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In optics and lens design, the Abbe number, also known as the V-number or constringence of a transparent material, is an approximate measure of the material's dispersion (change of refractive index versus wavelength), with high values of V indicating low dispersion. It is named after Ernst Abbe (1840–1905), the German physicist who defined it.
Varilux. Varilux is a brand name belonging to Essilor International, a producer of corrective lenses. The first version of the lens was invented by Bernard Maitenaz and released in 1959, and was the first modern progressive lens to correct presbyopia. The progressive lens is characterized by correcting near, intermediate and far vision.
Bernard Maitenaz, patented Varilux in 1953, and the product was introduced in 1959 by Société des Lunetiers (now Essilor). The first Varilux lenses' surface structure was however still close to a bifocal lens, with an upper, aberration-free half of the surface for far vision and a rather large "segment" for clear near vision.
An optical instrument is said to be diffraction-limited if it has reached this limit of resolution performance. Other factors may affect an optical system's performance, such as lens imperfections or aberrations, but these are caused by errors in the manufacture or calculation of a lens, whereas the diffraction limit is the maximum resolution ...
The add segment of the lens for near vision is the D-shaped area. A bifocal is a lens with two sections, separated by a line (see image to the right). Generally, the upper part of the lens is used for distance vision, while the lower segment is used for near vision. The area of the lens that caters to near vision is called the add segment.
On a brand-new episode of "Antiques Roadshow" Monday, a Fred Myrick scrimshaw tooth got a price tag that would probably put said fairy in a lot of debt. "Today, we're going to give it an insurance ...
Chromatic aberration. Focal length of lens varies with the color of light. In optics, chromatic aberration ( CA ), also called chromatic distortion, color aberration, color fringing, or purple fringing, is a failure of a lens to focus all colors to the same point. [ 1][ 2] It is caused by dispersion: the refractive index of the lens elements ...
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