Choosing between Abbe numbers or eyeball miniaturization

[Robert Martellaro]

-6.00 in 1.74 should go on a spherical 2.50 in a point focal design "punktal". My suggestion if a blank exists is push a little higher, 1.00 diopter is as far as i would push. So a 3.50 base, aspherize the back to compensate the error.

I used D. Meister's Optical Analysis Calculator to arrive at the +6 base curve value for best form 1.74 spherical. I believe that point focal designs try to minimize oblique astigmatism, so a -6 D 1.74 spherical design lens at 30° has .60 D of oblique astigmatism with a +2.50 BC, .12 D with a + 6 BC, and zero with a +7.25 BC. The +6 BC has less rms power error though, and is probably more representative of todays hybrid/compromised surface design goals.

Increasing the refractive index requires an increase in the base curve if we want to minimize oblique astigmatism and rms power error, if not corrected for by other means, that is, with aspheric/atoric surface designs.

Remember when 1.67 became available and many were not aspheric? The labs would incorrectly use flatter base curves for cosmetics but many folks complained of poor optics, primarily with their off-axis vision (aggravated by high levels of chromatic aberration). The premium lenses were aspheric, allowing for the use of flatter curves without too much compromise. This still goes on today, even with the use of "digital" lenses, depending on the lens design, implementation, and the skills of the optician.

Best regards,

Robert Martellaro

[MakeOptics]

I used D. Meister's Optical Analysis Calculator to arrive at the +6 base curve value for best form 1.74 spherical. I believe that point focal designs try to minimize oblique astigmatism, so a -6 D 1.74 spherical design lens at 30° has .60 D of oblique astigmatism with a +2.50 BC, .12 D with a + 6 BC, and zero with a +7.25 BC. The +6 BC has less rms power error though, and is probably more representative of todays hybrid/compromised surface design goals.

Increasing the refractive index requires an increase in the base curve if we want to minimize oblique astigmatism and rms power error, if not corrected for by other means, that is, with aspheric/atoric surface designs.

Remember when 1.67 became available and many were not aspheric? The labs would incorrectly use flatter base curves for cosmetics but many folks complained of poor optics, primarily with their off-axis vision (aggravated by high levels of chromatic aberration). The premium lenses were aspheric, allowing for the use of flatter curves without too much compromise. This still goes on today, even with the use of "digital" lenses, depending on the lens design, implementation, and the skills of the optician.

Best regards,

Robert Martellaro

6.00 is still best for as well. It's a Percival design, best for has many different forms depending on definition. Flatter curves make for better cosmetics, which have to be factored in for the average client. Assuming no asphericity. I use my own calculator https://makeoptics.com/harrychiling/...ess-calculator I know it's pedigree and can extend it if and when necessary so I prefer it. I have a copy of Darryl program and miss him much. That being said technical data, the raw math alone does not make an acceptable lens. Cosmetics is a huge an important factor, if it was not we could skip the 1.74 and go for a CR lens (absolutely not glass as the abbe between CR and glass is negligible but the weight difference would make the CR that much lighter), RMS is an interesting metric, square root of the sum of the squared power error and marginal astigmatism, we can defiantly learn a lesson balance is the key performance optics with optimal cosmetics is the sweet spot. I would hate to see a 6 base -6.00 without some sort of modern trickery. With asperic/atoric backs and blended myodiscs compromise is a thing of the past.

Once again always fun to watch your mind work Robert, thanks.