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    Re: (Fwd) The Most Anomalous Refraction Yet or What ?
    From: George Huxtable
    Date: 2009 Aug 4, 20:34 +0100

    |
    | > Greg Rudzinski wrote-
    | >
    | > "Even just the camera held to a single pane window surface and cocked
    | > slightly would create multiple reflections."
    |
    | And I had commented-
    | >
    | > Not if the glass itself has its surfaces parallel, in which case, for an
    | > object seen at infinity, the two images coalesce exactly, just as they
    do
    | > in
    | > the case of the two reflections from a back-silvered sextant mirror..
    Such
    | > a
    | > displacement as Greg describes calls for some degree of "wedginess"
    | > between
    | > the surfaces.
    |
    Greg replied-
    |
    | "If you can get your hands on a DSLR digital camera with a clear UV
    | filter screwed snug to the lens then look through the view finder at a
    | bright desk lamp through a window with the front of the lens touching
    | the window and tilted to one side or the other then you will see the
    | displacement effect. "
    
    My response was-
    
    | Yes, indeed you will, in the case of the close-by desk lamp. But not in
    the
    | case of an object at infinity, such as the Sun (as I wrote).  Greg should
    | try the experiment to see.
    
    On second thoughts, from Greg's mention of a UV filter, I now presume that
    Greg was referring to light reflecting back between the plane surfaces of
    the window glass and the UV filter. In which case, a secondary image of the
    Sun, seen via that double-reflection, would indeed be shifted in angle with
    respect to the main image, by twice the angle between those surfaces. That
    may indeed be occurring in the Sun image we're looking at, if there was such
    a filter, and the camera was looking nearly at right-angles to the window
    glass. But if that was indeed causing a second Sun image, that would be
    immediately obvious to the photographer, if using a hand-held camera, as the
    relative position of that second image would be highly sensitive to the
    slightest tilt.
    
    However, if there was no such plane-surfaced filter, any such reflection
    back from the camera would have the Sun's image greatly altered in size and
    in focus, as the only reflecting surface would then be the spherical outer
    surface of the camera's lens.
    
    George.
    
    contact George Huxtable, at  george{at}hux.me.uk
    or at +44 1865 820222 (from UK, 01865 820222)
    or at 1 Sandy Lane, Southmoor, Abingdon, Oxon OX13 5HX, UK.
    
    
    
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