Section 2 - Introduction to CCD Cameras
Page 32
Camera Array Dimensions Diagonal Field of View at 8" f/10
TC211 Tracking CCD 2.64 x 2.64 mm 3.73 mm 4.5 x 4.5 arcminutes
TC237 Tracking CCD 4.93 x 3.71 mm 6.17 mm 8.2 x 6.2 arcminutes
ST-5C 3.20 x 2.40 mm 4.00 mm 5.6 x 4.2 arcminutes
ST-237A 4.93 x 3.71 mm 6.17 mm 8.2 x 6.2 arcminutes
STV 4.74 x 2.96 mm 5.58 mm 8.2 x 5.1 arcminutes
ST-7XE 6.89 x 4.59 mm 8.28 mm 11.9 x 7.9 arcminutes
ST-8XE 13.8 x 9.18 mm 16.6 mm 23.8 x 15.8 arcminutes
ST-9XE 10.2 x 10.2 mm 14.4 mm 17.6 x 17.6 arcminutes
ST-10XE (XME) 14.9 x 10.0 mm 17.9 mm 25.1 x 16.9 arcminutes
ST-1001E 24.6 x 24.6 mm 34.8 mm 41.5 x 41.5 arcminutes
ST-2000XM 11.8 x 9.0 mm 14.8 mm 20.0 x 15.0 arcminutes
35mm Film 36 x 24 mm 43 mm 62 x 42 arcminutes
Table 2.2 - CCD Array Dimensions
2.4.6. Guiding
Any time you are taking exposures longer than several seconds, whether you are using a film
camera or a CCD camera, the telescope needs to be guided to prevent streaking. While modern
telescope drives are excellent with PEC or PPEC, they will not produce streak-free images
without adjustment every 30 to 60 seconds. The ST-7XE, ST-8XE, ST-9XE, ST-10XE, ST-10XME
and ST-2000XM allow simultaneous guiding and imaging, called self-guiding (US Patent
5,525,793). This is possible because of the unique design employing 2 CCDs. One CCD guides
the telescope while the other takes the image. This resolves the conflicting requirements of
short exposures for guiding accuracy and long exposures for dim objects to be met, something
that is impossible with single CCD cameras. Up to now the user either had to set up a separate
guider or use Track and Accumulate to co-add several shorter images. The dual CCD design
allows the guiding CCD access to the large aperture of the main telescope without the
inconvenience of off-axis radial guiders. Not only are guide stars easily found, but the
problems of differential deflection between guide scope and main scope eliminated.
Track and Accumulate is another SBIG patented process (US #5,365,269) whereby short
exposures are taken and added together with appropriate image shifts to align the images. It is
supported by the ST-7XE, ST-8XE, ST-9XE, ST-10XE, ST-10XME and ST-2000XM camera
software, but will generally not produce as good as results as self guiding, where the
corrections are more frequent and the accumulated readout noise less. It is handy when no
connection to the telescope drive is possible and also works best on cameras with larger pixels
like the ST-9XE or for cameras with smaller pixels in binned mode. For cameras with smaller
pixels imaging in high resolution mode such as the ST-7XE, ST-8XE, ST-10XE, ST-10XME and
ST-2000XM, SBIG is proud to make self-guiding available to the amateur, making those long
exposures required by the small pixel geometry easy to achieve!
2.5. Electronic Imaging
Electronic images resemble photographic images in many ways. Photographic images are
made up of many small particles or grains of photo sensitive compounds which change color or
become a darker shade of gray when exposed to light. Electronic images are made up of many
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