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    Re: Heath vernier sextant
    From: Alexandre Eremenko
    Date: 2012 Jul 23, 03:04 -0400

    Dear Stan,
    Congratulations with your new sextant.
    It looks like a very fine piece from your description.
    
    > 1) What are the eyepiece filters for?
    
    The eyepiece filters are for determining the Index Error from Sun
    and Moon. You do not use ordinary filters. The reason is that your
    ordinary filters may have some prizmaticity, and elemination of them
    permits you to determine the true Index error. (The possible prizmaticity
    of the eyepiece filter has no influence). This also permits you
    to determine whether there is any prizmaticity in the ordinary filters.
    Also: usually the horizon filters are different from the index filters.
    The eyepiece filter permits to to achieve EXACTLY the same illumination
    of the two images of the Sun which is very good for determining Index
    Error.
    
    > 2) I'm having a heck of a time trying to read the vernier scale.
    
    This requires some practice. And even with practice this is much slower
    than reading a drum. This was the reason why they replaced vernier scales
    with drums in the second half of XX century, though the vernier scales
    have several other advantages.
    
    The magnifier works
    but it seems that when I have it in a position to read the scale
    it blocks the light, making it difficult to read the scale.
    There is a diffuser screen that I imagine is supposed to help, but how?
    
    You turn in such a way that diffuser screen faces the Sun, and incline
    the sextant so that the Sun rays can penetrate obliquely
    (through the diffuser glass) between the
    scale and edge of the magnifier. Requires a little practice.
    
    It is harder with stars. As I understand your sextant has no illumination.
    You need a little flashlight (Celestaire has an excellent one) with which
    you iluminate the scale when you read it.
    
    > figuring out which of 50 vernier lines aligns with one on the arc
    > seems daunting.
    
    Yes! But after some practice this becomes easier: you learn to figure out
    quickly, which part of the vernier to look at (tzhe part where the vernier
    divisions "switch the side with respect to the scale divisions".
    Then you look very carefully at this place, to see which division is
    best alligned.
    
    I suppose yours is a 10" scale, of 6 1/2 inches radius.
    
    > 3) The sextant does not seem to have any adjustments
    > with holes where the "pick" tool would be used.
    
    Do not the mirror adjustment screws have holes for this pick tool?
    Or they are threaded for adjustment with fingers?
    
    It will help if you show some detailed photos.
    
    Alex.
    
    
    
    

       
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