish off surface etching from fungus is if you plan to sell the lens, IMHO, and if it's a coated lens and you polish off the coating to make it look pretty, you might get a better price for your lens but it's a little unethical IMHO. I expect all those 'mint' Leica lenses for sale on FleaBay have had some treatment of this sort. If the etching is bad enough to affect a LF lens, then your grinding might manage to keep the exact curvature of the lens, if you follow the proper pitch lap technique, but changing the thickness of the lens by polishing off a huge amount of glass might affect the lens' performance anyway. Even more so if it's a modern coated lens. I don't mind doing this to polish off a huge number of cleaning marks.

The polishing process will not remove more that a micron off the lens surface, which will not affect the optical performance. No I am not polishing to make it look "pretty", but to make the image sharp again. Fungus and microscratches make a diffused image. I wrote at the beginning; the decision to polish or not depends on the degree of damage and what the lens is worth to you. I had this damaged lens (the Apo-Ronar), shown in the example pictures, and it was worth for me to repair. Next example will be another damaged Apo-Gerogon lens, which I will show later, with lots of cleaning marks. But maybe polishing my own lenses will be unethical, I don't know.

The idea of using pitch is to preserve the curvature of original glass as done in the factory, not to make it "pretty". I don't think the "mint" lenses on eBay you mentioned had this procedure. I don't think re-boring and re-honing the cylinders on your worn-out engine is unethical. Yeah, you may sell it as a low mileage engine, which may be unethical. But re-boring a car engine on its own is a good thing without doubt, and always good to learn how to do it for those who want to.