PhoSim Tutorial 21: How to Simulate a Focus Test

PhoSim can simulate focus tests in the same way as is typical during telescope calibrations. A focus test moves the focal plane by various steps during the exposure. The focus command in PhoSim sets the number of steps, the step in microns, and the spacing between the focus steps in arcseconds. The following catalog generates a focus test on a random field.

rightascension 0

declination 0

moonalt -90.0

obstime 100.0

focus 15 50.0 5.0

stars 15.0 30.0 0.666

galaxies 15.0 30.0 0.666

The following command is used to generate the image below.

phosim catalog -c examples/quickbackground --ds9

The bright stars are visible with the 15 steps defined in the catalog. The first step is always double to get the correct orientation. The system is approximately in focus, since the best focus is approximately in the middle of the sequence.