Has anyone formed any opinions on Trivex yet?
Has anyone formed any opinions on Trivex yet?
I saw Hoya's lens, Phoenix, at Expo. Younger does not have their prototype, Trilogy, available yet. It was impressive.
I am not sure where it will impact the market. It reminds me of Spectralite but supposedly is more impact resistant. It is aspheric with a higher abbe than poly. We will have to wait and see.
Isn't that one of those things you put in the bottom of a pot of water when you boil it to protect the item being cooked from burning?
Clarifications seem to be required here. First, I work for one of them there HOYA labs (gasp), and have had the chance to do some of the testing on Phoenix. "Trivex" is the name of the raw material sold by PPG. "Phoenix" is HOYA's proprietary version of Trivex. "Trilogy" is Younger's name. Since the material hasn't actually shipped yet, it's pretty tough to have formed an opinion so far.
The material is actually nothing like Spectralite, other than having an index of refraction around 1.53 (Spectralite is 1.537). The material processes very similar to polycarbonate, and has the same level of impact resistance, as was demonstrated rather violently at Vision Expo East. Yet chemically speaking, it is nothing like polycarbonate either.
As stated, Trivex/Phoenix/Trilogy has a much higher Abbe value (43-46, depending upon who you listen to) than polycarbonate, thus eliminating the distortion covered ad nauseam in the General Topics. This material also performs better than poly on the ISO Robustness test, chemical resistance (acetone doesn't hurt it), and in tensile strength testing (also demonstrated at V.E.E.). One of its best features is superior drilling capabilities--superior to any other material we've used. As such, it stands out among mid-index materials, which are notoriously prone to cracking when drilled.
It would be wrong, however, to think of Trivex/Phoenix/Trilogy merely as a replacement for polycarbonate. With a higher index of refraction than CR-39, a very low specific gravity (1.11), and a nominal surfaced center thickness of 1.3 mm, Phoenix lenses are about 35% thinner than CR-39, and significantly lighter. The combination of three features (good optics, impact resistance, and lightness) is what the "Tri" nomenclature is all about. With any other material, you can only get 2 out of the 3.
Since Trivex/Phoenix/Trilogy refers to a material, it is neither spheric or aspheric. That would be a property of the lens design. The first lens designs that will hit the market will be HOYA's GP Wide progressive and spherical single vision. Other lens designs, including aspheric SV will follow later, as will a Transitions version.
Stay tuned.
RT
oh, RT, you sure do know the way to a dispenser's heart...any word on how long until it hits the market ?
Darn
And, all along I thought Trivex was that guy on Jeopardy and his wife as Abbe.
Ya learn something every day!
The word from HOYA Lens at V.E.E. was that we'll start seeing lenses in May, with greater availability in June.
I can't speak for Younger.
RT
On drilling any plastic, do you keep the cutting surfaces well oiled? You should.
Chip
What I said was that mid-index are notorious for cracking AFTER they've been drilled, not while they're being drilled. We won't produce mid-index drills because they just come back in two months after the guy took them off his face a little rough.
And no, we don't oil the lens material when drilling. Its not necessary, and the loud scream you heard was our AR coating manager contemplating the mess he'll have trying to coat lenses after they've been oiled up. When we did our initial tests drilling the Phoenix material, our guy purposely tried to ruin the lens by using poor drilling technique, and couldn't wreck it.
RT
RT
What market area do you see these lenses fulfilling? If the lens is not aspheric and has a lower abbe value than CR-39 why should I chose it? Impact resistance?
This material is perfectly capable of being offered in both aspheric and spherical designs, and I suspect that you'll see both soon. The first lens design you'll see is the HOYA Wide progressive, so asphericity/sphericity is a moot point. Again, asphericity is a LENS DESIGN characteristic, not a MATERIAL characteristic. Most CR39 lenses are not aspheric, and there seems to be little US demand for an aspheric CR39 lens. I guess I'm confused by your linkage of asphericity and material characteristics.
As you note, impact resistance is an obvious feature of this material. Poly has quite a few detractors because of real or perceived optical quality issues (refer to lengthy thread in General Discussion Forum). This new material gives you the same impact resistance, with a much higher Abbe value and all the other benefits mentioned earlier. You'd probably use it instead of poly and mid-index in many cases.
For the Rx range that you typically would use CR39 for, I doubt seriously that you'd find anyone that could tell the difference in Abbe between plastic and Phoenix. But the Phoenix lens would be thinner, lighter, more impact resistant, etc. Why wouldn't you use it, other than price?
I've heard that the Abbe value of the eye is in the 47 range, and thus lens Abbe above this value represents "wasted" quality. Like having a good stereo with mediocre speakers. Darryl? True?
RT
RT:
When you start stocking Pheonix you will have to post and let us know. It is worth a try.
I still don't understand why I should recommend a lens in this material other than I would be replacing a CR-39 with a more impact resistant lens with a lower abbe value with a thinner CT?
I do understand the difference between materials and lens design. Aspheric lens design reduces or eliminates optical abberations produced off axis. It increases the optical performance of any lens material. It is easy to demonstrate this feature to a patient. Much easier than showing the difference in index of refraction.
So what I am thinking is that this lens will be probably be available in stock SV pl-4D range and aspheric design comes later. If a wholesale lab is grinding the control of lens thickness can vary depending on the type of surfacing equipment.
Where do you think this will it fit in the market place?
[This message has been edited by Bev Heishman (edited 04-19-2001).]
RT has provided a very thorough primer on Trivex aka Hoya/Younger trade names. We've played with it for over a year and, from a labs point, find it very easy to process.
To Bev's point re: thickness, I'd like to add that the variables are more impact resistance and material than equipment. Mid-index lenses, other than Spectralite and now Trivex, are all rather "brittle" and significantly less impact resistant than CR-39. Trivex setsa new level. They all also tend to be a bear to surface with any consistency. Again, Trivex holds a power pretty well. All (except Spectralite) are less scratch resistant than CR-39; we use this standard to determine whether to apply a backside hard coat.
Back to the ol' value statement. We haven't received pricing yet but I would guess that our (lab) price is going to be 3 times that of poly. All in all, we feel that it will be priced comparable (on the high side) to other mid-index products.
Don't know how this chart will come out but:
Material Sp.Gr. Abbe I.R. Impact
Trivex 1.10 43 1.52 +++
Spectralite 1.21 47 1.58 +
Other M.I. 1.22 37 1.56 -
Poly 1.20 31 1.59 +++
CR-39 1.32 57 1.50 +
1.60 (1) 1.34 37 1.60 ++
1.60 (2) 1.22 42 1.60 ++
1.66 1.35 32 1.66 ++
Hope this helps.
Hi RT,Originally posted by RT:
[I]I've heard that the Abbe value of the eye is in the 47 range, and thus lens Abbe above this value represents "wasted" quality. Like having a good stereo with mediocre speakers. Darryl? True?/I]
I don't know for sure but I can look it up when I'm back in the office. If I had to guess I would say that it is closer to 67... The power of the eye is roughly 60 D with axial chromatic aberration of about 0.9 D. This should probably give an Abbe value of 60/0.9 = 67.
There are also a couple of points to make here. 1) I feel that lateral chromatic aberration (LCA) is generally more bothersome to the wearer than axial chromatic aberration (ACA). LCA creates the "color fringes" spectacle wearers may complain about in the periphery of their high-powered lenses. ACA blurs the color in images, which is less apparent. By the way, the ACA of the eye is also the basis for the Duochrome test. 2) The eye suffers mainly from ACA not LCA. Factors like the fixed optics of the eye, relatively small pupil, the Stiles-Crawford effect, and reduced retinal sensitivity in the periphery help minimize "color fringing" -- unlike spectacle lenses.
Best regards,
Darryl
PS
I should probably also add that this approximated Abbe value would be for the overall "simplified" eye, since an actual eyeball has several different refractive media and surfaces -- each with its own optical properties.
[This message has been edited by Darryl Meister (edited 04-20-2001).]
You should see some of the mid and hi index lenses that I have seen by smaller wholesale labs that haven't invested in state of the art surfacing equipment and length of time it takes to receive the product. Though some of the problem maybe they are not up to date in how to process these materials.
Bev, you called my hand and I'm forced to reply. Most mid-index lenses are abdominations that shouldn't be allowed on the market (from a processsors perspective). First, you could take 3 lenses, all with identical front curves, surface them on the same tools, and come out with 3 powers. Were you to use 10 lenses, you'd often come out with 5 powers. They drive us nuts! And, the thinner our customers ask us to grind the lens, the bigger the problems.
Second, many manufacturers "suggest" that they need not be backside coated for scratch resistance (S/R). We use a simple test to determine that; comparison to CR-39. If it's less S/R, we coat it. Of the group, only Spectralite passes. All the others require a backside coating, including Trivex. Now you put on an AR and, statistically, they won't pass impact testing at 1.5 (except Trivex).
It's interesting to note that Trivex, with an I.R. of 1.52 is being considered a mid-index. That must mean that glass is also...!!!
Yes, that is interesting to note. While I working on a standard for lens specification data for the Vision Council of America (which includes representatives from most major lens vendors), our group proposed the standard tooling index of 1.53 as the cut-off between regular index materials and high-or mid-index lens materials. I don't think that many eyecare professionals would consider a 1.52 lens material a "mid-index" lens material.Originally posted by Jim G:
It's interesting to note that Trivex, with an I.R. of 1.52 is being considered a mid-index. That must mean that glass is also...!!!
Best regards,
Darryl
Phoenix has an IR of 1.530, not 1.52.
Darryl,
I believe that the Abbe number of the eye is around 47 and its axial chromatic aberration is about 2.50D (the reason that ACA is not of concern to spec wearers). David Atchison of the optometry school at the Queensland University of Technology here in Australia, has just published a great book on the optics of the eye (Butterworth-Heinemann). It is at home at the moment so I don't have it to hand. The ACA of a 10D lens made in poly is about 0.33D, significantly less than the ACA iof the eye. As you say, the Transverse chromatic aberration is of greater concern and two authors have quantified this rather well. Dan Torgersen has written a rather nice short paper on the topic, quoting 0.16prism diopters of TCA as the level where visual acuity drops by one line. England's Mo Jalie has also quantified the significance of TCA, claiming that it becomes noticeable above 0.10 prism diopters of TCA. I have put the results of these authors into tables measuring the TCA at two points, 15 degress of visual angle (within which about 80 per cent of our vision occurs) and 30 degrees. It makes for interesting comparisons and puts the Abbe number into some perspective. You can, I believe, consider Jalie's threshhold as the very safe level.
Regards
David Wilson
Hi David,
Great comments.
2.50 D sounds quite a bit high for the ACA of the eye though. Even the highest value of I've seen was less than 2.00 D (Freeman). Tunnaclife quotes a value of 0.9. Though, few authors seem to state the specific wavelengths used. Unless the wavelengths are based upon standardized values (e.g., hydrogen C and F lines in the U.S.), a true measure of "Abbe value" can only be predicted. For instance, the farther into the blue end they measure, the more rapidly the ACA value will increase. Since the sensitivity of the eye rapidly drops off away from 555 nm, it's important that reasonable red and blue wavelengths are chosen.
Dan's paper summarizes, as many of the studies on chromatic aberration have, primarily the loss of visual acuity as a consequence of lateral chromatic aberration. It seemed to me that the investigators were more concerned about the amount of LCA that would reduce visual acuity, not necessarily the amount of LCA that the wearer found acceptable.
Frankly, in a dynamic situation -- such as one might encounter while using a peripheral portion of the lens -- I feel that most wearers wouldn't be troubled by a loss of one or two lines of acuity. I think the bigger issue is the actual "color fringing" effect itself, not the minimal loss in acuity. At this point, it becomes a visually disturbing perceptual phenomenon -- not just a slight case of reduced discrimination.
By the way, is that Atchison book the one that covers both the eye and visual optical instruments (published about 2-3 years ago)?
Best regards,
Darryl
Hi Darryl,
I agree with your comments about senstivity versus a drop in acuity. For the powers we are talking about, other aberration, notably oblique astigmatism, are more likely to be affecting acuity anyway (I think that Dan makes that point in his paper). Jalie consider the point where TCA is noticeable rather that where it affects acuity, so his figure fit well with your view.
As for the reference wavelength, we could probably go on forever on this topic, particularly the debate on whether we should be using the helium d line, as the US and Australia do, or the mercury e line, as the Europeans do. And, as you say, the debate is not just on the middle of the spectrum, it also affects the values used for C and F.
Atchison's book was co-authored by another Aussie lecturer (whose name escapes me and I've left the book on my desk at home again), but I believe that it is probably the book you were referring to.
I'll check it when I get home and let you know.
Regards
David
If I had to guess I would say that it is closer to 67... The power of the eye is roughly 60 D with axial chromatic aberration of about 0.9 D. This should probably give an Abbe value of 60/0.9 = 67.
Darryl,
This is indeed an interesting thread.... I'm now curious. If you'r saying the power of the eye is 60 D, which it is, that would indeed give an Abbe value of 67. Let's break the different refractive components of the eye down...cornea and crystalline lens(specifically. Say the cornea has a power of 45 D and the crystalline lens has a power of 15 D. Is the chromatic aberration the same in both? Will this change the equation? I would love to see the figures on this and where to get them.
We can never stop learning.
Diane
Hi Darryl and Diane,
As you say, Diane, this has developed into an interesting thread (at least to us!).
The book I mentioned earlier, Darryl, is Optics of the Human Eye by Atchison and Smith. It quotes figures from Le Grand who gives the Abbe values of the media as Cornea 56.01, Aqueous 53, Lens 50.01, Vitreous 53. The authors give an overall V value of 50.23. Bennett and Rabbitts claim that while the ACA for the central area between F' and C' is 1.17D the overall variation for the entire spectrum is 3.50D (quite a difference) and as Darryl said, the reason the duochrome test is so effective.
I couldn't find the short Torgersen article I was thinking of but I found another, even more comprehensive article by Dan, where he gives a value of ACA for the eye of 2.0D. He also quotes several studies in an appendix where the ACA is given by various authors as follows: Wald and Griffin 3.25, Ivanoff 1.42, Bedford and Wyszecki 2.40, Jenkins 1.58, Howarth and Bradley 1.82, Pease and Cooper 2.17, Lewis, Katz and Oehrlein 2.50, Mandelman and Sivak 2.08.
This is an excellent paper by Torgersen (having just re-read it) It is "A survey of ophthalmic spectacle materials:Physical properties and optical performance". March 1996. I believe it was done for your OLA.
Incidentally, the ACA is F/v, where F is the lens power and v the Abbe number.
Regards
David
Hi David/Diane,
Funny you should mention that... I just brought my copy of Smith and Atchison's "The Eye and Visual Optical Instruments" home tonight to do a couple of calculations! ;) It's actually a great source -- so thanks for reminding me of it the other day, David!
I think that our biggest difference comes from the selection of our reference wavelengths, as I mentioned earlier. Authors stating values of chromatic aberration across the entire visible spectrum will be closer to the 2-3 D range. Authors stating chromatic aberration based upon specific reference wavelengths (as spectacle lenses are) are generally be closer to 1 D.
Smith and Atchison give a regression equation in the book for determining the refractive index by wavelength for water, which is the principal component of the ocular media. After plugging the ANSI Z80.1 values for the various reference wavelengths into an Excel spreadsheet, I computed the refractive indices for the Helium d (yellow), Hydrogen C (red), and Hydrogen F (blue) lines. I then calculated the Abbe value at 55.18 (which the text also concurs with).
For the reduced eye, these values also produce axial chromatic aberration in the neighborhood of 1.10 D. I have seen values ranging from 0.9 D to a little over 1 D in most texts (Tunnacliffe, Rabbetts, et al) -- so there is good correlation for this value. Note, though, that this number will increase noticeably for reference wavelengths chosen farther into the blue and red ends of the spectrum. Across the entire visible spectrum, the chromatic aberration has been quoted from 2 D to 2.5 D (Atchison, Freeman, et al). This is in good agreement with the regression formula.
Best regards,
Darryl
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