next up previous contents
Next: Pointing Up: Telescope Previous: Telescope   Contents

Wavefront sensing

In April 2003 a full night of WFS observations were made. These results agreed with most of the previous measurements. The most important feature that can be seen in both sets of data taken in 2003 is a significant mean increase in astigmatism over the March 2002 measurements. These latter measurements were made before the aluminisation of the mirrors. After two reports from observers of elongated images we attempt to remove this offset in astigmatism by applying appropriate corrections to the M1 active optics system. A check of the mirror figure, after the correction, with the WFS in early August verified the astigmatism had been reduce to the pre-aluminisation level.

A consistent and most significant feature in all the data is a clear linear dependence of astigmatism with zenith angle and it the idea is that this in the future will be corrected for by the TCS through the active optics system.

Thomas Augusteijn 2004-01-06