The influence of the construction parameters of an optical system such as radii of curvature, refractive indices, thicknesses, and distances of lenses on the optical transfer function (O.T.F.) is discussed with the example of variation of radii. To find out the critical or uncritical parameters of a compound system, the Seidel coefficients (first aberration) are generally sufficient. Then the exact coefficients of wave aberrations are varied by given amounts and the corresponding O.T.F. is calculated and tabulated. The permissible variation of the coefficients for a given tolerance of O.T.F. in a limited spatial frequency range can be seen from the table. The presented technique is demonstrated for a lens of nine surfaces.