nodal point

noun 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.

n.

1. One of the two points in a compound optical system, located so that a light ray directed through the first point will leave the system through the second point, parallel to its original direction.axial point