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#REDIRECT ] |
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{{Redirect category shell|1= |
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'''Vertometer''' was the trade name of an instrument made by ] (B&L) and later by ]. |
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{{R from merge}} |
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Lensometer was the trade name of the nearly similar instrument made by ]. |
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{{R from duplicated article}} |
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Neither the Vertometer or the Lensometer is now being made. |
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}} |
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] is a generic name that can be applied to any lens measuring instrument. |
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''''''A '''vertometer''' is an ophthalmic bench instrument used to measure ] of a lens. It differs from a ] or ] which is a general dispensary tool for ]s to verify spectacle prescriptions at the laboratory. A vertometer, on the other hand, is a more precision instrument used to locate, mark, and index a lens optical center for edging, mounting, and construction of a ] ]. |
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== History == |
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The theory of geometrical optics uses ray tracing techniques. In many of his models, ] used a mathematical formula that measured a ] distance. This nomenclature prevailed throughout hundreds of years, during a time that studies of optics may have been misunderstood. Derived from the word, the measure of the focal length of a lens is represented by the reciprocal of the vertex distance in meters, or ]s. Vertometers measure ''sphere ± cylinder x axis'', and can be used to calculate prismatic power by indexing the optical center offset from the visual axis. An ink coated stylus is used to mark optic centers on the lens in the optical laboratory. A millimeter rule would be nearby for spectacle eyesize fittings. |
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== See also == |
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{{wikiversity|Understanding vertometry}} |
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* ] |
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* ] |
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* ] |
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== References == |
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* ''(includes picture of instrument)'' |
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] |
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] |
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