Meaning of focal plane

fo'cal plane"

Pronunciation: [key]
— Optics. Optics.
  1. a plane through a focal point and normal to the axis of a lens, mirror, or other optical system. Cf. principal plane.
  2. the transverse plane in a telescope where the real image of a distant view is in focus.
Random House Unabridged Dictionary, Copyright © 1997, by Random House, Inc., on Infoplease.