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Thread: Starting the New Year right......with a question!

  1. #1
    Cape Codger OptiBoard Gold Supporter hcjilson's Avatar
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    Starting the New Year right......with a question!

    Well, I'm here for my annual visit to Opthalmic Optics, and I brought a question with me.I have observed a phenomenon which I would like to have explained to me........in terms that I can understand!

    It occurs in the Christmas style set.Also in dimly lit resturants with red menus. ( I am SERIOUS!)If you are not currently in the Christmas set change to it now and if you have 2 functioning eyes, you will see it too.

    Find any thread with more than 1 page of replies.You will see the icon of a green page with a red one on top of it.The red page appears to be floating above the green.In the case of resturant menus the color of the menu is red, and the lettering is black.In dim light, the black lettering does the same thing!It is creating a 3 dimensional image on a flat surface.

    Now I remember that in the old 3D movies you had to wear cardboard glasses with one red and one blue lens, in order to get the effect.You could also get the effect by wearing polarized lenses, leading me to believe that this phenomoneom has to do with reflected light,and/or the color red.

    My question is this: What is happening....and why?

    Thus endeth my incursion into these hallowed halls!
    Last edited by hcjilson; 01-01-2002 at 08:25 AM.
    "Always laugh when you can. It is a cheap medicine"
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  2. #2
    OptiBoardaholic
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    Hi Harry, Happy New Year.
    I haven't thought about this until now but here are my thoughts for what they're worth. I'm sure that Darryl will correct my errors.
    The phenomenon you are describing sounds a little like the duochrome test used in refraction (where the subject is asked whether the print is clearer on the red or green background). The basis for this is that our eyes have a considerable amount of axial chromatism; that is, violet end of the spectrum, which includes green for the purposes of this explanation, is brought to a focus earlier than red. The amount of this axial chromatism is arguable (and we have argued about it in this forum) but the estimates vary betweem 2.50D and 1.00D. It depends on whether you are talking about the extremes of the spectrum or the traditional Fraunhofer F and C lines used to work out the Abbe number. So, if one colour is in focus the other will not be. If it is a near object you are viewing and you have focused on the green (and we are more sensitive to green than red) then your eyes will have accommodated and converged for the green. They will have over accommodated and over converged for the red, causing (I believe)this 3D effect.
    The 3D movie effect is different. The red and green lenses are selectively transmitting only a narrow range of wavelengths in their part of the spectrum. One camera shoots within the range transmitted by the green lens and one camera within the red range. Since the cameras are placed slightly apart they have the same 3D effect as our eyes. If you observe the screen without the specs you will note that it is blurry and appears to be red and green. The improved polarizing method uses polarized lenses with their axes at right angles to each other. The light from each camera is polarized, thereby only being transmitted by one or other of the lenses.
    Over to you, Darryl.
    Regards
    David

  3. #3
    Cape Codger OptiBoard Gold Supporter hcjilson's Avatar
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    Thanks David, I too will...

    Thanks David, I too will will await the master. Very cogent reply, you must be a marvelous teacher! Happy New Year to you as well.
    best from harry
    "Always laugh when you can. It is a cheap medicine"
    Lord Byron

    Take a photo tour of Cape Cod and the Islands!
    www.capecodphotoalbum.com

  4. #4
    Carl Zeiss Vision OptiBoard Gold Supporter Darryl Meister's Avatar
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    Hey Gang,

    Sorry -- been pretty busy for the last few days!

    Well, the problem you're describing sounds like something called "chromatic stereopsis." It is related to the chromatic aberration of the eye (as David pointed out) and the eccentricity of the pupil. In many cases, the green image will appear closer, but I think it is possible for the red image to appear closer (depending upon the direction of the pupil eccentricity). I hadn't really heard of anyone complaining about the effect before, but I looked it up in my copy of "Introduction to Visual Optics."

    Best regards,
    Darryl

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