Changes
/* Focusing the spectrograph */
Before each night's observations, you should focus the spectrograph. This is done using a scripted Hartmann sequence run from the SpUpNIC Control GUI. The process moves a shutter halfway into the beam, takes an arc exposure; then blocks the other half of the beam and takes a second arc exposure. The arc lines are then cross-correlated to measure the shift between the two. The procedure is repeated at a range of camera focus positions until the line shifts are minimised, indicating best focus. This procedure may be performed manually, but is typically run automatically, as follows:
# Take an arc to check that the grating angle is correct and to get an idea of the required exposure time (aim for at least about 1000 counts in the weaker lines): in the ''Exposure/CCD info'' pane on the ''Main View'' tab, select "Exposure type" = ARC from the drop-down menu, and enter e.g. 20 seconds in the "Exposure time" box.
# If satisfied with the arc obtained, locate the ''Hartmann focus sequence'' panel in the ''Instrument Setup'' pane on the ''Main View'' tab of the SpUpNIC Control GUI (if not, adapt the exposure time and grating angle as required before proceeding).
# Select the ''Auto'' tab and enter the parameters for the Hartmann sequence: 3.75 for the ''initial focus position'', 0.05 for the ''focus increment'' and 9 for the number of ''steps'' - with the system still set up as it was for the test arc (lamp on, arc mirror in beam), click ''Run''.
