"Fitting Button"

[skirk1975]

You know how Seiko utilizes the 10mm fitting butting (spherical center) on it's lenses. Do all 1.67 Hi-Index basically do this? If it came down to using Poly or 1.67 which would you do? Does that center actually make the difference. And don't tell me about Poly and ABBE (Mike DiSanto's Poly article changed my thinking). Remember, cost for us is a factor and we all know Poly is cheaper for us to get. Let's say the customer has a , umm...-6.00 lenses.

[Darryl Meister]

Many aspheric lenses use surfaces that are "nearly spherical" in the central region of the lens, simply because the asphericity of the surface doesn't depart significantly from a spherical surface near the center of the lens in many cases.

That said, if an aspheric surface is forced to remain spherical over a significant region of the lens where asphericity is actually required for good optics, excess optical aberrations are often introduced.

I've never actually seen any evidence supporting the visual benefits of this approach compared to the use of a fully aspheric surface, so you may want to consult with one of the companies claiming to use this feature.

[YrahG]

You know how Seiko utilizes the 10mm fitting butting (spherical center) on it's lenses. Do all 1.67 Hi-Index basically do this? If it came down to using Poly or 1.67 which would you do? Does that center actually make the difference. And don't tell me about Poly and ABBE (Mike DiSanto's Poly article changed my thinking). Remember, cost for us is a factor and we all know Poly is cheaper for us to get. Let's say the customer has a , umm...-6.00 lenses.

I like Seiko lenses they are good quality. I don't think that the spherical button is that big of a deal most aspherics aren't going to have enough eccentricity to create a significant deviation from a spherical surface in a 10mm region anyway so you might be able to say this about the majority of aspherics available on the market.

I also read that very same article and felt that it had many inaccuracies within it.

[AWTECH]

Lens design information

FYI: The lens designers with the company that provide the lens designs for Seiko lenses, probably have the access to the most patient information due to the fact they also own the facilities in Japan that have been producing freeform designs for about 15 years.

I don't know the exact data but by producing over 1,000 jobs a day for all of these years and having the feed back certainly give their lens designers access hugh clinical trial group. I am sure they use feed back from any problem issues to make improvements to their software.

My point is that over a 15 year time span if the 10mm spherical area could be improved by a little aspheric surface within this space, I would think they would have made this relative simple adjustment. (I also haven't checked but it maybe they have this patented and competitors are having to use an aspheric surface in this area) Many times the design information fed to the retail dispensers are based on the limitations due to patents turned into marketing spin by another.

An example would be the Definity lens, (when J&J introduced it), this was originally introduced with a non spherical front surface, or they would have been in conflict with the patent held for having a PAL with a spherical front. With a partial add on the front this patent was no longer a restriction that required a payment to someone else.

[Darryl Meister]

My point is that over a 15 year time span if the 10mm spherical area could be improved by a little aspheric surface within this space, I would think they would have made this relative simple adjustment.

Actually, it is a relatively simple matter to evalute the optical performance of a "spherical button" by ray tracing a spherical lens design with the same nominal front curvature.

As I mentioned earlier, constraining a flattened lens surface that should be aspheric in order to make it more spherical can compromise optical performance, since it represents a violation of "best form" principles. This is the whole reason that we use aspheric surfaces in the first place.

Consider the optical performance at 5 mm from the center of a +4.00 D lens with a spherical 6.00 D front curve:
Oblique Astigmatism = 0.07 D
Mean Power Error = +0.04 D

Now, consider the optical performance at 5 mm from the center of a fully aspheric 6.00 D front curve:
Oblique Astigmatism = 0.01 D
Mean Power Error = -0.01 D

While these numbers aren't huge, at least at 5 mm, the examples demonstrate that a perfectly "spherical" button can reduce optical performance compared to an aspheric surface.

I can't speak for the other major lens manufacturers, but Carl Zeiss Vision has never pursued such an approach because we feel that there is not sufficient visual advantage to justify the optical compromises involved.

area) Many times the design information fed to the retail dispensers are based on the limitations due to patents turned into marketing spin by another.

Given that other major lens manufacturers already have several patents on aspheric lens designs, isn't it just as likely that SEIKO invented a spherical button to avoid someone else's IP?

I can't speak for the other lens manufacturers, but Carl Zeiss Vision holds several patents on novel aspheric lens designs, some dating back 100 years.

In any case, eye care professionals have a choice in aspheric lens design strategies, which is never a bad thing.

[WFruit]

The short answer: As far as my research shows, all MR-10 resin 1.67's have the 10mm fitting button. The MR-8's do not, but they tend to be spherical anyway, so.....

Preference: I've got a OD: -6.75 -1.00 x163
OS: -5.75 -0.75 x013

I MUCH prefer the Seiko 1.67 (although I'm wearing a pair of Seiko's 1.74's now (I know my Rx doesn NEED it, but I wanted to try them)). I wore poly for years until I got into the optical industry. Sadly that was with Lenscrafters in the early '90's, so my choices were Poly or Spectralite. I choose the latter and have never worn Poly since (except my saftey glasses). Maybe I'm more sensative to Poly than most, but I see much better out of the 1.67's. I honestly don't know what the ABBE's are on any of the lenses; I know what I see better out of.

[Fezz]

The short answer: As far as my research shows, all MR-10 resin 1.67's have the 10mm fitting button. The MR-8's do not, but they tend to be spherical anyway, so.....

Preference: I've got a OD: -6.75 -1.00 x163
OS: -5.75 -0.75 x013

I MUCH prefer the Seiko 1.67 (although I'm wearing a pair of Seiko's 1.74's now (I know my Rx doesn NEED it, but I wanted to try them)). I wore poly for years until I got into the optical industry. Sadly that was with Lenscrafters in the early '90's, so my choices were Poly or Spectralite. I choose the latter and have never worn Poly since (except my saftey glasses). Maybe I'm more sensative to Poly than most, but I see much better out of the 1.67's. I honestly don't know what the ABBE's are on any of the lenses; I know what I see better out of.

This may help you a bit.

http://www.opticampus.com/tools/materials.php

This is a fantastic resource by a fellow Optiboarder, Darryl Meister.