Somebody help me!

**Alan W** · 04-05-2002, 09:24 AM

I'm no optical engineer, let me make that perfectly clear.
But, I think back on the "days" of the lenticular minus lens and stuff and ask myself.....self....
That lens was crude being basically spherical and an occasional toric surface. Yet, on a 1.523 or even a 1.49 cr39 thinness was achieved by careful selection of curves.
It seems to me that with the right combinations of aspherocity, parabolics and touch of motion control technology, the real need for higher index lenses, while I don't have a problem with them, would be diminished.
I just get this "feeling" that all the optics "ain't sittin" on what we get for $1.50 a piece from Nalco (trying to be funny, sorry!).

Are we using all of the tools of optics or are we also caught up in some commercialization? I'm also not throwing darts at science. I'm just trying to put things in their right context.

**Jeff Trail** · 04-14-2002, 07:46 PM

Alan,

Been away from the board for a good 3 or 4 weeks (gee it was tough) but signing back on and seeing that 800 posts since your "last visit" was amazing...
Now since no one else wants to "play" in your sandbox..oops I mean thread ;) maybe I can get the ball rolling...
I, like yourself, am not an optical engineer but a few things come to mind that might be relevant, one of the first things that popped to mind is what you are talking about seems to fall more under wave front optics than mixing curves along the same surface in variation to get fluctuation of power while lessening the steepness of the curve without using another index of refracted material.. if we did it your way without making use of the denseness of the material as well as the physical material than you would have waves all over the place.. since you would have to deal with the vertex of the lens in direct relationship to the eye...you would have to make the cuts so close and narrow it would not be cost effective and molding it? Yikes ..that SV cr39 stock lens is now $3,257.00 :p
I would think the most cost effective and easiest way are to manipulate the way light travels and bends using different materials.
I do still think that wave front optics is, in the long run, where we are headed if they can get the prices of producing it down to acceptable levels..
Than again I'm no optical engineer either... so anyone else want to drag out the shovel and pail and jump into the sandbox and play?

Jeff Trail

"just a lowly lab rat looking for the cheese"

**Alan W** · 04-14-2002, 10:43 PM

Need to know more aabout the wave front concept.
I'm thinking that since aspherocity on front surface yields a thinner lense and seemingly less magnification cosmetically, perhaps back side surfacing needs to be dealt with similarly. I know conventional surfacing doesn't provide for that. But, somehow, isn't technology around the corner with 3 axis computer aided surface design and lathe type surfacing a possible solution?

**Alan W** · 04-15-2002, 07:51 AM

Can you come out and play with me and Jeff?

Like, hurry, Dude . . . . there's a wave front coming in!

(Oh, that was sooooo funny.....sorry!)

**Jeff Trail** · 04-15-2002, 12:19 PM

Alan,

It is already out there, Zeiss makes a generator that will custom cut a PAL from a lens that starts out as a "sv".. of course the generator is around the $450 range.. or last time I read up on it.
I think I seen a pretty good debate that went off into wave front optics a while back.. it may have been hmm Dave Wilson who was off on a tangent about it..I can't remember right now.
Wave front will be most beneficial to PAL's more so than any other design and by manipulating the curves you can neutralize peripheral distortion and help eliminate and reduce chromatic aberrations. Of course the abbe value does have the biggest effect on chromaticism but by reducing the angle of the surface you can manipulate the angle of the internal reflection and move those rainbows around.
J&J idea of putting two materials into one lens to help with improving the optical field is a pretty good idea, but as you can see by the prices that it is not a cheap process as well as the size of the lab up in Roanoke, VA. where they are doing it.
One of the main problems right now is on paper theoretically we can do and solve a lot of these problems but reproducing it in a cost effective manner is where the problem falls.
If you poke around and get that info on the Zeiss generator do so it is a pretty interesting set up.. I forget the name of the model but maybe someone else knows right off.
I think we are at the point in PAL's where not much else can be done when you take into account you have to use the law of averages (convergence etc..) and now it is down to a numbers game where they use statistics to show how OUR distant visual field is a FULL 20% wider.. not telling you if it is 20% wider OU or each side... lets say it's 20% OU (which most of them base it on.. now that breaks down to 5% nasal and temporal...lets see we have around a 17 mm area so what vast improvement did we get not even a full mm on each side...saying 20% sure sounds better than getting the true numbers :-)

Jeff

"rambling on all over the place...hey it's Monday what do you want"

**Darryl Meister** · 04-15-2002, 06:21 PM

I would guess that analyzing wave front aberrations for spectacle lenses would be overkill, if not impractical. The majority of wave front applications that I am aware of involve systems with fixed optics, while the eye rotates behind a lens (i.e., eyewear is not a fixed optical system). I would also guess that these systems have pretty large apertures, while the pupil aperture of the eye is relatively small, and isn't terribly sensitive to some aberrations (such as spherical aberration and coma). Also, a certain amount of aberration is inherent in a progressive lens design, which would probably be much more significant than the "higher order" aberrations that wave front analysis also includes. For example, most progressive lenses are continuously variable surfaces, which means that they are not truly spherical at any point on the lens surface. Moreover, the optical performance of the eye is still limited by things like diffraction and photoreceptor density. Consequently, conventional ray tracing (as opposed to wave front analysis) is probably more than sufficient for ophthalmic lens design.

What Zeiss and a couple of other manufacturers are doing with custom-surfaced progressive lenses really isn't too far removed from conventional progressive lens manufacturing. However, instead of cutting a ceramic former or a metal mold to mass produce a given progressive lens design, they are simply cutting a single lens to the desired progressive lens design. Producing a single pair of lenses for an individual wearer allows, among other things, additional compensations to be incorporated into the progressive lens design, which are specific to that wearer (such as vertex, tilt, etc.). However, without the cost benefit and efficiency of mass production, this process is time-consuming and expensive. Also, it is difficult to fine and polish these custom-surfaced lenses, which presents other issues.

Best regards,
Darryl

**Alan W** · 04-15-2002, 07:03 PM

What about duplicating the front surface aspheric architecture (utilizing the correct curves to generate a desired presciption) on single vision on the back?
Would that not yield a thinner lens?

**Darryl Meister** · 04-15-2002, 09:16 PM

Alan W said:
What about duplicating the front surface aspheric architecture (utilizing the correct curves to generate a desired presciption) on single vision on the back?
Would that not yield a thinner lens?

With minus lenses, there is a slight thickness advantage to having the asphericity on the back surface. With plus lenses, the thickness advantage occurs when the asphericity is on the front surface.

Best regards,
Darryl

**Alan W** · 04-15-2002, 11:55 PM

Appreciate the clarification.

**Blake** · 04-16-2002, 09:14 AM

Wouldn't a lens with an aspheric back surface be the same as an atoric lens?

**Alan W** · 04-16-2002, 03:35 PM

Here's my moment to expose my ignorance . . . . .
And, probably insult your intelligence in the process without intending to . . . . without intending to ...without intending to!
I think the toric lens you refer to is a surface that has 2 different radii of curvature effectively 90 degrees to each other. One could be spherical, and the other cylindrical in architecture.
But, the aspheric surface is different. Imagine looking at the surface along the "z" axis. If you could see it with the naked (excuse the expression) eye you might be seeing a series of somewhat concentric "rings" each representing a part of a sphere with different radii. I'll stop there except to say that the purpose is to maintain a common focal point as the rotation of the eye varies which may not necessarily happen with a perfectly spherical surface. The added benefit is a thinner lens and in the case of a plus lens a reduction in the magnification of the eye as seen by other dudes or dudettes. Why do I get the feeling just I shot my foot off?

Darryl...please don't hurt me. I'm a frail old man!

Love,
Alan

**Darryl Meister** · 04-16-2002, 05:53 PM

I think the easiet way to explain it would be to say that the back surface is aspheric if it would've otherwise been spherical -- that is, there is no prescribed cylinder power. The back surface would need to be atoric if it would've otherwise been toric -- that is, there is cylinder power.

Best regards,
Darryl