# Optical Forums > Ophthalmic Optics >  Has anyone attempted an ophthalmic...

## Uilleann

...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:

----------


## MikeAurelius

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.

----------


## rbaker

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.

----------


## Darryl Meister

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

----------


## WFruit

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.

----------


## Jacqui

I've seen them, made a couple of pairs way back when. I think I'll agree with Darryl (surprising) on this.

----------


## Striderswife

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!

----------


## HarryChiling

Dragonlensmanwv still makes doublets he sent me one a few years back it was made of glass, contact him for more info on fabrication.

----------


## Barry Santini

Coddington vs Hastings triplet magnifiers also point up how to handle aberrations

----------


## DragonLensmanWV

> 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.

----------


## Robert Martellaro

> 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.

----------


## Darryl Meister

Robert, I think you and Mike are talking about Corning's old "Corlon" laminated glass+plastic lenses, invented around 1982.

Best regards,
Darryl

----------


## Uilleann

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!  :)

----------


## MikeAurelius

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.

----------


## MikeAurelius

YEAH!!! That was the stuff!!! Thanks Darryl

----------


## Darryl Meister

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 _F_V and a first lens _F_1 combined with a second lens _F_2 with Abbe values of _v_1 and _v_2, 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

----------


## MikeAurelius

It isn't the optics Darryl, it is the mechanical properties of the plastics.

----------


## Jacqui

What I keep wondering about is the adhesive. How will it affect the needed curves, etc.??

----------


## Darryl Meister

> 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

----------


## Darryl Meister

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

----------


## MikeAurelius

> 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.

----------


## MikeAurelius

> 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.

----------


## Jacqui

> 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.

----------


## MikeAurelius

> 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.

----------


## Darryl Meister

> 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.




> 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?




> 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.




> 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

----------


## Darryl Meister

Mike, on a personal note, I do believe that you have a great deal of insight and experience that many of the members of OptiBoard could find very valuable, whether I necessarily agree with everything you post or not. I only wish that you would approach our debates with a little more diplomacy.

Best regards,
Darryl

----------


## MikeAurelius

> 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.


Yes, and I noted that, but you conveniently IGNORED that part of my post to prove some point or another of yours.

This is what I wrote:




> 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.





> 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. Nevertheless, I do agree with your most current assertion that 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.


Then you are misunderstanding what I wrote. I never said or meant to imply that laminating glass to plastic was easier than plastic to plastic.




> 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.


True, to a point. Each time, the plastic material was a very thin wafer with a consistent thickness throughout. The COE issue does not rear its ugly head until you get inconsistent thicknesses, as in spectacle blanks with a prescription.




> 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 have simply have a great deal of experience at making poorly laminated lenses?


WOW. Go back and re-read what I was referring to:




> 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.


This referred to laminating a wafer of glass to a plastic/polycarbonate spectacle blank. We made thousands of glass to glass laminations, under the brand name "Auralite" which were used by fairly significant numbers of optical labs back in the 1980's and 1990's. We were the only company doing it at the time. We stopped when glass fell off, and X-Cel Optical is now making them the same way we did.




> 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 dubious personal anecdote, not necessarily scientific facts.
> 
> Best regards,
> Darryl


WOW again...geeze Darryl, you don't pull your punches, do you?

Have you ever spend any time in a glass lab, or is all your experience in plastics? Can you tell the difference between actual multi-decade hands on experience versus hypothetical theorums? Unless you been there and done that, you can blue sky all you want, but it doesn't change the fact that all you have are guesses and ideas instead of experience.

Tell you what. Hop on a plane and come up to Minnesota and spend some time with me in my lab. I've got no major secrets to keep and between myself and my father, you will learn a lot about glass.

----------


## MikeAurelius

> Mike, on a personal note, I do believe that you have a great deal of insight and experience that many of the members of OptiBoard could find very valuable, whether I necessarily agree with everything you post or not. I only wish that you would approach our debates with a little more diplomacy.
> 
> Best regards,
> Darryl


Diplomacy, eh? How does that tie with making the comment 'a great deal of experience at poorly laminated lenses'.

I have no burning desire to be right or correct, I know that I don't know everything there is to know, but I know what I know, and that has all been learned the hard way: hands-on experience in the lab and lens manufacturing since 1973.

I certainly believe that you know a lot about the physics of optics, but I do question whether you have the same level of knowledge on the mechanical, manufacturing side, especially in light of your comment about windshields and polarized lenses. You are trying to compare apples to grapefruits, and that's a poor comparison to make.

You also tend to pick nits, and if you are going to do that, I'm going to come back and call you on it.

Theoretical optics is a very cool and neat thing to know. But they are all theories until proven (or disproven) out in the lab.

----------


## Darryl Meister

> Yes, and I noted that, but you conveniently IGNORED that part of my post to prove some point or another of yours...


Mike, I have to get back to work for now, so we will again have to "agree to disagree" for the time being.

I, personally, feel like we are both arguing the same side of the same point at this stage, which seems unnecessary to me. Whether one of us has misinterpreted the point of the other's posts or not, there definitely seems to be a communication issue at work here.




> Have you ever spend any time in a glass lab, or is all your experience in plastics?


While I've spent a little time in the old Coburn (Eldon, MO) and AO (Southbridge) glass manufacturing plants, and certainly worked with glass lenses on a regular basis in my dispensing days, most of my manufacturing experience is in plastics. But this thread is about plastics.




> but I do question whether you have the same level of knowledge on the mechanical, manufacturing side,


No, to your point, I do not make laminated windshields. But, yes, I am familiar with materials science. And I am happy to talk about stuff like Griffith flaws and slumping on ceramic formers and coefficients of thermal expansion with you.




> WOW again...geeze Darryl, you don't pull your punches, do you?


Actually, given the nature of several of the derisive and otherwise insulting comments that you've directed at me two or three of these threads, including this one, I think that my responses to you have generally been the epitome of tact, under the circumstances.

Best regards,
Darryl

----------


## Darryl Meister

PS
I do also agree with you that the thickness of the components will play a significant role in the durability of a laminated product, if there are significant differences in mechanical properties, due to the induced stress/strain under expansion or contraction.

Best regards,
Darryl

----------


## HarryChiling

Darryl,

Thank you for your posts and insightfull knowledge.  I appreciate your theory and I have applied your suggestions in a plastic surfacing application enough time to know I rarely question your knowledge in the fabrication arena.  I don't really know how glass got into the mix as I would tend to shy away from any new applications of glass unless the technology was only available in glass.

While I appreciate Mike's posts they do seem to be steeped in that "old timers knowledge" and by admission is mostly trial and error in the lab.  I am sure that many break throughs came to be from that kind of tinkering if anyone were to try and fabricate anything in this day and age it would need to follow the most current methods available which would be theory first then trial and error to confirm that theory was correct or incorrect.

For the question at hand two plastics used as a doublet I would make a hypothesis that the power range for reduced chromatic abbe might be a narrow band of powers when other more significant errors were taken into account.  I still stand by the old method of proper material selection for reduced ch. ab.

I do like the pissing match though, but if I was to put any money on it sorry Mike but Darryl has the odds on this one and I would even put money on him having the oddson the next and subsequent ones.  The one thing I know about Darryl is he will tell you what he knows and as a true professional he will also tell you what he doesn't know and that my friend garners the utmost respect from me and many of my peers as evidence by his name and reputation in this industry.

----------


## MikeAurelius

LOL Harry! 

I don't plan on giving up the "old timers knowledge" as I consider it to be a treasure without price. But I think you misinterpret what I've been trying to get across, which is perhaps my fault for writing it badly. Every breakthrough in technology that I've ever seen has been because someone said "Hey, why can't we...?" and then someone gets to tinkering and integrating things that have never been brought together before and before you know it, there's a new method/process/invention. I think in this day and age, I'm considered a dinosaur of sorts, but that's the neat thing and works in my favor. As you may or may not know, the St. Cloud Minnesota area is a center for lens manufacturing, and at one time, in a 30 mile radius had 4 companies making fused glass bifocals: Lantz, Vision Ease, X-Cel Optical and Minoco (which later became Precision Cosmet). Add Aura Lens Products as a single vision glass manufacturer, and you had 5 companies in that area. Surrounding us were better than a dozen small, medium and large surfacing operations. Most of them have been sold to the large operations like Essilor, but we've still got a few independants around. That's the background that I cut my teeth on.

I learned my optics the old-fashioned way, standing behind the machines and making lenses, one after another. As did my father, back in the pitch and rouge days. In today's typical laboratory operation, how many true old-timers are left? Not too many I'd guess, as they don't tend to fit into the large lab culture. But these were the guys who drove innovation and help create what we have today (for what it's worth). 

Do you honestly think that the average inventor really cares about theory? Unless it is some kind of absolutely new thing-a-ma-bob, the theory already exists and the inventor is simply looking for a better way to do it. That's how the 3 axis CNC generators came to be. That's how 3 axis CNC edgers came to be. A better, faster way to do it. Ophthalmic lens theory is (for the most part) pretty well set in stone, and what we are seeing today is mere extensions of that theory. Sure, there's some fine tuning going on, for example the so-called "free form" designs, but really, when it comes right down to it, going back to another thread where we were discussing ANSI standards, does a "free form" design REALLY help the patient all that much when the standards themselves are being softened so much? I think not, and see the "free form" as one more gimmick to get more bucks out of the patient, the dispenser and the lab.

As far as a pissing match, though, I'm not trying to win anything. I'm having a 'spirited' discussion, yes, but I'm not out to win brownie points or anything. I was disappointed in his post about trying to compare laminated sheet glass to laminated lenses, and I was pleased to see that he backed off on that. There are always going to be differing points of view, and so far, yes, Darryl and I tend to see things differently and have some fairly strong opinions about them. We've agreed to disagree, and I respect that from him and let it go at that. If it was a true pissing match, I would have kept the pressure on. But since it wasn't I let it go. Because at the end of the day, there are still jobs to run and lenses to ship out the door, whether they be glass or plastic.

----------


## braheem24

> "free form" as one more gimmick to get more bucks out of the patient, the dispenser and the lab.


I'll have to pass that info along to the high cyl patients that cant stop grinning.

----------


## HarryChiling

> I learned my optics the old-fashioned way, standing behind the machines  and making lenses, one after another. As did my father, back in the  pitch and rouge days. In today's typical laboratory operation, how many  true old-timers are left? Not too many I'd guess, as they don't tend to  fit into the large lab culture. But these were the guys who drove  innovation and help create what we have today (for what it's worth).


I beg to differ on this statement, for the most part those innovations came from theory.  That's not to say that in downtime the occasional lab guy didn't create something of significance.  There are theories on process engineering, optics, materials, etc.  These theories are put to use when someone has an idea.  We look to theories to see if something is plausible before we waste time trying to invent otherwise you have inventors out there trying to invent perpetual motion and other such kookie ideas.  Many of the older shop guys I know performed duties in a lab that were fairly routine and amazingly the older guys I know worked off of charts for almost everything with very little knowledge on optical theory.  Most won't admit that those charts were created by the formulas that guys like Darryl and others have floating around in their heads.  Matter of fact I was just flipping through a book on surfacing "Ophthalmic Surfacing for plastic and glass lenses" by Richard J. Mancusi, it struck me as funny that there was a passage:

"Rule of Thumb

Plastic lenses have a tendency to come out weak.  The exact reason as to why remains a speculative.  Most labs use some form of arbitrary compensation based on experience rather than optical or mathematical soundness...."

Anyway what I know is that sometimes there are situations that experience will prevail over knowledge and there are other times when knowledge prevails over experience ultimately the best professionals in this field have a little of both.  You can't really discount Darryl's advanced knowledge of theory without consequently discounting your experience.  Both experience and knowledge are puzzle pieces you won't see the big picture without both.

I have heard stories of torching blocks and applying pitch like it was a lost art when the reality is that it is an antiquated system that was replaced by alloy.  Some processes, equipment, and materials have a shelf life and when that shelf life is reached often those that invested significant time and energy in perfecting those processes, operating those equipment, or learning everything about those materials have a hard time moving forward.  I am not saying glass has come to the end of the life cycle here, it's still useful in many applications and I don't see it being replaced.  Some of that old knowledge though is antiquated and has been replaced by newer methodology and if you are going to represent yourself as an expert then it's great to reference it as history but to try and pass it off as advanced technology can be a bit misleading.

BTW, Luzerne still processes glass in house and will probably never stop given our close proximity to the Amish who value the benefits of glass.

----------


## Darryl Meister

> Do you honestly think that the average inventor really cares about theory? Unless it is some kind of absolutely new thing-a-ma-bob, the theory already exists and the inventor is simply looking for a better way to do it. That's how the 3 axis CNC generators came to be.


I suspect that the guys at MIT, who invented the first CNC milling machines, would probably disagree with you. Not to mention that the theory and mathematics of milling complex surfaces are every bit as complicated as the circuits, encoders, servos, etcetera that actually do the physical work, which for that matter also relied on a helluvalot of theory and mathematics to design in the first place. I can assure you that the engineers building these machines didn't get their PhDs in Basket Weaving. ;)




> I'm having a 'spirited' discussion


I do enjoy spirited debate. It just leaves a bad taste in my mouth when that debate disintegrates into ad hominem attacks, so I hope we can avoid this in these threads.

Best regards,
Darryl

----------


## HarryChiling

> As a co-inventor on three different ophthalmic lens design patent applications, myself, I can tell you that, while certainly not always the case, figuring out _what_ to make is often the first step before determining _how_ to make it.


Patent numbers please? :D

----------


## MikeAurelius

> I have heard stories of torching blocks and applying pitch like it was a lost art when the reality is that it is an antiquated system that was replaced by alloy.


Oh, yes, that is antique, but what I was referring to was coating a polishing tool with pitch and polishing the lens with rouge. That's how you make lens curve masters (out of glass, of course!). We occasionally have an accident here and break or chip a curve master and have to make a new one, and that's how we do it. We don't use felt or polyurethane, we use pitch.




> Some of that old knowledge though is antiquated and has been replaced by newer methodology and if you are going to represent yourself as an expert then it's great to reference it as history but to try and pass it off as advanced technology can be a bit misleading.


Very true, but I hope I haven't done that. I use my history and training as a background and my knowledge base. I'm learning new things every day. After all these years, we just acquired a Coburn/Gerber Vector CNC generator (running glass of course). Because of the change in generating parameters going from a 113 to the Vector, I had to go back and rewrite a portion of the software I use to calculate my layout and curves. Perhaps that can be seen as reinventing the wheel, but it gives me a certain amount of pleasure to use something that I created myself rather than a hideously overpriced off-the-shelf solution that would need modification anyway before it could be used in my lab.

I deeply appreciate your comments though and enjoy the conversation.

----------


## MikeAurelius

> I do enjoy spirited debate. It just leaves a bad taste in my mouth when that debate disintegrates into ad hominem attacks, so I hope we can avoid this in these threads.
> 
> Best regards,
> Darryl


Darryl -- I don't believe I've engaged in any ad hominem attacks, but if I have, you have my deepest and most sincere apologies.

----------


## MikeAurelius

> I suspect that the guys at MIT, who invented the first CNC milling machines, would probably disagree with you. Not to mention that the theory and mathematics of milling complex surfaces are every bit as complicated as the circuits, encoders, servos, etcetera that actually do the physical work, which for that matter also relied on a helluvalot of theory and mathematics to design in the first place. I can assure you that the engineers building these machines didn't get their PhDs in Basket Weaving.


True, but didn't it first start as "why can't we...?" Invention seems always to start with an idea that builds on previous theory creating a new theory (or theories).

----------


## Barry Santini

Even the best ophthalmic lens and lens designs, no matter how carefully calculated or made, are not even close to being held to a theorectical-limit standard that astronomical telescopes are held to.
Having designed and made astronomical telescopes and eyepieces of the highest standard ( which is dictated only by what physics will allow), I can say that designing for a vision system of an evolved animal, and arguing what material or lab process is truly the best, is tilting at windmills.
No offense intended, but ophthalmic optics can be and is a precise science, up to a point.

Mike, I suggest that if you want to verify better ophthalmic optics by using your anecdotal eye, then maybe you should consider getting guided PRK, and getting closer to the 20/08 resolution threshold that your retinal mosaic is capable of (at least , by physics theory)

----------


## Darryl Meister

Easy there, Barry... Aren't you selling eyeglass lenses, not refractive surgery?!? ;) Keep in mind that, while wavefront-guided corneal ablation can yield vision that approaches the diffraction limit of resolution in theory, this is rarely ever achieved in practice due to variations in wound healing and so on. In most cases, vision is not much better than what the patient could achieve with eyeglasses, although it is generally superior to conventional corneal ablation, which results in significant spherical and other high-order aberrations.

Best regards,
Darryl

----------


## MikeAurelius

> Mike, I suggest that if you want to verify better ophthalmic optics by using your anecdotal eye, then maybe you should consider getting guided PRK, and getting closer to the 20/08 resolution threshold that your retinal mosaic is capable of (at least , by physics theory)


Barry -- I rely on my digital lensometer to verify my lenses. You have to work fairly hard to fudge a DL, whereas an "analog" lensometer can be mis-read, maladjusted or simply screwed with. Every morning and every afternoon, I check the calibration of the DL. In the years that we've had it and others previous to it, they have never mis-read. 

Can the numbers off a DL be messed with, sure, but if I catch someone doing it, they will be out on the street pretty doggone fast with the imprint of my shoe on their butt.

----------

