The FOC Exposure Simulator, FOCSIM, provides the capability to simulate almost any FOC exposure and to calculate diagnostics about the image. FOCSIM, the FOC exposure SIMulator, uses the most current description of the FOC and its filters along with an input spectra (either from an on-line catalog or user-supplied file) to simulate an image from the FOC and provide the count rate within the image. ... Where to Find FOCSIM . ... How to run FOCSIM . ... What Sources can FOCSIM Simulate . ...