The CCD camera allows multiple astronomical objects to be recorded on the same image and the detector is linear so that photometric information can be obtained. Unlike photograph film, which has grains positioned in a random fashion on the film and a variety of grain sizes, the CCD pixels are equally spaced in rows and columns. This consistency of spacing allows the position of stars to be determined very accurately. Once the image is taken with a CCD camera the image is read by the computer and converted to an electronic file. The raw image in electronic format can now be processed in a variety of ways to enhance the image, for example, the images can be stacked, rotated, filtered, re-formatted, have quantitative measurements taken, etc.
A commonly used CCD camera is the Santa Barbara Instruments Group (SBIG) ST-8E (shown in Figure 16.2). The heart of the SBIG ST-8E CCD camera is the KAF-1062E CCD chip. The KAF-1062E has a detection surface that is composed of an array of 1530 x 1020 pixels, which are each 9 microns square. The CCD chip is thermoelectrically cooled to 25 °C below the ambient air temperature to suppress electronic noise generated within the chip. Each pixel converts the energy in the light into electrons that are trapped in the pixel. After the exposure is complete, the camera's electronics reads the number of electrons in each pixel. This information is then converted to a black and white image on the computer screen.
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