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principal focus

noun, Optics.
focal point (def 1).
Origin of principal focus
First recorded in 1825-35 Unabridged
Based on the Random House Dictionary, © Random House, Inc. 2018.
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Examples from the Web for principal focus
Historical Examples
  • The magnifying power is greater as the lens is more convex and the object near to the principal focus.

  • By aperture is meant the angle obtained by joining the edges of a lens with the principal focus.

  • The focal length of the lens was 150 feet, and the mirror was placed about 15 feet within the principal focus.

  • The former of these two has a lateral focus, besides the principal focus or pole.

    The Plurality of Worlds William Whewell
  • To avoid confusion, this focal length is known as the principal focus, and is denoted by the symbol f.

    How it Works Archibald Williams
  • This point is termed the “first principal focus” (German der objektseitige Brennpunkt, the object-side focus).

  • (B) principal focus, focal length, virtual focus, conjugate foci.

    Physics Willis Eugene Tower
  • The strip is made to run in a groove across the principal focus.

    The Royal Observatory Greenwich

    E. Walter (Edwared Walter) Maunder
  • The greater the refractive power of the lens, the greater the bending, and the nearer the principal focus to the lens.

    General Science Bertha M. Clark
  • The distance from the principal focus to the center of the lens is the focal length or principal focal distance of the lens.

    Physics Willis Eugene Tower
British Dictionary definitions for principal focus

principal focus

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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