Given the efficiency of the new camera and the increased number of guide stars provided by the new guide star catalog it has been decided to limit the area covered by the guide probe where to look for guide stars. This will limit any problems when doing offsets where one wants to keep the same guide star as the guide star is less likely to fall out of reach of the guide probe. The area will be chosen such that at least 10 stars will be found above the detection limit of the system over the whole sky.
With the guide stars falling in a similar area on the sky with respect to the instrument in use, one would expect any relative distortion to be similar. We plan to implement a system in which the guide star will be automatically detected and centered on the camera, which combined should improve the effective pointing of the telescope significantly.
In any case, at all times guide stars from the whole area available to the guide probe can be selected which should avoid any problems in case of bad weather or special (e.g, offset) requirements.
It was found that the `blue' filter position listed for the guide camera actually did not contain a filter but was effectively blocked. A new blue-green filter was installed which can be useful when doing spectroscopy in the blue (to counter the effects of atmospheric diffraction).
Thomas Augusteijn 2006-05-08