Free Form SV vs Digital SV
Got a fun one I've been mulling over. Is there a real difference between free from and digital in single vision lens. I use both and have yet to see a any difference, granted I have a low rx.
If I understand the tech behind them a digital sv is basically a free form. Or is free from strictly for progressives?
Freeform/digital (there are differences but I'm not 100% clear on the difference) is not strictly for progressive lenses (there are digital designs in Bifocals as well) If you're a lower power then you probably not going to notice a significant difference, there is not yet significant unwanted prism and astigmatism in your prescription (unless you are doing a very large lens), there was recently a thread about when everyone starts using digital single vision lenses http://www.optiboard.com/forums/show...most-from-FFSV.
:^) Thank You
I am new to business (kind of) i was licensed in Texas for 8 years then was out and now I am back one the differences is FF / Digital vs Aspheric. I have been asked a few times, and I am not confident in my answers. Is there a way to simply state the big difference and application purposes I would enjoy reading?
To me, some labs are confusing people by trying to capitalize on this term digital.
Meaning one of digital single vision:
You can cut a single vision using the digital process, which will produce a slightly more accurate power. Traditional equipment fine/polish usually pulls tools in tenths of a diopter. The new equipment which is referred to as digital by some can cut lenses and polish lenses at a hundredth of a diopter.
Meaning two of digital single vision:
The same digital process can be used to cut a more optimized design calculated by a digital / free form software. This is a more optimized aspheric designed for the patients prescription.
Hope this helps.
I think that jspayneii has summed up the difference nicely. In each case, these lenses are fabricated by free-form or digital surfacing equipment, which is capable of producing virtually any smooth optical surface. However, when discussing the use of these terms, particularly in the context of wearer benefits, it is very important to understand how these terms apply differently to the method of manufacturing versus the method of optical design:Originally Posted by Boldt
Digital lens or digitally surfaced lens can refer, in the most general sense, to any lens fabricated using free-form or digital lens surfacing equipment. Free-form surfacing equipment can virtually any smooth optical surface, including conventional spherical and toric surfaces. Further, when producing conventional spherical and toroidal surfaces, there is no rounding error as there is with hard lap polishing (hard lap tools produce a rounding error of up to +/-0.05 D).
Free-form lens, on the other hand, can refer to any lens that has been fabricated using free-form lens surfacing equipment with at least one free-form surface that lacks point, plane, and rotational symmetry. Consequently, a "free-form" lens should have at least one free-form surface generated by free-form lens (or "digital") surfacing. Free-form surfaces include progressive surfaces as well single-vision aspheric and atoric surfaces or surfaces of greater complexity.
Customized lens will refer to free-form lenses that have had the optical design optically optimized for the individual wearer prior to free-form surfacing using the exact prescription data of the wearer, either for a specified position of wear or for an default position of wear. This optical optimization results in wider, clear fields of view for the wearer. For progressive lenses, the lens design may also be customized for lifestyle, fitting height, et cetera.
Optical optimization will result in a lens design that should provide wider, clearer fields of view for the wearer, particularly in stronger powers, prescriptions with cylinder, or significant lens tilt in the position of wear. This is really the visual benefit that eyecare professionals most often associate with "free-form" or "digital" lenses, although not all so-called digital lenses actually provide this benefit to the wearer.
"Digital" lenses that have been fabricated using free-form or digital surfacing equipment do not necessarily provide any visual benefits to the wearer, because conventional spherical and toric lens can also be fabricated with this technology, and frequently are. In fact, less reputable companies can rely on this confusion in the marketplace when marketing their lenses in order to exploit this misconception.
Any progressive-like surface fabricated using free-form or digital surfacing is considered to be a free-form surface by definition, because the surface lacks point, plane, and rotational symmetry. However, a so-called free-form progressive lens design may or may not be optically optimized in some way for the wearer, depending upon the product. So not all free-form progressive lenses are customized progressive lenses.
This has led to much of the confusion in the marketplace, because the term "free-form" has inaccurately become synonymous with optical customization of the lens design. In fact, there are "free-form" progressive lenses that are produced by simply combining a standard semi-finished progressive lens design with an Rx surface, resulting in performance comparable to traditional lenses.
For free-form single-vision lenses, true free-form surfaces are typically aspheric, atoric, or even more complex surfaces that result from optically optimizing the lens design for the prescription in an assumed position of wear (either specified or default). So, for single-vision lenses at least, "free-form" lenses are frequently "customized" lenses that provide some visual benefit to the wearer.
For progressive lenses, on the other hand, neither the use of "digital" nor "free-form" is really an indication of optical improvements for the wearer. In order to determine whether your digital or free-form lens of choice is truly a customized lens, you should request the technical details from the lens manufacturer or laboratory. Otherwise, you may very well be selling benefits to your patients that your lenses are not actually delivering.
Best regards,
Darryl
Last edited by Darryl Meister; 12-03-2013 at 12:51 AM.
Darryl J. Meister, ABOM
"Further, when producing conventional spherical and toroidal surfaces, there is no rounding error as there is with hard lap polishing (hard lap tools produce a rounding error of up to +/-0.05 D)."
Darryl, that was an informative post.
A couple of questions I have are 1) whether the humans can detect .05 D changes and 2) whether in practice, if free form lenses actually deliver what is promised on a consistent basis. I wonder whether there is a greater chance of subtle or latent defects in the production of FF lenses, compared to conventional. The equipment is super-sophisticated and might be more prone to producing errors which go undetected by conventional means such as a lensmeter most of us have in office. The suppliers don't, as far as I know, map every single pair of lenses produced....
While conventional lenses are far less sophisticated in their promise, I suspect there might be a degree of reliability and repeatability that is higher than with FF due in part to simpler production methods.
A lot of the customization/optimization is done based on measurements taken with the customer wearing the frame with factory Demo lenses. Most demo lenses are either 5 or 6 base. We all know that lenses are much flatter today with lower base curves and the frames often do not fit the same after prescription lenses are installed. Temples get mis-aligned, panto can be altered, the weight of the lenses changes the frame position on the nose, etc... Numerous adjustments are made at the delivery which can EASILY over-ride the original parameters measured. Lens stress effects due to curve mismatch of the frame and prescription lenses, lens sizing etc... can have an impact as well, perhaps more with FF, I suspect.
If FF is as good as advertised, the mathematics and science being well established, it is interesting that the big labs continue to introduce new and better products at such a fast rate. I haven't read about any new great mathematical discoveries, since Fermat's last theorem was cracked not too long ago, and no Nobel prizes have been awarded to lens designers. I suspect a lot of the new products reflect unproven marketing claims and possibly engineering tweaks which are able to correct previous errors in production methods. But I'm an incorrigible skeptic.
FF is NEVER about a 0.05D discernable difference. Really good lenses, like Zeiss Individual, are always about qualities and properties that CANNOT BE MEASURED with conventional in-store equipment. They are the ultimate "take my word for it" lenses.
Just last nite I delivered a new set of Zeiss Individual 2 progressives to a client. He was wearing poly Auto II progressive. The Individuals were 1.60 index, with an Rx change from 4.50 Cyl to 5.50 Cyl (amongst other stuff). The FIRST thing the client said to me before trying on the glasses was "WHY ARE THESE SO EXPENSIVE?"
The last thing he said after wearing them for 5 minutes was "I've never seen so clearly!"
I admonished him that his sight will only get better over the next few days. I had discussed the pricing difference at the time of order, which was $200 more for the Zeiss. He Ok'd it, but told friends and family who said he was "nuts" to pay so much for lenses.
When he left, he was reading the Zeiss Individual pamphlet I gave him intently...and smiling.
Thank you Zeiss, for making me look so good!
Barry
Last edited by Barry Santini; 12-03-2013 at 09:59 AM.
Great points Darryl! "Free-form" is a registered trade mark of Shamir for their digital processing.
"Just last nite I delivered a new set of Zeiss Individual 2 progressives to a client. He was wearing poly Auto II progressive. The Individuals were 1.60 index, with an Rx change from 4.50 Cyl to 5.50 Cyl (amongst other stuff)."
I don't doubt for a second you delivered a terrific pair of lenses with a spot on prescription. There are so many variables at play that make your client say WOW.
How much is a function of the free form or the particular lens you chose vs another is what is purely anecdotal. It just isn't science until you control each variable....and test.
Shamir trademarked "Freeform". No hyphen.
No. As Barry indicated, any "improvements" due only to the use of soft lap polishing in order to eliminate rounding errors are not discernible to the eye. This is why it is important to determine exactly what visual benefits, if any, your free-form lenses of choice are actually delivering. If the lens design has not actually been optically optimized, many of the claims regarding "clearer" or "wider" fields of view are most likely overstated.
If a free-form lens manufacturer refers only to improvements due to the actual free-form surfacing process, such as "0.01 D resolution," then there is a good possibility that the lens design is not actually customized for the wearer in any meaningful way. Free-form lens surfacing does allow for a fairly accurate replication of the lens design, but this process is also susceptible to manufacturing errors, as you suggested in your post.
Similarly, for progressive lenses, referring only to improvements due to placing the progressive viewing zones on the back of the lens does not imply the use of any optical optimization for the wearer. Placing the viewing zones on the back of the lens blank only increases the field of view through a typical lens by 10%, give or take. And, in reality, the exact same effect could be achieved by simply widening the viewing zones on the front of the lens blank.
On the other hand, a truly customized free-form progressive lens that has been optically optimized for the exact prescription and position of wear parameters of the wearer can deliver fields of view that are up to 50% wider with considerably less power error than conventional progressive lenses, depending on the prescription. And these benefits are independent of (or in addition to) any other benefits that may be associated with the use of a back-side or dual-surface lens design.
You are exactly right. Due to the kinematics of the soft lap polishing process, in particular, a great deal of process engineering and ongoing quality control is necessary in order to maintain consistently accurate products. A variety of process parameters need to be refined. Lens mapping every lens in production may not be practical but, at the very least, lens manufacturers should map lenses when first qualifying the process and then as needed for quality auditing.
Yes, adjustments can confound the original position of wear measurements, which is why it is always important to pre-adjust the frame before taking these measurements (or even traditional fitting height and PD measurements, for that matter). Also, I recommend utilizing frame measurements of tilt and wrap, not lens measurements, for the reasons that you stated. However, other lens manufacturers may require lens measurements, so I would confirm with your particular supplier.
That said, even if your initial position of wear measurements are slightly off, you are still most likely providing values that are closer to the actual values than providing no values at all. So, your optical performance should still be at least marginally improved. You have a propagation of errors that occurs in the eyewear delivery chain, from prescribing lenses in 0.25 D steps to fitting errors to conventional base curve limitations to fabrication rounding/errors to ANSI tolerances. I advocate reducing those errors where feasible.
On a side note, capturing position of wear measurements is also another meaningful way to differentiate your service from, say, an online optical outlet.
Best regards,
Darryl
Darryl J. Meister, ABOM
"On a side note, capturing position of wear measurements is also another meaningful way to differentiate your service from, say, an online optical outlet."
Well said Darryl. Huge statement in my humble opinion!!
I have just a couple of comments regarding these observations:
1. "Free-form" technology as it relates to the lens design process varies considerably from manufacturer to manufacturer. So it is really misleading to think of all of these lenses sitting in a general category of "free-form = good." The use of "free-form" lens surfacing does not imply any particular level of customization or optical benefit. Because not all free-form lenses are alike, over-generalizing detracts from potentially important points of product differentiation, both to eyecare professionals and to consumers.
2. The mathematics of single-vision and progressive lens design are indeed fairly well established at this point. However, as an enabling technology, free-form lens surfacing does allow lens designers to surpass the limits imposed by the use of a small number of conventional (semi-finished) lens blanks. So, for instance, new free-form lenses may offer increasing levels of customization that continue to close the gap between the visual requirements of the wearer and what is strictly possible to deliver on two lens surfaces.
Best regards,
Darryl
ps,
Nice reference to Fermat's Last Theorem!
Darryl J. Meister, ABOM
Darryl,
I appreciate your posts, and I have learned from reading them.
What are these "lens designers" actually designing? where does one study this? Is there a school of engineering for ophthalmic lenses?
I cant help but feel there is claims-abuse with a lot of this lens designing and there is a very healthy dose of marketing involved.
The process itself, using CAD CAM software to sculpt a lens with a drill bit is a big departure from "conventional" surfacing indeed. But the drill path, the mathematics of it, should be quite well established as to what is a good design. The laws of physics haven't changed and there is still plenty of distorsion in ALL progressives.
Where are the scientific papers, the peer-reviewed double blind studies that any of this is REAL and not just marketing hype? why do we just accept a big commercial company's claims about this or that?
I think we are both very much in agreement that the mathematics of progressive lenses have not changed markedly in recent years. But, as I mentioned in my previous post, I don't know that anyone is really claiming that they have changed. The benefit of free-form technology is not really in improved mathematics, although certain lens manufacturers are now able to fill in more of the variables of existing mathematics with real values from the actual wearer.
As you alluded to, above, progressive lenses are constrained by the geometry of smooth surfaces, and modern lenses from reputable lens companies have generally approached the mathematical limits of reducing unwanted surface astigmatism. Nevertheless, we can still explore different balances between the distance, intermediate, and near zones; variations the peripheral hardness; changes to the add power profile; effects of different front and back surface combinations; and so on.
We can also investigate more subtle optical effects related to binocular vision, interaction of high-order wavefront aberrations, lens design preference as a function of ametropia, et cetera. So, for instance, progressive lenses have improved over the years from simple, rotated (symmetrical) designs to asymmetrical designs to horizontally symmetrical designs and so on, with features like variable near insets, adjustments for the position of wear, dominant eye, and whatever tomorrow brings.
I think we all know from experience that no single progressive lens design will work for every single wearer. And there will probably always be an opportunity to make refinements to these lens designs, no matter how good they currently are. But, in the context of free-form lenses, we are really talking about the capability of certain lens manufacturers to make changes (sometimes subtle, sometimes dramatic) to the lens design that are not otherwise be possible with conventional mass lens manufacturing.
You are generally not going to learn progressive lens design at a university, due to the proprietary nature of the work, although enough of the mathematics and principles involved have come into the public domain that you may occasionally run into someone in academia experimenting with it. Usually, someone with a physics or mathematics background joins a lens company, and is then trained by other lens designers. In Germany, it is probably more common to hire an optical engineer.
I can only speak for the company that I, personally, work for, Carl Zeiss Vision, and we actually make all of that stuff available (please feel free to message me directly, if you want these materials, because I would prefer not to get into product-specific discussions on OptiBoard). Otherwise, I can only defer you to your particular lens supplier of choice. But I certainly agree that not all lens suppliers will make these details available.
Best regards,
Darryl
Darryl J. Meister, ABOM
Companies such as Hoya or Zeiss are the only ones willing to share the white paper clinical studies. I may also add that Hoya is the only company that takes the FF process one step further by producing a double surface bi-aspheric FF product in PAL (Mystyle) and SV (Nulux ep).
Other companies claim they also do the same thing, but I've analyzed all the other manufacturers FF PALS and they are all 100% backside design with spherical front, which in my opinion is a cheap version of FF production line on a $3 lens blank.
Darryl,
As always, thanks for the very clear and thoughtful reply.
For my part I find your posts to really stand out for quality and style.
"As you alluded to, above, progressive lenses are constrained by the geometry of smooth surfaces, and modern lenses from reputable lens companies have generally approached the mathematical limits of reducing unwanted surface astigmatism."
That sums up pretty well what I am awkwardly trying to say - that at this point a lot of new lens designs are sort of like rearranging deck chairs when the most optimal arrangement has probably already been found, until some breakthrough new technology arises. The claims that a further rearrangement of the same sort is now giving X% more of this or that is utter nonsense, because to give more of this you must lose more of that. Until new technology arises.
This is a really great forum, I enjoy checking in every day to read and learn. And rant.
If the mathematics of progressives is so well established - why the explosion of new styles. Marketing cynicism surely has some truth here - they are offering digital versions of 30 year old lenses(!?!?) , not to name names. But if Optiboard is to be believed, many of us gravitate to the same manufacturers and styles as "better" designs. And they are the same names popping up. If they were all roughly the same would that happen? Interesting also that the top of the line designs don't always appear to deliver top of the line results. Mabye good measurements and good fittings mean something after all? The internet might not have us yet.
For the record, I feel like I'm jumping into a shark tank with a ham around my neck contributing to this line with some of the smartest guys in this industry. Thanks for listening.
I have several "compendiums" from Essilor on Varilux lenses.
B
All I can say is I have a pair of SV stock poly, AR (my rx is mild -2.00 ish). I can see very clearly with those. I also have Zeiss individual SV lenses poly, AR and I see better with them. I notice less swim. (But I never noticed swim in the other pair. I just notice the Zeiss are better)
Superb explanations by Darryl...................cleared up some fog.
One point in my mind that is not totally clear yet is: Now that we can process lenses to much higher accuracies with the new dfigital equipment, I am wondering what has become of the refractionist who produces the precriptions ?
Have they updated their techniques to produce more accurate prescriptions to match the new capabilities of the lens industry ?
Is this a trick question?
Loved the explanation. Have to admit I'm still lost on the difference in manufacturing techniques, since I've never been in a big manf. lab. Any chance you guys could dumb this down for a novice? I understand how a CNC machine works, if that helps clarify the area of my mis-understanding :)
interesting to hear some comments from some top notch refractionist .................
That all depends on the answers we get...................................
Sounds real great to be able to make a lens to 100th of a diopter exact and sell forr a lot more money, but can we actually diagnose visual capabilities to that degree ?
Would be interesting to hear some comments from some top notch refractionist with a doctors degree.
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