The assignment of aberration tolerances for optical systems suffering from wave-front aberrations greater than λ/4 is worth further studying. In this paper it is shown that "low" contrast resolving power of optical systems can be taken as an appropriate criterion for assessing image quality, where the optical transfer function can be evaluated approximately in terms of the sums of Legendre polynomials. Accordingly, the best program of aberration correction and tolerences in the case where certain aberration constants are inevitably present and others are adjustable in optical design can be obtained. The results so obtained as applied to aberrations of small magnitude comparable to λ/4 conform well to the Strehl Deffinitionshelligkeit method.