Astigmatism and field curvature of lithography lenses can be measured with an error less than 30 nm using an optical microscope and conventional resolution test patterns. A sequence of through-focus images, recorded in positive resist, are examined with an optical microscope to determine the smallest lines remaining after development. It is only necessary to judge existence of lines; no dimensional measurements are required. Imperfections in fabrication and design that limit the resolution of most lithography lenses are easily identified by this new technique. The method for doing the measurements, the analysis, and recent application to characterization of lithography lenses are presented.