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A short sighted question

  1. Jul 22, 2009 #1

    A friend of mine is short sighted. She told me that when she looks in a mirror, objects that are reflected from a distance appear blurred in exactly the same way they do as when she looks at them directly (from the same distance). She also told me that objects that are near but small are not blurred. Surely a distant reflection is indestinguishable from a small object near by because the reflected image is actually formed on the mirror (not behind the mirror at a distance).

    How and why is short sightedness apparent in reflected images?
  2. jcsd
  3. Jul 22, 2009 #2
    The image formed is called a virtual image, and is actually located behind the mirror. This diagram explains it pretty well

    http://upload.wikimedia.org/wikibooks/en/8/8b/Virtual_image.gif" [Broken]

    The rays in reality come from the actual object being reflected, and it is as though the brain is 'fooled' into thinking the light has come from behind the mirror, not, as you state, from the surface of the mirror.
    Last edited by a moderator: May 4, 2017
  4. Jul 22, 2009 #3


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    Another way of thinking about it is that actual distance means nothing to your eyes. The 3D world is projected onto your eyes in the same way it is projected on a mirror. You'll notice when you take an eye exam you stand still =)
  5. Jul 22, 2009 #4


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    A cool future technology would be contact lenses that collect the light and then re-project it directly onto your retina. You could then have "deep focus" where foreground and background objects are simultaneously crystal clear.
  6. Jul 22, 2009 #5


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    I found something peculiar, along this line, when I was a kid. Anybody remember Viewmasters? They're like a set of binoculars that you put a pair of parallax-shifted pictures into and look through. The result is a fully 3-D image (my favourite was scenes from the original Star Trek series). I had to wear my glasses to use it, even though the pictures were a couple of inches away from my eyes.
  7. Nov 11, 2009 #6
    its not jus the brain dat's fooled.....cameras also see the image at a dist behind the mirror.....n they don' hav brains.....
  8. Nov 11, 2009 #7


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    Stick something to a mirror and try to focus your sight ob both, the thing on the mirror and the distant relfection. If the reflected image was formed on the mirror, you could see both sharp at the same time, but you can't.
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