A Community Devoted to the Preservation and Practice of Celestial Navigation and Other Methods of Traditional Wayfinding
From: Tony Oz
Date: 2019 Apr 27, 02:05 -0700
Being an "armchair navigator" eager to "improve" the result of long history of sextant design I replaced the lightest horison shade with a polariser filter. The idea was to obtain the possibility to enhance the Moon-sky contrast (for lunars) and to more adaptively remove the glare off the seas. The filter used was a professional grade photographic piece by a reputable manufacturer.
The test result: a complete failure.
Though the filter surfaces are flat they are NOT parallel! As I was rotating the filter to accomodate to the glare - there was ±3 arcminutes image shift introduced. The filter occured to be a sort of an optical wedge/prism.
Further I wanted to also use a pair of such (linear-polarising, not circular!) filters as an adjustable shade - now that is out of question!