Abstract
Using the concept of matrix theory for lens design, a triplet lens can be replaced by a singlet lens which has an equivalent system matrix without changing its optical performance. Then, using third order Siedel's first aberration coefficient of the singlet lens is equal to zero, and the focal length and the physical length of the triplet lens are kept constant as constraints, an algebraic technique for optimizing a triplet lens is derived. Results show that this new optimizing technique is more effective than other conventional techniques for optimizing a triplet lens in the case of plane waves.