Ray-tracing simulated telescope point-spread function used in this paper. The images show the response of one eROSITA mirror module to a point-source at different incoming photon energies (from top to bottom: 1, 3 and 7 keV) and different angular distances from the optical axis (from left to right: on-axis, 15′, 25′). The colour scale in each panel is linear and encompasses the tenfold increase between the minimal (light red) and maximal (black) intensity, thereby emphasising the typical shape distortions due to Wolter optics.