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Thread: Question about Tscherning Ellipse

  1. #1
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    Question about Tscherning Ellipse

    Let’s say I got wild one day and decided to order a +2.00 sphere on an 8 base the way that is recommended on the ellipse. If I then order an aspheric design, will the increase in curvature enhance the performance of the lens or cancel out the aspheric benefits (or turn them into optical errors)? Would the asphericity change based on the modification to the base curve?

    i suppose the question is only for dual surfaced single vision.

    can somebody please clear this up for me?

  2. #2
    One eye sees, the other feels. OptiBoard Gold Supporter
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    Quote Originally Posted by Jaketull View Post
    Let’s say I got wild one day and decided to order a +2.00 sphere on an 8 base the way that is recommended on the ellipse. If I then order an aspheric design, will the increase in curvature enhance the performance of the lens or cancel out the aspheric benefits (or turn them into optical errors)? Would the asphericity change based on the modification to the base curve?

    i suppose the question is only for dual surfaced single vision.

    can somebody please clear this up for me?
    It would increase aberration off-axis. "Best form" or "corrected curve" lens shapes ideally have about the same vision at the center as in the periphery, as the eye tracks across the lens.

    Flattening the lens away from best form shape reduces the thickness and weight slightly, and provides a nicer looking profile for plus powered lenses, but will increase off-axis aberration. The workaround is to introduce asphericity or atoricity (for astigmatism) to correct for this error.

    Follow the manufacturer's charts carefully when utilizing semi-finished blanks- deviation from their recommended values can introduce significant aberration.

    See:

    https://www.2020mag.com/article/choosing-base-curves

    Comprehend and commit to memory:

    http://opticampus.opti.vision/cecour...l=lens_design/

    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

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