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    Re: Sight Tube vs. 4x40mm Scope
    From: Jeremy C
    Date: 2011 Apr 23, 14:46 -0400
    I will second these comments as they mirror my experiences with lower magnification scopes and traditional mirrors.  I have a much harder time locating the star and then rocking the star which means spending more time obtaining the observations.  While in the middle latitudes, this might not be a significant problem, in the tropics, with the much shorter twilight duration, this can mean fewer observations with a good horizon.
    Greg was also using Sirius, the brightest star.  I wonder what result he would get from a second order star?  I expect that his numbers would be much worse.
    In a message dated 4/22/2011 10:31:13 P.M. Eastern Daylight Time, gregrudzinski@yahoo.com writes:

    Just how much of a difference is there between a sight taken with a 4x40mm scope with a perfect horizon using a whole horizon mirror as compared to a sight tube with a hazy horizon and a split mirror ? Below are my results.

    U.S. Navy MK 3 with whole horizon mirror and 4x40mm scope making ten observations of Sirius during evening twilight onto a very sharp horizon.

    -Avg. intercept from shoreside chart position of 0.5' moa with a scatter of 0.7' moa (8 kts. of wind)

    Cassens & Plath with split horizon mirror and sight tube making ten observations of an afternoon Sun onto a hazy but sharp horizon.

    -Avg. intercept from shoreside chart position of 0.8' moa with a scatter of 2.7' moa (8 kts. of wind)

    Comments- It only took ten minutes to make ten observations using the whole horizon mirror vs. fifteen minutes to make ten observations with the split horizon mirror. The scope can be focused to a sharp image where the sight tube requires squinting and blinking to maintain an equivalent sharpness. Rocking the sextant is noticeably easier with the whole horizon mirror. Even though accuracies of the two sets of observations are close the scatter is four times larger with the sight tube thus making the 4x40mm scope the better choice for single observations.

    Greg Rudzinski
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