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    Re: Simex Mariner Polarized Shades...How Well Do They Work/10X Inverting Scope
    From: Frank Reed
    Date: 2009 Jan 14, 19:20 -0800

    You wrote:
    "Speaking as a photographer, there's a lot to be said for a variable
    polarizing filter.  OTOH, most good sextants have filters that are
    effective at dimming glare along the horizon, below the sun.  I
    wouldn't go out of my way for just this feature."
    Right. No reason to go out of one's way for this, but they do work. 
    Incidentally, some sextants included these polarizing shades as far back as 
    the Second World War. You mentioned horizon glare... While some polarizing 
    filters are used to eliminate the reflected light off the water (which tends 
    to be polarized in a way that can be easily filtered), that's not what's 
    going on here. These filters are crossed polarizers. The idea is that you can 
    vary the angle at which they cross, by turning one of the pair, and reduce 
    the total brightness of the light passed through.
    I should mention that some of the sextants that come up on ebay have been in 
    storage for as much as twenty years. I bought one recently that appeared to 
    be absolutely brand new, with the original packing materials in the case, 
    that was manufactured in 1976. That's a great thing EXCEPT that sometimes the 
    lubricants have dried or otherwise changed where they're exposed to air, and 
    parts may be "frozen". In particular, the housings that hold the rotating 
    polarizer in sextants may seize up. A little gentle prying with a very thing 
    screwdriver blade got mine moving again.
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