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Main mirror alignment

It was noted by Michael Anderson that the mirror alignment procedure made after the last aluminization did not work properly and that the current alignment of the mirrors is likely not to be optimal. The main question is the tilt of the focal plane which needs to be checked. Depending on the tilt we should decide what to do after the next aluminization which is for seen for next year.

To check the focal plane tilt a through-focus series of images on a moderately crowded field (an open cluster) was made with ALFOSC and repeated with the rotator turned 180 degrees to separate the tilt of the focal plane from the tilt of the instrument detector with respect to the telescope. The results with ALFOSC were ambiguous and the test was repeated with MOSCA for 4 different rotator positions. The data are currently being analyzed.

Thomas Augusteijn 2005-10-27