ESO Faint Object Spectrograph and Camera

The ESO Faint Object Spectrograph and Camera (EFOSC) was mounted on the ESO 3.6-metre telescope, at La Silla Observatory, in 1984.

The studies to build a low dispersion spectrograph for the ESO 3.6-metre telescope started in 1981 and in September 1982 a decision was taken for a focal reducer type of instrument to be used at the Cassegrain focus. The studies, analysis and optical design of the instrument were finished in 1983 and the integration tests started in Garching at the beginning of 1984. The first telescope test was successfully performed in June 1984 and the instrument was available for general use in April 1985.

EFOSC could be used in eight different modes, namely: direct imaging, long-slit spectroscopy, slitless spectroscopy, echelle spectroscopy, imaging polarimetry, spectropolarimetry, coronography, and multiple object spectroscopy.

The optical and mechanical layout of main components present on EFOSC were as follows: an aperture wheel holding a number of slits that was situated in the Cassegrain focal plane of the telescope; then a collimator that produced a beam with a diameter of 40 mm passed through a filter or grism (if working in spectroscopic mode), that were mounted in the filter and grism wheels respectively, and an F/2.5 camera focused the beam onto a CCD that had an iris shutter in front of it. The CCD was a 512 by 512 pixels of 27 by 27 μm size and the images were transmitted to two different systems (called IHAP and MIDAS) that allowed on-line data processing.

As Claus Madsen explains in his book, The Jewel on the Mountaintop, Daniel Enard’s design for EFOSC became the model when building a similar type of instrument elsewhere, and the optical design by Bernard Delabre, another of the ESOs unsung heroes, has become a standard for many of the instruments at ESO and in several other observatories.

EFOSC was decommissioned from the ESO 3.6-metre telescope and replaced by EFOSC2 in October 1997.


EFOSC on the ESO 3.6-metre telescope

This table lists the global capabilities of the instrument.

Location: Decommissioned
Telescope: ESO 3.6-m telescope
Focus: Cassegrain
Type: Spectrograph; Camera
Wavelength range: 350–1000 nm
Special resolution: 0.8–5.6 nm
Spectral resolution: 0.14–2.5 nm/pixel
First light: June 1984
Science goals:
  • Direct imaging
  • Long slit spectroscopy
  • Slitless spectroscopy
  • Echelle spectroscopy
  • Imaging polarimetry
  • Spectropolarimetry
  • Coronography
  • Multiple Object Spectroscopy
Images taken with the instrument: Link
Images of the instrument: Link
Press Releases with the instrument: Link
  • ESO