Celestron CGEM II 800 RASA Telescope

The 203mm f/2.0 Astrograph for Deep-Sky Imaging

The 8" RASA is engineered for one purpose: to capture breathtaking, wide-field images of the deep sky in a fraction of the time required by conventional telescopes. Its native f/2.0 optical system requires significantly shorter exposure times, reducing tracking errors and often eliminating the need for an autoguider on brighter objects. With a 400mm focal length, you can frame enormous targets like the Andromeda Galaxy (M31) or the entire Veil Nebula complex in a single shot.

The 4-element lens group, incorporating rare-earth glass, produces razor-sharp stars across a 22mm image circle, perfectly matched to modern CMOS and smaller CCD sensors. The optical design is optimized for an extended 400-800 nm wavelength range, ensuring that more light from your target is focused sharply, resulting in brighter, more vibrant images.

Advanced OTA Design: Ultra-Stable Focusing and a 12V Cooling System

Celestron has equipped the 17 lb RASA optical tube with features designed for serious imagers. The Ultra-Stable Focusing System uses a precision linear ball bearing to mitigate primary mirror shift, ensuring focus remains exact and repeatable as you slew across the sky. This system provides the stability necessary for critical focusing at f/2.0.

To help the optics reach thermal equilibrium quickly, an integrated air-cooling system with a 12V fan is built into the rear cell. This minimizes tube currents and ensures your images are as sharp as possible from the start of your session. The design also includes an integrated filter mount and a removable optical window, allowing you to use specialized light pollution filters while maintaining peak optical performance.

CGEM II Mount: A 40 lb Capacity Platform for Stable Tracking

The CGEM II equatorial mount is an ideal platform for the 8" RASA. Its 40 lb load capacity handles the 17 lb optical tube with more than enough reserve for your camera, filter wheel, and guide scope. The heavy-duty tripod is built with 2" diameter steel legs, providing a rigid, vibration-resistant foundation for your imaging.

At the heart of the mount are low-cog DC servo motors with integrated optical encoders, delivering the smooth, accurate tracking essential for long-exposure astrophotography. A dedicated autoguide port is included for connecting a guide camera, and with Permanent Periodic Error Correction (PPEC), you can train the mount to compensate for inherent worm gear inaccuracies, dramatically improving your tracking before you even start guiding.

GoTo & Imaging Control: NexStar+ with 40,000+ Objects and PPEC

The included NexStar+ hand control puts a database of over 40,000 celestial objects at your fingertips. After a simple alignment procedure, the mount can automatically locate and track any object you choose. Celestron's innovative All-Star Polar Alignment allows you to achieve a precise polar alignment using any bright star, so you don't need a clear view of Polaris.

The CGEM II is engineered for the modern imager. It can track well past the meridian, allowing you to capture exposures through the best part of the night sky without interruption. The included DC power cable and Celestron's Starry Night Special Edition software provide everything you need to connect to a PC and begin your imaging journey.

RASA 8 vs. Hyperstar SCT: Optical Purity and Field Illumination

While a Hyperstar lens converts a standard SCT into a fast imaging system, the RASA is a dedicated astrograph designed from the ground up for f/2.0 performance. This integrated design provides superior optical performance and field illumination compared to a converted SCT.

• Optimized Baffling: The RASA's internal baffles are engineered specifically for its wide, fast field, minimizing stray light and maximizing contrast in a way that a multi-purpose SCT cannot.
• Superior Illumination: The RASA provides 93% illumination at 11mm off-axis, ensuring bright, even lighting across the entire 22mm image circle without the significant vignetting common in Hyperstar systems.
• Integrated Features: With its built-in cooling fan, filter mount, and ultra-stable focuser, the RASA is a complete, purpose-built imaging instrument, not an adaptation.