Hubble WFC3 PSFs generated using TinyTim, assuming a flat spectrum, F814W filter, point source in the center of detector 1, 1.78 answered to cryptic final question "Focus, secondary mirror despace? [microns]", from https://www.stsci.edu/hst/instrumentation/focus-and-pointing/focus/secondary-mirror-moves. Plots below are for 5x sub-pixel sampling and show PSF value / pixel area:
Hubble WFC3 PSFs generated using TinyTim, assuming a flat spectrum, F814W filter, point source in the center of detector 1, 1.78 answered to cryptic final question "Focus, secondary mirror despace? [microns]", from https://www.stsci.edu/hst/instrumentation/focus-and-pointing/focus/secondary-mirror-moves. Plots below are for 5x sub-pixel sampling and show PSF value / pixel area: