focal plane

noun

, Optics.

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

Example Sentences

The total movement of the half-object glass is double the distance between the star images in the focal plane.

From Project Gutenberg

Rays of light from some distant object are converged by the objective (D) and form an inverted image (ab) at the focal plane (F).

From Project Gutenberg

If any error of convexity exists in the plate, the focal plane is disturbed, and the eyepiece must be moved out.

From Project Gutenberg

The photographer must change the plate, set the focal plane shutter, and press the release.

From Project Gutenberg

The focal plane of the light is elevated 93 ft. above high water.

From Project Gutenberg