Strehl ratio and aberration balancing

The relation between the Strehl ratio and the wave-front variance is analyzed from the point of view of aberration balancing. For some given set of aberrations the Strehl ratio is calculated along two different parametric paths in the aberration space: one corresponding to the minimum wave-front variance and the other to the maximum Strehl ratio. The case of the combination of different orders of coma, spherical aberration, and astigmatism are shown. A simple graphic is presented to show, at constant wave-front variance, the departure of the Strehl ratio from a constant value. The wave-front-balancing functions corresponding to the maximum Strehl ratio are shown to be discontinuous or stepwise functions.