NavList:
A Community Devoted to the Preservation and Practice of Celestial Navigation and Other Methods of Traditional Wayfinding
Re: Sextant mirrors
From: Bill B
Date: 2007 Oct 09, 19:32 -0400
From: Bill B
Date: 2007 Oct 09, 19:32 -0400
George wrote > Well, it shouldn't, if they are made of decent glass, with the two surfaces > really parallel. However, larger pieces of glass are usually used for the > roof of an artificial horizon, and so there might be a temptation to use > poorer quality than for a sextant mirror. Even so, I would be surprised if > the glass was bad enough to have enough "wedge" shape in it to produce the > multiple images that Fred mentions. As he says, we'll see, when he reports > back on his reflected sky images. I have switched to the Davis AH, but was using 50-weight motor oil with black oil-soluble aniline dye (really opaque) with a piece of float glass on the top of a 4" x 12" container about 3/8" from the oil surface. I did get multiple images with the sun. I had one image off the oil, another bright image off the surface of the glass. At times, if the geometry was right, it seems a third dim image was visible. I surmise it was kicked off the oil to the bottom surface of the glass and back onto the oil. Probably more kicking around but too dim to see or off the viewing angle. It helped to have the container a bit off level laterally, as the oil surface was then not parallel to the glass surface, and the images were offset left to right. Otherwise it could take a bit to find the correct image under some circumstances. I recall Alex telling us he had some strange results with his AH, only to discover he was using an image reflected off his glass table top instead the image of from Davis AH. It happens. Bill --~--~---------~--~----~------------~-------~--~----~ To post to this group, send email to NavList@fer3.com To , send email to NavList-@fer3.com -~----------~----~----~----~------~----~------~--~---