In previous OTF computer programs, various geometrical optical aspects of image formation appear often to have been ignored. The neglect of factors associated with anamorphotic imagery, pupil aberrations and vignetting, and a shift of focal plane can lead to considerable errors in the computed values of the transfer function, particularly for high-aperture or wide-angle systems. In addition, the numerical integration processes employed have not always been entirely satisfactory in terms of efficiency, generality, and convenience.