Role of asphericity in optical design

A recent paper by Hall examined two optical design studies in which aspheric surfaces were used to benefit the system. In the case of a Petzval lens system the material cost was reduced. In a Maksutov system the introduction of aspheric surfaces resulted in increased freedom of choice in terms of system length and cost. The examples chosen were unrelated and represented radically different problems. The designs were created heuristically. The design process used manually corrected seidel aberrations, followed by damped least squares optimisation. Being isolated problems, the study gave no insight into the general problem of aspheric optical design. The problem is complicated by the intractability of the algebra involved in obtaining general solutions from seidel theory. Because of the difficulty involved, there is also not much spherical design precedent on which to base a study of aspheric systems.