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    Re: Which diameter of the sun in digital photos ?
    From: Greg Rudzinski
    Date: 2009 Aug 21, 13:25 -0700

    Marcel,
    
    Yes I have compared and cross checked DSLR vertical and horizontal
    terrestrial angles with Sun diameter measurements. I haven't had any
    problems getting 2 minutes of arc accuracy (precision about 1 MOA) or
    better using a 50mm lens. I confidently trust the digital camera
    celestial navigation concept for practical use aboard small craft even
    in rough weather.
    
    On filtering: If the circular polarizing or neutral density filters
    are hand held in front of the lens so that only the Sun is filtered
    and not the horizon then you should get some useful images.
    
    One other thing to try is the varying of exposure with photo software.
    The changing diameter of the Sun with over exposure is obvious during
    this manipulation process.
    
    Greg
    
    On Aug 21, 12:38�pm, Marcel Tschudin 
    wrote:
    > Greg, thank you for your suggestions.
    >
    > For this exercise I'm using always the same camera having always the
    > same lenses.The sun's diameter is measured in a photo-program after
    > removing all colours except green and in some cases even removing all
    > but blue. I fear to put an other hand-held filter in front since I
    > have to measure the distance to the horizon which still must be
    > visible, since the main purpose is to measure the sun's distance to
    > the horizon. I have so many only faintly visible sun pictures
    > confirming the obtained scale that I'm fairly confident that the value
    > corresponds to what the camera 'sees'.
    >
    > Have you ever tried with the same lenses to compare the pixels per
    > degree you obtained for the sun with those of landscape features?
    >
    > Marcel
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