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Thread: I think Zeiss is now in a very good position for a change.

  1. #26
    Compulsive Truthteller OptiBoard Gold Supporter Uncle Fester's Avatar
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    The smoke continues to flow from my ears and obscures the room.

    Can you dumb this down for the mathematically challenged?

  2. #27
    Master OptiBoarder lensgrinder's Avatar
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    Quote Originally Posted by Uncle Fester View Post
    The smoke continues to flow from my ears and obscures the room.


    Can you dumb this down for the mathematically challenged?



    In order for a lens to be free from astigmatic blur at all gaze angles light should come to a point focus on the far point sphere(center of rotation - focal length of the lens). This imaginary sphere is used as a reference point. If light focuses behind or in front of the sphere the lens will not be clear. You may have experienced this when a wearer looks in the periphery and states it is not as clear as it is in the center.
    Dr Marius Tscherning discovered that two forms exist where a lens will be free from astigmatism(each one of these forms had been previously discovered independently by Ostwalt and Wallaston). For example a -5.00 that is 2 mm thick with a 27 mm center of rotation in CR-39 should be placed on either a 16.73 D BC or a 4.64 D BC. If you change the power to -4.75, this changes the two base curves to 16.84 D and 4.78 D. Based on Tscherning's work the ZIESS Punktal and AO's Tillyer lens were created.
    Corrected curve theory is based on Tscherning's ellipse. Corrected curve theory groups powers that will have a certain amount of astigmatism in a series of base curves.
    As our focus changes the far point sphere becomes the near point sphere, which will require a new form to be free from astigmatism.
    FFSV lenses corrects the astigmatism for each gaze angle in the distance portion, however, in the past they did not correct the astigmatism produced at near.


    I hope this helps.

  3. #28
    OptiBoard Apprentice Lawman Nick's Avatar
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    *edit*

    nevermind, question answered. Please delete
    Last edited by Lawman Nick; 06-22-2020 at 03:16 PM. Reason: I'm a big ol' bonehead

  4. #29
    Compulsive Truthteller OptiBoard Gold Supporter Uncle Fester's Avatar
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    Thanks- this did help with a second closer reading of drk's always erudite posts.

    If this came to me easily I very much doubt I would be an optician.

    I still get nervous selling something that seems to fix for most what isn't broken. or seemingly they didn't know it was broken until I'm selling it.

    Too often I fear the what if- such as when a patient gets switched to the latest and greatest and expects immediate results only to return later asking for a redo (and worse, refund) for the more expensive lenses.

    So I often qualify the change with a proverbial "your results may vary".

    With the right patient who doesn't like the change I've even lightened the mood with a "Who are you going to believe? The optical engineers or your own d*amn eyes!"

  5. #30
    Master OptiBoarder AngeHamm's Avatar
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    Quote Originally Posted by Uncle Fester View Post
    Too often I fear the what if- such as when a patient gets switched to the latest and greatest and expects immediate results only to return later asking for a redo (and worse, refund) for the more expensive lenses.
    I'll take "Varilux S Design" for a thousand, Alex.
    I'm Andrew Hamm and I approve this message.

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