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Thread: My project

  1. #1
    What's up? drk's Avatar
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    My project

    I would like your input on a project I'm going to undertake:

    "The comparison of different lens materials"

    I would like to compare thinness, weight, optical clarity, and price.

    For thinness, I think the factors involved are only index, min CT allowable, and asphericity.

    For optical clarity, the only abberration we have information on is chromatic abberation. I assume because this is the only variable between materials, and other abberrations are constant.

    For price, I would get some small sample of prices from wholesale labs.

    For weight, I would have to compare a value that includes specific gravity and thickness.

    My goal is to have an ordinal scale with those characteristics. Then, I'd like to combine characteristics into more "real world" profiles of the lens materials, such as:

    Thinnest and lightest
    Thinnest and best optics
    Lightest and best optics
    Thnnest and lightest and cheapest

    probably by giving the lenses a weighted average of the base rankings.

    Any input? Thank you.

  2. #2
    Objection! OptiBoard Gold Supporter shanbaum's Avatar
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    Quote Originally Posted by drk

    For thinness, I think the factors involved are only index, min CT allowable, and asphericity.
    "Asphericity" is not a property of materials.

  3. #3
    What's up? drk's Avatar
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    Quote Originally Posted by shanbaum
    "Asphericity" is not a property of materials.
    Quite true. More correctly, I should say I'm comparing lens designs. Thanks.

  4. #4
    OptiBoard Professional RT's Avatar
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    You'll probably need to specify some Rx ranges, and quite possibly the type of mounting (drill, groove, hide-a-bevel, etc.). Why? Some mountings have minimum EDGE thickness requirements--grooves have to have an edge at least as thick as the nylor line. In order to achieve that edge thickness may require bumping the minimum CENTER thickness in higher indices, on lower powers.

    That is to say, I can easily engineer a case where the highest index is not the thinnest lens. In fact, I can easily engineer a case where all materials have the same edge thickness, but the lower index lenses have thinner centers! In that strange case, the lower index lens would actually be lighter, even if the specific gravity were identical to the high index lens. But start bumping up the power, and the results reverse.

    You may be disappointed if you're looking for absolute answers.
    RT

  5. #5
    What's up? drk's Avatar
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    RT,

    Thanks for the imput. I'm inferring that you have software that will calculate, based on parameters input, the best material?

    If so, why can't we get it at the clinical level?

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    Quote Originally Posted by drk
    Quite true. More correctly, I should say I'm comparing lens designs. Thanks.
    To this point, once you start comparing lens designs you open the aberation can of worms. There are some lenses produced well and others produced less well, this will result in aberation as a function of manufacturing error. The best way to measure this is by power maping but this is costly and time consuming. I suppose you have to draw a line somewhere but I don't know where.

  7. #7
    OptiBoard Professional RT's Avatar
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    Drk: I don't have such software. Lab software will calculate the intended edge and center thickness for each job, but is designed to produce the instructions necessary to fabricate the job. It assumes that you've picked the material. If you're really on the fence on a job, your lab's Customer Service people can probably give you some results on the phone that will help with your decision.

    I have seen remote ordering systems that allow you to compare the edge thickness of various materials given the Rx, frame trace, and frame type. These systems don't typically suggest a material, but rather allow you to compare. Not sure if such systems typically caclulate weight of the lens, which was another factor in your question.

    You'd probably also want to factor in price. Are you willing to pay 20% to get 10% thinner? How much would you pay to get 0.2 mm thinner on the edge? In some cases, the answer is probably "Zero". In others, the patient may insist on the absolute thinnest, and cost be damned.

    What you'll probably end up with is a two-dimensional table, where you have powers in one dimension, materials in the other, and the values would be your ordinal score. The best material for a -1.00 may not be the best material for a -8.00.
    RT

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