Mirror reflectivity

The procedure when wet cleaning the main mirror has be changed, where paper is used to dry the mirror instead of blowing air. This both is much faster and leaves less stains on the mirror.

Reflectivity measurements and ALFOSC photometric zero point monitoring suggest that there are no dramatic changes in the reflectivity, just the expected steady decline. The last aluminisation is now more than 4 years ago, but that aluminisation was not completely successful as the reflectivity was not fully restored. The current values are around (or slightly below) the values found shortly before the last aluminisation so it was decided to proceed with the aluminisation that we already tentatively had planned for the coming summer.