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Thread: 1.56 aspheric vrs 1.6 for a plus rx.

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    1.56 aspheric vrs 1.6 for a plus rx.

    This is a general question, not px specific.
    What would look better cosmetically and have better optics and less distortions.
    For a moderate +ve rx?
    1.56 aspheric 55 or 60 diameter vrs 1.6 60 or 65 diameter?

    Thanks all.

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    Probably quite similar.

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    I agree with Robert_S that you would need a caliper to tell the thickness difference.

    Aspheric would soften the peripheral magnification for cosmetics but I prefer 1.6 for scratch resistance.

    Mild to moderate rx's I've never found aspherical to create wow effects in optics performance.

    In the US we only have stock 60 blanks in cr39 that I'm aware of.

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    What's up? drk's Avatar
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    Asphericity is not for optics, I don't think.

    It's for fixing optics back to baseline, from screwing up the optics from flattening the lens to look and feel nice and thin.

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    Quote Originally Posted by Optikaye View Post
    This is a general question, not px specific.
    What would look better cosmetically and have better optics and less distortions.
    For a moderate +ve rx?
    1.56 aspheric 55 or 60 diameter vrs 1.6 60 or 65 diameter?

    Thanks all.
    You asked about 55 or 60 mm diameter vs. 60/65. The size should be no more than what is necessary for the order.

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    One eye sees, the other feels. OptiBoard Gold Supporter
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    Quote Originally Posted by Optikaye View Post
    This is a general question, not px specific.
    What would look better cosmetically and have better optics and less distortions.
    For a moderate +ve rx?
    1.56 aspheric 55 or 60 diameter vrs 1.6 60 or 65 diameter?

    Thanks all.
    The difference in thickness due strictly to refractive index is roughly equal to the ratio (1.60 - 1.00) / (1.56 - 1.00) = 0.93, or 7% thinner.

    We won't use finished blanks for plus hence the diameter makes no difference.

    Flatter curves reduce the thickness, weight, and sag depth (less bulbous, reduced vertex), but some folks reject the change due to spatial perception issues, especially older, long term wearers of non-aspheric lenses, primarily with hyperopes.

    Hope this helps,

    Robert Martellaro
    Roberts Optical Ltd.
    Wauwatosa Wi.
    www.roberts-optical.com
    ~~~~~~~~~~~~~~~~~~
    Science is a way of trying not to fool yourself. - Richard P. Feynman

    Experience is the hardest teacher. She gives the test before the lesson.



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    Quote Originally Posted by drk View Post
    Asphericity is not for optics, I don't think.

    It's for fixing optics back to baseline, from screwing up the optics from flattening the lens to look and feel nice and thin.
    If it’s done Willy nilly (like the old Super Modular for aphakic Rx’s),yea it was for weight and cosmetics, but done correctly, it also helps cancel off axis surface astigmatism. It can provide a wider, clear field of view. As example, it’s used in camera lenses.

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    What's up? drk's Avatar
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    I wonder if we're talking about two different things.

    I may be spouting old information from the days of molded lenses, and you may be using updated digital surfacing information?

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    Even molded benefit, in a given power range, if the aspheric amount is calculated, for a given spherical power. ( For toric powers, ideally, an atoric design would be most accurate. )

    Unlike CL’s, our eyes deviate from the OC, or central vision. As we look off center, peripherally, we encounter off axis surface astigmatism. Varying the concave or convex surface of a given lens powers asphericity from the OC can cancel/diminish the surface astigmatism we encounter ( flattening the curvature out from center on plus powers , stepping it on minus.) that’s the part that make them look thinner, it just so happens, it also improves off axis viewing…If calculated for a given power/range.

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    One eye sees, the other feels. OptiBoard Gold Supporter
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    Using a flatter than 'best form' base curve is one way to introduce oblique astigmatism and power error- introducing asphericity can clean up those errors.

    From Darryl Meister's 'Ophthalmic Lens Design' with the full text available at Opticampus.

    https://www.2020mag.com/article/opti...-of-lens-forms
    Roberts Optical Ltd.
    Wauwatosa Wi.
    www.roberts-optical.com
    ~~~~~~~~~~~~~~~~~~
    Science is a way of trying not to fool yourself. - Richard P. Feynman

    Experience is the hardest teacher. She gives the test before the lesson.



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    Master OptiBoarder optical24/7's Avatar
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    Quote Originally Posted by Robert Martellaro View Post
    Using a flatter than 'best form' base curve is one way to introduce oblique astigmatism and power error- introducing asphericity can clean up those errors.
    Exactly, we want to use flatter BC’s for the reasons you mentioned a few posts up..( thickness, weight, vertex, sag..), but because we are pursuing flatter curves, we need to introduce asphericity/atoricity to comp for induced errors in, as you said, not using best BC’s.

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    Quote Originally Posted by Robert Martellaro View Post
    The difference in thickness due strictly to refractive index is roughly equal to the ratio (1.60 - 1.00) / (1.56 - 1.00) = 0.93, or 7% thinner.

    We won't use finished blanks for plus hence the diameter makes no difference.

    Flatter curves reduce the thickness, weight, and sag depth (less bulbous, reduced vertex), but some folks reject the change due to spatial perception issues, especially older, long term wearers of non-aspheric lenses, primarily with hyperopes.

    Hope this helps,

    Robert Martellaro
    I’m finding this out all too well at my new job. We see a lot of kids with +7.00 or higher. I make them flatter hoping that kids are adaptive but to no avail.

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