FOSC's

Instruments build at Copenhagen University Observatory

Since 1992 we have build a number of focal reducer instruments:

Instrument       Telescope                          F#       Delivered/Production Period

 1. DFOSC         DK1.54m, La Silla          8.6      Nov. 1992
 2. ALFOSC     NOT2.5m, La Palma    10.0      March 1993/October 1996
 3. BFOSC         Bologna, 1.52m                8.6       July 1993
 4. WFOSC        Vienna, 1.5m                    8.6       Nov. 1995
 5. AFOSC         Asiago, 1.82m                 8.9       Nov. 1995
 6. BFOSC         Beijing, 2.16m                  9.0       May 1997
 7. NFOSC        Napoli, 1.5m                     8.6       Sept. 1998
 8. IFOSC          IUCAA, Pune, 2.0m    10.0       1999-2000
 9. HFOSC        IIA, Hanle, 2.0m              9.0       1999-2001
10. TFOSC       Tubitak, 1.5m                   7.7        2001-

The instrument come basically in two versions, one where the light path is bended 100 deg right after the telescope focus, and one with a straight ligth path. Only the instruments for Beijing and IUACC have the straight ligth path, all the rest are similar in their basic mechanical construction to the original DFOSC for the Danish 1.54m. The instrument ALFOSC was originally build for the IAA, Granada, for use with the Spanish 1.5m at Carlar Alto. The instrument is now on loan for the Nordic Optical Telescope from IAA for a period of three years (until mid-2000).  The HFOSC was delivered with calibration unit and a complete CCD camera system. Work has now started on the TFOSC, an instrument for the Tubitak National Observatory,
Turkey.

The optics for all instruments (except for IFOSC, HFOSC and TFOSC) was calculated by Bernard Delabre, ESO in understanding with Sandro D'Odorico, ESO. The optics for the instruments DFOSC, ALFOSC, and BFOSC are idential (these instruments were build together). The optics for WFOSC almost identical to the DFOSC optics. For the optics for AFOSC the collimator was changed a bit to conform with the telescope optics. The NFOSC is essentially identical to the DFOSC optics. The optics for BFOSC (Beijing) is different from the DFOSC optics. The optics for IFOSC is an adaption of the BFOSC (Beijing) optics using Ohara glasses (as FK54 is now practically unavailable). This adaption is done by IUCAA. The optics for HFOSC will be an improved version of the original DFOSC optics done by Bernard Delabre and modified by E. Langenbach, FISBA. The optics for the TFOSC will be a modified version of the HFOSC optics.

You can find descriptions of some of the instruments around. On the ESO, La Silla you can find the DFOSC-homepage from where you can go to a users manual and to verious tecnical reports. At the Nordic Optical Telescope you can find a home page for ALFOSC. At the Asiago Observatory you will find the home page for AFOSC. At the Bologna Observaory (Loiano) there is a home page for the telescope from where you can get a manual of BFOSC. 

Description of DFOSC and similar instruments

General:
DFOSC is a focal reducer instrument, which means that by using a collimator (with the same F-number as the telescope) and a camera, one can reduce the effective focal length of the telescope. The basic advantage of this is two fold: a) a larger field can be covered using a given detector and b) dispersive elements can be inserted bewteen the collimator and the camera. Thus the instrumnet can function in both direct imaging mode and spectroscopic mode, and one can shift beween these towo mode in seconds.


Mechanics:

DFOSC consists mechanically of an optical bench on which the coillimator and the camera are placed. Also fastned on the optical bench are three wheels: an aperture wheel in fromt of the collimator, in the telescope focal plane, a filter wheel and a grism wheel both between the collimator and the camera in the parallel light beam. Between these latter two wheels is a rotational shutter. All wheels have 8 positions. The camera can be moved relative to the end-flange of the instrument. The three wheels have theeth on the outer circumference and are moved by a stepper moter driving a smaller toth wheel through a gear. Also the wheels are given a small preload. This makes it possible to position the wheels with an accuracy of around 5 microns for that part of the wheel which is in the light beam Weight is around 120kg (including mounting flange and cryostat), length is ca. 750mm.


Electronical:

All functions: turning the three wheels, the shutter and moving the camera are controlled by individual stepper motors. Each function is controlled by separate and identical electronic boards, which are multiplexed, so that DFOSC can be controlled via a standard RS232 serial connection. DFOSC can be controlled either from a workstation or from a PC.


Software:

A high level graphic user interface using IDL has been developped.


Optics:

The optics has been calculated by Bernard Delabre at ESO, by agreement with Dr. Sandro D'Odorico, ESO.


Grisms:

Here you can see the sensitivity curves of grism3, grism4, grism5, grism6, grism7, grism8, grism9, grism10, grism11, grism12, and grism13


Last updated July 20, 2001 by Per Kjaergaard Rasmussen