|Ken Gebhart from Celestaire could have the answer as he is likely to have specified the ASTRA IIIB sextant index mirror.|
--- On Tue, 1/27/09, email@example.com <firstname.lastname@example.org> wrote:
From: email@example.com <firstname.lastname@example.org>
Subject: [NavList 7172] How flat do sextant mirrors need to be?
Date: Tuesday, January 27, 2009, 12:20 AM
I recently checked some old sextant mirrors against a tenth wave
optical flat prior to resilvering them and found that the greatest
deviation was a half wavelength. 3 mm modern mirror float glass
compared favourably, suggesting a cheap solution to replacing
deteriorated mirrors in old
I have posted some images in my blog on my website www.sextantbooks.com
Can one of our erudite members suggest how flat the mirrors need to be on
theoretical grounds? I have vague memories that people aimed for a quarter wave
when making the flats of amateur Newtonian telescopes, but this may well be
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