Image Quality Criteria Derived from Skew Traces

Simple inspection of spot diagrams is often enough to guide design by indicating the optimum imagery which results from variation of system parameters. However, quantitative criteria are necessary for the control of computation by stored-program machines. Skew traces yield data from which these criteria may be evaluated by methods (some old and some new) sketched below. In some cases, spot positions are enough. In others, optical path differences are also required. By such means, it is possible to determine what depth of aspherical figuring, if any, is desirable for a given system, and what other parameter values optimize the system in the sense of a given test. No universally satisfactory single criterion exists, but maximum reciprocal aberration and minimum required retouching are suggested as being often useful.