The CCD camera pictured above (silver in color) is based on the TC245 CCD chip made by Texas Instruments. The chip itself is 755 pixels wide by 242 pixels deep, and you have your choice of reading out an image 378 pixels wide by 242 pixels deep or 252 pixels wide by 242 pixels deep. The CCD is the light sensor in the camera; like most electronic components today, it is a silicon integrated circuit chip. When an image of a celestial object falls on the CCD, the light is converted into an electrical signal. (The term "CCD" stands for "charged coupled device," describing how the signal is "read out" from the CCD chip. The TC245 CCD chip itself is smaller than a postage stamp.
To work well for astronomy, the CCD must be cooled to a temperature of -30 degrees Celsius. To accomplish this, inside the camera the CCD is mounted on a thermo-electric cooler, which acts like a pump, extracting heat from the CCD. This Peltier device used as a cooler for the CCD chip is compact and simple. When power is applied to the module, heat flow occurs. The heat pumping capability is related to the current applied to the module. In this Peltier module, current is approximately the supply voltage divided by 1.65 ohms. In the camera, a water cooling system removes the excess heat from the camera body. Even with coolant circulating, the Peltier module has limitations which should not be exceeded. The operating voltage must not exceed 8.6 volts and the module current must remain below 6 amperes at all times.
Cooling a CCD reduces the effects of thermally induced signals, or dark current. When the CCD is shielded from light, charge accumulates in the photosite and the photosite will become saturated, or filled with charge, after a period of time. The colder the CCD is, the longer it takes for thermally induced charges to fill the well. The dark current decreases approximately by half for every 7 degrees Celsius (12.6 degrees Fahrenheit) drop in temperature.
Pictured above is a gray box which contains the camera interface electronics. Inside this box is a 12 bit A/D (analog-to-digital) converter which transforms the analog signals from the CCD chip into digital values that can be stored in the computers memory. The CCD camera has no "smarts" of its own. Software running on a computer serves as the "brains" of the operation. The software sends commands to the camera through the computer's parallel printer port.
The images displayed on the Planets and Mosaic links on this website were taken using a modified Logitech QuickCam VC color CCD camera pictured above. The camera base, lens assembly, and filter were removed from the stock camera, a camera T-Ring was centered on the camera housing and glued in place using a 5 minute epoxy. A Celestron T-Adapter is screws into the camera T-Ring. To date I have taken several images using this arrangement and have been pleased with the results. I purchased my Logitech QuickCam from Best Buy for $79.00.
Note: Modifying the camera in this manner voids the manufactures warranty.