Celestron CGEM - 925 Computerized Telescope CGEM Series Manual - Page 49

CCD Imaging, Auto Guiding

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Another way to reduce vibration is with the Vibration Suppression Pads (#93503). These pads rest between the ground and tripod feet. They reduce the vibration amplitude and vibration time. CCD Imaging SCT telescope's versatility allows it to be used in many different f-number configurations for CCD imaging. It can be used at f/6.3 (with the optional Reducer/Corrector), f/10, and f/20 (with the optional 2x Barlow) making it the most versatile imaging system available today. This makes the system ideal for imaging deep-sky objects as well as planetary detail. The key factors for good CCD imaging are; exposure time, field-of-view, image size, and pixel resolution. As the F/# goes down (or gets faster), the exposure times needed decreases, the field-of-view-increases, but the image scale of the object gets smaller. What is the difference between f/6.3 and f/10? F/6.3 has about 2/3 the focal length of f/10. That makes the exposure time needed about 2.5 times shorter than at f/10, the field of view 50% larger compared to that of f/10. (see Table below) Telescope Model Focal Length & Speed C8 C9.25 C11 Standard Cassegrain f/10 80" (2032mm) 93" (2350mm) 110" (2800mm) With Reducer/Corrector f/6.3 50.4" (1280mm) 58" (1481mm) 69" (1764mm) Table 7-3 Auto Guiding The CGEM mount has a designated auto guiding port for use with a CCD autoguider. The diagram below may be useful when connecting the CCD camera cable to the telescope and calibrating the autoguider. Note that the four outputs are activelow, with internal pull-ups and are capable of sinking 25 mA DC. 49

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49
Another way to reduce vibration is with the Vibration Suppression Pads (#93503). These pads rest between the ground and
tripod feet. They reduce the vibration amplitude and vibration time.
CCD Imaging
SCT telescope's versatility allows it to be used in many different f-number configurations for CCD imaging.
It can be used
at f/6.3 (with the optional Reducer/Corrector), f/10, and f/20 (with the optional 2x Barlow) making it the most versatile
imaging system available today.
This makes the system ideal for imaging deep-sky objects as well as planetary detail.
The key factors for good CCD imaging are; exposure time, field-of-view, image size, and pixel resolution.
As the F/# goes
down (or gets faster), the exposure times needed decreases, the field-of-view-increases, but the image scale of the object gets
smaller. What is the difference between f/6.3 and f/10?
F/6.3 has about 2/3 the focal length of f/10.
That makes the exposure
time needed about 2.5 times shorter than at f/10, the field of view 50%
larger compared to that of f/10. (see Table below)
Telescope
Model
Standard
Cassegrain f/10
With
Reducer/Corrector
f/6.3
Focal
Length &
Speed
C8
80" (2032mm)
50.4" (1280mm)
C9.25
93" (2350mm)
58" (1481mm)
C11
110" (2800mm)
69" (1764mm)
Auto Guiding
The CGEM mount has a designated auto guiding port for use with a CCD autoguider.
The diagram below may be useful
when connecting the CCD camera cable to the telescope and calibrating the autoguider. Note that the four outputs are active-
low, with internal pull-ups and are capable of sinking 25 mA DC.
Table 7-3