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focus

focus in optics, the point at which rays converge after reflection by a concave mirror or refraction by a convex lens , also known as a real focus. The point from which rays appear to diverge after reflection by a convex mirror or refraction by a concave lens is known as a virtual focus. See image .

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focus

A Dictionary of Nursing | 2008 | Â© A Dictionary of Nursing 2008, originally published by Oxford University Press 2008. (Hide copyright information) Copyright

focus (foh-kŭs)
1. n. the point at which rays of light converge after passing through a lens.

2. n. the principal site of an infection or other disease.

3. vb. (in ophthalmology) to accommodate (see accommodation).

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focus

The Concise Oxford Dictionary of English Etymology | 1996 | | Â© The Concise Oxford Dictionary of English Etymology 1996, originally published by Oxford University Press 1996. (Hide copyright information) Copyright

focus point toward which lines, rays, etc. converge XVII; point at which an object must be situated so that a well-defined image of it may be produced by the lens; centre of activity XVIII. — L. focus fire-place, domestic hearth.
So focal XVIII.

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T. F. HOAD. "focus." The Concise Oxford Dictionary of English Etymology. 1996. Encyclopedia.com. 18 Dec. 2009 <http://www.encyclopedia.com>.

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	FOCUS Enhancements Announces Pro AV 1280 Professional Broadcast Quality Video Scan Converter. Business Wire; 3/26/2002
	Focus Enterprises Establishes San Francisco Office, Adding Two Partners: David M. Roberts and Robert J. Netter, Jr. Business Wire; 3/3/2004
	FOCUS Joins with Floberg and Associates to Expand Resources. Business Wire; 9/5/2007

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