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Question about optics: glasses

  1. May 19, 2011 #1
    Hi everyone,

    I was riding home today and got water all over my glasses. It annoyed my until I got home - I looked up at a light, and I could focus really clearly on something that was splattered on my glasses. It looked like it might've been dirt, or mud, because it almost seemed to zoom in enough to see individual particles (or constituents?) of whatever it was. My explanation off the top of my head is this:

    Due to the differing refractive index of glass and water, when a thin film of water is spread over the surface of a lens, you're creating a crude telescope. When light is incident from far enough away (so that incoming light rays are parallel), it zooms in on whatever is splattered on the surface. When you move too close to the source, the incoming light is no longer uniform (the rays aren't parallel) so it scatters off whatever is splattered on the surface. I guess it just so happened that the focal length was just rigth for what was splattered on my glasses.

    Seems kinda cool to me, and it was definitely zooming in on something. Am I on the right track? If not, can anyone explain it?

    Thanks! :)
  2. jcsd
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