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    Re: Suitable Sextants
    From: Joel Jacobs
    Date: 2005 Oct 11, 21:32 +0000
    Alex,
     
    Sometimes the proof of the pudding is in the eating.
     
    Take a proper Star scope and couple it with a small size horizon mirror, and note the results at twilight.
     
    Also take a sextant with small mirrors and use what ever scope you are most comforatble with and try some high altitude sun sights. Note the results.
     
    I suggest it will be like your use of an inverting scope on land vis-a-vis at sea.
     
    You never notice the difference until you're at sea.
     
    Joel
     
    --
    Visit our website
    http://www.landandseacollection.com


    -------------- Original message from Alexandre E Eremenko <eremenko@math.purdue.edu>: --------------


    > Joel,
    > Thanks. It seems to me that in both cases it is the
    > diameter of the telescope objective lens that is most relevant.
    > Provided that the mirror occupies the whole field of view.
    > Indeed, once this is the case,
    > increased mirror will not send more light
    > into the scope. Same about motion.
    >
    > So you probably mean that in the old sextants with small mirrors
    > the mirrors did not occupy the full field of view,
    > and some of this field of view was thus wasted, correct?
    >
    > Alex.
    >
    >
    > On Tue, 11 Oct 2005 joel-jacobs@att.net wrote:
    >
    > > Hello Alex,
    > >
    > > Large mirrors collect more light and transmit more though the op! tics which are
    > an advantage in taking twilight sights.
    > >
    > > The second adavantage is that celestial objects tend to move around on the
    > horizon mirror due to the motion of the vessel or of the sight taker. They also
    > seem to move more when taking high altitude sights. The larger size mirrors
    > provide more surface area for the body to dance on before being lost from view.
    > >
    > > Also try WD 40, a moisture displacement chemical, to minimize affects of
    > spray.
    > >
    > > Joel
    > > --
    > > Visit our website
    > > http://www.landandseacollection.com
    > >
    > >
    > >
    > >
    > > -------------- Original message from Alexandre E Eremenko
    > : --------------
    > >
    > >
    > > > Dear Joel,
    > > >
    > > > > 1. The larger the size of the! mirrors, the better.
    > > >
    > > > I always read and hear this, but I am not sure that
    > > > I understand exactly why the larger mirrors are better.
    > > > Can you explain?
    > > >
    > > > > 2. Sextants with enclosed tangent screws
    > > > > are prone to having them freeze
    > > > > unless they are cleaned after use when
    > > > > there is spray.
    > > >
    > > > This I confirm, even with my small experience.
    > > > The remedy is to wash it with fresh water after
    > > > a spray. And the fresh water is sometimes scarce
    > > > on a small boat.
    > > >
    > > > Alex.
    >
       
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