Stimulated emission depletion (STED) microscopy is a powerful tool for the study of sub-micron samples, especially in biology. In this article, we show a simple, straightforward method for modeling a STED microscope using Zemax geometrical optics ray tracing principles, while still achieving a realistic spot size. This method is based on scattering models, and while it employs fast ray-tracing simulations, its output behavior is consistent with the real, diffractive behavior of a STED de-excitation spot. The method can be used with Zemax Black Boxes of real objectives for analysis of their performance in a STED setup and open perspective of modeling, tolerancing performance, and then building advanced microscope systems from scratch. In an example setup, we show an analysis method for both XY and Z excitation and de-excitation intensity distributions. This method can simplify the design of custom STED setups by proper modeling of the resolution performance.
