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    Re: SNO-T "night" sight tube?
    From: Brad Morris
    Date: 2018 Nov 22, 22:35 -0500
    Alex and Bill

    There is no doubt you gentlemen are correct.  The application of anti-reflective coating is better for light transmission as it cuts down on interior reflections.  I stand corrected on that point.

    When observing the bright object (sun, moon, planet, star) it should be centered in the optics.  I have scopes which have crosshairs to help insure the object is centered.  Reflections, therefore, will also be on the centerline of the optics. 

    AR coatings were developed very late in the sextant game.  From a brief investigation, I get that AR was commonly available from the 1930's or 1940's.  I most certainly could be wrong about that, but it looked like a WW2 enhancement.  The sextant era fundamentally ends with GPS, the early 1970's.  What of all the sextants manufactured before AR?  Am I to understand that these devices are incapable of an observation?  Clearly they are not.  Think of how long CN was practiced without AR and then they managed that without AR.  

    It was from this standpoint I provided my comment.  I do not think of AR as a fundamental requirement of sextants.  It sounds like it is a very nice enhancement, but hardly a show stopper if unavailable. 

    Neither of my instruments has AR, they were manufactured too early.  Yet they are fully functional and provide accurate results.  I am sure Tony will have no issues obtaining very respectable results with his sextant, even if it doesn't have AR.


    On Thu, Nov 22, 2018, 10:05 PM Alexandre Eremenko <NoReply_Eremenko@fer3.com wrote:

    Dear Brad,
    Thanks for the video.
    You wrote:
    > I am unsure as to what utility, if any, anti-reflective lenses would have in celestial navigation.  AR coatings attenuate the light transmitted through the lens. 
    Apparently this is not so: AR coating INCREASES the amount of light passing through the lens, not attenuate it.
    See, for example:
    First I was a bit confused with terminology, but when I found the Russian translation of AR, I realized that this is
    very familiar to me. The Russian term is more suggestive "????????????? ??????" which literally means
    "enlightened optics". It allows MORE light to pass by surpressing reflection.
    The reason to use it in astronomical instruments is exactly the same as the reason for its use in binoculars.
    It must be especially important in the night (Galileo) scopes.

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