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Focusing a projected image

  1. Dec 3, 2008 #1
    Why can an out-of-focus picture on a screen from a projector be corrected by an
    intervening lens, while a lens cannot correct the out-of-focus image once
    impinged on the screen?
  2. jcsd
  3. Dec 3, 2008 #2


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    Staff: Mentor

    When the light hits the screen, the direction the rays travel is not preserved due to the specular reflection. Replace the screen with a mirror and you can re-focus the light.
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