Wavefront sensing

A summary report of the tests made over the past few years using the ALFOSC wavefront sensor (WFS) was made. The most significant aberration of the telescope is astigmatism that has an altitude dependence. From the WFS data a fit to the amplitude variation has been made but consistent measurements of the angle have proven difficult.

The new seeing data-base was used to look at the possible effect of the aberration by making a fit of the variation of ellipticity as a function of altitude, principly to look for the variations in angle but also to see if the amplitude varies. From the analysis it seems that the dominate angle is 10 degrees off vertical with respect to the altitude motion. This is actually the angle of the currently applied correction suggesting we are applying too large a correction. Measurements have been made to check if the applied zernike terms are too large, but the data has not been looked at yet.