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focal plane

noun, Optics.
a plane through a focal point and normal to the axis of a lens, mirror, or other optical system.
Compare principal plane.
the transverse plane in a telescope where the real image of a distant view is in focus.
Origin of focal plane
First recorded in 1890-95 Unabridged
Based on the Random House Dictionary, © Random House, Inc. 2018.
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British Dictionary definitions for focal plane

focal plane

the plane that is perpendicular to the axis of a lens or mirror and passes through the focal point
the plane in a telescope, camera, or other optical instrument in which a real image is in focus
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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