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Meaning of nodal point

nod'al point'

Pronunciation: [key]
— Optics. Optics.
  1. either of two points on the axis of a lens or other optical system, determined by extending an incident oblique ray and the corresponding refracted ray to the axis for the pair of rays that are parallel outside the optical system. Also called
Random House Unabridged Dictionary, Copyright © 1997, by Random House, Inc., on Infoplease.