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    Dual Polarized Hybrid Digital SLR Sextant
    From: Greg Rudzinski
    Date: 2009 Jan 20, 18:01 -0800

         The attached photo shows a 135mm lens and a pair of circular polarizers 
    with a homemade bris mini sextant fixed to the forward polarizer surface 
    (double stick tape was used). Celestial navigators with an interest in 
    photography will enjoy building and using this system.
         Preliminary calibration was performed from a known position and height of 
    eye with a hand held 10 mega pixel SLR Canon Rebel Xti using an adapted fixed 
    135mm Super Takumar Pentax lens. A precision of two pixels (or .29 minutes of 
    arc) was achieved with Acorn photo software. The attached calibration image 
    (shutter 1/4000, ISO 200, f 8, Monochromatic) for 10° 08.6' hs does show 
    multiple overlapping images of the sun which could be caused by extra 
    reflections of an optically imperfect handmade mini sextant. Consistency can 
    be maintained by always using the lowest lower limb of the multiple images.
         If aperture priority is used try ISO 200 then work up to ISO 800 for a 
    less bright sun so that shutter speed is kept high. This will help reduce the 
    effects of hand shake.
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