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    Re: Bris does not work
    From: Greg Rudzinski
    Date: 2012 Jul 29, 09:40 -0700

    Bill N,

    The diagram is exaggerated to show two images when actually the two reflected images appear to be overlapping. The attached image shows a bright elongated reflected image of the Sun as I am seeing it through my homemade Bris. I suspect that this elongation is the overlapping of two separately reflected images from the front and back of the microscope slide glass. Not sure though. It would be nice to get rid of the elongation and have a circular image of the Sun. There is also a fuzziness to the upper and lower limbs. The sides left and right remain sharp.

    Greg Rudzinski

    [NavList] Re: Bris does not work
    From: Bill Noyce
    Date: 29 Jul 2012 07:40
    Hi Greg --
    I think your picture is not correct. In fact, if the surfaces of the glass are parallel, only one image of the sun should appear, even though light reflects off both the front and the back surface.

    In your picture, if the solid ray enters the eye, then the dotted one does not. It's probably better to draw the rays "backwards" -- ie, starting at the eye and coinciding until one of them is reflected by the front surface of the glass. The other ray is refracted (as Alex pointed out), reflected off the back surface, and then refracted again as it leaves the glass. As long as the front and back surfaces are parallel, then:
    1. The two refractions cancel out
    2. The rear-reflected ray emerges parallel to the front-reflected ray, displaced by a fraction of an inch.

    The sideways displacement can cause nearby objects to produce two images (a kind of parallax effect). But over 93 million miles, the fraction-of-an-inch displacement is entirely negligible, so the front-image and the back-image are superimposed. (In fact, there are more reflections, but -- as long as the glass has parallel surfaces -- they all coincide.)

    -- Bill N.
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