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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.

  2. #77
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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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  3. #78
    Master OptiBoarder OptiBoard Silver Supporter lensmanmd's Avatar
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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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    Master OptiBoarder AngeHamm's Avatar
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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.
    I'm Andrew Hamm and I approve this message.

  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.

  6. #81
    One eye sees, the other feels OptiBoard Silver 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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  7. #82
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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.

  8. #83
    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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    Quote Originally Posted by lensmanmd View Post
    Atoric and aspheric backside freeform processing has reduced the off axis aberrations. STP processing using the turning tip has eliminated the lap/pad compensation and heat induced aberrations from toric surfacing, providing cleaner finished optics, but I wouldn't put Poly at the top of lens pyramid.

    Poly has improved over the past 3 decades. Processing has improved. COGs and profitability are awesome for the labs. Still, there are better materials on the market.
    what is the meaning of STP?
    Thanks

  10. #85
    Master OptiBoarder OptiBoard Silver Supporter Barry Santini's Avatar
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    Quote Originally Posted by Robert Martellaro View Post
    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.

    Best regards,

    Robert Martellaro
    True. But what’s often forgotten in the abbe-of-the-human-eyeball discussion is that the blue induced at the retinal plane from color error is always present—even if our eye has evolved to no longer notice it. So the eye’s effective threshold for noticing the blur induced by color error has been artificially (via evolution) elevated.

    I believe this is one part of the reason why improper base curve choice, less than optimal lens design choice, and low material abbe can sum up and surpass this not-noticed threshold.

    This is especially true for hyperopes wearing progressives and segmented lenses for reading.

    B

  11. #86
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    Quote Originally Posted by Barry Santini View Post
    True. But what’s often forgotten in the abbe-of-the-human-eyeball discussion is that the blue induced at the retinal plane from color error is always present—even if our eye has evolved to no longer notice it. So the eye’s effective threshold for noticing the blur induced by color error has been artificially (via evolution) elevated.

    I believe this is one part of the reason why improper base curve choice, less than optimal lens design choice, and low material abbe can sum up and surpass this not-noticed threshold.

    This is especially true for hyperopes wearing progressives and segmented lenses for reading.

    B
    For example, +3.00 sph. PALs in poly on a 4 base?

  12. #87
    Master OptiBoarder OptiBoard Silver Supporter Barry Santini's Avatar
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    Yup

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