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    Re: accurate sextant
    From: Fred Hebard
    Date: 2008 Feb 22, 14:37 -0500

    I'm mostly resisting any national comparison jokes here.
    
    On Feb 22, 2008, at 10:38 AM, Alexandre E Eremenko wrote:
    
    >
    >
    > George,
    >
    >> What struck me was its rather strange
    >> (to me) construction, in that the
    >> index arm swings on the "wrong" side of the frame;
    >
    > This is not exactly so. The arm moves INSIDE the frame.
    > If you look carefully you see that the frame has
    > a complicated shape which allows the arm to move
    > inside. The handle is attached to the
    > "other part of the frame", behind
    > the arm. Of course you can call the part of the
    > frame behind the arm a bridge, but it is an integral
    > part of the frame. The purpose of this
    > arrangement is to protect the arm.
    >
    > Freiberger has similar construction of the frame.
    > In general Freiberger looks very similar, except
    > it does not have the inverting scope and does not
    > have the scale magnifier/illumination device.
    >
    >> I ask those familiar with this
    >> instrument whether they see any
    >> advantage in the straight-through, inverting,
    >> 6x telescope, compared with an
    >> equivalent, non-inverting, prismatic ocular
    >> of similar power and
    >> light-grasp? Presumably,
    >> the prismatic would be a bit heavier; are there
    >> other differences?
    >
    > It is very much lighter, and lets more light through.
    > In this telescope, the light passes through only two lenses.
    > All astronomical telescopes-refractors are made this way,
    > and the reason is to minimize the loss of light.
    > So the designers of this telescope surely had the
    > same reason.
    > In addition, this is the only "modern" sextant telescope
    > that has wires. Wires are handy for many adjustments,
    > and make it easier to hold the object in the center of
    > the field.
    >
    > In the old days (until approx. 1940-s) many sextants had
    > inverting scopes with wires. However the SNO scope has
    > a substantial advantage in comparison with these old
    > scopes: much larger field of view, and much larger
    > diameter of the objective lens. Again this lets more
    > light through.
    >
    > Alex.
    >
    >
    >
    > >
    
    
    
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