NavList:
A Community Devoted to the Preservation and Practice of Celestial Navigation and Other Methods of Traditional Wayfinding
Re: accurate sextant
From: Alexandre Eremenko
Date: 2008 Feb 22, 10:38 -0500
From: Alexandre Eremenko
Date: 2008 Feb 22, 10:38 -0500
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. --~--~---------~--~----~------------~-------~--~----~ To post to this group, send email to NavList@fer3.com To , send email to NavList-@fer3.com -~----------~----~----~----~------~----~------~--~---