CAFOS (Calar Alto Faint Object Spectrograph)

CAFOS at the 2,2m telescope

CAFOS (Calar Alto Faint Object Spectrograph), is a focal-reducer which changes the 2.2m telescope's f-ratio from f/8 to f/4.4. With imaging, spectroscopy, polarimetry and Fabry-Pérot-Etalon capabilities, designed to work in visible light. 

Available at: Cassegrain station of the Zeiss 2.2 m reflector

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In a nutshell

Direct Imaging:
Scale: 45.3 µm/" or 0.53"/pix
FoV: 16' diameter
Filters: Standard filters (Johnson, Cousins, Gunn, SDSS) and  a large set
of interference filters are available.

Slit: 11' length and variable width, 0.6" to 12". CAUTION: the center of the slit changes with its width!
Grisms: Three grism sets (400Å/mm, 200Å /mm, 100Å /mm) provide spectral dispersions of ~10Å /pix, ~4.5Å /pix and ~2Å /pix, at different wavelength ranges.

CAFOS is equipped with a Wollaston prism and a rotatable λ/2 plate that provides:
Imaging polarimetry: With or without a stripe mask, two polarized images separated 18".
Spectropolarimetry: In combination with the grisms mentioned above.

Fabry-Pérot Etalon:
Narrow band images in the 600 < λ < 1000 nm region at a resolution of R = λ/Dλ = 500.


Observing with CAFOS

CAFOS user guide
pdf version

Exposure Time calculator for Imaging and Spectroscopy
Dome Flat Fields with CAFOS
Requesting observation time with CAFOS
Service mode observing template for Imaging and Spectroscopy
Night logsheet


More information

Technical data

Detector characteristics
Zero points
Atlas of lines of the calibration lamps
Characterisarion of the CAFOS linear spectropolarimeter

Calar Alto Press releases

Possible satellite detected around the Trans-Neotunian object Varuna
Polarized light from a brown dwarf: where lies the dust at play ?
Calar Alto Observatory has embarked on an ambitious project with the University of Peking for the study of black holes
Rewinding stellar evolution: The last 400,000 years of mass loss from a star
A "hot Jupiter"challenges planetary formation theories
The fastest stars in the universe
Asymmetric supernova explosions
A new class of dim supernovae
Echoes from the past
18 billion of suns support Esintein
The faintest globular clusters of the Galaxy
Deep Impact space mission from Calar Alto
Formidable explosions
The most luminous quasar state ever observed


The instrument has been founded by the Spanish Ministery of Science ICTS project ICTS-2009-32 (using FEDER funds). Fondo Europ eo de Desarrollo Regional, "Una manera de hacer Europa".