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Thread: Calculating Lens Thickness

  1. #1
    Rising Star McAnerin's Avatar
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    Confused Calculating Lens Thickness

    I know the Opticampus site, among others, have various lens thickness calculators on them, however, I am interested in making one of my own, as a pet project, and to better understand the math. So far, I am able to calculate with a relatively small margin of error minus powered spherical lenses. However, as I frequently deal with sphero-cyls and hyperopes, the math falls apart anytime I have to give it a number that I actually DO want an answer for.

    So the question is -

    I'm looking for a formula to approximate the thickest (edge on a minus, and centre on a plus) portion of lens given a sphero-cylinder power. I will leave the example that broke my calculator:

    Frame - A: 53 ED: 54 DBL: 16
    PD - 62
    Sphere +4.00
    Cylinder -5.00
    Axis 179
    Minumum ET/CT - 1.5mm

    This combo whomped my calculator for some reason, resulting in a read of only the minimum thickness, which I'm using 1.5mm for.

    Any math whizzes have a formula?
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  2. #2
    OptiWizard
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    Calculating the thickness can get quite complicated especially with progressive lenses. To keep it simple and have a reasonable result you need the axis of the ED then determine the curves at that axis and calculate the thickness. Do the same at 90 and 180. Which ever result is the highest will be the thickness. This will only work for non progressives.

  3. #3
    Master OptiBoarder
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    I use this text book when teaching Optical Math.

    Optical Formulas Tutorial - 2nd Edition (elsevier.com)

    Click image for larger version. 

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  4. #4
    Master OptiBoarder lensgrinder's Avatar
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    Follow this link
    I used polycarbonate on an 8.00 BC to obtain the values.
    When using the approximate thickness formula, you should put this through a while loop to get a more accurate value.

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