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 it is typically run automatically, as follows:
* # Take an arc to check that the grating angle is appropriate for your desired wavelength range, and to get an idea of the required exposure time (aim for at least ~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. 10 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: 3.6 7 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). A bug in the software causes the Hartmann routine to fail if the camera focus isn't first set to the "initial focus pos", so enter 3.7 in the Camera focus "REQUESTED" box above, then click "Go". Once the focus has changed, click ''Run''to start the Hartmann sequence. * # The slit width will automatically be set to 1.05" and the exposure type will switch to HARTMANN, then the GUI will grey out and not be available during the focus sequence (although you will see the ''Current Camera Focus'' field changing and the Hartmann shutters indicate ''Moving''.* # On completion of the sequence: in the SpUpNIC Quick-Look GUI, in the log box to the right of the spectrum display window, you will see a list of focus positions and their corresponding pixel shifts. Best focus corresponds to a shift of zero.* Enter # The camera focus should automatically be set to the best focus value, but if it isn't, enter the best focus into the ''Requested " Camera Focus'' box on the SpUpNIC Control GUI's ''Instrument Setup'' pane and click ''Go''.* The Hartmann sequence ends with the shutter out of the beam, but for some reason it sends the slit width be sure to zero! So select the desired slit width in the ''Instrument Setup'' pane and click ''Go''. Check that it goes to the required position, click ''Go'' again if it does not do it the first time.
* Select "Exposure type" = ARC and take an arc to confirm that the focus looks good.
* Click on the arc mirror in the schematic to switch off the arc lamp and move the arc mirror out of the beam.