Nordic Optical Telescope
The Nordic Optical Telescope (NOT) is an astronomical telescope located at Roque de los Muchachos Observatory, La Palma in the Canary Islands. The telescope saw first light in 1988, and was officially inaugurated during September 1989. Regular observing started in 1990. It is funded by Denmark, Sweden, Norway, Finland, and (since 1997) Iceland. Access is provided directly to astronomers of the funding countries, and of all nationalities through international time allocation committees. The main mirror has a diameter of . The optical forming was done at the optical laboratory at the Tuorla Observatory, on mirror blanks made of  Zerodur at Schott Glaswerke in Mainz, Germany. While the NOT was designed as a passive telescope, with the mirror sufficiently thick to keep its shape even without an active feedback loop, its mirror was designed to be suspended on a pneumatic support system. The designers had planned that this and the flexibility of the mirror would allow for the implementation of a so-called active optics system, a feature that was then under development for ESO's New Technology Telescope. In 1992, such an active optics system was installed at the NOT. Instrumentation. The NOT operates three instruments that can  be mounted -only one at a time- under the Cassegrain focus: There are two more instruments, permanently mounted on a folded-Cassegrain configuration. Retractable folding mirrors allow to switch in short time from the main instrument to either of them. Visitor Instruments. The NOT has been host to a number of instruments on a "visitor" status. Future. A new instrument for the NOT is currently under development, under the working name of NTE. This new instrument is meant to be mounted permanently in the Cassegrain focus, providing imaging and spectroscopic capabilities both in the full optical and near-infrared range . See also. List of largest optical telescopes in the 20th century