To study the quantitative impact of diffractive optical elements on lens design and glass selection, a Zeiss Tessar lens (f/6) with and without a diffractive optical element is optimized with respect to the wavefront performance by a Zemax(R) Hammer routine. Optimization includes the selection of glasses as well as the geometry of the optical elements. In a first run, these are all refractive elements. In a second run, one refractive element is replaced with one diffractive surface. In a third run, the diffractive surface is introduced as an additional feature.
It is found that one refractive element can be replaced with a diffractive surface at a moderate loss of lens performance. This holds, however, only for an optimized glass selection, which is found to be particularly important. In the case of four refractive elements plus diffractive surface, an according result is obtained. The diffractive surface will improve the overall system performance if and only if the glass selection is appropriate.
Glass selection tends to be both a science and an art. It is the intent of this paper to remove the "mystique" surrounding glass selection, primarily based on the chromatic properties of the glass, and to show via careful parametric analyses how we can optimally select glasses for lenses of different f/numbers, spectral bands, and performance requirements. The important roles of refractive index and Abbe number as well as partial dispersion will be considered. Using the SCHOTT glass map, six separate and identifiable regions along with glasses within each region will be discussed. The goal for this paper is to make glass selection easier to understand.