NavList:
A Community Devoted to the Preservation and Practice of Celestial Navigation and Other Methods of Traditional Wayfinding
Re: accurate sextant
From: Fred Hebard
Date: 2008 Feb 22, 14:37 -0500
From: Fred Hebard
Date: 2008 Feb 22, 14:37 -0500
I'm mostly resisting any national comparison jokes here. On Feb 22, 2008, at 10:38 AM, Alexandre E Eremenko wrote: > > > 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 -~----------~----~----~----~------~----~------~--~---