Celestron CGX 1100 RASA Equatorial Telescope

The CGX 1100 RASA: An f/2.2 System for Advanced Imagers

This system is engineered for advanced deep-sky imagers who require speed, a wide field of view, and high resolution. The RASA produces images in a fraction of the time compared to other optical tubes, and its large image circle and 620mm focal length suit wide-field imaging, huge mosaics of the night sky, surveying and even comet hunting.

The astrograph is an imaging-only instrument; there is no provision for visual use with an eyepiece. Every component is optimized for DSLR and astronomical CCD cameras, and experienced imagers can take this portable mount to a dark sky site and enjoy the conveniences of a larger observatory mount.

RASA Optical Design: A 4-Element Corrected Schmidt Astrograph

The Rowe-Ackermann Schmidt Astrograph (RASA) design places the camera at the front of the optical tube, operating at the primary focus. Light passes through a Schmidt corrector, reflects off the primary mirror, and then travels through a 4-element rare-earth glass lens group before reaching the sensor. This gives images free of false color and aberrations like coma and field curvature, with minimal vignetting. The design wavelength range is 400 to 700 nm.

The central obstruction is 114mm, 41% of the aperture diameter.

279mm Aperture at f/2.2: Light Gathering and a 43.3mm Image Circle

The 279mm (11") aperture gathers 1588 times more light than the human eye, enabling the detection of faint deep-sky objects. The f/2.2 system allows shorter exposure times compared to traditional f/10 imaging, without sacrificing resolution. Because shorter sub-exposures are possible and the short focal length lessens tracking demands, autoguiding will not be required in many cases.

The 43.3mm optimized image circle captures pinpoint stars on the largest imaging chips, and performance is still excellent for sensors with diagonals up to 52mm.

Camera Integration: 55mm Back Focus for Large Sensors

The RASA 11 is engineered for seamless integration with modern cameras. Two adapters are included: a 42mm T-thread adapter (M42x0.75) and a wider M48 adapter that can be used with full frame cameras with minimal vignetting. Both allow 55mm from the adapter to the sensor; DSLR cameras need a T-ring for their make and model, and astronomical cameras with less than 55mm of backfocus need a spacer. Sensors larger than 43mm diagonal need a custom adapter.

The camera attaches to the front of the RASA's lens group housing via a knurled retaining ring. To rotate the camera, loosen the ring no more than 1/8 turn, rotate it and retighten. Back focus measured from the collar is 72.8mm, and Celestron publishes a drawing of camera adapter requirements for custom adapters.

Ultra-Stable Focus System (USFS) and 12V DC Cooling

Focusing an f/2.2 system requires extreme precision. The RASA 11 features Celestron's Ultra-Stable Focus System (USFS), built around a precision linear ball bearing. It minimizes focus shift (lateral motion of the primary mirror during focusing that shifts the image) and mirror flop (movement of the mirror as the telescope points to different parts of the sky). The USFS is compatible with the optional Celestron Focus Motor (#94155-A).

To ensure peak optical performance, an integrated 12V DC MagLev fan reduces cooldown time and provides airflow through the dust-filtered optical tube. It runs from the included battery pack (8 AA batteries, not included) or any 12V DC supply of at least 100mA with a 5.5mm/2.1mm tip-positive plug.

The CGX Mount Head: 55 lb Capacity with DC Servo Motors

The CGX is a German equatorial mount designed specifically for astrophotography with heavy payloads. It carries the RASA 11 with ease; the instrument load capacity is 55 lbs and the optical tube weighs 43 lbs. DC servo motors slew at up to 4° per second.

Its design goals included a lower profile head for a more compact, more stable setup, remote-operation-friendly home and limit optical sensors, easier polar alignment adjustments and improved cable management. Software limit switches stop the mount before it reaches the built-in mechanical hard stop.

Tripod and Dual Saddle: A Stable Foundation for the 43 lb OTA

The CGX tripod has 2" diameter steel legs, weighs 19.2 lbs and comes with an accessory tray. The legs have height index marks.

The mount head attaches to the optical tube via a dual-format saddle plate. This saddle is compatible with both the wider CGE dovetail bar (included on the RASA 11) and the narrower CG-5 dovetail.

NexStar+ and CPWI: A 40,000+ Object Database with PC Control

The CGX system is controlled by the NexStar+ hand controller, which features a database of over 40,000 celestial objects. For more advanced control, the mount includes Celestron's PWI (CPWI) telescope control software. When connected to a PC via the mount's USB port, CPWI provides a graphical planetarium interface for pointing the telescope and advanced mount modeling for pointing accuracy.

The system also includes a license for Starry Night Special Edition software and the SkyPortal app. The NexStar+ hand control also has a USB port for computer control.

All-Star Polar Alignment: Precision from 3° to 65° Latitude

Achieving a precise polar alignment is critical for astrophotography, and the CGX mount simplifies this process with Celestron's All-Star Polar Alignment routine. It lets you polar align on a bright star without a view of Polaris. The latitude range is 3° to 65°.

For permanent or semi-permanent setups, the CGX also features Permanently Programmable Periodic Error Correction (PPEC). It records the mount's periodic error once and keeps the correction in memory.

Autoguiding and Imaging Workflow with the CGX 1100 RASA

While the RASA's f/2.2 speed often makes autoguiding unnecessary for short exposures, the CGX mount is fully equipped for it. An Autoguide Port is provided for connecting a guide camera. The CGE dovetail bar on top of the RASA 11 tube gives a connection for optional accessories like a guidescope.

System Weights and Transport: A 150.2 lb Observatory-Grade Kit

The Celestron CGX 1100 RASA is a substantial system with a total weight of 150.2 lbs. Its components weigh:

• Optical Tube Weight: 43 lbs (19.5 kg)
• Mount Head Weight: 44 lbs (20 kg)
• Tripod Weight: 19.2 lbs (8.7 kg)
• Counterweights: 44 lbs total (4 x 11 lbs)