Proximate ray tracing and optical aberration coefficients

Algebraic ray-trace equations for axially symmetric optical systems are expanded in terms of system parameters and paraxial variables. The results are the paraxial ray-trace equations and equations for third-, fifth-, and seventh-order deviations from the paraxial ray. These equations, which approximate real rays in an extended region about the axis, are used to trace a selected set of rays to the image space. Deviations of given order are then related to equal-order terms in the aberration expansion. The resulting set of linear equations is solved for aberration coefficients.