The INT dome by moonlight
The Isaac Newton Telescope or INT is a 2.5m optical telescope run by the ING at Roque de los Muchachos on La Palma in the Canary Islands. It was originally situated at Herstmonceux Castle in Sussex, England, which was the site of the Royal Greenwich Observatory after it moved away from Greenwich due to light pollution. It was inaugurated in 1967 by Elizabeth II.
However, Herstmonceux suffered from poor weather, and the advent of mass air travel made it plausible for UK astronomers to run an overseas observatory. In 1981, the INT was shipped to La Palma, where it has remained ever since.
Today, it is used mostly with the Wide Field Camera (WFC), a four CCD instrument with a field of view of 0.5 square degrees which was commissioned in 1997. The other main instrument available at the INT in earlier times was the Intermediate Dispersion Spectrograph (IDS).
The INT is a Cassegrain telescope, with a 2.54m diameter primary mirror and a focal length of 7.5m. The mirror weighs 4,361kg, and is supported by a polar disc/fork type equatorial mounting. The total weight of the telescope is around 90 tonnes. The f/3.29 Prime focus, used with the WFC, allows an unvignetted field of view of 40 arcminutes (approximately 0.5 square degrees). There is also a secondary focal station, the f/15 Cassegrain focus, which possesses a 20 arcminute field of view and was the mount point for the IDS.
The pointing accuracy of the telescope is around 5 arcseconds, but a sophisticated autoguider, which tracks a given guide star and makes small corrections to the telescope tracking, allows a guiding accuracy of better than 0.3 arcseconds.
INT Homepage (http://www.ing.iac.es/Astronomy/telescopes/int/index.html)