NavList:
A Community Devoted to the Preservation and Practice of Celestial Navigation and Other Methods of Traditional Wayfinding
How flat do sextant mirrors need to be?
From: Bill Morris
Date: 2009 Jan 26, 22:20 -0800
From: Bill Morris
Date: 2009 Jan 26, 22:20 -0800
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 instruments. 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 irrelevant. Bill Morris --~--~---------~--~----~------------~-------~--~----~ Navigation List archive: www.fer3.com/arc To post, email NavList@fer3.com To , email NavList-@fer3.com -~----------~----~----~----~------~----~------~--~---
