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    Re: Sextants with Polarizing filters
    From: Fred Hebard
    Date: 2006 Feb 7, 01:07 -0500

    On Feb 7, 2006, at 12:45 AM, Frank Reed wrote:
    
    > Fred, you wrote:
    > "The one polarizing-shade  sextant with which I have worked had
    > noticeable shade error."
    >
    > Yes, I'm  sure plenty of polarizers have shade error. All I'm
    > saying is that
    > there shouldn't be any intrinsic reason for them to have more
    > shade  error
    > than standard shades.
    >
    
    Just to clarify, I'm assuming this means you accept Joel's statement
    that polarizing-shade sextants have greater shade errors than other
    types, serious errors (from the standpoint of a lunar).  I see no
    reason to doubt Joel's statement, although we have a pretty small
    sample thus far.
    
    Could the error be related to the mechanics of the mounts, not
    holding the rotatable glass perpendicular to the optical axis?
    Alternatively or additionally, the constant flexing of the shade as
    it's adjusted might lead to more error than simply swinging it in or
    out of the path? Or how about the polaroid glass itself, could there
    be problems there?
    
    
    

       
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