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    Re: Heath vernier sextant
    From: Alexandre Eremenko
    Date: 2012 Jul 24, 04:08 -0400

    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,
    > -----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

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