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Thread: Aspherical to Spherical switch point

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    Aspherical to Spherical switch point

    Hi everyone. I have a quick question, we do edging in office and I've been noticing that sometimes our aspheric stock lenses are causing the temples to bow. Any suggestions on when we should order spherical lenses instead?

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    What's up? drk's Avatar
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    I'm not a lab guy, and I don't know the answer.

    Can I chime in, so I can learn?

    You are saying that the faceform of the frame is flattened in some cases when you use too flat a front surface (aspheric) lens?

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    Yes, the faceform flattens out and the temples go from parallel to angled inward toward the front.

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    What's up? drk's Avatar
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    Here's my rough guess.

    Each frame has a range of base curves that will fit it. Probably from about +2.00 to +8.00.

    I would imagine that metal frames are the least forgiving. I would imagine plastic frames are the most forgiving.

    I think you have to do a "Sophie's Choice" when you are presented with a job to make that is a mismatch: a. keep the frame, change the base, or b. keep the base, change the frame.

    Now, you have an optical that is making those choices...I would imagine you tell the optician: in extreme cases, pay attention to the frame choice.


    As to your lens inventory, I would suppose that you chose too many aspherics and not enough spherical lenses. I think you probably should stock spherical and order aspheric, not the other way around. Let's see what the experts think.

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    If your edger allows you to customize your bevel, try to match the base curve of your bevel to match the frame.

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    Master OptiBoarder OptiBoard Silver Supporter lensmanmd's Avatar
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    This is not just a phenomena that occurs with aspheric lenses. I would venture a guess that this also happens with spherical lenses on acetate frames. I will agree with Alex Camblor, and will take it one step farther. Along with curve matching the frame, if your edger has the capability, add a 5 degree taper as well. If using an Optronics edger, the 5 degree taper body and blades are available.
    The taper, or angled bevel, will reduce the bevel area that comes in contact with temporal edge of the frame, in turn, reducing the amount of splay.
    If the taper bevel is not an option, then a slight step will also work, if your edger has this capability as well.
    If none of these options are available, then use a bevel curve option. These are available on most edgers.
    I bend light. That is what I do.

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    Santinelli variable bevel functions have changed my ability to finish acetate/tr90/plastic frames by a huge margin. Other wise what I used to do on my LE9000 was take a little off the back on a hand wheel or with sandpaper, that works very well also, but a computer controlled variable bevel is so much better its hard to describe. Took me about 6 months to really master it, and no more squeaking frames either when you can perfectly match the bevel width to the frame's.

    Also don't discount that some people are used to / prefer asphericity in their lenses. Taking that away can lead to less satisfaction (as can adding it to some people). Backside freeform aspheric lenses should also be on the table when altering basecurve for frame fit, obviously there is a cost associated with this, but there are costs associated with dissastisfied patients/clients also.
    Last edited by Tallboy; 07-24-2019 at 11:08 AM.

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    Quote Originally Posted by Alex Camblor View Post
    If your edger allows you to customize your bevel, try to match the base curve of your bevel to match the frame.
    Also note that with very flat lenses vs frames, this procedure causes thickness to be pushed out front on the temporal side (and nasal depending on decentration).

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    Quote Originally Posted by Oscar View Post
    Also note that with very flat lenses vs frames, this procedure causes thickness to be pushed out front on the temporal side (and nasal depending on decentration).
    This is where experience and practice comes into play. This will apply to both the nasal and temporal corners, BTW. Most acetates are 3-5 curve, but with .50BC lenses, this can get tricky. 3 curves are typically no-brainers, but 5 can be a pain. Splitting the difference and using 3 will yield good results. My go-to is 3 with a 1.2 front bevel. Works well on the 7EX and the MEI.
    I bend light. That is what I do.

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    One eye sees, the other feels. OptiBoard Gold Supporter
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    Quote Originally Posted by Rhone View Post
    Yes, the faceform flattens out and the temples go from parallel to angled inward toward the front.
    A significant decrease the wrap angle after insertion, possibly due to flat BCs, should increase the temple spread angle (outwards). The opposite is true for steeper BCs, which I see much more commonly, probably because contemporary frames are design for fairly flat BCs.

    A routine bench adjustment (roughly match the POW measurements if provided) is required at this point in the fabrication process.

    Some endpieces are upset by thick edges (higher minus or BO prism), requiring some type of step bevel too prevent the spread angle from significantly increasing (outwards).

    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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    Quote Originally Posted by Oscar View Post
    Also note that with very flat lenses vs frames, this procedure causes thickness to be pushed out front on the temporal side (and nasal depending on decentration).
    When I can foresee lens mounting issues, I will use a guided variable bevel like tallboy mentioned. My LEX1200 variable bevel defaults to 0.8mm front/1.0 and 0.3mm wide and it works really well most of the time but sometimes I will make minor tweaks to the settings depending on what the bevel layout is showing me i.e pushing bevel forward or back.

    I have done lots of trial and error with the variable bevel and it has been a huge improvement for me and I feel like we have much less issues with frames falling out of adjustments, etc. I also specify base curves 100% of the time when ordering uncuts.

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    Quote Originally Posted by Alex Camblor View Post
    When I can foresee lens mounting issues, I will use a guided variable bevel like tallboy mentioned. My LEX1200 variable bevel defaults to 0.8mm front/1.0 and 0.3mm wide and it works really well most of the time but sometimes I will make minor tweaks to the settings depending on what the bevel layout is showing me i.e pushing bevel forward or back.

    I have done lots of trial and error with the variable bevel and it has been a huge improvement for me and I feel like we have much less issues with frames falling out of adjustments, etc. I also specify base curves 100% of the time when ordering uncuts.
    At least you understand the science behind base curves. I have seen many people demand a 2 base to fit a flat frame when the rx is +8.00

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    A good example of a 1.25 BC lens in a 4.5 Z frame. 3.5 curve with a 1.2 bevel on a 7EX with a 5 degree taper body. Nothing sticks out front, very little on the back of a -6. Good frame for the RX
    Cold mount. No splay. 4pt without any adjustments.
    Click image for larger version. 

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    I bend light. That is what I do.

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    Oh snap lensman wants to start posting glasses pics. ;)

    Show it to me from the front, the side that matters!

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    TB. I’ve already shipped it. Same day turn w/AR. Here is an alternative view, though.

    Click image for larger version. 

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    Last edited by lensmanmd; 07-25-2019 at 12:32 AM.
    I bend light. That is what I do.

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    What's up? drk's Avatar
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    Nice.

    So the gist of this thread is that, after choosing the right base curve for the power (and considering a little fudge here or there), that bevel customization is the most powerful tool?

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    Bingo, doc.
    I use photography as an analogy. DSLRs are powerful tools. Takes great shots on Auto, but once you go Manual, a whole new level of creativity and control awaits.
    I bend light. That is what I do.

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    This will show that I pretty much fart dust. All you Old timers will understand.
    Guided bevels are nothing new. The technology in today’s CNC edgers just makes it easier.
    I still remember training bench techs on using the pan hard rod. What? It isn’t just form rimless? Ha!
    Weco 440. The pan hard rod was an analogue version of guided bevels! Do I miss it? Heck no, but I still know how.
    I bend light. That is what I do.

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    Quote Originally Posted by lensmanmd View Post
    This will show that I pretty much fart dust. All you Old timers will understand.
    I think you're at fossil fuel level

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    1.67, 1.5 nominal basecurve aspheric in a 5 base frame, no splay.

    Girl wouldn't wear her glasses for the last 3 years she got somewhere else because she hated how they looked, here they look better. And no I didn't do 1.67 and poly, even though my employee ordered it that way



    Attached Thumbnails Attached Thumbnails fmIiU2M.jpg  
    Last edited by Tallboy; 07-25-2019 at 03:25 PM. Reason: edit

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    TB, this is a tough one. -4.5 and -0.5. Until she gets over her RX, not much you can do. Nothing that even a custom bevel can overcome. See it all the time here.
    Not to be too anal, but the OD looks a tad twisted compared to the OS. Could be the angle that I’m seeing through.
    I bend light. That is what I do.

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    lt was, unfortunately these lux frames often come into the shop out ofbench, I fixed it. Thanks for noticing.;)

    And yeah its a doozy, at least she's young

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    OD A mx looks a lot longer than OS? Could be the angle of the picture.

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    Quote Originally Posted by Oscar View Post
    OD A mx looks a lot longer than OS? Could be the angle of the picture.


    Must be the angle measured out perfect on graph paper, man I need to clean it up and call the dad now :) the frame has a weird curve on the top and bottom, I don't buy lux frames anymore, but this is how it looked when I got it in the lab, I guess its how it came from Lux to us.

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    Master OptiBoarder OptiBoard Silver Supporter lensmanmd's Avatar
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    That's the tough part about posting pics here....too many critics!
    We are what we are. Better to have vocal critics than silent critics, I say....
    BTW, did I mention how much I dislike LUX frames?
    I bend light. That is what I do.

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