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principal focus

noun

, Optics.


principal focus

noun

  1. another name for focal point
“Collins English Dictionary — Complete & Unabridged” 2012 Digital Edition © William Collins Sons & Co. Ltd. 1979, 1986 © HarperCollins Publishers 1998, 2000, 2003, 2005, 2006, 2007, 2009, 2012


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Word History and Origins

Origin of principal focus1

First recorded in 1825–35
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Example Sentences

The distance from the principal focus to the center of the lens is the focal length or principal focal distance of the lens.

The point midway between the vertex V and center of curvature C is called the principal focus, F.

The principal focus of a concave mirror may be observed by holding the mirror in a beam of sunlight entering a darkened room.

The greater the refractive power of the lens, the greater the bending, and the nearer the principal focus to the lens.

If the light be placed beyond the principal focus of the lens, the rays will converge to a point some distance ahead of it.

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