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    Re: Sextant optics
    From: Ken Gebhart
    Date: 2004 May 3, 21:25 -0500

    on 5/2/04 6:02 AM, Jim Thompson at jim2{at}JIMTHOMPSON.NET wrote:
    
    > 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
    > -----------------------------------------
    >
    It?s amazing what the internet will dredge up, isn?t it?  Some background on
    the Celestaire suit against the Custom?s Service is thus:  A new Harmonized
    Tariff System (HTS) was adopted some 10 years ago, which caused all entry
    classifications to be re-examined in the context of the new wording.  Prior
    to this, marine sextants had been firmly classified as non-optical
    instruments. In fact Celestaire sought and obtained a customs binding ruling
    that the Freiberger Drum Sextant (Zeiss in the UK) was specifically
    classified as non-optical.  Reasoning was that a sextant is merely an angle
    measuring device (an evolution of the cross staff), and that the mirrors
    only aided seeing both the star and the horizon at the same time , and did
    not enhance human vision as such.  IOW they were not ground to magnify an
    image.  The telescope was admittedly enhancing to human vision, but was
    optional since many sextants did not use scopes, and was classified as an
    accessory taking the same classification as the primary instrument.
    The new HTS came along and the Customs Service saw  an opportunity to reap
    extra revenue by deeming the sextant as optical.  The difference was small,
    0% vs. 5.6% duty, but the threatening issue was the US not renewing China?s
    Most Favored Nation (MFN) status.  Should this have occurred, the duty would
    have gone to 50%.  Unfortunately Celestaire lost the suit, but fortunately
    China joined the WTO and the issue became nearly moot.
    
    Ken Gebhart
    
    
    

       
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