A Community Devoted to the Preservation and Practice of Celestial Navigation and Other Methods of Traditional Wayfinding
From: Marty Lyons
Date: 2016 Sep 21, 05:47 -0700
I made a Bris using glass welding filters, are about 2" x 4-1/4", but I still get an occasional flash in my eyes from the real sun. I think used a #12 filter and two clear filters set roughly 10 degrees apart. Apparently the angles are not critical becasue you will calibrate it to your particular angles. The angles should be slighlty different between the plates. It's getting hard to get glass welding filters as the move is toward polycarbonate shields. I do wear sun glasses with it now.
I am not sure how to to the reverse calculations though.