NavList:
A Community Devoted to the Preservation and Practice of Celestial Navigation and Other Methods of Traditional Wayfinding
Re: Centring Error Detector
From: Alexandre Eremenko
Date: 2007 Jan 12, 10:19 -0500
From: Alexandre Eremenko
Date: 2007 Jan 12, 10:19 -0500
Phil, > - if exist a book describing precisely > the use of this instrument, It exists and I even have a photocopy of it. It's the book on Hezzanith sextants. It is listed among the sextant accessories, and there is a clear picture of it. The centring error detector of Hezzanith is just a set of few prisms with a simple arrangement to attach them to the front of a telescope. One prizm for each angle, 30, 60, 90, 120. The arrangement is so extremelly simple that I even thought of making one. The question is whether one can have a prizm made to specifications (and to high precision of 0.1' say). But even if one cannot, the prisms with approximate angles can be used, you can just measure the angles of the prisms in advance with a sextant which is known to have no arc error. The principle of work was described by Frank, but let me repeat: it is very simple. One prism turns the incoming ray from a star, say by 30 degrees, and sends it to the telescope. Another ray from the same star goes throuygh the normal way (reflected in the sextant mirrors) and also to the telescope. When you see the two images coincide, the sextant should show 30 degrees+arc error at 30 degrees. You need several prisms, one for each angle. Alex. --~--~---------~--~----~------------~-------~--~----~ To post to this group, send email to NavList@fer3.com To , send email to NavList-@fer3.com -~----------~----~----~----~------~----~------~--~---