Described here is an approach to aberration tolerancing utilizing aerial image parameterization based on photoresist capability. A minimum aerial image metric is determined from either a characterized resist process or desirable resist attributes and includes definition of resist exposure, diffusion, and development properties. Minimum aerial image requirements can then be correlated to resist performance to allow for the evaluation of various feature sizes and types. This allows, for example, the prediction of lens performance through focus, across the field, and in the presence of small levels of internal flare. Results can then be compared with more conventional optical metrics such as Strehl ratio, partial coherence contrast, or image threshold CD. Results are presented for three commercial small field catadioptric 193 nm lithographic lenses. Aberration levels for each lens at several field positions and at several wavelengths has been described using 37. Zernike polynomial coefficients. Minimum aerial image requirements have been correlated to resist performance to allow the evaluation of various feature types, a unique situation when no mature 193 nm resist process existed. Additionally, the impact of modified illumination on aberrations is presented.