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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 ...
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 ...
The cost of the surgery can be significant. According to ASPS, the average cost of a surgeon’s fee for cosmetic breast reduction is $6,771. Additional fees may include anesthesia and hospital or ...
Clear lens extraction, also known as refractive lensectomy, custom lens replacement or refractive lens exchange is a surgical procedure in which clear lens of the human eye is removed. Unlike cataract surgery , where cloudy lens is removed to treat cataract , clear lens extraction is done to surgically correct refractive errors such as high ...
ALICE is a term to describe those whose income is above the Federal Poverty Level — so they don’t qualify for public assistance — yet they don’t earn enough to cover basic expenses such as ...