Like to get some feed back on digital lenses. House brands vs. name brands. I have some success but having reading problems with others. Which drop are you using, heard 15mm is most used. Compensated or not. Like to hear from you.
Like to get some feed back on digital lenses. House brands vs. name brands. I have some success but having reading problems with others. Which drop are you using, heard 15mm is most used. Compensated or not. Like to hear from you.
Most House or Generic lenses will be less expensive, but there is always a reason for that. I am the middle of some tests, but the best way to explain it is with a premium progressive there can be over 10,000 point files involved, rendered by a computer of course, for most possible options. With a generic or house lens you may only have 800 point files. As a consequence, something is lost, but what is lost will vary with each brand. In many cases the adaptability is lost, which means as the add power increases the reading area will suffer. In a premium lens most designs must change with the add power so that reading area is not lost, however, with less point files and and as add power increases (and thus distortion) reading can narrow.
The other thing that is missing with generic or house brand lenses is wearer trials, many of those lenses have never been tested on real wearers, in high adds, high cyls, or in hyperopes. As a result you are left finding out the hard way where the design "breaks". As it seems you have.
Generic brands will make different compromises in different areas, so one fault may not hold true across different brands. There is just no way to tell until something goes wrong.
Wow, thanks for that sharpstick777, perfectly concise and useful explantion!
I agree Dan. Great post as always Sharpstick!
Can this be dumbed down from point files too pixels for a picture.
Again- trying to relate to the layperson who might get lost in talking about point files?
Okay....Originally Posted by Uncle Fester
I've gotten a bit of an education from one of our members, and what I had previously written is quite...wrong. Mea culpa!! Hopefully my teacher will pop into this thread and further all of our educmacations.
Last edited by MikeAurelius; 07-09-2013 at 03:30 PM.
Now that you've joined the conversation, Mike, are there any generators anywhere that will produce digitally surfaced glass lenses. I imagine there must be something in precision optics, and there must be some demand in Europe and Asia.
Oh heck yah. But they are programmed for precision optics and even more hideously expensive than top-end ophthalmic jennies.
SatisLoh SPM-60 as an example. They do aspherics all the time all day long. But it isn't the machinery so much as it is the programming. Any decent x-y-z plus rotation can make a progressive superfine cut, the problem is programming the beast, and then surfacing the glass. Glass needs time and pressure, and pressure is the biggie. You will lose a lot of precision as the lens fines out.
If you look at how glass 1st surface progressives are made, they are actually drawn down into a mold on the back surface, and the front conforms to the mold. The mold is stainless steel, and is perforated to all a vacuum pump to draw the softened glass down onto it. A glass lens is ground and polished to a spherical surface, for example a 5 base, then is placed onto the mold. The mold is placed into an oven, both glass and mold are brought up to the softening point of the glass, and vacuum is applied to the mold. The glass is drawn down onto the mold, then the kiln starts to cool down, then anneal the glass to ensure there is no remaining strain.
It's far easier to make front progressives in glass this way than it is to surface them. All you have is the original cost of the design & translation to CNC to make the mold and the repeating cost of mold making.
My recommendation regarding the OP is to try the lenses, learn what you can, and keep moving forward. Digital lenses are a great improvement in optical quality, but they still work like a progressive lens. Design is still king over process. If you are having troubles, treat it like any other lens that an outside patient comes in wearing with difficulties.
I use house lenses as a limited product offering, and any time that a patient has had a problem, it could be solved through adjustments to the frame. I don't know what others are doing, but I do not position digital house brands as a premium product. I position them as a better cheap-o lens.
Now that I have read this, I need to question my understanding of what a point file is. I was always under the impression that it was more or less the data fed (essentially x,y,z coordinates) to the CNC machine so that it knows where to move to make its cuts. Is this true or is it something completely different? If it is in fact this, then are you more or less saying that premium progressives are capable of producing 10,000 unique lenses while in-house may only be able to produce 800 unique lenses?
Last edited by AustinEyewear; 07-10-2013 at 03:43 PM.
The calculations are made, as I understand it, as a 3D mesh. Think of taking a handful of puddy, grabbing it in the middle, and pulling it outward so as to stretch the puddy making it take a different shape. Try to make it in to a sphere. It is hard (if not impossible) to make a sphere by grabbing it with your whole hand and stretching. However, if you had a few extra hands helping, you would be able to get closer to making a perfect sphere.
An in house lens might have 800 hands spread out in a grid, each pulling on the puddy to make the right shape. A premium lens might have 10,000 hands pulling on the puddy, there by getting much closer to the ideal sphere shape.
If that doesn't make sense, I will ad pictures later.
Thanks ThatOneGuy. I think my question could use some clarity. I envision the process like this:
measurments -----> Software algorithm produces lens design --------> Lens Design --------> Point File -------> CNC ------> lense
I just re-read everything and I think my use of Zeiss was distorting my perception of the question. Yes, your understanding seems to be correct as to what sharpstick777 was saying.
In the case of Zeiss, however, they are using infinite point files because they generate the lens "on the fly," instead of having a pre-existing lens idea. What I have liked about Zeiss (if I understand anything) is that they do what I call real free form. Other manufacturers are using a limited number of point files (10,000 vs 800 per the example), meaning that basically, where as a traditional lens had ~100 different design variations (BC * Add * corridor, etc), the digital lenses have 10,000+ designs via modifications through cnc to the original 100.
and yes, point files are the xyza coordinates where a = angle of the tool. If I am the lens design, and you are the cnc machine, then the point file is the telephone allowing us to communicate effectively.
Sharpstick, are you saying that a single premium free form progressive lens can contain up to 10,000 point files or that the lens design software contains over 10,000 point files variations?
Just out of curiosity, have you EVER seen the results of large wearer trials in which the "presented lens" did NOT preform well? Isn't this just another marketing ploy? What SHOULD count is how do YOUR patients or clients adapt. We are extremely proud of our Integrity brand (not a "house lens"). We put out name on it and stand behind it. The main reason we can offer Integrity at a lower price is that we are not paying for corporate marketing, national advertising or dispenser kickbacks. We count on our customers to know their patients AND their product. Just sayin'...
If you have integrity, nothing else matters. If you don't have integrity, nothing else matters
Laramy-K Optical
Standard point files are in fact two-dimensional arrays of sag values. The x and y coordinates are implied by the size of the array and the number of points (that is, there are no x and y values in the files - only z's). You might think that "the more points, the better", but that's really not the case. Machines ultimately have to produce tool paths that are continuous; they do this by curve-fitting given the supplied points. At some resolution, additional points are superfluous (the same is true of edgers, by the way). At least one generator provider was initially incapable of using very high-resolution files, when the standard point file started to be used around 2007.
Some LDS suppliers use "seed files" and some don't; Zeiss is not the only one that doesn't. In fact, some LDS use seed files for some designs and not for others. A seed file is essentially a shortcut, relieving the program of having to generate a starting surface every time. The seed file may not be a "point file" itself; it could be (for example) a set of coefficients for spline functions, which are used to produce continuous curves.
Thanks for chiming in shanbaum - I was hoping you would :) My next question was related to what I quoted from you, which is: Is the number of points specified just semantics? In otherwords, I imagine the software generating what could potentially be an infinite number of points. Thus as you say, this is curve-fitted.
To me, it seems all machines would require the same number of points, so when we say we deliver 10000 points or 800 points, what we really are referring to is how accurate the software is, how much work it does to create the lens design. I'm not really articulating what I want to ask but hopefully this gets the question across?
Generators can handle a range of numbers of points. Lens Design Systems vary in the number they produce; some are settable.
An infinite number of points would not be useful; it would take an infinite amount of time to generate.
I wouldn't connect resolution of the SDF with "accuracy", and I don't think that the quality of a design is necessarily improved by doing optimizations at ever more points, beyond some minimum. There comes a resolution at which, both in terms of the design as it's generated, and the number of points contained in the SDF, the more points in either case would have no measurable or discernible impact on the product.
I'm starting to believe that we've been duped. I have tried house brands, Premium brands, and everything in between. While there are some myopic pt's that see better out of the digitals, Hyperopes and minor powers do not seem to see that much of a difference.
Now I know this opinion will cause a ruckus, but I have better success out of traditionally surfaced progressives. I still dont know for sure if this is a buyers remorse issue or if the industry as a whole is trying to make more money out of us and the pt's.
From my perspective (for the record, only glass, and I only offer one style of progressive and I don't have a non-adapt policy), I don't think it's a con job.
I've seen enough threads on this board about non-adapts that a change to a different style seems to resolve the issue. What does interest me though is the discussion on generating the progressive. This whole discussion completely overlooks the fact that the generating does absolutely nothing if it isn't backed up by an equally precise surfacing operation. And, for the record, I've never actually watched backside progressives being surfaced post generation, so I might be off-base. Be that as it may, I believe that if the surfacing operation isn't at least as precise as the generating process, you are going to lose a lot of detail in the fining and polishing.
Based on what I've seen talked about, I do think that there are an overwhelming number of progressive designs available, both in front and back side designs, more than 2 or 3 standard deviations would tend to fall into. Does the industry need that many designs? It seems to me that when progressives first arrived on the scene (read the wonderful history thread in the main forum), that adaptation was more of a transition from fixed focal point to floating focal point adaptation issue. Now, with umpteen hundreds of designs, it has increased the difficulty of the dispenser to find the right design to fit the patient -- the focus has changed from the lens to the patient. I don't know if this is a good thing or a bad thing, but to me, that seems to be the issue here.
Mike I think you are onto something here. I too have never personally surfaced backside progressives. But I have heard from several sources that the polishing is where they can get messed up. Basically freeform lenses can be "ruined" by the polishing process easier than conventional lenses.
With that being said are there any generators out there that cut so clean that you dont have to polish?
Also with so many lens designs now I think the industry as a whole is creating a monster.
About the only thing I disagree with sort of is I'm still on the fence if it's a con job or not. I think the big company's do not want individual labs surfacing conventional progressives anymore. They can make more money off of us if they do it at thier labs. They pump us all up on the technology side of things and most of us have bought the hype
Mike, direct surfacing never involves fining. The process depends almost totally on the generator producing a near-specular surface. The polishing operation is performed by only-slightly-glorified sphere machines (ok, some machine vendors may dispute that, but some of them are exactly that) using conformable laps, and it is crucial that the material removal in that stage of the process be uniform and very close to zero.
I think that your observation regarding the number of designs is correct - it is really hard for dispensers to understand the differences amongst them. You can look at power maps ad infinitum, but they don't tell you how the lens will actually perform. That's one of the reasons my friend Rick may chime in with a message about the importance of extensive wearer trials.
(Crafter, the answer is no, there is no generator that produces a lens that does not require polishing. Of course, as with any production step, something can go wrong in that one).
Not being one to see conspiracies everywhere, I am not inclined to call digital lenses a “con job.” There are two distinct aspects to these products. The first one is the one that we were all thinking about back in the 80’s, after progressive lenses became established, that we could turn single vision blanks into progressives, if we could just figure out how to produce the required complex surface on the back. The introduction of new machining technology made that possible. Only then did a lot of people start thinking about the fact that this technology enabled a new level of per-lens customization. Those two features – making progressives out of relatively cheap blanks, and elevated individual customization – pull in opposite directions with regard to the value proposition. The former suggests that you should be able to have less expensive products, especially in exotic materials that bore high blank costs for semi-finished progressives. The latter suggests that the lenses can bear a higher price throughout the supply chain, because they afford additional value that was previously unobtainable.
Personally, I haven’t been happy with conventional progressives since I started to wear freeform progressives, but I haven’t tried many conventional ones lately.
Shanbaum -- this grasshopper thanks you for your insight and wisdom!
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