PROXIMATE RAY TRACING AND OPTICAL-ABERRATION COEFFICIENTS

The Cox scheme of pseudo-ray-tracing, in which algebraic ray-trace equations are expanded to fifth order in terms of direction cosines, is modified by utilizing expansions in terms of direction tangents. The results are paraxial ray-trace equations and equations for third-, fifth-, and seventh-order deviations from the paraxial ray. These equations are used to trace a selected set of rays to the image space and deviations of given order are related to equal-order terms in the aberration expansion. The set of linear equations is then solved for aberration coefficients.