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Thread: hagi

  1. #1
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    hagi

    Antireflection coatings

    Why is that with with some AR coats we see a green reflection of lights if the lens is held at a certain angle, and with others we see a purplish hue. With some lenses its possible to see more thatn 1 reflected colour.

    AR coats can be single or broadband. If a green AR coat is applied to the lens will we see a greenish reflections of lights if lens is held at a ceratin angle.

    Our practice supplies AR coats that are green, blue or gold.
    Are there any other colours that are available.

    Whats does UTMC stand for?

    Thanks

  2. #2
    Forever Liz's Dad Steve Machol's Avatar
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    Re: hagi

    hagi said:
    Whats does UTMC stand for?
    http://www.utmc.org/

    :D


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    Master OptiBoarder Darryl Meister's Avatar
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    To make a long story, long...

    Imagine a thin coating that is 1/4th as thick as the wavelength of a particular color of light. A percentage of the light is reflected when it strikes the front of the coating. A percentage of the remaining light is also reflected when it strikes the back of the coating (at the boundary between the coating and the lens). This light will travel through 1/4th its own length as it passes through the coating, since the coating is 1/4th of the length of the light wave. After it is reflected from the back of the coating at the lens, it will then have to travel back through the coating -- and back through 1/4th of its own length again. This reflected light will then meet up with the light originally reflected off the front of the coating, but will differ in "alignment" with the other light by 1/2 the length of its wave (1/4 + 1/4 = 1/2).

    A difference in alignment (or phase) of 1/2 means that the trough of one light wave will line up with the peak of the other light wave. When these two light waves are added together, their troughs and their peaks cancel each other out. So, by being out of sync -- or out of phase -- with the light reflected off the front by 1/2 its wavelength, the light reflected off the back will interfere and cancel out the light reflected off the front.

    Now, since each color of light has its own wavelength, a given coating (which only has a single thickness) can only completely eliminate one color of light. The remaining light reflected from the lens is still visible. The reflex you see on an antireflection coating is this remaining light. However, multilayer coatings, which (as the name implies) have more than coating, can eliminate several color ranges.

    Say your coating produces a purple reflection (a combination of red and blue) because it eliminates green light by having a coating of the correct thickness for the color green. However, when light strikes that coating at an angle, it is now traveling farther through the coating than if it had reached the coating head on. This extra distance means that it will no longer be out of phase with green wavelengths, but will be now out of phase with other colors, instead. Consequently, different colors are eliminated, leaving you with a different residual -- or reflex -- color.

    Best regards,
    Darryl

  4. #4
    Master OptiBoarder Joann Raytar's Avatar
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    Re: hagi

    hagi said:

    Whats does UTMC stand for?
    I believe the first part is Ultra Tough...?...Coating. I am not sure what the M stands for. Of course, I am not sure that I got the ultra tough part correct either.

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    Master OptiBoarder OptiBoard Silver Supporter Jubilee's Avatar
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    UTMC

    Ultra Tough Multi Coat

    It is Sola's answer to Crizal :)

    Anti Reflective coating with a scratch coating supposedly making it more resistant to scratches compared to other a/r coatings.

    I haven't used any of these lenses, so I can't tell you whether it is as good as the competitor or not.

    Cassandra

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