A quiz for you.

[drk]

Which is heavier?

1. A pound of a.) feathers or a pound of b.) lead?

2. A dice-sized chunk of a.) trivex or b.) polycarbonate?

3. A kid who is +9.00 in a.) polycarbonate or b.) trivex?

4. A +9.00 kid's glasses made in a.) polycarbonate or b.) trivex?

[lensmanmd]

Which is heavier?

1. A pound of a.) feathers or a pound of b.) lead? Both are 1 lb

2. A dice-sized chunk of a.) trivex or b.) polycarbonate? B

3. A kid who is +9.00 in a.) polycarbonate or b.) trivex? How big is the kid? What is he/she wearing?

4. A +9.00 kid's glasses made in a.) polycarbonate or b.) trivex? Trick question. Frame size matters, but B most of the time.

Bonus Question

5. A +9.00 kid's glasses made in a.) poly or b.) 1.60? This will be fun.......

[drk]

Aaah.. Thank you.

Question 4 is what I want to know. We have readily available calculators for edge thickness by material, but alas no weight calculators for high plus.

The argument goes: "Yeah, a cube of trivex is lighter than a cube of poly, but poly's 1.59 and trivex is 1.53 so overall poly will be lighter". But I don't know how you'd prove that other than cut them both and weigh them on a scale.

[lensmanmd]

Aaah.. Thank you.

Question 4 is what I want to know. We have readily available calculators for edge thickness by material, but alas no weight calculators for high plus.

The argument goes: "Yeah, a cube of trivex is lighter than a cube of poly, but poly's 1.59 and trivex is 1.53 so overall poly will be lighter". But I don't know how you'd prove that other than cut them both and weigh them on a scale.

Specific gravity, my friend, not index of refraction.
That said, decentration due to frame size can negate specific gravity savings due to added thickness. It's a delicate balance.

[drk]

Specific gravity is based on volume, so the equation is:

grams/volume X volume

But we don't know the difference in volume (which is based on index of refraction) so we can't compare. :(

[Lensman11]

You can calculate the answer not at an engineering level. Poly is 10% thinner than Trivex and 10% heavier so the end result is they will way the same.

[drk]

I love it!

[Jason H]

Please fit a +9.00 d child in a frame that fits. Once you do the quiz doesn't matter.

[drk]

I hear you, Jason!



This is her. We did use Trivex, and we did a blue roll. Looks pretty good, if you ask me.

The asian-fit bridges are pretty great, though.

[drk]

Here were her old glasses (from Warby Parker):

[Uncle Fester]

Wow! Just WOW!!

Scout's honor she's not wearing -6.00 CL's behind that "Just say no can do" frame???

[DanLiv]

You can calculate the answer not at an engineering level. Poly is 10% thinner than Trivex and 10% heavier so the end result is they will way the same.

Thanks for solidifying this suspicion for me! For my own brain happiness I also confirmed via Darryl Meister's incredible Spectacle Optics application.

Apart from weight, poly also has the advantage of slightly reduced magnification, and you can couple that with traditional aspheric to further reduce mag (doe anyone even manufacture traditional aspheric Trivex blanks?). Also you can reliably get poly to 1.0mm or knife-edge thinness, attempts I have made to do the same in Trivex never come out as precisely thin.

The only thing I use Trivex for is when I really want poly but: high cyl and I'm a little concerned about the ABBE, SV, correctable to 20/20, in a grooved or rimless frame. If not all these factors are met, I'll stick with poly or 1.60.

[Uncle Fester]

I hear you, Jason!



This is her. We did use Trivex, and we did a blue roll. Looks pretty good, if you ask me.

The asian-fit bridges are pretty great, though.

DOH!

Just remembered the date!!!

[Prentice Pro 9000]

Correct me if I’m wrong: trivex is lighter but has a lower refractive index, so you need more material than you would need in poly for the same Rx. Essentially they come out the same weight.

As a rule I tend to go with poly in weight matters . I know opticians will cry about the ABBE value, but I’ve never had a problem especially if people have been in poly for forever anyways. With plus lenses, poly almost always comes out weighing less and darn near the same size (you can knife edge them much better than high-index)

eh…

[Robert Martellaro]

On a more serious note, at these powers (>±7 D) the surface design must be aspheric/atoric to achieve best form (minimal oblique astigmatism and mean power error). However, poly or 1.67 and others have an Abbe value too low to be practical, inducing .3∆ @ 10mm and .5∆ @ 15mm of lateral chromaticism.

Best regards,

Robert Martellaro

[jefe]

Here were her old glasses (from Warby Parker):

Wow! Those glasses really make her eyes pop!

[Kwill212]

Correct me if I’m wrong: trivex is lighter but has a lower refractive index, so you need more material than you would need in poly for the same Rx. Essentially they come out the same weight.

As a rule I tend to go with poly in weight matters . I know opticians will cry about the ABBE value, but I’ve never had a problem especially if people have been in poly for forever anyways. With plus lenses, poly almost always comes out weighing less and darn near the same size (you can knife edge them much better than high-index)

eh…

Here is Younger's take on it, which seems to jive with the spectacle optics program. Trilogy trivex.

[drk]

Ooo, that's fun. Thanks Q!