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A myodisc or myopic disk is a corrective lens with a steep concave curvature that is fitted on the posterior surface of a carrier lens, or a high power single-vision lens specially ordered with slab-off the edge, creating a central prescription disc. These are used for correction of extremely high myopia often seen in low vision patients. [1]
High-index: 1.60 ≤ n d < 1.74; Very high index: 1.76 ≤ n d; This is a general classification. Often for marketing purposes, materials with n d values that are at or above 1.60 can be referred to as "high-index". Likewise, Trivex and other borderline normal / mid-index materials may be referred to as mid-index.
A typical polymer has a refractive index of 1.30–1.70, but a higher refractive index is often required for specific applications. The refractive index is related to the molar refractivity, structure and weight of the monomer. In general, high molar refractivity and low molar volumes increase the refractive index of the polymer. [1]
The shortest wavelength's index is , and the longest's is . Abbe numbers are used to classify glass and other optical materials in terms of their chromaticity . For example, the higher dispersion flint glasses have relatively small Abbe numbers V < 55 {\displaystyle V<55} whereas the lower dispersion crown glasses have larger Abbe numbers.
Standard refractive index measurements are taken at the "yellow doublet" sodium D line, with a wavelength (λ) of 589 nanometers. There are also weaker dependencies on temperature , pressure / stress , etc., as well on precise material compositions (presence of dopants , etc.); for many materials and typical conditions, however, these ...
Chromatic aberration also affects black-and-white photography. Although there are no colors in the photograph, chromatic aberration will blur the image. It can be reduced by using a narrow-band color filter, or by converting a single color channel to black and white. This will, however, require longer exposure (and change the resulting image).