The Eye As A Lens (Part 2)


An illuminated object consists of many point sources spread over an area. It emits parallel rays when it's far away,
but the rays are diverging when the object is nearby. For a nearby object to be seen clearly, all its points must be in focus.

  • Drag the source back and forth. Note that it is not focused because the eye is "relaxed" (focused at infinity.)
    The lens of a normal eye flexes and strains to adjust its focal length and to bring near sources to focus.
  • Drag the source to an arbitrary point within the constraining rectangle and click the "Strain" button. Repeat at will.
  • Click "Relax" to bring the eye lens back to its relaxed state.
  • Drag the source to the extreme left, "Strain", then drag the source up and down. The spot on the retina hardly moves.
  • Drag the source to the extreme right, "Strain" and drag the source up and down. The spot on the retina moves a lot more.

    1.  The increasing angular separation causes objects to appear larger as they move closer.
    2.  Increased angular separation means that the object appears larger, i.e. is magnified.

    Credits
    Authored by Kevork Spartalian, University of Vermont, based on Davidson College physlets.