NavList:
A Community Devoted to the Preservation and Practice of Celestial Navigation and Other Methods of Traditional Wayfinding
Re: Mirror recoating
From: Peter Monta
Date: 2019 Mar 27, 12:07 -0400
From: Peter Monta
Date: 2019 Mar 27, 12:07 -0400
If the reflective surface is not coincident with the center of the scale - all the markings are wrong. Try this with a protractor.
The index bearing must be well centered, yes, but this is unrelated to the mirror. If the mirror is translated a little, that will not affect the rotational center of the index arm. It will waste a little light (if the movement results in some vignetting), but that's it.
Some prior discussions on NavList have mentioned that some sextants have the mirror surface on or very near the axis of rotation and some do not. My Astra, for example, is a couple of millimeters away if I remember right. Doesn't hurt anything, but does complicate the rule-of-thumb to set the index mirror perpendicular to the frame.
Cheers,
Peter
