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Thread: how to tell if lens is AR coated or not?

  1. #1
    Join Date
    May 2018
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    Default how to tell if lens is AR coated or not?

    Is there an easy way to tell? I can scratch the edges if there's a procedure involving that. This is a general question I fell I should know, not just laser collimator lenses.

  2. #2
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    ... look on eventual entry reflections - good AR coating should minimize them ...

    Viktor

  3. #3
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    Hold it so you can see a reflection off the surface while you wipe some alcohol on it. If it is uncoated, there will be no color change. If it is AR coated, the thin layer of alcohol seen as it evaporates will give color to the reflection because it index-matches to the coating (which is designed to be used in air). The colors come from thin-film interference.

  4. #4
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    May 2018
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    Thank you, do you mean something like this you get with soap bubbles? https://78.media.tumblr.com/tumblr_l...g7o3o1_250.jpg

  5. #5
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    Yes. The colors may be weak, and will disappear when the alcohol has evaporated.

  6. #6
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    Quote Originally Posted by Eidetic View Post
    Hold it so you can see a reflection off the surface while you wipe some alcohol on it. If it is uncoated, there will be no color change. If it is AR coated, the thin layer of alcohol seen as it evaporates will give color to the reflection because it index-matches to the coating (which is designed to be used in air). The colors come from thin-film interference.
    Cool! Learned something new today...

    Adam

  7. #7
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    ... are all AR coatings resistent to alcohol? -- could be a probelm, if not ...

    Viktor

  8. #8
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    Quote Originally Posted by VDX View Post
    ... are all AR coatings resistent to alcohol? -- could be a probelm, if not ...

    Viktor
    I have no idea, but it reminds me of trying to remove dicros from mounts on my first (Chinese) RGB projector close to 20 years ago. (I was gutting it and wanted the dichro mounts.) I used mineral spirits and when that didn’t work I used heavy duty paint remover. Surprisingly the dichros survived and still worked. Ahhh, the dumb things I’ve done over the years!

    David
    "Help, help, I'm being repressed!"

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