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    Re: Sun squash- was Green Flash and Longitude
    From: Bill B
    Date: 2006 Jan 21, 17:38 -0500

    > Questions:
    >
    > Why did he not use the GPS for its normal purpose?  Perhaps he was becalmed
    > and bored.
    > Why upper limb not lower?
    > My digital cameras do not record seconds so the time will never be accurate.
    > I think the image of the sun would be burnt out so the limbs will not be clear
    > if the horizon can also be seen.
    > How high was the sun - would a decent photo be possible (wide angle - he says
    > zoom?)
     Snip
    > Sounds like a semi-plausible joke to impress gullible friends!
    
    Agreed, and some astute observations.
    
    If the sun is at a reasonable elevation for observation, it would require
    something on the order of 17 f stops to drop brightness to an acceptable
    level for an average camera. The dynamic range of most cameras is on the
    order of 8 to 10 f stops.  Therefore the sky and horizon would be black.
    
    In PhotoShop CS, one can make several exposures of a landscape, optimizing
    shadow, midtone, and highlight exposures, and the program will align and
    composite the image for you.  This effectively increases the camera's
    dynamic range.
    
    In the case where the sun is blown out in the optimal horizon exposure, and
    the horizon gone in the optimal sun exposure, there are no reference points
    to register the images for alignment.  One would have to tripod mount the
    camera on a steady platform to pull that trick off.  Not going to happen in
    his case.
    
    > If he got longitude was this near sunset/sunrise so sun close to the horizon?
    > What has the focal length, sensor size and number of pixels across the image
    > got to do with the calculation?
    
    Nothing.  All we need is a ratio of pixels that make up the sun's width to
    diameter in minutes.  With that we could measure other distances in pixels
    and convert to minutes of an arc--assuming it could be photographed.
    
    > "....line length and divided by 60" - I thought he was counting pixels?
    
    If he converted pixels to minutes, then by diving by 60 he could get decimal
    degrees.
    
    And if a frog had wings...
    
    Bill
    
    
    

       
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