Wavefront sensing

After the replacement of the main mirror, WFS measurements were made and it was found that the same aberrations exist as before aluminisation, i.e. principally the astigmatism zenith dependency is still there. Some more WFS measurements are proposed to verify the TCS zernike values with respect to the measured ones before another attempt can be made to correct the aberrations with the active optics.

One thing that has not been tested after the aluminisation is the level of off-axis aberrations. Any such aberration does not affect observations with the current instruments but might affect observations with FRED, which is also the best instrument to check for it. This will be looked at when it becomes clear when FRED will arrive.