Boundary Layer Seeing, part 2

This video was recorded an hour later. The mirror was cooled by means of a front placed fan like in this photo . In the meanwhile the temperature dropped below freezing. Compared to the former recording, the turbulent front layer is now reduced. However, because the fan blows onto the mirror centre, the mirror does not cool uniformly and bends (making a depression in the centre). This causes the appaerance of shperical aberrations, that can be noticed by the fact that the shadow of the secondary is shrinked now. Of course the mirror will recover its figure in the time.