Page 1 of 2 12 LastLast
Results 1 to 25 of 42

Thread: Has anyone attempted an ophthalmic...

  1. #1
    Eyes eastward... Uilleann's Avatar
    Join Date
    Jan 2007
    Location
    Utah
    Occupation
    Dispensing Optician
    Posts
    3,237

    Has anyone attempted an ophthalmic...

    ...achromatic doublet lens? Just thinking back to my much more active astro days, and wondered if anyone had been brave and tried working out any sort of viable achromat doublet type design in ophthalmic plastics as opposed to glass? Not sure if the weight/thickness would make them commercially viable. Or the cost. Or even if the slight (i assume) increase in chromatic clarity would even be appreciated by a typical human eye in average spectacle viewing scenarios.

    Just wondering out loud. :D

    Bri~
    :cheers::cheers::cheers:

  2. #2
    Banned
    Join Date
    Jul 2010
    Location
    St. Cloud, Minnesota
    Occupation
    Ophthalmic Technician
    Posts
    3,089
    Aye yup. We made achromats all the time, using crown and hilite (1.70) or 1.80 index glass.

    Plastics and polycarbs don't work because of the difference in coefficients of expansion. Any temperature change (walking out into 90+ from airconditioning or from 72 inside to -30 outside) usually pulls the lens elements apart. We tried about 60 different UV cements from about every manufacturer we could, and only one batch from one supplier met the test. And the next batch of the same glue failed.

    Benson Optical (Minneapolis) back in the 80's (?) had a process to laminate a thin layer of plastic on the back of a glass lens.

    The biggest problem is, as you mentioned, thickness.

  3. #3
    Master OptiBoarder rbaker's Avatar
    Join Date
    May 2000
    Location
    Gold Hill, OR
    Occupation
    Other Optical Manufacturer or Vendor
    Posts
    4,401
    The benifits, if indeed any, would be far exceeded by the difficulty of finding someone to fabricate the darn things, the cost and delivery time. It would also present an interestig challange when the customer came back in a few weeks and wanted the scratched lenses replaced at no charge. I guess its just too muuch hassle for what it's worth.

    I'll also bet you that not one out of a hundred people selling glasses would know what you were talking about these days.

  4. #4
    Master OptiBoarder Darryl Meister's Avatar
    Join Date
    May 2000
    Location
    Kansas City, Kansas, United States
    Occupation
    Lens Manufacturer
    Posts
    3,700
    I second that opinion. Since an achromatic doublet would be relatively thick anyway, you'd probably be better off just sticking with a single, lower index lens material with a high Abbe value if optics are the biggest concern, especially once you factor in cost and delivery time. In most prescriptions, I doubt that the subtle difference in optical performance between an achromatic doublet lens and a high-Abbe lens would merit the cost and inconvenience to the patient. High-index materials with relatively high Abbe values, like MR-8 1.60, are available now as well, so there is less need to compromise optics for cosmetics nowadays.

    Best regards,
    Darryl
    Darryl J. Meister, ABOM

  5. #5
    Rochester Optical WFruit's Avatar
    Join Date
    Nov 2007
    Location
    Rochester, NY
    Occupation
    Optical Wholesale Lab (other positions)
    Posts
    1,273
    For those who don't know: http://en.wikipedia.org/wiki/Achromatic_lens

    And yes, I will admit to having to look it up to find out what they were. But I learned something new, so that's ok.
    There are rules. Knowing those are easy. There are exceptions to the rules. Knowing those are easy. Knowing when to use them is slightly less easy. There are exceptions to the exceptions. Knowing those is a little more tricky, and know when to use those is even more so. Our industry is FULL of all of the above.

  6. #6
    Underemployed Genius Jacqui's Avatar
    Join Date
    Oct 2003
    Location
    Frostbite Falls, Mn.
    Occupation
    Optical Wholesale Lab (other positions)
    Posts
    7,417
    I've seen them, made a couple of pairs way back when. I think I'll agree with Darryl (surprising) on this.

  7. #7
    Master OptiBoarder Striderswife's Avatar
    Join Date
    Sep 2006
    Location
    USA
    Occupation
    Dispensing Optician
    Posts
    934
    Very, very cool. I also had not ever heard of this, and I don't know that I would have the opportunity to do anything with this new knowledge, but thanks! Thank you, WFruit, for the Wiki link!
    It's nice to be important, but it's more important to be nice.

  8. #8
    ATO Member HarryChiling's Avatar
    Join Date
    Apr 2005
    Location
    Nowhereville
    Occupation
    Other Eyecare-Related Field
    Posts
    7,765
    Dragonlensmanwv still makes doublets he sent me one a few years back it was made of glass, contact him for more info on fabrication.

  9. #9
    Master OptiBoarder OptiBoard Silver Supporter Barry Santini's Avatar
    Join Date
    May 2000
    Location
    Seaford, NY USA
    Occupation
    Dispensing Optician
    Posts
    6,008
    Coddington vs Hastings triplet magnifiers also point up how to handle aberrations

  10. #10
    Master OptiBoarder OptiBoard Gold Supporter DragonLensmanWV's Avatar
    Join Date
    Oct 2006
    Location
    The Greatest Nation
    Occupation
    Optical Retail
    Posts
    7,645
    Quote Originally Posted by HarryChiling View Post
    Dragonlensmanwv still makes doublets he sent me one a few years back it was made of glass, contact him for more info on fabrication.

    Sorry, Harry, I did not make those, a commercial optical place here did those. My edging woman's husband made those.
    DragonlensmanWV N.A.O.L.
    "There is nothing patriotic about hating your government or pretending you can hate your government but love your country."

  11. #11
    One eye sees, the other feels OptiBoard Silver Supporter
    Join Date
    Jul 2002
    Location
    Wauwatosa Wi
    Occupation
    Dispensing Optician
    Posts
    5,458
    Quote Originally Posted by MikeAurelius View Post
    Benson Optical (Minneapolis) back in the 80's (?) had a process to laminate a thin layer of plastic on the back of a glass lens.
    I'd guess about 1983. The idea was to decrease the weight of glass lenses, primarily photochromics. I remember asking Keith West after his presentation if this was a gimmick (it's not a gimmick dammit!), and that I was lucky to still have a job the next morning.
    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.



  12. #12
    Master OptiBoarder Darryl Meister's Avatar
    Join Date
    May 2000
    Location
    Kansas City, Kansas, United States
    Occupation
    Lens Manufacturer
    Posts
    3,700
    Robert, I think you and Mike are talking about Corning's old "Corlon" laminated glass+plastic lenses, invented around 1982.

    Best regards,
    Darryl
    Darryl J. Meister, ABOM

  13. #13
    Eyes eastward... Uilleann's Avatar
    Join Date
    Jan 2007
    Location
    Utah
    Occupation
    Dispensing Optician
    Posts
    3,237
    In particular, I was wondering of a strictly plastic combination. I wasn't aware if it had been attempted in the past, or if it offered either A: noticeably improved optical characteristics, or B: the possibility of matching the thickness of a standard ophthalmic lens blank of a given power.

    Theoretical day-dreaming really is all. Interesting discussion though, me likey! :)

  14. #14
    Banned
    Join Date
    Jul 2010
    Location
    St. Cloud, Minnesota
    Occupation
    Ophthalmic Technician
    Posts
    3,089
    It could conceivably be done with plastic, but the coefficient of expansion (COE) would still have to be very close to the same for both materials. In glass, typically it doesn't matter because there really isn't any "give"; plastic would probably have to be within a 6 to 8 point difference depending on the flexibility of the cured cement. Additionally, you'd have to be sure that the materials can form (and hold) a very close curve, within about 6 to 8 newton rings. A best fit would be a center "contact" which would ensure that you could get any bubbles from the cement out between the two lens components.

    Our pass/fail test was to alternately freeze then place lenses in 80 degree water. Then warm the lenses up to 125 degrees to simulate sitting on a dash board, and placed in the freezer again. If the lenses can take 3 cycles of that, then they won't come apart.

    Edging can be problematic, I'm not sure the lenses could withstand a dry fly cutter, they probably would have to wet edged with a diamond.

  15. #15
    Banned
    Join Date
    Jul 2010
    Location
    St. Cloud, Minnesota
    Occupation
    Ophthalmic Technician
    Posts
    3,089
    YEAH!!! That was the stuff!!! Thanks Darryl

  16. #16
    Master OptiBoarder Darryl Meister's Avatar
    Join Date
    May 2000
    Location
    Kansas City, Kansas, United States
    Occupation
    Lens Manufacturer
    Posts
    3,700
    I don't see why you couldn't use two plastics. I did some quick "back of the napkin" calculations. Assuming negligible center thickness, given a specified back vertex power FV and a first lens F1 combined with a second lens F2 with Abbe values of v1 and v2, respectively, the power of the first and second lenses would need to be:



    and,



    In order to produce an achromatic doublet with the specified back vertex power. I haven't confirmed these calculations yet, but I'll try to do that tonight, unless someone finds similar formulas in a textbook or online in the meantime.

    Best regards,
    Darryl
    Last edited by Darryl Meister; 08-03-2010 at 10:06 PM. Reason: Sign error
    Darryl J. Meister, ABOM

  17. #17
    Banned
    Join Date
    Jul 2010
    Location
    St. Cloud, Minnesota
    Occupation
    Ophthalmic Technician
    Posts
    3,089
    It isn't the optics Darryl, it is the mechanical properties of the plastics.

  18. #18
    Underemployed Genius Jacqui's Avatar
    Join Date
    Oct 2003
    Location
    Frostbite Falls, Mn.
    Occupation
    Optical Wholesale Lab (other positions)
    Posts
    7,417
    What I keep wondering about is the adhesive. How will it affect the needed curves, etc.??

  19. #19
    Master OptiBoarder Darryl Meister's Avatar
    Join Date
    May 2000
    Location
    Kansas City, Kansas, United States
    Occupation
    Lens Manufacturer
    Posts
    3,700
    Quote Originally Posted by Mike
    It isn't the optics Darryl, it is the mechanical properties of the plastics.
    I provided the formula in case anyone here would ever care to try to make a doublet, not because I was under the impression that no one had tried it before simply because no one had "done the math." The formulas for glass doublets would be identical.

    Also, I do not agree with you that it is more difficult to laminate two plastics because of their mechanical properties than it is to laminate glass and plastic. In fact, low- and high-index ophthalmic plastics have very similar coefficients of thermal expansion and moduli of elasticity. Glasses, on the other hand, have significantly lower values for both, on an order of magnitude.

    This is one of the reasons that premium hard coatings often have colloidal silica added to the resin to increase compatibility with AR coatings. The addition of silica, the chief ingredient in glass, increases the hardness of the coating while serving as a intermediary buffer between the mechanical properties of the plastic substrate and the brittle, ceramic AR stack.

    Nor do I think that maintaining the correct curves with two plastic lenses is considerably more difficult than doing the same with a plastic and glass or even a two glasses combination. You will most likely have to use hard lap tools on one or both of the interface curves either way, which will minimize any errors due to lens casting. And the glue layer will fill in any difference, although this may influence the power calculations slightly.

    I should add that PixelOptics routinely sells laminated-like lenses made from combining a variety of plastics, including MR-7, Trivex, and polycarbonate.

    Best regards,
    Darryl
    Last edited by Darryl Meister; 08-03-2010 at 09:45 PM.
    Darryl J. Meister, ABOM

  20. #20
    Master OptiBoarder Darryl Meister's Avatar
    Join Date
    May 2000
    Location
    Kansas City, Kansas, United States
    Occupation
    Lens Manufacturer
    Posts
    3,700
    I verified my calculations. The combination of lenses described above should eliminate axial/longitudinal chromatic aberration.

    As a general rule of thumb, the power of the lens with the higher Abbe value will have to be stronger than the other lens by a factor equal to the ratio of the higher Abbe value to the lower Abbe value. So, if the first lens has an Abbe of 60 and the second lens has an Abbe of 30, the first lens must be 60/30 = 2 or twice as strong.

    Best regards,
    Darryl
    Darryl J. Meister, ABOM

  21. #21
    Banned
    Join Date
    Jul 2010
    Location
    St. Cloud, Minnesota
    Occupation
    Ophthalmic Technician
    Posts
    3,089
    Quote Originally Posted by Darryl Meister View Post
    Also, I do not agree with you that it is more difficult to laminate two plastics because of their mechanical properties than it is to laminate glass and plastic. In fact, low- and high-index ophthalmic plastics have very similar coefficients of thermal expansion and moduli of elasticity. Glasses, on the other hand, have significantly lower values for both, on an order of magnitude.
    That's fine with me, however, I've been laminating lenses since the early 1980's and have plenty of practical experience to back up what I'm writing about. If you go back and read what I wrote, I said that the two elements need to have COE's that are withing a couple of numbers of each other. Glass and plastic are far apart, and while a lamination may hold for a short time, it will not hold indefinately through a series of expansions and contractions. This is experience talking, Darryl, not theoretical hypothesis.

    Nor do I think that maintaining the correct curves with two plastic lenses is considerably more difficult than doing the same with a plastic and glass or even a two glasses combination. You will most likely have to use hard lap tools on one or both of the interface curves either way, which will minimize any errors due to lens casting. And the glue layer will fill in any difference, although this may influence the power calculations slightly.

    I should add that PixelOptics routinely sells laminated-like lenses made from combining a variety of plastics, including MR-7, Trivex, and polycarbonate.

    Best regards,
    Darryl
    I don't believe I wrote that it was difficult, I wrote that it was necessary. Both curves will have to be spun on a sphere grinder/polisher (not a cylinder machine) to maintain spherocity and eliminate induced cylinder. Glue will fill, but only up to a point. Glue needs to be a uniform layer throughout the contact area in order for it to function properly. Remember that the glue layer is only about 1/10th of a millimeter. Variations center to edge will cause weaknesses in the bond and lead to delamination. Again, this is hands-on experience speaking.

  22. #22
    Banned
    Join Date
    Jul 2010
    Location
    St. Cloud, Minnesota
    Occupation
    Ophthalmic Technician
    Posts
    3,089
    Quote Originally Posted by Jacqui View Post
    What I keep wondering about is the adhesive. How will it affect the needed curves, etc.??

    Most modern UV curing cements do not attack monomers/polymers unless the plastic is somehow suseptible to acetone. Most of the cements are based on some form of styrene and have other various components added to thicken or thin or increase/decrease bonding. As far as affecting curves, the cement itself has an index of refraction, but since the layer is so thin (usually about 1/10th of a mm) it has no effect on power.
    Last edited by MikeAurelius; 08-04-2010 at 08:28 AM.

  23. #23
    Underemployed Genius Jacqui's Avatar
    Join Date
    Oct 2003
    Location
    Frostbite Falls, Mn.
    Occupation
    Optical Wholesale Lab (other positions)
    Posts
    7,417
    Quote Originally Posted by MikeAurelius View Post
    Most modern UV curing cements do not attack monomers/polymers unless the plastic is somehow suseptible to acetone. Most of the cements are based on some form of styrene and have other various components added to thicknen or thin or increase/decrease bonding. As far as affecting curves, the cement itself has an index of refraction, but since the layer is so thin (usually about 1/10th of a mm) it has no effect on power.
    I think it would depend upon the Rx and how well the two elements fit.

    With modern casting methods, why can't a duplex be cast?? We did similar things with an Opticast system, so a large scale system should be able to handle a Cr-39 and 1.70 combination.

  24. #24
    Banned
    Join Date
    Jul 2010
    Location
    St. Cloud, Minnesota
    Occupation
    Ophthalmic Technician
    Posts
    3,089
    Quote Originally Posted by Jacqui View Post
    I think it would depend upon the Rx and how well the two elements fit.

    With modern casting methods, why can't a duplex be cast?? We did similar things with an Opticast system, so a large scale system should be able to handle a Cr-39 and 1.70 combination.
    Yes, as far as fit is concerned, it is a critical point. As I said the curves need to be very close, within 8 newton rings or so.

    I'm not familiar with casting duplexes, but what comes to mind immediately is the interface zone between the two materials. In order to meet the criteria of a doublet, one lens is biconvex one lens is biconcave. The interface zone between the two elements would have to be very tightly controlled or you lose the "doublet" math to correct for chromaticity.

  25. #25
    Master OptiBoarder Darryl Meister's Avatar
    Join Date
    May 2000
    Location
    Kansas City, Kansas, United States
    Occupation
    Lens Manufacturer
    Posts
    3,700
    Quote Originally Posted by MIke
    If you go back and read what I wrote, I said that the two elements need to have COE's that are withing a couple of numbers of each other. Glass and plastic are far apart, and while a lamination may hold for a short time, it will not hold indefinately through a series of expansions and contractions
    And if you go back and re-read my post and Uilleann's post, which you were responding to with your statement regarding laminated plastic, you may realize a couple of things:

    1. We were talking about laminating two plastics, after a brief discussion about laminating plastic to glass. He was not asking about laminating plastic to glass, but rather a "strictly plastic combination." So your own response to your last post actualy contracts your original response to Uilleann, which isn't necessarily the first time you've done that in these threads.

    2. Although your post actually implies that it is easier to laminate plastic to glass than plastic to plastic, which you now seem to contradict, I do agree with your most current assertion: Glass and plastic are "far apart," which is why half of my last post is dedicated to that very topic. So I'm not sure what you're attempting to argue with me about.

    That said, while I will continue to argue that there is nothing preventing anyone from laminating plastic to plastic, I do not agree with you that one cannot reliably laminate glass and plastic together.

    Glass laminated to plastic has been reliably used in many applications. Most notably, automobile windshields, which last for years and are subjected to extreme environmental conditions, are laminated. In the spectacle industry, glass+plastic lenses were often used prior to the widespread use of plastics, including glass polarized spectacle lenses, Corlon bonded photochromic lenses, Igard safety lenses, etcetera.

    Quote Originally Posted by Mike
    I've been laminating lenses since the early 1980's and have plenty of practical experience to back up what I'm writing about
    Judging by the majority of your posts, and the nature of your company for that matter, your experience seems to revolve primarily around glass. Further, if your laminated glass lenses "only hold for a short time," wouldn't that suggest that you simply have a great deal of experience at making poorly laminated lenses?

    Quote Originally Posted by Mike
    This is experience talking, Darryl, not theoretical hypothesis
    And, yes, from our previous debates, I am very well aware of the fact that many, if not most, of your posts rely on rather personal anecdote and conjecture, often of a somewhat dubious nature, not necessarily on scientific facts.

    Quote Originally Posted by Mike
    Yes, as far as fit is concerned, it is a critical point. As I said the curves need to be very close, within 8 newton rings or so.
    On a side note, I should add that very few of the eyecare professionals reading your posts are going to be familiar with Newton's rings or interference fringes, and even fewer will have a set of glass masters that they could actually use to measure them. The same goes for errors in wavelength. I would recommend, instead, referring to errors in surface sagitta (in millimeters) or curvature (in either diopters or reciprocal meters).

    Best regards,
    Darryl
    Last edited by Darryl Meister; 08-04-2010 at 10:35 AM.
    Darryl J. Meister, ABOM

Thread Information

Users Browsing this Thread

There are currently 1 users browsing this thread. (0 members and 1 guests)

Similar Threads

  1. why become an ophthalmic technologist?
    By plainjane in forum General Optics and Eyecare Discussion Forum
    Replies: 1
    Last Post: 03-08-2009, 12:07 AM
  2. Ophthalmic Sales Rep in MO or MN
    By fmorgan3 in forum The Job Board
    Replies: 0
    Last Post: 07-16-2008, 09:26 AM
  3. Need Help For Ophthalmic Question!
    By cyinteo in forum Ophthalmic Optics
    Replies: 18
    Last Post: 03-01-2007, 12:14 AM
  4. Ophthalmic Instruments
    By elena in forum Optical Marketplace
    Replies: 12
    Last Post: 01-26-2007, 02:54 PM
  5. Ophthalmic Assistants
    By qs group in forum The Job Board
    Replies: 0
    Last Post: 12-02-2002, 09:38 PM

Bookmarks

Posting Permissions

  • You may not post new threads
  • You may not post replies
  • You may not post attachments
  • You may not edit your posts
  •