New Technology Telescope
Characteristics
It saw first light in 1989 and is owned by ESO. It is fitted with active optics (not to be confused with adaptive optics) allowing it to obtain an excellent image quality while only having a thin, lightweight mirror, kept in shape with a number of actuators beneath. The NTT was later cloned, resulting in the TNG.
Although other pre-existing telescopes such as the Nordic Optical Telescope had lightweight mirrors supported by actuators, the NTT is claimed to be the first telescope using full active optics. Its design as well as the design of its enclosure (the building protecting it) included many revolutionary features, from whence it was named. In particular, great care was taken to ensure a good ventilation of the telescope, and to avoid heat sources in around the telescope. Since its construction, the NTT has undergone several upgrades which continued to improve its quality. It was used as a real-life test bench for the engineering concepts and software used for the Very Large Telescope
The New Technology Telescope initially had the same problem as the Hubble Space telescope - the mirror was ground to the wrong shape due to a mis-calibrated null corrector. However, the active optics system of the NTT was able to correct that error without refiguring the mirror.