In tolerancing a lens system, it is necessary to know the effects of fabrication and alignment errors on the image quality. In this report, the wavefront aberration due to a small parameter perturbation is derived. This may be calculated from ray tracing through the nominal system only, and its linearity is extremely useful for tolerancing. The results are applied to the calculation of the variance, or rms, of the wavefront as a tolerancing criterion.
M. Rimmer, "Analysis of Perturbed Lens Systems," Appl. Opt. 9, 533-537 (1970)