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    Re: Sextant Comparisons
    From: Fred Hebard
    Date: 2004 Mar 20, 12:15 -0500

    Doug,
    
    No, I don't collect older equipment.  I have been trying to acquire a
    sextant suitable for lunar observations, so I look for sextants with
    defects on Ebay that might still be serviceable.
    
    I have one British Husun that only has the "star scope."  It's a 2.5x
    power scope.  It's my understanding that a more powerful one would give
    more precise readings.  I checked this by buying an old Simex-type
    sextant, which subsequently was sold.  I have been looking for another
    Husun with the inverting telescope or another instrument.  The Cassens
    & Plath was the first that came up which was suitable.
    
    In comparing the Cassens and Plath to the Husun, I would say, overall,
    that I prefer the Husun at this time.  It's prettier, with the
    silver-inlayed arc; this increases my fondness for the instrument.  The
    black crinkle finish is nicer than the Cassens and Plath's.  All the
    screws are varnished or painted brass; there's no aluminum to corrode
    with steel screws or react with the brass or bronze (There's no
    corrosion on my Cassens and Plath; it doesn't appear ever to have been
    used for extended periods).
    
    The 2.5x scope on the Husun has a very wide field of view, wider than
    the 4x "star scope" on the Cassens and Plath.  I have seen no optical
    aberrations in the Husun, while the Cassens and Plath star scope has
    chromatic aberration, which rather surprised me (reddish fringe on the
    bottom of the image and bluish fringe on the top).  The aberration
    makes it more difficult to check index error by measuring the sun's
    semidiameter.
    
    The handle on the Husun is straight up and down.  This makes some
    lunars easier, whereas the tilted handle on both brands of Plaths,
    while it makes looking at the horizon easier on the wrist, makes lunars
    more difficult.  When holding the instrument between shots or while
    waiting, the Husun is less fatiguing to hold
    
    The star scope on the Husun is in close to the horizon mirror.  This
    centers weight in the instrument, making it less fatiguing to hold.
    Being close in to the horizon mirror, the smaller mirror does not
    restrict the field of view of the instrument as much as one might
    suppose.  I suppose the larger mirrors would be "faster" optically,
    however.
    
    The perceived weight of the two instruments is similar.  I have not
    actually weighed them.
    
    The lamp on the Husun can be swung around to illuminate my wrist band
    when recording data.  The lamp on the Cassens and Plath is guided to
    illuminate the scales only, making recording data more difficult.
    
    The box on the Husun is significantly smaller than the box on the other
    instruments.
    
    These are my impressions after two days.
    
    Fred
    ------------------------------------------------------------------------
    Frederick V. Hebard, PhD                      Email: mailto:Fred{at}acf.org
    Staff Pathologist, Meadowview Research Farms  Web: http://www.acf.org
    American Chestnut Foundation                  Phone: (276) 944-4631
    14005 Glenbrook Ave.                          Fax: (276) 944-0934
    Meadowview, VA 24361
    
    On Mar 19, 2004, at 5:44 PM, Royer, Doug wrote:
    
    > By the way,do you collect older sextants?Don't you also have some older
    > British equipment you wrote about in the past?Just curious.
    
    
    

       
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