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Opposite resulting combinations of primary colors

  1. Aug 18, 2013 #1
    fragments of film

    I read a book called the "Holographic Universe". It explained how a hologram is generated. One aspect of hologram creation holds a puzzle that the book I read did not know the answer to. I have not found the answer anywhere and I am looking for a solution to this puzzle. The puzzle is this: Why is it that any segment of holographic film can produce the image of the entire hologram?

    I will not go into how a hologram is produced unless it is requested of me to do so...but in the end a laser goes through a two dimensional film that creates the three dimensional image which we call a "hologram". When the entire film is in one piece the image is clear and crisp. Yet, as I wrote, if only a fragment of the film is present for the laser to go through, the entire image, the same image that the whole piece of film creates, is created. The only difference is that when only part of the film is being shot through with a laser, the end image is not as crisp, not as clear, slightly fuzzy.

    If I remember correctly, to imagine holographic film is to think of looking at a body of water frozen in time that has had the effect of many pebbles tossed into it. On the film there appears circles within circles within circles that interact with with other circles within circles within circles on the film. So my riddle that still remains unsolved is why and/or how does a fragment of this film, have the ability to produce the entire image?
     
    Last edited: Aug 18, 2013
  2. jcsd
  3. Aug 19, 2013 #2

    sophiecentaur

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    A hologram is a diffraction pattern. The 'sharpness' of a diffraction pattern is governed by the width of the hologram pattern, in the same way that a narrow beam can be produced by a wide parabolic reflector antenna.

    I would advise against any analogy (see also the vast number of other threads about the use of analogies) for a hologram. It really doesn't help with understanding and is likely to yield huge misunderstandings. It's all down to the Maths of Fourier Transforms and you can't do better than the Maths (to even approach its message) in this instance.
    Basically, a hologram is formed as a diffraction pattern of the original object and it made using two beams from a single laser, where one beam is reflected by the object and it interferes with the other, reference beam. The resulting diffraction pattern is infinitely wide and (necessarily) only a part of it is recorded on a film. As it happens, the diffraction pattern of a complete diffraction pattern is the same as the original scene / object. By using only a part of the hologram pattern, the reconstructed scene is not complete - but instead of losing large chunks of the original (as you would if you chopped off a bit of a photograph), you just lose some degree of the detail in all parts. Hence, a small piece of a hologram will produce an approximate reconstruction of the original object.

    Familiar example:
    One very simple form of hologram is the familiar pattern from the Two Slits experiment. If the fringes that are formed (recorded on film, for instance) have coherent light shone through them, an image of the original two slits is formed. Using all the fringes will give a sharp image of the slits but using only a few of the fringes will give a fuzzy image.

    PS Where do the 'Primary Colours" come in?
     
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