Santini - Looks Like He Nailed it!

[John@OWDC]

LOL
Well - that went about as predicted... some things never fail.

Folks - PLEASE - IOT has a world-wide brain trust of doctorate level engineers, mathematicians, physicists and ophthalmologists cooperating in their lens designs.
They are literally running super computers for their modeling.
If IOT designs a lens with a set parameter then it is the best possible design capable within the rules/laws of physics.
They aren't randomly placing anything to appease history or old school beliefs about anything.

Right - a company striving to be on the cutting edge of lens technology and they are going to say, "4 below because we have always done it that way."
Seriously?

[drk]

Ophthalmologists? Puhleeeze.

[drk]

What's more, John, is that you are far too eager to bend the knee to "smart people" and "math" and whatever else. Have some pride, and look around...there's a crap ton of brain on this website over the years.

And what's more and more, no ivory-tower geek has worked 30 yrs with the END USERS. Real, live people.

[Kwill212]

How can you possibly call grinding vertical prism in single vision lens prism thinning not even a minute relevance of being correct.

I assume this nonsense remark is aimed at me. What would you prefer I call grinding yoked prism into a SV lens for cosmetic purposes, if not prism thinning?

[Lensman11]

Prism thinning can be applied to a progressive style or executive style to make the lens thinner. The add portion of both of these lens styles is thinner than the distance portion adding base down prism makes the bottom thicker or closer to the thickness of the distance portion this allows the entire lens to be made thinner. This does not apply to a single vision lens or any segmented bifocal. Prism on a sv lens is just prism it will move the optical center and it will make the lens thicker the opposite of prism thinning.

[Kwill212]

Prism on a sv lens is just prism it will move the optical center

WHICH IS EXACTLY WHAT I SAID IT WOULD DO...

and it will make the lens thicker the opposite of prism thinning.

You can't possibly be telling me that a -4.00 single vision lens, fit with the OC 6mm above the datum is going to be made thicker by grinding 2D of base up prism.

[Lensman11]

It will be be thicker on the bottom. You are not understanding what prism thinning is doing to the lens. There are simple
technical papers and pictures on line take two minutes and read one of them. Prism thinning has no relevance to grinding prism in a sv lens the purpose is different even though mechanically it is the same. Prism thinning is generally not done in minus lens because it does not make the lens thinner unless the reading power is greater than the distance power. -0.50 add +2.00 prism thin -4.00 add +2.00 do not prism thin. In your sv example the center will not be thicker but the lower edge will make it a +4.00 and the center will increase.

[Kwill212]

It will be be thicker on the bottom.

And thinner at the top, thus evening out the thickness imbalance top to bottom of the lens due to the fitting height, thereby making it cosmetically better.

You are not understanding what prism thinning is doing to the lens.

There are simple technical papers and pictures on line take two minutes and read one of them.

I know exactly what prism thinning does to a lens, and I have read plenty of papers on the subject. Even ::gasp:: read some books too! Please stop with your condescending, holier than though, BS.

Which is why I said "Prism thinning OF A SORT" In a FFSV lens it would mean leave the fitting cross in front of the pupil, thus maintaining the integrity of the lens design, while simultaneously moving the prp down to even the top and bottom thickness of the lens by grinding yoked prism. This makes a better cosmetic finished product.

Don't tell me to take 2 minutes to read a paper if you can't take 10 seconds to read an optiboard comment correctly.

[drk]

I really like how we can make optics compelling.

[Lensman11]

Sorry if you took it the wrong way You should talk to the lens designer about your thoughts on this. When you manufacture a free sv lens the prp is not on the lens it is created on the back. When you add prism where does the prp go that would depend the design criteria There is limit to what amount of prism a ff generator can do mechanically.

[drk]

Lensman 11 is taking over for Chip Anderson. I can dig it.

[NAICITPO]

I really like how we can make optics compelling.

[lensmanmd]

*Grabs popcon* watching the egos run amok

[Barry Santini]

Drk:
yes, he is aniso:

-8.00 OD
-5.50 (SE) OD

Splitting the imbalance in an aniso Rx is what most every progressive PRP position serves to do.

And we’re not playing with the OC in freeform—we’re deciding on where the PRP will be.

B

[Uncle Fester]

I think I am not alone when I say Barry Santini has forgotten more optical knowledge than I have.* I consider his education level as at least equal to an OD's.

fwiw- Optiboard quickly humbles many of us and keeps many from posting for fear of getting into the ring as Bantamweights taking on Heavyweights. But I've taken enough blows to the head over 47 years as a journeyman optician fighter that I don't know any better than to keep getting up off the mat and continue posting;)

I appreciate how he boxes accordingly and doesn't think a first round knockout is the goal of this, Steve Machols' special place. But a place to come hang with fighters from all weight classes.

*Well- he doesn't forget and that's what makes him different from moi!

[drk]

Splitting the imbalance in an aniso Rx is what most every progressive PRP position serves to do.

Has that been established? I mean, yeah, we're in this ray-trace/freeform age, now, and the "old ways are gone and they're better left alone". But I really want to know if it had to do with pantoscopic tilt compensation more than a preemptive attack on a relatively rare situation (anisometropia).

And we’re not playing with the OC in freeform—we’re deciding on where the PRP will be.

Prism reference point is where you read the intended prism for the lens (note that isn't put where the eye is!).
Optical center is where a ray isn't deviated prismatically (nor refracted, for that matter, right?)

In the case of a zero intended prism lens, then, they are the same thing.


Help me out, here. Are you just arguing semantics? "No O.C. in freeform PALs because it's not a radially/rotationally symmetric lens with a single/double radius of curvature but a complex surface that defies conical section geometric description" kind of stuff?

[drk]

Here's an article from one of your buddys, Barry. I'm just going to post stuff for fun. It's not to argue any "points" (<--puntal intended)(<--pun inside of a pun intended).

https://www.2020mag.com/article/my-l...eference-point

[Barry Santini]

If by "branded" you mean compensated freeform lens, yes. If not, Martin's Rule applies.

I know many optis know how to calculate Martin’s rule. But I strongly suspect—based on how many school faculty I have asked—that most do not know what Martin’s rule is doing.

Martin’s Rule of Tilt is trying to help align the image shell of the lens being fitted to the retina of the same eye, for all gaze angles up to a semi field radius of 25 degrees for a well designed, corrected curve lens. By doing so, you reduce—but not wholly eliminate—most off axis blur (NOT DISTORTION!!) arising from oblique astigmatism and/power/focal plane error. To do this exactly, one would need to know the Center of Rotation (CoR) for that eye. The CoR is measured from the back vertex of the fitted lens to the apex of the cornea, and from the cornea to the CoR. In order to be a rule, some assumptions have to be made. In Martin’s Rule:

1. The fitted vertex distance is assumed approximately 13.0 to 13.5mm.
2. The cornea to CoR is assumed to be 13.5 to 14.5mm for horizontal eye movements (for a Total CoR range between 26.5mm to 27mm)
3. If the eye’s axial length or the fitted VD significantly departs from these assumptions, Martin’s Rule starts to break down.

What Martin’s rule does NOT take into account is how adjusting the OC position can negatively impact (not in order)

1. The effect of abbe
2. The specific off axis Rx error in both the primary gaze and within the primary semi field of view
3. The binocular impact, including static and dynamic versions of both prism and magnification.

More current research on the position of the CoR can be found here:

https://onlinelibrary.wiley.com/doi/...acle%20lenses.


THE ONLY freeform lens design that does all three comes from Shaw lens. And it does so by demoting cosmetics behind the fidelity of the optical result. But Rodenstock’s latest lenses use the power of individual and averaged full biometrics (corneal radius, thickness, Rx, PD and more to overcome and dramatically surpass the great fudge we call Martin’s Rule.

And before anyone here posts a reply, please do not anecdotally state that you and your customer’s experience has been good enough with current stock finished lenses, aka, 20/Happy.

Free Form SV is the way to go. I like and use IOT Endless, SV4Sant, Zeiss Individual SL and, on a more limited basis, Shaw SV.

This topic alone should be on every Advanced Master’s exam—if I had my way.

B

[drk]

Martin’s Rule of Tilt is trying to help align the image shell of the lens being fitted to the retina of the same eye, for all gaze angles up to a semi field radius of 25 degrees. By doing so, you reduce—but not wholly eliminate—most off axis blur (NOT DISTORTION!!) arising from oblique astigmatism and/power/focal plane error. To do this exactly, one would need to know the Center of Rotation (CoR) for that eye. The CoR is measured from the back vertex of the fitted lens to the apex of the cornea, and from the cornea to the CoR. In order to be a rule, some assumptions have to be made.


In Martin’s Rule:

1. The fitted vertex distance is assumed approximately 13.0 to 13.5mm.
2. The cornea to CoR is assumed to be 13.5 to 14.5mm (for a Total CoR range between 26.5mm to 27mm)
3. If the eye’s axial length or the fitted VD significantly departs from these assumptions, Martin’s Rule starts to break down.

Good stuff.

What Martin’s rule does NOT take into account is how adjusting the OC position can negatively impact (not in order)

1. The effect of abbe
2. The specific off axis Rx error in both the primary gaze and within the primary semi field of view
3. The binocular impact, including static and dynamic versions of both prism and magnification.

THE ONLY freeform lens design that does all three comes from Shaw lens. And it does so by demoting cosmetics being the fidelity of the optical result.

This is a Shaw Lens commercial, almost verbatim.

I've talked to Shaw, who is a good guy, and he defers humbly to his scientists. But he's a big market-vodoo-speak guy, and it needs disambiguated.

I'm very willing to believe that the designers at Shaw, probably like the designers at Zeiss or IOT or Shamir, have figured out a way to improve upon the "first order approximation" of the lens tilt formula being compensated. (I'm guessing Darryl's program does a pretty straightforward, workable job of it...if he has that feature, like he does for wrap.) So that's great but I doubt unique to Shaw.

Abbe? I doubt there is a cure.

As to what he calls "dynamic and static prism" that just applies to anisometropes. It's just prismatic imbalance in straight-ahead gaze and the increasing prismatic imbalance off axis.

Same with magnification differences...just anisometropes and even less an issue than prism, IMHO.

BUT! Shaw said his guys have a pretty sophisticated method of offsetting some of the goofy prismatic imbalance and whatever significant mag error that comes from ansio Rx. My limited experience (n=2) says that he's absolutely right.

Bottom line: for aniso, Shaw is my choice.

[pezfaerie]

Lensman 11 is taking over for Chip Anderson. I can dig it.