While the success of the ESO 2.2-m telescope already casted doubts on some traditional dome concepts, the real revolution in enclosure design came in the early 80s with the Multi-Mirror Telescope (MMT), in Arizona. The designers of the MMT were led by the particular telescope structure and financial budget constraints to make a box-like sharp-edged building, which rotated together with the telescope about the azimuth axis. The telescope observes through a large opening which makes it quite exposed to the wind and it is also placed quite low on the ground.
In all respects the MMT building was exactly the opposite of previous standards for telescope enclosures, but it proved itself nevertheless very adequate. In particular the MMT was reported to have a remarkably good seeing [Beckers 81], which was attributed to the natural wind ventilation allowed by its large opening, the same effect that all previous domes wanted to avoid.
A main lesson of the MMT experience is that it has revealed a fundamental ignorance of the physics of local seeing, which had been hidden behind the effort given to the large and costly constructions of conventional domes.
