Isaac Newton Telescope

Coordinates of the INT
Latitude:	28° 45' 43.4" N (+28.762°)
Longitude:	17° 52' 39.5" W (-17.878°)
Ground floor height:	2336 m

The optical system of the Isaac Newton Telescope (INT) is a conventional Cassegrain with a paraboloidal primary mirror and a hyperboloidal secondary. The primary has a diameter of 2.54 meters (the original 98-inch primary mirror was replaced by a 100-inch mirror when the INT was moved to La Palma) and a focal length of 7.5 meters, giving a focal ratio of f/2.94 at the uncorrected primary focus. A three-element corrector with a flat rear surface and increased back focal distance, is used at the prime focus to give an unvignetted field of 40 arcminutes at f/3.29. On axis, 80% of the light from a point image lies within a circle of 0.3 arcseconds in diameter. The two secondary mirrors give f/15 Cassegrain and f/50 Coudé foci (although the latter was never implemented). A summary of the optical characteristics of the INT is shown below.

	Prime Focus	Cassegrain Focus
Focal length (mm)	8357	38130
Focal ratio	f/3.29	f/15
Field diameter (arcmin) - no vignetting - 50% vignetting	40 52	20 22
Scale (arcsec/mm)	24.7	5.41
Diameter of central obstruction (mm)	914	914

The telescope has a polar disc/fork type equatorial mounting. Current telescope operational range is as follows:

• Zenith distance < 70°
• - 6 h < hour angle < + 6 h (above pole)
• Declination > -30° 09' 30"

Note that the lower windshield causes vignetting for zenith distances > 57 and it can be raised for such observations.

A more detailed description of the optics and the mounting of the INT is available in the Observers' Guide. The INT's Telescope Control System runs on a DEC Alpha machine. For more information please see the INT TCS manual.

For other facts on the INT see the public information web pages.

The instruments offered at the INT starting from Semester 06B are

• the Wide Field Camera (WFC)
• the Intermediate Dispersion Spectrograph (IDS)
  

For applying for observing time and preparing observations, please visit the ING Astronomy web pages.

Note that the WFC and the IDS will be scheduled in minimum blocks of 4 weeks, as the ING can only support a small number of instrument changes every semester. For this reason, we invite the community to present large programmes to make the best use of the INT (smaller proposals asking no less than 4 nights are still accepted however).

As of August 2003, the INT is fully operated by visiting astronomers and no telescope operator is available. A detailed introduction to the telescope is given by ING students, who stay at the telescope until midnight of the fist night of an observing run. ING staff astronomers will be available for
contact prior to the observations, and will be at the telescope in the afternoon of the first day of each run.  Being alone at the telescope for most of your observing run, it is very important that your read carefully the documentation on health and safety.

A detailed description of how to operate the telescope and the instrument is contained in the Wide Field Camera Home Page and in the IDS Home Page respectively.

When the laser is working at the WHT, INT observers should monitor the TELESCOPE SUMMARY in the Laser Traffic Control System web page, in order to check if there is any limitation in the INT pointing because of collisions with the laser.