Santa Barbara Instrument Group ST-5C, Operating Manual

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Section 1 - Introduction to CCD Cameras
Page 10
The ST-5C camera is a two piece system consisting of an Optical Head and a CPU. The Optical
Head houses the CCD and Preamplifier and the CPU contains the Readout and Control
Electronics. The CPU is powered by an external 12 VDC source. For users in the US and in
Japan, wall tranformers rated at 12 VDC / 2 Amps are supplied, for users outside these areas a
Cigarette Lighter Adapter is provided. Finally, the CPU interfaces to the PC through the
Parallel Port and is controlled by the software.
Examining the Optical Head in more detail shows the "front end" of any CCD camera
which is the CCD sensor itself. In this case the CCD is the Texas Instruments TC255. The CCD
is cooled by mounting it on a thermoelectric (TE) cooler. The TE cooler pumps heat out of the
CCD and dissipates it into the camera body where it is removed by convection and conduction
to the atmosphere.
Since the CCD is cooled below 0°C (32 °F), some provision must be made to prevent
frost from forming on the CCD. The camera has the CCD/TE Cooler mounted in a windowed
hermetic chamber sealed with an O-Ring. The hermetic chamber does not need to be a vacuum,
and contains a desiccant packet to absorb the small amount of moisture that might condense.
Other elements contained in the optical head include the preamplifier and a rotating
shutter wheel. The shutter wheel makes taking dark frames a simple matter of pushing a
button on the computer. Remember that the shutter wheel does not perform the task of timing
the exposure, it merely blocks the light from the CCD to facilitate taking dark images. Timing
of exposures is based upon the electronic clocking scheme applied to the CCD. Also, the shutter
wheel can be replaced by a Color Filter Wheel which allows taking Tricolor images and dark
shuttering.
The Microcontroller acts as the "brains" of the camera electronics. It is responsible for
starting and stopping exposures in the CCD, clearing the CCD at the start of the exposure and
transferring the image into the CCD's storage area at the end of the exposure. The
microcontroller also regulates the CCD's temperature by monitoring the temperature sensor
and adjusting the power to the TE cooler. Finally, the microcontroller provides control of the
Shutter/Filter Wheel and the Telescope Port that is used when Autoguiding.
The final element of the camera system is the host computer and operating software.
The CCDOPS software runs under Windows 95, Macintosh OS and MS-DOS and is used to
acquire, display and process images from the camera. As you will learn, CCDOPS is a powerful
package with a user-friendly interface. It is unequaled in the industry. Also, third party
software packages such as Software Bisque's SkyPro for Windows will support the ST-5C
Advanced CCD Camera and open up a whole realm of capabilities including integrated
Telescope and Camera control.