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Hi Alex:

The devices commonly called "Night Vision" are light amplifiers, not IR
based scopes like were used in W.W. II.  They take the existing light
and make it brighter.  Although I have not done it, I expect that in the
middle of an ocean on a moonless night you could in fact see the horizon
with a night vision scope.

Astronomers call the optical type of scope you describe a "rich field"
scope.  That means that the exit pupil diameter is about 7 mm, which is
the diameter of a night adapted eye.  For example a 7x50 binocular has
an objective diameter of 50 mm which when divided by the 7 power
magnification yields about 7 mm exit pupil.  Any scope whose objective
diameter divided by it's magnification that yields about 7 mm is good
for viewing with a dark adapted eye.  For daytime use where the eye's
pupil is only a few mm diameter you can use a scope with a smaller exit
pupil diameter.

Have Fun,

Brooke Clarke, N6GCE
--
w/Java http://www.PRC68.com
w/o Java http://www.pacificsites.com/~brooke/PRC68COM.shtml
http://www.precisionclock.com

Alexandre Eremenko wrote:

> 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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