[ Abstract | Components | Setup | Performance | In use | Future and aims ]
CCD-based cameras can be seperated into two mayor categories: one uses the high-quality and expensive device for "static" photography, that is: taking pictures of galaxies and minor-planets a.s.o. The other one uses the cheap and easily available cameras, which deliver a standard video-signal. Because of the increased use of CCDs in industrial products, the latter cameras have become even cheaper throughout the last few years. Since March 1999 there's a CCD-videocamera in use at the Car-Hiking Astronomical Observatory and this is a description of the setup.
| Pixels | 250,000 = 433x577 |
| Synchronisation | internal |
| Scanning system | 2:1 interlace |
| Minimum Illumination | less than 0.1 lux |
| S/N ratio | 46dB |
| Electronic Shuttle | 1/60-1/100,000 s |
| Power Source | DC 12V (330mA) |
| Dimension | 32mm x 32mm x 25mm |
| Manufacturer | elta |
| item-number | 2207N |
Currently I use the camera with its standard lens (3.6mm f/2.0) in
eyepiece-projection mode. Though it would be possible to place the camera
without lens directly in the focal plane of the telescopes objective,
the eyepiece-projection allows for adjusting the optics in different ways.
From the number of pixels and the size 3.3 mm x 4.4 mm of the chip
follows a pixel-size of about 7.5 microns. The main-telescope of my observatory
produces an approximatly 11 micron picture of a 1 arcsecond big light-source.
In eyepiece-projection mode one can chose to observe the full field
of the eyepiece or just a part of the imagine in highest resolution.
x / f = X / F
decribes, how the size of the image x behind the cameras lens is related
to the image-size X in the focal plane of the telescope. f is the lens'
focal length, F the focal length of the eyepiece.
Different lenses are available and can be combined with the eyepieces of
the telescope.
One advantage of this method is, that the video-camera can still be used
in everyday use, such as recording ones guitar-playing or whatever. Another one
is, that one hasn't to bother about dust ruining the chip.
Tests with the 16" f/5, a 9mm Nagler eyepiece and the standard
camera-lens were promising.
The faintest stars, which could be detected in a night of modest
atmosperic transparency, were of magnitude 10.5, tracking was easy, even
with the Alt/Az mounting. The tests were carried out in Heuchelheim and
watched by an interested crowd of pedestrians.
Objects this night: Castor, M44, M35, Trapezium. Galaxies and Planetaries
escaped detection, but still, here are some possibilties.
One reason for this lack of performance on such objects might be (especially
planetaries) that this camera turned out to be a infrared sensitive one.
During one test I had a black part of a slide film mounted right before the
lens. Actually NOTHING happened on the monitor. Hence, it's not a
big miracle, that the camera doesn't perform well on planetary nebulae
which emit only in a narrow band.
During the last few years the main field of use proofed to be the work in
public observing sessions.
One thing is: recording events connected with the moon. A video tape with
a "moonshot" (sorry, hehe) is always a nice thing to show.
If you have more than one person standing at the scope, it's sometimes
difficult to guide the person looking through the scope and entertaining
the other ones at the same time. Here the camera is useful; it's for example
possible to explain things first on the monitor and allow the direct view
afterwards. One very nice thing about the video system is, that it is live
and alive !
One of the club members of the Astro-AG Heuchelheim, Horst Koch, had
another very good idea. He uses the camera as a guiding tool. He just puts
it behind a crosshair eyepiece. Instead of watching the guide star directly
in the eyepiece, he watches it on the monitor. This is very conveniant and
makes long guiding sessions more comfortable.
This video-equipment allows for use at different occasions:
What is left to be done ?
(c) by Frank Leiter