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    Re: Heath vernier sextant
    From: Alexandre Eremenko
    Date: 2012 Jul 24, 12:01 -0400

    Stan,
    I suppose you did not miss the message of Ridge White,
    telling you what the adjusting pin is for:-)
    
    (I never adjusted this sextant myself, and thought that these things
    are for adjustment with fingers. It turns out that they are only caps
    which cover the real adjusting screws).
    
    And in general, the box and accessories look like they match the sextant.
    So all issues you were worrying about have been successfully resolved:-)
    Except the difficulty with reading the scale, but this is certainly
    the matter of practice.
    
    Alex.
    
    
    
    >
    >
    >  Alex,
    >
    > Thanks for looking.  As you said, maybe your Heath booklet or Bill can
    > provide an answer.
    >
    > Yes, the certificate number matches the number on the sextant, which can
    > be seen in the photograph, on the arc above "Eltham".
    >
    > You may be right about the age of the sextant.  Too bad there is no Heath
    > web site that lists serial numbers and dates of manufacture.  However,
    > judging from the certificates shown on Bill's web site and elsewhere, it
    > appears that this certificate is from the same facility that typically
    > certified Heath sextants.
    >
    > Stan
    >
    >
    >
    >
    >
    > -----Original Message-----
    > From: eremenko 
    > To: NavList 
    > Sent: Tue, Jul 24, 2012 4:09 am
    > Subject: [NavList] Re: Heath vernier sextant
    >
    >
    >
    > Stan,
    > Thanks for the pictures.
    > I have no idea what the pin is for.
    > Perhaps Bill Morris knows.
    > (When I come home in August I can look into my Heath booklet,
    > perhaps there is some hint there).
    >
    > The certificate shows a number. Is this number stamped anywhere on
    > the sextant?
    >
    > I conjecture that the sextant may be older than 1940,
    > and that the certificate is not the first one in its life.
    > (I don't know when exactly Heath discontinued the vernier sextants,
    > but my Heath booklet printed in 1940-s does not mention them).
    >
    > Alex.
    >
    >> Alex,
    >>
    >>
    >>
    >>
    >>
    >>
    >> -----Original Message-----
    >> From: Alexandre E Eremenko 
    >> To: NavList 
    >> Sent: Mon, Jul 23, 2012 3:05 am
    >> Subject: [NavList] Re: Heath vernier sextant
    >>
    >>
    >>
    >> 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.  This is the first I have heard of this.  Interesting, but it
    >> seems
    >> to me that you would want to measure the index error in the
    >> configuration
    >> you are going to use to take sights, no?
    >>
    >>> 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.  Although I have had access to vernier
    >> sextants in the past, I have always sanely chosen to use micrometer drum
    >> types.
    >>
    >> 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.  Yes, and
    >> you
    >> are right about practice.  I have been using it with sunlight
    >> illumination, and have found that if I hold the sextant at just the
    >> right
    >> angle (diffuser with respect to sun) I can see the scales better and
    >> have
    >> been getting better at reading it.
    >>
    >> 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.  I have been playing with a
    >> red
    >> LED indoors.  Not as easy as in sunlight, but, again, holding it at the
    >> correct angle with respect to the diffuser helps a lot.
    >>
    >>> 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 understand the part about switching sides, but I still
    >> am finding it difficult.  Practice, practice, practice.
    >>
    >> I suppose yours is a 10" scale, of 6 1/2 inches radius.  Exactly.  Have
    >> you been peeking?
    >>
    >>> 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?  Just finger
    >> adjustments.
    >>
    >> It will help if you show some detailed photos.  A few photos attached.
    >>
    >> Alex.
    >>
    >> Stan
    >>
    >>
    >>
    >>
    >>
    >>
    >> Attached File: http://fer3.com/arc/img/120125.p1050711.jpg
    >>
    >> Attached File: http://fer3.com/arc/img/120125.p1050712.jpg
    >>
    >> Attached File: http://fer3.com/arc/img/120125.p1050714.jpg
    >>
    >>
    >> View and reply to this message: http://fer3.com/arc/m2.aspx?i=120125
    >>
    >>
    >>
    >
    >
    >
    >
    >
    >
    >
    >
    >
    >
    >
    > View and reply to this message: http://fer3.com/arc/m2.aspx?i=120142
    >
    >
    >
    
    
    
    
    

       
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