NavList:
A Community Devoted to the Preservation and Practice of Celestial Navigation and Other Methods of Traditional Wayfinding
From: Frank Reed
Date: 2012 May 15, 07:55 -0700
The filters, as Gary has already noted, are polarizing filters. These include one neutral density filter as a "base" level and then a pair of crossed polaroids. One of the polarizers can be rotated which lets you "dial in" exactly the amount of shade you need for a particular sight. It sounds great in principle, but in practice a set of four standard filters is really just as good. Polarizing filters became popular during the Second World War. For example, I have a USN Mk. II sextant with polarizing filters. Many of these "Tamayalikes" also had polarizing filters, but they never really caught on. They're a nice novelty.
-FER
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