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Thread: Stress in 1.67 Lens...

  1. #1
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    Stress in 1.67 Lens...

    Hello...

    I work for a national chain... I won't say which one as I don't wish to start a flame war... anyways, I quite simply no longer trust my in-store lab and no longer wish to have my eyewear made by them. I have never purchased a pair of glasses from my store that has not had to be remade. Sad, no?

    Anyways, I am mostly one-eye dominant (one eye is amblyopic and of not much use to me) and I'm at about a -4.00 -1.75 in my good eye. With just one good eye, any tiny little minute error bothers the hell out of me.

    I'm currently dealing with a pair of glasses that will be going into a third remake. My lab had issues getting my PD correct first. The first two times I was in aspheric polycarb and this time I decided to go for 1.67's with a premium AR to get away from any distortion I might have been experiencing in the poly.

    Still, I cannot see clearly unless I look out towards the right edge of my lens. My first thought was that my lab jacked up my PD once again. But the PD is dead on this time. So I put my lenses under the polariscope. I was horrified! You should see the amount of stress in these lenses. There is an area offset towards the right (right about where I look to see clearly) where there is nearly no stress at all.

    Here's my question... am I crazy? Should there be all this stress in a 1.67 lens... and would it even really affect the way I'm seeing out of the lens? I talked to my GM about it over the phone and he seems to have no idea what I am even talking about. I told him I want my glasses remade at another store because I no longer trust my lab, as they have screwed up so many of my glasses (and every single pair of my mother and sisters' glasses as well that they have ever purchased), and he said he needs another lab manager from another store to take a look to see what I'm talking about... like he does not believe me. Am I crazy? Does anyone have any thoughts on stress in a lens and how it affects the optics?

    Thanks!
    Last edited by co_mac; 11-06-2007 at 07:58 PM. Reason: trying to remain anonymous

  2. #2
    ATO Member HarryChiling's Avatar
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    It's possible to get stress in any lens material, if it was edged too big, you'll get stress in the lenses. If you are looking to eliminate the "distortion in poly" if you are talkign about the chromatic aberration then try a 1.60 or Trivex. If you are talking about the stress present in poly from the injection molding process then you could always go with resolution lenses as they have less stress in them, but when a poly lens is edged down to correct size the edging process releases some of that stress. Have you mentioned to the optician that's measureing you that your are amblyopic? Do they know what amblyopia is? How did they measure the PD? Have you asked your lab to allow you to edge your own lenses?

    It might be worth going to an independent optical shop in your area that someone here may recommend.
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  3. #3
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    Remove lenses from frame. Inspect for stress. If not present, put lenses back in frame mark stressed areas. Grind off by hand a little at a time in each stressed spot until all stress releaved. This used to be standard practice in mounting glass lenses.

    Chip:cheers:

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    Bad address email on file yks-7's Avatar
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    One has to remember that tension is normal in mounted lenses, because thats what keeps them from falling out . Yes in the old days you could hand edge out a spike or two of pressure, but if you use the polarascope with a lens and squeeze it, you will be amazed at how much distortion you can create. Look at string frames would you accept one loose ? because thats the way you will have no stress with them! As far as the stress in CO MACs' lens I would look at how much abberation was created in surfacing, also question whether its an aspheric or spherical design. in our shop the 1.67 lens will show us production probs (temps pads water/polish flow etc) right away. Just my 2 p
    Don

  5. #5
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    if your Rx is -4.00 -1.75, get a stock 1.60 lens. Higher ABBE, just as thin. My guess is a surfacing problem, too. Poly and 1.67 is where we see this.
    Is it because of the low abbe, or because these lenses are less tolerant to heat, pressure, humidity, etc in the lab? I don't know; I have no experience w/ surfacing. But that is what I see when dispensing.

  6. #6
    Allen Weatherby
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    Problem with Lab and Stress???

    Quote Originally Posted by MarcE View Post
    if your Rx is -4.00 -1.75, get a stock 1.60 lens. Higher ABBE, just as thin. My guess is a surfacing problem, too. Poly and 1.67 is where we see this.
    Is it because of the low abbe, or because these lenses are less tolerant to heat, pressure, humidity, etc in the lab? I don't know; I have no experience w/ surfacing. But that is what I see when dispensing.
    I would agree with MarcE on this. The 1.60 42 abbe stock AR lens, then you are not faced with worrying about the surface quality.

    You also may have the Rx checked to make sure you are not trying to fit a round peg into a square hole.

    I doubt that the problems you have experienced were stress related.

  7. #7
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    Blue Jumper Stress...................

    Some plastic materials will show stressed areas under a polariscope without having been cut or suffer stress from tension mountings.

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    Another point of view

    I was reading your initial post on this thread and a question pop into my mind: Which side is your "good eye"?


    There are three things you should keep separated: stress, chromatic dispersion and power aberration.

    Stress on a 1,67 material is quite common and, in general, pain free since it is necessary a lot of stress to induced deformations that suffice to produce image distortion. On poly, with a dispersion index elevated (or abbe number lowered, since they are the inverse of each other) and under special circunstances, the stress induce distortion and the high chromatic dispersion could add up an produce visivel and discomforting signs.

    But the reason why I was wonder which is your "good eye" is because all lenses have power aberrations that increase with diameter (allow me this inaccurate by incompletion statement, just for the sack of this argumentation). So, if your prescription is not ajusted to you and by chance the right side of the lens produces aberration that compensate your remaining refraction error, I would say exactly what you was saying in the initial post.

    Resuming, if i was to bet, my horse would be "prescription".:D

  9. #9
    OptiBoard Professional jrumbaug's Avatar
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    "I cannot see clearly unless I look out towards the right edge of my lens."

    Have you refraction confirmed. When I run into people that only see good out of a small spot of the lens, it tells me they don't like the prescription that is in most of the lens.

    Jim Rumbaugh

  10. #10
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    Hey Jim,

    Welcome to Optibaord!


    :cheers::cheers::cheers:

  11. #11
    Master OptiBoarder mshimp's Avatar
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    Have you put the lens into an optical oven at 190 degrees for 15 min to destress the lens. At times chucking pressure can "wave" or "warp" the lens.

  12. #12
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    Quote Originally Posted by Fezz View Post
    Hey Jim,

    Welcome to Optibaord!


    :cheers::cheers::cheers:

    Good to see ya here, Jim - about time. I've know Jim for...heck, almost 30 years! We used to be co-workers.

    And Jim- It's always Fezz's fault!:D:D:D
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