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    Used sextants
    From: Mal Misuraca
    Date: 1998 Jan 12, 12:06 PM

    Responding to Jim's questions about used sextants and the Davis Mark 25.
    
    The Davis Mark 3, the cheapest sextant on the market, is a marvel.  It
    makes no claim to be other than it is, and what it is can be taken in by
    just looking at it.  I have taught navigation uysing the Mark 3 and
    always advocate buying and using one until you are certain you have
    progressed past its capabilities.
    
    The Mark 3 has no optics, only a sighting hole.  This means that the
    image of the sun is quite small, and if your eyesight is not perfect, it
    may also not be as sharp as you would like.  Nonetheless, it is good
    enough to navigate safely anywhere on sun, moon, planets, and very bright
    stars.
    
    The Mark 25 has a telescope, so we would be tempted at first glance to
    say it is a material improvement over the Mark 3, and in some senses
    perhaps it is.  But what optics are these?  They are plastic, quite cheap
    formed plastic, not hard glass optics, and they are decidedly not very
    good.  They are not sufficiently an advance on the Mark 3 sighting hole
    to say that the Mark 25 is a substantial improvement over the Mark 3.
    
    The upshot, in my experience, is that you should consider by-passing
    plastic sextants beyond the Mark 3 and look for a good used metal sextant
    with good optics as your permanent sextant.
    
    Having come to that, what sextant, and where to look for it?
    
    The Freiberger, which I believe you mentioned, is a good sextant, and
    there are many of them around.  The Astra III-B, which has also been
    around for many years now, is certainly a better sextant, and it has very
    much better optics.  The Freiberger has a small objective, the lens
    through which the light enters the scope, and consequently gathers far
    less light that the large objective of the Astra.  I have not owned an
    Astra, but have used one on the odd occasion, and I think it is better in
    all respects.
    
    The great advantage of optics over the sighting hole of the Mark 3 is,
    first, light gathering, then resolution.  The larger the objective, the
    more light is gathered, then concentrated; the better the optics and
    their resolution, the more probable it is that you will see a
    concentrated pinpoint of light when looking at a faint star, or a nice
    round and sharp sun or moon.
    
    I suspect that the Astra and the Frei would be comparable in mechanical
    ways, but in optics it seems to be the Astra is clearly the better of the
    two, and both are light years ahead of the Mark 25.
    
    Hew Schlereth mentioned that he used an Ebbco, which is a British plastic
    sextant with plastic optics, and I have tried the Ebbco in the past, with
    much less success than Hew.  For me, it was not much past the Mark 25, if
    at all, and again way short of the better metal sextants.
    
    You should look in the back of regional sailing mags in the classifieds.
    Look for the ad that starts "Cruising gear for sale. . . ."  Buried in
    the ad is likely to be something like "sextant and box, $75."  That's
    your best bet.  I even saw a C. Plath Navistar Classic once not long ago,
    which sold virtually new for $750, a discount on the current retail of
    $3,000 and change.  I see Tamayas and Freibergers regularly at very major
    discounts.
    
    Good luck.
    
    Mal Misuraca
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