What kind of cameras work best with the Celestron CGEM II 800 RASA?
Celestron designed the 8" RASA for color astronomical CMOS cameras, smaller CCD cameras and mirrorless cameras. It is optimized for sensors up to a 22mm diagonal and performs well up to 32mm; APS-C mirrorless sensors are a good choice. Full frame 42mm sensors work with poor edge performance, Celestron does not recommend camera bodies over 4" in diameter, and it is not compatible with DSLR cameras due to their large obstruction and long backfocus.
Can I use the Celestron RASA 8 for visual observing with an eyepiece?
No. The 8" RASA is a dedicated astrograph designed purely for imaging. The focal plane is located at the front of the telescope where the camera is placed, and there is no provision to attach a diagonal or eyepiece for visual use.
What is the benefit of the All-Star Polar Alignment on the CGEM II mount?
It lets you polar align without a view of Polaris and without a polar finder scope. After aligning on stars, you slew to a bright star, and the mount moves to where that star would be if it were accurately polar aligned; you then center it using only the mount's latitude and azimuth adjustments. The procedure can usually be completed in about 15 minutes.
Is the CGEM II mount's 40 lb payload capacity enough for the 17 lb RASA OTA plus accessories?
Yes. The 40 lb capacity handles the 17 lb optical tube with ease, leaving lots of capacity to spare for your camera and accessories.
What do the 25mm and 29mm back focus distances on the RASA 8 mean?
The RASA 8 has two critical back focus measurements for attaching your camera sensor at the correct distance for a flat field.
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29mm: where the sensor belongs, measured from the top surface of the lens group cell. Cameras with more than 29mm of backfocus cannot be used.
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25mm with included adapter: This is the required back focus distance when using the included M42 (T-thread) camera adapter. For example, a camera with 17mm backfocus needs 8mm of M42 extension rings. Get within 1mm of the required distance.
Do I need an autoguider with the Celestron CGEM II 800 RASA?
Not always. Thanks to the fast focal ratio you can, in many cases, skip the autoguider completely. For an even higher level of tracking accuracy, the CGEM II has a dedicated autoguider port to correct residual tracking errors.
How does the RASA 8's cooling fan help with imaging?
The fan cools the optics to the ambient temperature by pulling air through mesh vents on the rear cell, which also keep dust out. Run it from the included battery pack (8 AA batteries, not included) or a 12V DC source supplying at least 100mA, and unplug it when you are ready to image.
What is Permanent Periodic Error Correction (PPEC) on the CGEM II mount?
All mounts have some periodic tracking error caused by tiny gear imperfections. PPEC lets you run a routine to record it only once; the recording is kept in memory and then corrects the mount's periodic tracking error.
Can the CGEM II 800 RASA track an object past the meridian without flipping?
Yes. The CGEM II images through the meridian and does not need a meridian flip until the object is a full 20° past it.
What adapters are included for attaching a camera to the RASA 8?
The Celestron CGEM II 800 RASA comes with two of the most common adapters for astrophotography cameras: an M42 (T-thread) camera adapter and a C-thread camera adapter. This allows you to connect a wide variety of dedicated astronomy cameras right out of the box.
