Method for measuring magnification of an afocal optical system

The present invention relates generally to afocal optical systems and, more particularly, to methods and apparatus for accurately measuring the magnification of afocal optical systems. A method is taught for measuring magnification of an afocal optical system. The method comprises the steps of directing a collimated light beam through the afocal optical system; intercepting the collimated beam exiting the afocal optical system with a prism; generating two reflected return beams at a first angle therebetween with the prism; passing the two reflected return beams through the afocal optical system; observing an interference pattern created by the two reflected return beams after exiting the afocal optical system; measuring a spacing between at least two fringes of the interference pattern; determining a second angle between the two reflected return beams exiting the afocal optical system using the spacing of the at least two fringes of the interference pattern; and comparing the second angle between the two reflected return beams exiting the afocal optical system to the first angle between the two reflected return beams immediately exiting the prism to thereby measure the magnification of the afocal optical system.