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    Re: Sextant optics
    From: Joel Jacobs
    Date: 2004 May 2, 12:44 -0400

    Jim,
    
    I recall that when Nautech,  was a direct importer of sextants and their
    telescopes, in combination and separately, that we had a similar issue with
    customs. I clearly recall that we had a team of customs people visit our
    facility, which included the head supervisor of that group, so they could
    see first hand what we were arguing about. My memory is very hazy, but I
    think that when we brought a sextant in with its attendant scope, it came in
    a lower rate, than when we brought in sextant telescopes seperately. The
    latter was assessed a higher rate and they were classed in the same
    classification as binoculars and telescopes. We had a pleasant meeting, but
    didn't change anyone's mind.
    
    In respect to the other part of your question, I don't believe that many of
    the manufactures manufactured their own scopes. They most likely would go to
    a company who had all the tools and talent and have something designed to
    fit. I doubt that they would even have submitted design criteria other than
    provide a test bed sextant. I suggest that one of the reasons most sextants
    have the same fork design is because of it being more efficient for the
    optics company and therefore less costly. Carl Zeiss is one example. Their
    scopes are used on Russian, and German sextants and fit Tamaya. Maybe George
    Huxtable knows who may have made the English scopes.
    
    Joel Jacobs
    
    
    
    
    ----- Original Message -----
    From: "Jim Thompson" 
    To: 
    Sent: Sunday, May 02, 2004 7:02 AM
    Subject: Sextant optics
    
    
    > The thread on the AstraIIIb's split mirror was very helpful, but did not
    > thoroughly review the subject of sextant optics, and raised more questions
    > in my mind.  We have not yet thoroughly described issues of depth of
    field,
    > field of view, magnification, and glass and lens manufacture with respect
    to
    > modern sextants.
    >
    > I have been prowling around the Internet looking for online information
    > regarding sextant optics to fill in the gaps.  My guess is that these are
    > closely guarded industrial secrets, or that there is information buried in
    > specialized print publication that has not made its way to the Internet
    yet.
    > And we do not have optics specialists on this list.  I am not in a
    > geographic position that allows me to explore the print literature on this
    > subject.
    >
    > Meanwhile I did turn up this distracting web page, where Celestaire
    appealed
    > to the US Government to redefine sextant tariff law for the AstraIIIb:
    > http://www.law.emory.edu/fedcircuit/july97/97-1005.html
    > "Celestaire ... appeals the order of the United States Court of
    > International Trade (defining) marine sextants as "optical navigational
    > instruments" ... dutiable at 5.6% ... rather than as "other non-optical
    > navigational instruments" ... which are not subject to a tariff."  It
    > demonstrates how lawyers can argue the definition of a sextant, including
    > whether they are metal instruments or not.  The central argument by
    > Celestaire seemed to be that sextant optics do not primarily aid human
    > vision, but are subsidiary to the purpose of measuring angles.  "It is
    > uncontested that sextants are navigational instruments; we are only asked
    to
    > determine whether they are optical ones or not."  The court concluded that
    > "the immediate purpose of the sextant is to allow the user to see the sun
    > and the horizon at the same time - an act which the user could not
    otherwise
    > do. The intermediate purpose is to accurately measure angles which can
    only
    > be estimated by the naked eye. It is only the ultimate purpose, to
    determine
    > navigational position, that does not have to do with enhancing human
    vision
    > ...".  The Court  found in favouring of continuing the tariff, "Because a
    > sextant aids or enhances human vision ... through the use of its
    > non-subsidiary split-image mirror...".
    >
    > So the court reaffirms that split mirror optics indeed aid human vision,
    but
    > ... precisely how?
    >
    > Jim Thompson
    > jim2{at}jimthompson.net
    > www.jimthompson.net
    > Outgoing mail scanned by Norton Antivirus
    > -----------------------------------------
    
    
    

       
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