The characteristics of a rotating polygon scanner in relation to its flat field lens are expressed as a function of relatively fixed system parameters. They include the desired resolution, number of facets, scan duty cycle, and desired pupil relief distance (to the flat field lens or to the first physical obstruction in the optical path). Account is taken of beam enlargement on the facet due to non-normal landing, and of provision to avoid excessive beam truncation at the ends of scan. Also, the location of the polygon with respect to the optical axis is determined from system parameters. Equations are provided which govern the polygon dimensions and its relationship to associated components, and application procedure is summarized.