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    Re: Metal versus plastic or better telescope?
    From: Greg Rudzinski
    Date: 2012 Mar 27, 11:02 -0700

    Randall,

    The USNO web sight does provide SUN data. See attached pic 81 showing the SUN above horizon, pic 137 below horizon (negative Hc). Pic 138 shows no SUN because it is below 12* negative altitude which is when civil twilight ends after sunset.

    Venus is very bright right now so shade it with the lightest shade and be sure the two images are overlapped when using the artificial horizon.

    Regarding optics- Be sure the lens is clean and focused. When at sea lenses,filters, and mirrors need to be checked for salt residue which interferes with observation clarity. Lenses and mirrors can fog up when going from the controlled climate of the pilot house to the open bridge wing. Give the sextant a few minutes to adjust to the climate change before making an observation.

    Greg Rudzinski


    [NavList] Metal versus plastic or better telescope?
    From: Randall Morrow
    Date: 27 Mar 2012 07:35

    I recently acquired an Astra IIIB on eBay. The results with my Davis Mark 15 were good for stars but sun and moon sights as well as index correction sights were less "stellar". (pun intended, sorry) Inferior optics may have contributed to this difficulty.
    Here are the first results with a metal sextant and a mirror AH, index correction of (+) 0.2: (GPS 35*19.5 N, 119*05.5W)

    The Davis sextant would change angles if you squeezed the handle too tight and I could never get two sun-index correction sights that were the same. Seeing the point of tangency of the sun and the moon was always difficult due to what I described as optical distortion/lack of resolution of the shapes or the brightness of one image washing out the other. This Astra moon sight is the best I have ever done and I attribute this to a better telescope with more resolution. The extra weight of the metal instrument will take getting used to but I think I can officially retire my Davis. I hope sun sight have improved as well as the moon but I have wait to do manual sight reductions as the USNO web page does not include the sun.

    Randall F Morrow PT
    Ergonomics Safety Consultant
    Bakersfield

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