On eikonal distribution in the aperture of a two-mirror telescopic system

Abstract

The derivation of the formula describing the eikonal distribution in the aperture of an axially symmetric two-mirror system with the source displaced from the focus in an arbitrary direction is presented. The secondary focus of the system is assumed to be at infinity. The formula takes into account three terms of the eikonal expansion in powers of the source displacement. The accuracy of the derived formula has been analyzed by comparing the results of the calculation of the eikonal in the aperture of a Schwarzschild two-mirror aplanatic system obtained with the use of this formula to the results of the exact geometrical-optics calculation.