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Thread: I need a reference resource.

  1. #1
    What's up? drk's Avatar
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    I need a reference resource.

    A. Is there anything on line that will give the approximate best-form base curve based on lens power?
    B. If it could vary by material, that would be quite nice.

    The reason: the VSP lab made a pair of -1.00 D poly lenses for a zyl frame with a +4.50 base, but the front keeps flattening and the glasses fall off.

    I'm going to try to remake on a steeper curve, and 1.) I don't know if +6.00 is unreasonable, and 2.) I don't know if +4.50 is corrected curve.

    Any help on either of these?

  2. #2
    Master OptiBoarder OptiBoard Gold Supporter Judy Canty's Avatar
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    Deleted.
    Last edited by Judy Canty; 10-01-2015 at 10:28 PM.

  3. #3
    One eye sees, the other feels OptiBoard Silver Supporter
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    Quote Originally Posted by drk View Post
    A. Is there anything on line that will give the approximate best-form base curve based on lens power?
    B. If it could vary by material, that would be quite nice.
    http://www.opticampus.com/files/spectacle_optics.zip

    The reason: the VSP lab made a pair of -1.00 D poly lenses for a zyl frame with a +4.50 base, but the front keeps flattening and the glasses fall off.

    I'm going to try to remake on a steeper curve, and 1.) I don't know if +6.00 is unreasonable, and 2.) I don't know if +4.50 is corrected curve.
    A +6 to +20 is best form for a poly -1.00 D for a spherical design, with less than .07 D of oblique astigmatism, rising to .11 D with a +4 base. Aspheric designs must use the base curve recommended by the lens manufacturer. An aspheric poly -1.00 D would probably be placed on a +2 to +4 base, depending on the degree of asphericity.

    You might want to pull that frame from your display if it can't hold a thin, low minus Rx!

    Hope this helps,
    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.



  4. #4
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    Quote Originally Posted by drk View Post

    I'm going to try to remake on a steeper curve, and 1.) I don't know if +6.00 is unreasonable, and 2.) I don't know if +4.50 is corrected curve.

    Any help on either of these?
    In a situation as described, measure FBC and order the appropriate design Attitude and VSP has a design for FFSV Unity X or extreme (something like that) for frames with +6 and +8 BC.
    I didn't attend the funeral, but I sent a nice letter saying I approved of it. Mark Twain

  5. #5
    Compulsive Truthteller OptiBoard Gold Supporter Uncle Fester's Avatar
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    I'd push a change to trivex on the 6 base. It's stiffness really helps keep the frame shape in low powers and of late it's my material of choice to proactively deal with this issue.

    Works great on Silhouette's new ultra thin expensive semi rimless frames.
    Last edited by Uncle Fester; 09-03-2015 at 04:47 PM.

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    Master OptiBoarder OptiBoard Gold Supporter
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    Also know that there will be an extra charge to you for any lenses ordered with a specified base curve. Even if your base curve makes more sense than the one they chose, thus is the will of VSP.

  7. #7
    O.D. Almost Retired
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    Quote Originally Posted by drk View Post
    A. Is there anything on line that will give the approximate best-form base curve based on lens power?
    B. If it could vary by material, that would be quite nice.

    The reason: the VSP lab made a pair of -1.00 D poly lenses for a zyl frame with a +4.50 base, but the front keeps flattening and the glasses fall off.

    I'm going to try to remake on a steeper curve, and 1.) I don't know if +6.00 is unreasonable, and 2.) I don't know if +4.50 is corrected curve.

    Any help on either of these?
    6 would be reasonable in my opinion, but if the "front keeps flattening" that may be because the bevel has too flat a curve on it rather than the base curve being too flat. Ask them to steepen the bevel curve to match whatever curve the frame has (of course you'll want to remove the lenses and restore the desired frame curvature and do not remount those lenses in there or you'll just re-flatten the frame).

  8. #8
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    Time to invest in an edger that you can specify the curve of the bevel and add or remove size from the shape....Have you noticed on their unity stock lenses you can get a +1.50 on a 3bc and a -3.50 on a 4 bc?? that bugs me...

  9. #9
    What's up? drk's Avatar
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    Thank you, all.

  10. #10
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    Most zyls are a 4 base so the lens should fit if sized properly. There is a problem but it is probable not the bc of the lens but the tracing and the edging is off enough to push the lens out of the groove.

    We match all lens curves to frame curves and cut them to match if it is at all possible.

  11. #11
    Master OptiBoarder AngeHamm's Avatar
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    Don't forget the extreme importance of knowing your frame stock as well. You'll get a lot of patients with extreme prescriptions who just have to have a frame whose material, shape, or mounting style is fairly-to-completely wrong for it. Be prepared to adjust base curves to suit, and educate your patients on the compromises they should expect.
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  12. #12
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    Quote Originally Posted by Tallboy View Post
    Also know that there will be an extra charge to you for any lenses ordered with a specified base curve. Even if your base curve makes more sense than the one they chose, thus is the will of VSP.
    Ew, Really?

  13. #13
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    Quote Originally Posted by optilady1 View Post
    Ew, Really?
    Yes it will either be charged to you by "oversized lens" (2799 code I believe)

    I found this out by calling to find out why a pair of sunglasses I ordered which were 58 mm in the A measurement with 4 mm of decentration I was charged for "oversized lenses" this was because I specified 4 base lenses so they would match the lens in the frame.

  14. #14
    Master OptiBoarder MakeOptics's Avatar
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    Quote Originally Posted by drk View Post
    A. Is there anything on line that will give the approximate best-form base curve based on lens power?
    B. If it could vary by material, that would be quite nice.

    The reason: the VSP lab made a pair of -1.00 D poly lenses for a zyl frame with a +4.50 base, but the front keeps flattening and the glasses fall off.

    I'm going to try to remake on a steeper curve, and 1.) I don't know if +6.00 is unreasonable, and 2.) I don't know if +4.50 is corrected curve.

    Any help on either of these?
    http://makeoptics.com/harrychiling/b...ess-calculator

    DONE - It calcs but doesn't show, I will change that this week.
    Last edited by MakeOptics; 09-08-2015 at 07:41 AM.
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