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Enlarged image observed

  1. Aug 17, 2016 #1

    andrevdh

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    1. The problem statement, all variables and given/known data
    This is not really a homework or coursework question, but might be of interest to readers of this forum.
    It concerns what I have viewed on two separate occasions which baffles me.
    The setup was different it the two instances, but there are similar elements in both.
    In both cases I saw an enlarged "image" of some small structures that was positioned at quite a distance from me. They were illuminated by a bright distant source from behind the fine structure of which I saw an enlarged "image".

    In the one case the fine structure was my hair which was illuminated from behind by a distant bright light bulb (thus a point source producing plane waves). By looking at it in a mirror in front of me I saw the hair (and my ear :) ) greatly enlarged. The mirror was covered by (very fine) condensation drops (from a hot shower). I was wondering how such small condensation drops can be responsible for seeing an enlarged image?

    In the other case the enlarged image did not persist. It dissappeared when I blinked, so the way it was produced might not be similar.

    Again a distant bright light source (a street lamp) illuminated a fine structure - in this case the weave pattern of a curtain (at night time with the room in darkness). I saw a greatly enlarged image of the weave pattern of the curtain (which was located several meters away from me). This was quite a baffling experience that I am having difficulty in understanding.

    Maybe someone can throw some light on the matter :)

    2. Relevant equations
    diffraction of light? (by the small structures - hair, threads in the curtain)
    interference of light? (of the waves from the diffraction created by the edges of the small structures, allthough in the first instance I also saw an enlarged image of my ear :) )
    refraction of light? (by the small condensation drops - light being reflected back from back side of drops)

    3. The attempt at a solution

    Could these setups produce an enlarged virtual nearby image for me to view? I must add that I am nearsighted and in both cases I saw these without any glasses. The second instance produced a redicously enlarged image of the weave.
     
  2. jcsd
  3. Aug 17, 2016 #2

    haruspex

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    Can you clarify...
    Did the images subtend a greater angle at your eye, or did they appear correspondingly further away?
     
  4. Aug 18, 2016 #3

    andrevdh

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    It is always difficult to tell where the image is located when you eye focusses on it (for me anyway).
    Currently my (rather old) eyes can only focus at computer screen distance :) ~40 cm
    What I saw in the bathroom I would think was further away than that, my be located at the mirror surface where the condenstation occured since my focus had to shift to see my face (which is of cause located at the same distance behind the mirror).

    The second setup occured very long ago (35 years?) when I was much younger and my eyes had a much larger range of accomodation. Here I got the impression that my eyes were focussed extremely closeup, almost like looking at my nose, but it was long ago. In spite of that one do not forget something like that easily since it is so unusual (maybe that contributed to my interest in optics?).

    And yes, in both cases the image appeared much larger than one would expect, like somehow a large magnification of the original object was somehow produced, especially in the second case where it seemed that the curtain weave was right up against my eye and I am seeing it much enlarged where in reality the curtain was located several meters from me.
     
    Last edited: Aug 19, 2016
  5. Aug 19, 2016 #4

    Stephen Tashi

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    There are many many times when I've looked through a window screen at night at a distant light and seen what appeared to be an enlarged pattern of the screen. This doesn't happen every time I look out a window at night and I haven't studied the circumstances when it does happen. I have the impression it occurs when I'm looking out of a window across the room from me at a "point" light source that is blurred to a larger spot because I'm not wearing my glasses. You may be able to add many more such experiences to you life if you experiment a little.
     
  6. Aug 19, 2016 #5

    haruspex

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    With a repeating pattern, like a curtain weave, it is possible to get a false binocular focus. I.e., the left and right views are combined one or two pattern repeats off. But the angle subtended at the eye by the patten interval should not change, so you would either see a finer weave closer or a larger weave further away. That does not seem to fit what you describe.
     
  7. Aug 22, 2016 #6

    andrevdh

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    Glad to hear that someone else have observed it Stephen :)

    haruspex - not sure what you are saying. Maybe that the brain is reconstructing the image in order to make sense of it, resulting in an enlarged view (and skipping some fine structures in the process)?
    Just to be clear the curtain was located at quite a distance from me.

    Stephen, I suspect that one have to hold the head (on a cushion :) and eyes perfectly still in order to see it.

    I attempted to photograph it in the lab using a sodium spectrum tube positioned about 14 meters away and the small piece of cheese cloth about 3 meters away (the threads in the cheese cloth is not a completely regular pattern though) - no success. With my eye I could see some of the fine structure of the cloth, but I remembered seeining the curtain weave much more enlarged previously. I am getting the idea that one need a large sheet of the material in order to observe the effect.
     

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    Last edited: Aug 22, 2016
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