Optics any ray that traverses an optical system and suffers no net change in direction. The system may displace the refracted ray with respect to the incident nodal ray. Nodal rays occur in concentric optical systems , as well as paraxial and Gaussian systems. Paraxial Optics cardinal points on the paraxial axis where a Gaussian nodal ray is aimed at or appears to originate from.
Every paraxial system has two nodal points.
Optics center of symmetry of a concentric optical system . Paraxial Optics common nodal point of a zero-offset paraxial system.