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    Re: Horizon Shade Polariser
    From: Francis Upchurch
    Date: 2016 May 6, 18:34 +0100

    May I confirm that polarizing filters offer the same UV light/retina protection as standard filters?



    From: NavList@fer3.com [mailto:NavList@fer3.com] On Behalf Of Greg Rudzinski
    Sent: 06 May 2016 18:09
    To: francisupchurch@gmail.com
    Subject: [NavList] Re: Horizon Shade Polariser



    If two polarizers are screwed together with one polarizer filter flipped in the frame then you have a variable Sun shade. This is very useful at the index mirror when the sky is overcast, hazy, or partly cloudy. I filter this way when doing DSLR camera CN. I like older Vivitar linear polarizers best for this purpose. C&P uses polarizers stock on their current line of sextants.

    Greg Rudzinski

    From: Michael Bradley
    Date: 2016 May 6, 02:59 -0700

    Beg leave to report a useful component available on ebay, Phot-R 40.5mm Circular polariser, costs 3.50 North Atlantic money.

    It has a 1.5" circular polariser, rotatable, built into a slender circular frame. Fits into a 40.5 mm circular hole ( in home brew bespoke brass sheet shade frame ).

    I've used it to replace the normal 'light' horizon shade on my Freiberger Yacht Sextant, and using it in the classic way to cut out reflected glare the horizon is much easier to resolve for morning and afternoon sunsights  over water. 

    Excuse for doing it this way - my metal working skills with 2.5mm sheet brass are better that my non existent glass working skills. Also the case of  a Yacht Sextant has very little space between the case side and the horizon shade, anything fatter would not fit. And it costs very little to build, cheaper than buying a sheet of polariser.

    Result - water horizon glare reduction without buying a premium sextant.

    Photos attached

    Michael Bradley 55 North

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