to be within $5\degr{}$ of the quasar, to minimize differences in the solar illumination angle, and the stars were observed in the orbit immediately following the quasar observations, to best match the orbital day/night cycle. The HST flight calendar builders also attempted, where possible, to schedule our quasar and PSF observations [*immediately*]{} after an HST target from a different program in a similar part of the sky as our quasar, so as to further mitigate differences in orbital thermal variations between our first and subsequent orbits on that quasar and PSF target. This special request was possible to schedule for some of our quasars. PSF star exposures were alternated in F125W and F160W to fully sample the focal variation within an orbit [for details, see @Mechtley2012]. Additionally, the stars were selected to have ($J-H$) colors similar to the quasars, since the diffraction-limited PSF also varies with wavelength. In wide filters, redder sources can have a measurably broader PSF than bluer sources.

Four exposures were taken in each orbit of quasar and PSF star observations, using the four-point box sub-pixel dither pattern to improve PSF sampling and assist in the rejection of bad pixels and cosmic rays. Critically-sampled images were reconstructed 