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Non-reflective coatings

  1. Apr 27, 2004 #1
    I'm sure this will seem simple to some of you, but it's driving me nuts! It concerns non-reflective coatings for cameras and binoculars.

    I understand how a coating, with thickness of 1/4 the wavelength of a color (say green), can cause destructive interference and reduce reflection. Basically, the light reflected from the air-coating interface is 1/2 wavelenth out of phase with light reflected from the coating-glass interface, and those two reflected rays cancel out. All the textbooks and websites I've looked at make the assumption that by reducing reflection, transmission is increased.

    That's where I can't make the connection. Sure, the reflected light is cancelled out, but how does that increase transmission of light into the optical instrument? Is the reflectivity decreased somehow?

    To me, reflecting at two interfaces seems to only reduce the amount of transmitted light even more.

    Thanks for looking at my question. :smile:
  2. jcsd
  3. Apr 27, 2004 #2


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    Science Advisor

    A quick and simple answer is "conservation of energy". The energy in the light goes somewhere. Destructive interference does not make energy disappear.

  4. Apr 27, 2004 #3
  5. Apr 27, 2004 #4
    Thanks for your responses everybody. I don't get it fully, but the topic is becoming clearer to me. I think if I considered light more as a wave, and less as a ray, then I might get it. Thanks for your help.
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