The Frequency Response of Optical Systems

In optical systems the pencils forming images of extra-axial object points are generally oblique to both the object and image planes. The diffraction image of a point source observed in an oblique image plane differs significantly from that obtained in a plane normal to the image-forming pencil. The theory of the frequency response of optical systems is formulated for this more general case. The resulting formulae are used to relate the response obtained between object and image planes perpendicular to the optical axis to that obtained between planes perpendicular to the principal rays. It is shown that no loss of generality is introduced by the restriction to unidimensional objects. Some general properties of the response function for optical systems having aberration are derived.