The DEIMOS internal focus can change significantly on a daily basis; hence, it's advisable to refocus the spectrograph each afternoon. Since the offsets between various filters appear to be stable over time, the standard procedure is to focus the instrument in direct imaging mode using the R filter and dome illumination. Once the focus in this fiducial filter is measured and set, the instrument's automated filter focus discipline software will adjust the internal focus as needed to account for the changes in the filter. This document describes the procedure for measuring the fiducial focus.
DEIMOS Utilities > Run/analyze focusloop (R+dome)This will configure the spectrograph appropriately for R-band dome images, acquire a sequence of 7 focus images every 1000 focus units from -5000 to -11000, analyzethe results, and display a focus map and best focus value.
Return to the Afternoon Checklist.