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Abbe number. 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 ...
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.
Purpose. The purpose of a dental cleaning is to remove tartar and plaque from the surface of your teeth, in between your teeth, and on your gums. Dental plaque is the sticky film of bacteria that ...
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.
It launched the payments program in March after a hack at Change Healthcare on Feb. 21 by a group called ALPHV, also known as "BlackCat", disrupted medical insurance payments across the United States.
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 ...
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 ...