focal plane

noun

Optics.

1. a plane through a focal point and normal to the axis of a lens, mirror, or other optical system.

2. the transverse plane in a telescope where the real image of a distant view is in focus.

focal plane

noun

1. the plane that is perpendicular to the axis of a lens or mirror and passes through the focal point

2. the plane in a telescope, camera, or other optical instrument in which a real image is in focus

Word History and Origins

Origin of focal plane¹

First recorded in 1890–95