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Re: Simplified Bris Sextant (calibration)
From: Bill B
Date: 2012 May 15, 17:35 -0400
From: Bill B
Date: 2012 May 15, 17:35 -0400
On 5/15/2012 3:21 PM, Greg Rudzinski wrote: > You should see a comfortable blue disk with the polarizers filtering the > maximum. You can't just stack two polarizers. It is necessary to take > one of the polarizers out of the frame and reverse it over then install > back into the frame. Test by flipping one of the polarizers 180* > relative to the other while off the lens. Greg Thanks for this and the following explanation. I was doing some reading on polarizing filters when your message(s) arrived. Some of it above my pay grade ;-) http://www.lenstip.com/115.2-article-Polarizing_filters_test_About_light_and_polarization.html It looks like it may well be possible to stack circular polarizing filters for light reduction as the subject side is a linear and that is converted to circular by the next film so it does not foul up the prism/two-way mirror ability to calculate exposure and distance (DSLR). Are your filters of the newer circular or the traditional linear variety? If traditional linear, I am not clear why one filter has to be flipped. Isn't just a film sandwiched between two pieces of glass? An interesting bit of trivia: Bees use polarization for orientation and navigation. Must have learned that from the Vikings? Bill B.