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    Re: Night Vision Scopes
    From: Jos� Otavio O. de Almeida
    Date: 2005 Jun 27, 17:10 -0300

    The Zenith Night Vision Scope amplifies light over a broad frequency band,
    part in the visual, part in the infra-red segments of the spectrum. With
    some moonlight it does discern the horizon, allowing  taking sights, albeit
    with a precision somewhat reduced due to the unsharp image obtained.
    ----- Original Message -----
    From: "Alexandre Eremenko" 
    Sent: Monday, June 27, 2005 2:39 PM
    Subject: Re: Night Vision Scopes
    >I have never used a night vision device,
    > but on a pure theoretical ground I predict
    > that it will NOT help to see the sea horizon:-)
    > (And for the stars and the Moon you don't need
    > any night vision anyway).
    > Can anyone verify this theoretical prediction?
    > :-)
    > Alex.
    > P.S. I mean the common modern night vision devices based on infrared
    > radiation. Another tipe of "night vision scope" was invented
    > in XVIII century, and this was simply a Galileo scope
    > with small magnification and with large
    > object lens diameter. (Approximately of the same type as
    > the standard straight non prismatic scopes of modern sextants).
    > These scopes indeed help with horizon or any other object at
    > night simply because they collect more light.
    > Alex.
    > On Sat, 25 Jun 2005, george huxtable wrote:
    >> Robert Eno wrote-
    >> >Has anyone used a night vision scope for conducting star sights at
    >> >sea?  The idea intrigues me and in theory it sounds like it would work,
    >> >but I do not know anyone who has actually used one at sea.
    >> An interesting question. Presumably you would use it in place of the
    >> telescope, to show up both star and horizon. Otherwise, how well would
    >> the
    >> sight-line of such a night scope be defined? And how would you check for
    >> index error?. I only ask, because I am quite unfamiliar with such
    >> instruments.
    >> Could a digital camera be used for the same purpose? Amateur astronomers
    >> use quite ordinary arrays for looking at stars.
    >> I think one of the difficulties would be the fast motion of the images
    >> with
    >> respect to the screen as the vessel wobbled underfoot. The human eye is
    >> good at assessing the relative positioning of star and horizon, even
    >> while
    >> they are whistling across his field of view. An electronic screen could
    >> find that job to be more difficult. Perhaps some image stabilisation
    >> would
    >> be needed also.
    >> But a sextant with lots of electronics attached: wouldn't that be getting
    >> the worst of both worlds? The most satisfying aspects of a sextant are
    >> its
    >> precision and its basic SIMPLICITY.
    >> George.
    >> ===============================================================
    >> Contact George at george@huxtable.u-net.com ,or by phone +44 1865 820222,
    >> or from within UK 01865 820222.
    >> Or by post- George Huxtable, 1 Sandy Lane, Southmoor, Abingdon, Oxon OX13
    >> 5HX, UK.

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