There were a few reports of elongated star images. A problem with the optics can safely be excluded, though it can be that in some cases the elongation comes from observing with the telescope out of focus or at very high zenith distance where we know there is some variation in astigmatism which is not corrected. One possible thing that might cause elliptical star images are periodic errors in the drives of the telescope. These are in principle corrected in software, but the effect of the periodic errors in the altitude and azimuth drive will vary as a function of the position on the sky and any correction might be more or less effective. Tracking tests did not show any problems, but more tests should be done with the telescope pointing to different areas of the sky.

Thomas Augusteijn 2006-02-02