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    Re: Sextant mirrors
    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.
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