EFOSC Overview

General Characteristics and Observing Modes

EFOSC2 is a focal reducer multi-mode instrument using multi-layer coated all-transmission optics. It is permanently mounted at the Nasmyth B focus of the 3.58m New Technology Telescope. The wavelength range of operation is between 305nm and 1100nm. The field of view is 4.1'x4.1'.

The following observing modes are available (links take you to detailed instructions for visitors for each mode):


EFOSC2 observing modes:
IMA imaging
MOS multi-object spectroscopy (masks, mode decommissioned in 02/2023)
LSS longslit spectroscopy
IPOL imaging polarimetry
SPOL spectropolarimetry
COR coronography

The NTT is equipped with a differential tracking, so all of the observing modes above can in principle be used on moving targets as well. Note however that differential guiding is not currently possible on the NTT.

Instrument Optics

The main instrument optics consists of

The camera is opened to F/4.9 with a focal length of 200mm. The NTT plate scale is 5".36/mm, therefore the focal plane scale of EFOSC2 is 8".60/mm, since the telescope is F/11.


The CCD#40 is a Loral/Lesser, thinned, AR coated, UV flooded, MPP chip controlled by ESO-FIERA. It's size is 2048 x 2048 pixel, the pixel size being 15mux15mu, or 0.12"x0.12" on the sky. The 2x2 binned pixels of the default CCD readout modes will be projected to 0".24 on the sky.

Four readout modes are offered for scientific purpose:

  • Mode 00: Slow mode and Binning 1x1
  • Mode 02: Slow mode and Binning 2x2
  • Mode 30: Normal mode and Binning 1x1
  • Mode 32: Normal mode and Binning 2x2 (standard)
  • New binning modes will be offered (3x3, 4x4, and unequal binning (1x3 etc) for spectroscopy) soon

The fast mode is not characterised and only used for tests and acquisitions.

More Information

For more detailed information, please consult the EFOSC2 manual and look at the detailed pages under Instrument Description on the left hand navigation window.