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Re: Lens Polishing

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Posted by Robert May on December 13, 1999 19:06:32 UTC

Removing coatings can be an interesting problem. Unfortunately, you didn't say what you used to remove the coating (which may be almost anything)and then polish the lens. If all you have done is make a pitch lap and use cerium oxide on it to polish the surface, you may not have gotten through the coating yet. Another item is that you have to use water to lubricate the lap and cerium oxide or you'll be basically having real problems. If you look at the surface of the lens with a 10x or higher eyeloupe you should be seeing grains of the cerium oxide embedded in the lens's coating if what you say is true. You shouldn't be using any grits of alum. oxide or such as that stuff will change the radius of the lens very quickly. You may damage a lens the first time around but they should have suggested that you try the process on something that you can stand to lose first - something that is always a good idea to do. I also assume that you have dissasmebled the lens and are dealing with just the glass element. If not, you will never be able to get anybody to properly recoat the lens element. When you are doing the polishing, use strokes that leave about 1/6th of the glass over the edge of the lap and don't push fast. 1 stroke out or back is about the right speed. Go faster and you run a big risk of changing the shape of the lens very quickly. I also hope that the surface that you are cleaning off the coating is indeed a spherical suface or you will probably never get the proper shape of the lens back again. For reference about how little I am talking about, look up the Foucault test and see what the test measures.

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