Guide star acquisition

A few improvements have been made to the guide star selection. To protect the guide camera very bright stars ($<$9 mag) are excluded from the search for guide stars, while for stars brighter than 11.7 mag a grey filter is put in the beam. It has been noted that for the faintest stars in this range the guide star can often only barely be seen and might not be detected by the system. Basically, the change from using the grey to not using it was to steep and a scheme was implemented where an intermediately attenuating filter (a `yellow' filter) is used for the faintest `bright' stars. Also, the selection system was changed such that no guide star is selected near to a star (closer that the size of the guide camera's field of view) that is excluded because of its brightness.

One of the most stringent limitations on areas available for guide stars is that defined for beam-switching observations with NOTCam which require offsets larger than the field-of-view of the camera (4$\times$4 arcmin for the wide-field camera). To improve this, separate areas were defined for each direction where a bigger area can be used in each separate case. These options have now been verified.