NavList:
A Community Devoted to the Preservation and Practice of Celestial Navigation and Other Methods of Traditional Wayfinding
Re: Sextant Error and Whole Horizon Mirrors
From: Aubrey O?Callaghan
Date: 2002 Jul 10, 08:18 -0400
From: Aubrey O?Callaghan
Date: 2002 Jul 10, 08:18 -0400
One of my sextants is a Cetus Russian sexant. The magnifying telescope has all the bells and whistles referred to by Bruce, inverting image and parallel wires. However it has a split mirror. Aubrey. At 21:03 09/07/02, you wrote: >Chuck- > >The only way I know of for sure to overcome the problem you are talking about >is to have one of the old-fashioned sextants or circles with an inverting >'scope. I've never been so fortunate as to use one but, besides being more >powerful and having a wider view, the inverting 'scopes had parallel wires in >the field of view so it was easy to keep the objects in the middle while you >made contact. > >The problem you are describing is the problem of keeping the plane of the >observation parallel to the plane of the instrument. It's not much of a >problem for small angles but gets bad with wider angles. If you have a copy >of my "Tables for Clearing" look under "Odds and Ends" for a discussion of >this, and a table showing the effect in different situations. > >It's also what I'm talking about in the last paragraph of that July 7th >posting. It seems your experience and conclusions are about the same as mine, >though my sextant isn't whole horizon. I hope other members will experiment >too. > >Bruce