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How come things shrink?

  1. Jul 15, 2005 #1
    If someone paints a realsize picture of a person, then walks 100 yards to where you stand and hands you this painting, the painted person is of course still the same size as the real person. But if photons bring you a picture of the same person (i.e. seeing) still standing 100 yards away, the picture shrinks. What happens here?
  2. jcsd
  3. Jul 15, 2005 #2

    Doc Al

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    Perhaps I don't understand your question, but are you asking why things appear smaller as they get further away? Because they subtend a smaller angle. Our brains are able to adjust for familiar objects of known size: We "know" that those people across the park aren't really 1 inch tall as they might appear.

    But our perspective can be fooled, since our assumptions of relative size are based on our experience and environmental cues. How about this: http://psylux.psych.tu-dresden.de/i1/kaw/diverses Material/www.illusionworks.com/html/ames_room.html
  4. Jul 15, 2005 #3
    Yes, you understood me right. But what exactly happens when you subtend a smaller angle? Does the photons gather data about the space between me and the person 100 yards away, so that visual system can shrink the image proparly?
  5. Jul 15, 2005 #4


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    No, it's just that your line of sight sweeps through a smaller angle to cover an object that has moved far away, and it is this angle (outside of any process borrowing from experience) which is our perception of "size".
  6. Jul 15, 2005 #5


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    Check out the attached image. It show how the eye images two objects of the same size at different distances. Note that the image projected on the retina for the furthest object is smaller that the for the closer object and that is because the angle is formed is smaller.

    Attached Files:

  7. Jul 15, 2005 #6
    Thanks! Just what I needed.
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