NavList:
A Community Devoted to the Preservation and Practice of Celestial Navigation and Other Methods of Traditional Wayfinding
Re: Sextant scopes and an old-bold empiricist
From: George Huxtable
Date: 2006 Apr 14, 15:10 +0100
From: George Huxtable
Date: 2006 Apr 14, 15:10 +0100
About finding the magnification of a sextant telescope, Gary LaPook wrote- | Or, if you can dissassemble the telescope, you can find the focal length | of the objective and of the eyepiece. Then the magnification is the | focal length of the objective devided by the focal length of the eyepiece. | | To find the focal length of these lenses simply focus the image of the | sun onto a piece of paper by adjusting the distance from the lense to | the paper until the edge of the image of the disk of the sun has sharp | edges as projected onto the paper. Measure the spacing between the lense | and the paper at this point and you then know the focal length of the lense. ===================== All very well for two types of telescope; the inverting astronomical type and the prismatic. Not, however, for the Galilean, opera-glass scope, which you can tell because it doesn't invert, yet is without the obvious bulges of a prismatic. For that type, the eyepiece is a diverger, not a converger. On its own, it will not give an image of the Sun, or anything else, in the way that Gary describes. George. ======================= contact George Huxtable at george@huxtable.u-net.com or at +44 1865 820222 (from UK, 01865 820222) or at 1 Sandy Lane, Southmoor, Abingdon, Oxon OX13 5HX, UK.