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Thread: Poly for the win?

  1. #76
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    The abbe value of Trivex is the same as the abbe value of the human eye. There is no better material for eliminating Ca why is Prentice rule a rule and not a law.

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    Quote Originally Posted by Lensman11 View Post
    The abbe value of Trivex is the same as the abbe value of the human eye. There is no better material for eliminating Ca why is Prentice rule a rule and not a law.
    I am a little rusty on this one but don't Abbe's add each other in some way? If you have chromatic aberration in one lens, a space, and the same chromatic error in another, in the end, you will have double chromatic aberration attenuated by the space between them.
    Last edited by vfpamp; 02-25-2020 at 08:42 AM.
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    Quote Originally Posted by Lensman11 View Post
    The abbe value of Trivex is the same as the abbe value of the human eye. There is no better material for eliminating Ca why is Prentice rule a rule and not a law.
    Human eyes can not detect the chromatic aberration if the Abbe number is above 40. With that in mind, why not 1.6 for +3 and up, or -4 and up? Yes, it is less impact resistant and weighs about CR39, but beyond that, it is thinner, has high tensile strength so it is good for 3 piece and nylor, and the ABBE is 42 vs 44.
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    Quote Originally Posted by lensmanmd View Post
    Human eyes can not detect the chromatic aberration if the Abbe number is above 40. With that in mind, why not 1.6 for +3 and up, or -4 and up? Yes, it is less impact resistant and weighs about CR39, but beyond that, it is thinner, has high tensile strength so it is good for 3 piece and nylor, and the ABBE is 42 vs 44.
    I love 1.60. Love love love it. But it doesn't come in very many PAL, photochromic, stock, or polarized options, so its place in my dispensary is extremely limited.
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  5. #80
    What's up? drk's Avatar
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    Quote Originally Posted by vfpamp View Post
    I am a little rusty on this one but don't Abbe's add each other in some way? If you have chromatic aberration in one lens, a space, and the same chromatic error in another, in the end, you will have double chromatic aberration attenuated by the space between them.
    That sounds right to me, but I never thought about that.

    I do know that there is such a thing as an "apochromatic doublet" that somehow does a reversal of one lens' chromatic aberration for a pure outcome. So what you say makes sense.

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    One eye sees, the other feels. OptiBoard Gold Supporter
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    Quote Originally Posted by Lensman11 View Post
    The abbe value of Trivex is the same as the abbe value of the human eye. There is no better material for eliminating Ca why is Prentice rule a rule and not a law.
    Because our eyes suffer from a high degree of axial/longitudinal chromatic aberration, we don't notice it in ophthalmic lenses. Instead, they are affected by transverse/lateral CA.

    WRT rule or law, I'd throw in postulates and principles, choose one, and call it a day.

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    Quote Originally Posted by AngeHamm View Post
    I love 1.60. Love love love it. But it doesn't come in very many PAL, photochromic, stock, or polarized options, so its place in my dispensary is extremely limited.
    Maybe is the lens styles I use, but I have never had an availability issue in 1.60.

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    Eyes eastward... Uilleann's Avatar
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    Quote Originally Posted by drk View Post
    ...I do know that there is such a thing as an "apochromatic doublet" that somehow does a reversal of one lens' chromatic aberration for a pure outcome. So what you say makes sense.
    It works in refracting telescopes, and some camera lens types - but I don't believe the tolerances required hold up to offer any real optical advantage with spectacle lenses, and mobile human eyeballs.

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