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    SNO-T and horizon shades
    From: UNK
    Date: 2013 Oct 4, 10:18 -0700

    I have a SNO-T (Soviet SNO-T) sextant - numbered 80945, 1980 - with which I have a problem. Perhaps of interest to other list members to discuss. The problem is that the horizon shades don’t cover the view completely when I use them together with the Galilean scope. There is an unprotected crescent down to the left. Annoying and perhaps not good for my eye when I “take down” the sun to the horizon starting with index at zero - a method preferred by W.E. Morris but not by Bruce Bauer. The problem could be the same with other sights with the sun involved. I could of cause avoid locking at the sun in that way but that is no explanation to the problem : why is there an uncovered area? Why aren’t the horizon shades centred to the centreline of the scope and the horizon mirror? Why aren’t the horizon shades larger? See attached photo.

    One answer could be that the Galilean scope is a star scope not intended to be used in daylight. In fact the problem doesn’t arise with the astronomical scope mounted even though a shade is out of centre in this case too. And I have read many recommendations to use the star scope when taking sun sights. I do that myself because I have difficulties handling the sextant with the inverting, astronomical scope. Not experienced enough, I am afraid. And risking my eye.

    I haven’t found any answer to my question in The NAUTICAL SEXTANT by W.J. Morris. Nether in THE SNO-T SEXTANT by the same author but I can have missed it. Both otherwise excellent and of the utmost interest to me – a SNO-T owner - and of course well known to list members.

    The photos in THE SNO-T SEXTANT could all have been photos of my own sextant. I can’t see any difference at all. One photo - figure 2 : light paths in sextant – is of special interest with respect to my problem. It shows a light ray coming in from the horizon into the centreline of the Galilean scope. The ray hit the horizon shade off centre exactly as can be seen in the attached photo of mine SNO-T.

    Can the horizon shades be wrongly mounted? Both on mine sextant and the one illustrated in THE SNO-T SEXTANT? For example upside down? There is a photo - figure 3 - showing that alternative in W.E. Morris’ blog The USSR SNO-T sextant dated as late as 5 August 2011. The address is:

    Questions to other SNO-T owners. How are the horizon shades mounted on your sextants? Would turning the shades around do any good?
    I could try but I hesitate to take anything apart before I know for sure.

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