fo'cal plane"

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.

focal lengthfocal-plane shutter


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