NavList:
A Community Devoted to the Preservation and Practice of Celestial Navigation and Other Methods of Traditional Wayfinding
Re: Molasses as an artificial horizon
From: Brad Morris
Date: 2017 Oct 2, 20:22 -0400
From: Brad Morris
Date: 2017 Oct 2, 20:22 -0400
Hi Bob
When you get a front surface mirror, the vendor will indicate the flatness as a function of wavelength. A very good mirror is flat to lambda/10 (lambda being 1 wavelength). That flatness comes as a function of thickness.
I once installed a 12 inch diameter mirror, flat to lambda/15. If we select lambda as 600 nanometers (red light), then that mirror was flat to 40 nm, over the full 12". The thickness of that mirror (by 20 year recollection) was about 40-50 mm. The mirror thickness is to guarantee flatness when supported by only three points. Self weight deformation is held to a minimum! Of course, that mirror was enormously expensive.
Its some food for thought. A quality mirror will last forever and can be resilvered!
Brad
On Oct 2, 2017 4:39 PM, "Bob Goethe" <NoReply_Goethe@fer3.com> wrote:
I purchased a conventional mirror, and got dual reflections...one from the front of the glass, and one from the silvered surface on the back side of the glass.
So those who are getting good results from mirrors, are we talking front-reflecting mirrors?
My first look into front-reflecting mirrors is that I am going to have to order it from somebody online. All of the mirrors available throgh local retail seem to have a rear reflecting surface.
Thanks for your counsel on this, friends.
Bob
