Go back!

The DWARF Camera System

Deep sensing Wide Angle Recording Facility

Till Credner, 1996

Why to put a big professional CCD-System together with a small camera lens and use this in Astronomy?

When imaging extended objects, the focal ratio of the optics gives the photon density at the focal plane. So no matter if a big 1m-Schmidt telescope with f/2 or a small f/2 camera lens is used, the same detector yields the same limiting magnitude for the surface brightness. On the other hand big Schmidt Telescopes have a high resolution. But how to substitute an unsensitive 50 x 50 cm2 photographic plate with such a big CCD system? This is still almost impossible. And the advantages of CCDs are their high quantum efficiency, the large dynamic range and the linearity.
So in all this means:
Attaching a CCD-Camera to a small optics, a much better sensitivity to extended objects is reached than with a big photographic Schmidt-Telescope at the same focal ratio. And due to the large dynamic range, the linearity and the direct digital presence of the data, the scientific content is much higher.

The DWARF just before it has seen the first light. It was installed on a small amateurs mount.

With the help of the CCD-Group of the Astronomische Institute Bonn (Klaus Reif: Vier Millionen Bildelemente, SuW 31, 300 [3/1992]) the DWARF was created. A 20482 pixel CCD-System cooled by liquid nitrogen and a photographic lens with focal length of 100mm and f/2 were installed on a small amateurs mount.

Comet C/1996 B2 (Hyakutake) observed from Hoher List (25.3.96, Exposure 180s). For observing comets not only the large field of view but also the speed of the camera system is of special importance. Tail structures can change very fast, so that short exposures are necessary to get sharp images and to follow these temporal changes.

The extended, but very faint Galactic Cirrus in Ursa Major detected with the DWARF (10.3.96, Exposure 3 x 10 min, Hoher List). It was first found by Alan Sandage 1975 with the 1.2m-Palomar Schmidt Telescope on a four hour (!) exposure. The surface brightness is 25 mag/(")2 or even fainter (Sandage, A.: 1976, AJ81, 954). Compare this image with one taken by the infrared satellite IRAS.

Meanwhile the DWARF is permanently piggy backed on the Astrograph of the Hoher List Observatory. Some more DWARF images can be found here.

Technical data:
CCD-Chip Optics
Ford Loral
Zeiss Planar
20482 pixel f=100mm, f/2.0 f=200mm, f/4.0
Size 3 x 3 cm2 Field of View: 17 x 17 degrees2 8.6 x 8.6 degrees2
Pixel size 15 x 15 micron2 Scale: 30 "/pixel 15 "/pixel
Filters with D=50mm or larger can be placed in front of the lenses.

Astronomical Institutes of the University of Bonn

Till Credner (credner@allthesky.de)