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    Re: Sun squash- was Green Flash and Longitude
    From: Bill B
    Date: 2006 Jan 20, 04:01 -0500

    > Yup.
    >
    > Good catch Bill!
    
    As the old saying goes, pick off the easy meat, then work on points for
    style. It was bogus, IMHO, from the git go.
    
    "He knew the focal length of the lens, the size of the sensor in the camera
    and the number of pixels across the image."
    
    One point at a time:
    
    "He knew the focal length of the lens"
    
    Which matters, why?  Perspective is a matter of distance, not focal length.
    An experiment--Take a camera, use the longest (focal length) lens you have
    or highest zoom setting, and move back to include your house, mailbox, and
    other landmarks in the frame.  Now (without moving) use the widest-angle
    lens or lowest zoom setting you have.  Enlarge the portion of the wide-angle
    shot matching the telephoto image to the same size as the telephoto shot.
    The perspective will be exactly the same.  Ditto for the horizon and object
    at an "infinite" distance from the same location.
    
    "...the size of the sensor in the camera..."
    
    Again, so what?  Size of the sensor vs. focal length/angle of view
    determines magnification, not perspective. The sensor is just a matrix/grid
    that determines resolution.  Without going into depth about coverage, focal
    length and view angles, yadda yadda yadda; if the resolution is sufficient
    to provide enough pixels in the "grid" for accurate measurement, it's a done
    deal.
    
    "...and the number of pixels across the image."  As you know by now, I do
    not hate repeating myself.  So what? All the author proposes is using the
    sensor grid that transforms photons into 24 bit deep (or more) pixels as a
    measuring device.  (Sorry about too much information, but for this
    explanation, bit depth does not matter much. 16+ million colors or 256
    colors matter only if it would help the eye/software in resolving a color
    image. Sun and horizon, relatively high-contrast boundaries.
    
    In the end all the matters is that the sensor created a grid that we can
    calibrate/measure against known values (in this case, sun SD vs. elevation).
    Is this idea new to the list?  Nope.  Frank suggested it in his digital
    photos of Chicago from the shores of Indiana.  The only question might be
    lens/sensor distortions of the image.
    
    That being said, I chose the obvious to pick on first.
    
    To Frank Swift:
    
    Unless this was a not-so-clever hoax on your part, I don't support shooting
    the messenger (it keeps me alive;-), and apologize if you are accurately
    recounting a published article.  Perhaps GPS is forbidden in the race and
    some sort of "GPS watch" was used as the $30 radio-signal-controlled
    timepiece doesn't work in those waters?
    
    It just struck my funny bone.  Digital camera, computer with a cel nav
    program (Davis?), $$ professional image-editing software (PhotoShop),
    Nautical Almanac data, (and in my mind's eye--pods on the mast etc. relaying
    data from 1 of the big 2, or 3, racing-software programs working with the
    boats polar diagrams.) The only thing missing was a radar gun. 
    
    Bill
    
    
    

       
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