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Celestron 8" RASA Rowe-Ackermann Schmidt Astrograph with CGEM II Equatorial Mount - 12020

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SKU: CEL-12020

Celestron 8" RASA Astrograph w/CGEM II Mount

  • The flat field over the entirety of an APS-C sensor is void of optical distortions such as field curvature, coma, astigmatism, and chromatic aberration.
  • A new Ultra-Stable Focus System with six precision sealed ball bearings to basically eradicate image shift is included.
  • Seamlessly add a Light Pollution Imaging Filter into the optical path using the 8" RASA's internal filter mount.
  • Covers the spectrum from 390 nm to 800 nm, a much wider range compared to most telescopes, to allow a greater percentage of sharply focused light to pass through.
  • The most recent version of the highly esteemed CGEM equatorial mount, the CGEM II is capable of accepting payloads weighing up to 40 lbs., providing a strong, reliable platform for a fully loaded 8" RASA.
  • The drive system consists of low cog DC Servo motors with integrated optical encoders, steel worm gears supported by precision sealed bearings, and brass worm wheels, to ensure smooth and accurate slewing and tracking.
  • All-Star Polar Alignment, Permanent Periodic Error Correction (PPEC), and adjustable tracking through meridian are among the functions supported by the CGEM II's proven NexStar+ computerized telescope control technology that will come in handy for many imagers.


With the combination of this 8" Rowe-Ackermann Schmidt Astrograph (RASA) and CGEM II German Equatorial Mount kit, plus an optional camera, you'll have everything necessary to capture breathtaking images of wide-field deep sky wonders.

RASA Performance Made For Everyone

Capture incredible wide-field images of deep sky objects in only seconds with this portable Celestron 8" Rowe-Ackermann Schmidt Astrograph (RASA). With its exceptionally fast f/2.0 optical system, the 8" RASA provides an ideal complement to modern color astronomical CMOS cameras, smaller CCD cameras, and mirrorless cameras. This fast focal ratio and patented optical design generates sharp images with terrific detail that will allow you to skip the autoguider altogether in many cases. Weighing in at a modest 17 pounds allows the 8" RASA to be easily transported to most remote dark sky sites.

Delivering a flat field free of optical aberrations, this Celestron 8" RASA imaging telescope provides razor sharp stars over the entire field of view. For a much more affordable cost compared to longer focal length telescopes, the 8" RASA is capable of capturing spectacular images of deep sky objects without the issues typically encounted with these aforementioned systems.

The latest addition to the RASA family, this 8" version offers greater portability at a much reduced cost compared to the highly touted 11" RASA, which was launced in 2014 to much acclaim. With the addition of the 8" RASA to the lineup, a wider range of astrophotographers will now be able to enjoy the RASA design's benefits. Many of the same thoughtfully designed features present in the 11" RASA are also present in the 8" RASA such as the integrated air-cooling system, internal filter mount, and sturdy CGE dovetail mounting bar.

Made specifically for imaging applications, the 8" RASA is not suitable for visual use. Traditional eyepieces cannot be accommodated as the prime focus focal plane is located at the front of the optical system.

Shorter Exposure Times and Virtual "Real-Time" Observing

Since the 8" RASA has an f/2.0 optical system, imagers are able to use shorter exposure times to capture detail in faint objects. When combined with sensitive cameras and proper "live stacking" software, this astrograph telescope can provide an almost real-time observing experience. View images on a computer instantly that are brighter and more detailed than can be seen in much bigger telescopes with the naked eye.

Ultra-Stable Focus System

To coincide with the launch of the 8" RASA, Celestron is introducing a new focuser design that alleviates lateral movement of the primary mirror while the telescope is focusing, slewing, or tracking. This makes focusing easier, as well as more stable and accurate than ever before. At the core of this Ultra-Stable Focus System is two sets of precision bearings that have been precisely aligned and tested during construction for results that are guaranteed to be optimal.

Built for Today's Latest Cameras

Contrary to larger Rowe-Ackermann Schmidt Astrographs that are compatible with DSLR and large CCD cameras, the 8" version was designed with regards to color astronomical CMOS cameras, smaller CCD cameras, and mirrorless cameras. This telescope is not suitable for use with standard DSLR cameras. Optimized for up to 22 mm diagonal sensors, the 8" RASA also offers sufficient performance with sensors up to 32 mm diagonal. Many mirrorless cameras use APS-C sized sensors that would be an excellent option. 42 mm full frame sensors are also compatible, but performance will suffer at the edges of the sensor while field illumination is decreased. Furthermore, Celestron does not recommend pairing the 8" RASA with any 4" diameter or larger camera body.

Unique Optical Design

Celestron's patented RASA optical design contains a Schmidt corrector, primary mirror, lens group, and optical window. The lens group utilizes four rare-earth elements. The 8" RASA's optics are designed to perform over a wider spectral range compared to many other telescope designs. While most telescopes only function well over the visual region of the spectrum (400-700 nm), the 8" RASA functions well over an extended 390-800 nm spectral range. Because of this, more light emitted from your target astronomical object is allowed to be sharply focused in the image.

With many imaging systems, optical performance will not be affected by the addition of an extra piece of flat glass such as a filter. This is not the case, however, with telescopes that features ultra fast optics like the RASA. To address this, Celestron's engineers have added a detachable optical window to the RASA design to enable maximum optical performance preservation even if a filter is added or if a camera already contains its own optical window. A Light Pollution Imaging Filter expressly designed for the 8" RASA is available as an optional accessory that takes the place of the optical window.

Celestron StarBright XLT coatings cover all refractive optical surfaces, while enhanced aluminum coatings cover the primary mirror. This keeps light transmission high throughout the whole optical system. With the 8" RASA, you'll get better optical performance and field illumination than with "Hyperstar SCT" systems.

Celestron CGEM II Computerized GoTo Equatorial Mount

The Celestron CGEM mount has been a very popular equatorial platform for several years, but never a company to “gather moss”, it was decided that the Celestron CGEM should have a make-over on the outside and the inside.

At first glance, one can see that the Celestron CGEM II equatorial mount is more ergonomic than its predecessor, with longer lock levers to make it easier to make adjustments to your mount. Also, the new heavy duty dual-style saddle plate is designed to accept either CG-5 (Vixen) or CGEM (Losmandy) mounting dovetails so that virtually any optical tube assembly can be mounted in minutes without the need for an adapter.

Celestron CGEM II series mounts offer a generous weight capacity of 40 pounds. Optical tubes as heavy as an 11" EdgeHD can be attached to this portable yet sturdy mount, while still being able to easily break it down into manageable pieces for travel to star parties or dark sky sites near you. The CGEM II mount weighs 40 pounds without counterweights and the tripod, which has also been updated, and weighs just 20 pounds.

Speaking of the tripod, this model has 2” stainless steel legs for rigidity and support, with graduated markings on each leg to make leveling fast and easy. The spreader bar pushes against the legs to make them incredibly sturdy, while the interior of the spreader offers receptacles for a few extra eyepieces so they are in easy reach when observing.

The electronics of the Celestron CGEM II, whether designed for the previous CGEM or new to the CGEM II model, will allow you to set up, use, and maintain your mount with these innovative features:

  • A built-in All-Star Polar Alignment program lets you accurately polar align on any star in the sky without having a view of the celestial pole. No polar finderscope necessary!
  • Past the meridian tracking for seamless imaging across the best part of the sky.
  • With PPEC, or Permanent Periodic Error Correction, you can train out the periodic error on your worm gears once, and the system will remember the PEC recordings.
  • The CGEM II is capable of slewing at 5 degrees per second, getting you where you want to go fast!
  • There is a USB 2.0 port on the bottom of the NexStar GoTo controller to allow you to not only update the firmware of both the controller and the mount, but to connect directly to a PC with your own ASCOM-supported software.
  • With the touch of a button you can visit over 40,000 stars, galaxies, nebulae, planets, clusters, and more. The built-in celestial database also allows for 100 user-defined objects and will give you expanded information on 200 of the best objects in the sky.


Celestron 8" RASA with CGEM II Equatorial Mount Specifications

OTA Info

  • Optical Design: Rowe-Ackermann Schmidt Astrograph
  • Aperture: 203 mm (8")
  • Focal Length: 400 mm
  • Focal Ratio: f/2.0
  • Central Obstruction Diameter: 93 mm (3.66"), 46% of aperture diameter
  • Light Gathering Power: 843x the human eye
  • Rayleigh Resolution: 0.68 arcseconds
  • Dawes Resolution: 0.57 arcseconds
  • Image Circle: 22 mm (0.86")
  • Usable Field: 32 mm (1.26"), 4.6º with only minimal loss of performance at the edge of the field of view
  • Wavelength Range: 390 - 800 nm
  • Spot Size: <4.6 μm RMS across image circle
  • Optical Coatings: StarBright XLT
  • Off-Axis Illumination: 93% at 11 mm (0.43")
  • Optical Window: 46 mm (1.81")
  • Backfocus Distance: 29 mm (1.14"); 25 mm (0.98") with included camera adapter
  • Optical Tube Material: Aluminum
  • Optical Tube Length: 628 mm (24.7")
  • Optical Tube Diameter: 235 mm (9.3")
  • Optical Tube Weight: 17 lbs.
  • Focuser: Ultra-Stable Focusing System
  • Additional Features: Air-cooling system, integrated filter mount
  • Dovetail: CGE mounting bar

Mount & Tripod Info

  • Mount Type: Equatorial
  • Mount Electronics: Computerized with GoTo
  • Weight Capacity: 40 lbs.
  • Hand Controller: NexStar
  • Objects in Database: 40,000
  • Latitude Range: 15º - 70º
  • Mount Slew Speeds: Up to 5º per second
  • GPS: No, but accepts GPS Accessory
  • PPEC: Yes
  • Mounting Style: Vixen or Losmandy dovetail plate via included dual saddle plate
  • Counterweights: One @ 17 lbs.
  • Mount Weight: 40 lbs.
  • Tripod: 2” diameter stainless steel legs
  • Tripod Weight: 20 lbs.