User:Dan Polansky/Corrective lens

Aspheric lens
Aspheric lens are allegedly thinner than spheric ones; to be verified.

Aspheric lens reduce distortion at the edges of the lens as compared to spheric ones; to be verified.

Do aspheric lens increase chromatic aberration as compared to spheric ones? An editor seems to think so:
 * "In my experience, aspherics have created unacceptable chromatic aberration and mis-focusing 15+ degrees off the direct line of sight, to the point where I feel driving would be dangerous." --Nick Hill at Talk:Corrective_lens

See also:
 * Aspheric_lens

Chromatic aberration
High-index lens tend to have higher chromatic aberration AKA color distortion. This directly depends on the Abbe number, listed in ; the higher the Abbe number, the lower the distortion.

See also:
 * Chromatic aberration

Links:
 * chromatic aberration, britannica.com

Weight
The effectively lightest material for corrective lens for glasses for many combinations of prescription and diameter seems to be Trivex. The weight of a lens depends on two factors: the volume of the lens and the density of the used material. Hi-index materials provide lower volume of a lens, albeit often at the cost of higher density. Trivex leading to lightest lens follows from Materials for spectacle lenses by Mo Jalie; verify for yourself; danger of error on my part. There, by combining the data from Table 2, Table 3, Table 4, and Table 5, lens made from Trivex appear to be the lightest for diameter 40 and 50; Trivex is represented in table 2 in row 4, starting with "1.532 / 1.10"; for diameter 60, material "1.74 / 1.4" comes out the same as Trivex: 10.2 g; for diameter 70, materials represented as "1.710 / 1.4" and "1.74 / 1.4" outperform Trivex in weight by a narrow margin (Trives: 17.8 g vs. "1.710 / 1.4": 17.7 g vs. "1.74 / 1.4" 17.1 g). These tables are for -5.00D lenses; with higher-prescription lens and high diameter, other materials may outperform Trivex as for weight.

Ideally, one should be able to determine the weight from the index, density, center thickness, prescription, and the diameter using a formula; I am unable to do that.

The characteristics in Table 2, Table 3, Table 4, and Table 5 of Mo Jalie are as follows:
 * nd - index AKA refractive index
 * D - density (g/cm3)
 * ct - center thickness (mm)
 * et - edge thickness (mm)
 * wt - weight (g)
 * diameter - diameter of the lens (mm)

Trivex is marketed by HOYA under the Phoenix brand (PNX), by Younger Optics under Trilogy brand, by Augen Optics and by X-Cel Optical.

Frame weight: The weight of the lens is one of the two components of the overall weight of glasses. Glasses can be made as light as possible by minimizing both lens weight and frame weight. Frame weight can be minimized by using rimless frame made from titanium; the choice involved is the one of (a) rimless frame and (b) titanium rather than steel. While the density of steel usually ranges between 7.75 and 8.05 g/cm3 (as per Steel), the density of titanium is 4.506 g/cm3 (as per Titanium), making the same-volume titanium frames up to 1.78 times lighter. It would have to be clarified whether titanium frames really are being made of the same volume as steel ones. Moreover, titanium rimless frames seem to be made from titanium alloys, so the density of the alloy would have to be considered instead of the density of titanium alone.

Ophthalmic material property tables
The following originates from Glasses. It can be in part confirmed in the following sources:
 * OptiCampus Material Reference Chart, opticampus.com
 * Materials for spectacle lenses by Mo Jalie