Quote:
Originally Posted by Leo.G
If using for visual they wouldn't be such a problem would they?
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This is only a cosmetic issue. Scratched products don't sell well even when the scratch has no effect on the intended use.
I think I mentioned earlier that I made a 10" f/16 Dall-Kirkham before, a long time ago. Well, fortunately, I still have the test plate I made back then for figuring the secondary mirror. This test plate was manually polished and figured with a Foucault test apparatus as I did not have an interferometer at the time.
Today I had a go at testing it with the Bath interferometer and the summary of the test is on the attached screenshot image.
The test plate was made much larger than the secondary in order to avoid possible edge figure problems. As the test results show, the inner 70mm of the test plate is quite adequate for the purpose.