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A point at which rays of light or other radiation converge or from which they appear to diverge, as after refraction or reflection in an optical system: the focus of a lens. Also called focal point.
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See focal length.
(noun)
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The distinctness or clarity of an image rendered by an optical system.
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The state of maximum distinctness or clarity of such an image: in focus; out of focus.
(noun)
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An apparatus used to adjust the focal length of an optical system in order to make an image distinct or clear: a camera with automatic focus.
(noun)
American Heritage(R) Dictionary of the English Language, Fifth Edition. Copyright (c) 2011 by Houghton Mifflin Harcourt Publishing Company. Published by Houghton Mifflin Harcourt Publishing Company. All rights reserved.