Changes
/* Setting up the grating */
====Setting up the grating====
* '''N.B.''' We have now installed a physical brake on the SpUpNIC suffered severe grating to address the instability problem mentioned below. One cannot change problems which have been incrementally reduced through various interventions, the grating angle when last of which was the brake is applied, and we have disabled the ability introduction (in early November 2016) of a pneumatically-actuated lock to change clamp the grating mechanism at the user-defined angle in software to prevent accidental damage. This The lock is under software control and can thus be rede-enabled, but only when activated by the brake is not applieduser in order to adjust the grating. A technician is therefore required We are delighted to disable report that the brake and change lock has eliminated the last of the play within the grating angle. mechanism! And hence Flexure remains a sad reality for changing gratings Cassegrain spectrgraphs though as well, since the angle needs to be set to zero in order to remove/insert a grating. * '''Warning:''' During your start-off you will have been told they swing about the grating instability problem. We applied a mechanical fix when sky on the instrument is off the telescope in early Aprilbacks of telescopes. This improved the situation, but did not completely resolve the issue - so until such time as we have eliminated the problem, Thus we urge still recommend that users to bracket all their target observations with arcs (to be taken immediately before and after the object exposures) so as to minimise the impact of the declination-dependent movement of the gratingcalibrate out any remaining shifts due to flexure.
* The angles listed in the second last column of the table below will get one into the range where lines are visible for a given grating, then adjust the grating angle to obtain the desired wavelength range - consult the arc maps in the right-hand column of the table, or see the ones in the old spectrograph user manual (a hard copy is available in the warm room).
