Celestron RASA 8 8-Inch Rowe-Ackermann Schmidt Astrograph

Model #91073

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General Information

Optical design Rowe-Ackermann Schmidt Astrograph
Aperture 203mm (8-inch)
Focal length 400mm (15.74-inch)
Focal ratio f/2.0
Central obstruction diameter 93mm (3.66-inch) (46% of aperture diameter)
Light gathering power (Compared to human eye) 843x
Resolution (Rayleigh) 0.68 arc seconds
Resolution (Dawes) 0.57 arc seconds
Image circle 22mm (.86-inch) Ø, 3.15°
Useable field 32mm (1.26-inch) Ø, 4.6°, only minimal performance loss at edge of FOV
Wavelength range 390 - 800 nm
Spot size < 4.6 μm RMS across image circle
Optical coatings StarBright XLT
Off-axis illumination 93% at 11mm (.43-inch) off-axis
Optical window 46mm (1.81-inch) Ø
Back focus with included camera adapter 25mm (.98-inch)
Back focus from top of threaded collar 29mm (1.14-inch)
Optical tube Aluminum
Optical tube length 628mm (24.7-inch) length | 235mm (9.3-inch) diameter
Focuser Ultra-Stable Focusing System
Optical tube weight 17 lb (7.7 kg)
Other features Air-cooling system, integrated filter mount
Dovetail CGE Dovetail Bar 
Product Description

Celestron RASA 8 8-Inch Rowe-Ackermann Schmidt Astrograph - 91073-CELESTRON

Capture spectacular wide-field deep sky images in seconds with Celestron 8-Inch Rowe-Ackermann Schmidt Astrograph (RASA 8). This incredibly fast f/2.0 system is the perfect companion to today’s color astronomical CMOS cameras, smaller CCD cameras, and mirrorless cameras. Thanks to its fast focal ratio and patented optical design, you can produce sharp, detailed images and, in many cases, skip the autoguider completely. Weighing in at just 17 pounds, it’s easy to transport your 8-inch RASA to the most remote dark sky locations.

RASA Performance Made for Everyone

The 8-inch RASA is an imaging telescope that delivers a flat field without optical aberrations for razor sharp stars across a wide field of view. It can capture stunning deep-sky astronomical images without the challenges typically presented by longer focal length instruments at a fraction of the cost of those systems. With the 8-inch RASA, a wider range of astroimagers can enjoy the benefits of the RASA design. It includes features such as the integrated air-cooling system, internal filter mount, and sturdy CGE dovetail mounting bar. Purely designed for imaging, the 8-inch RASA cannot be used visually. The prime focus focal plane is located at the front of the optical system, so it cannot accommodate a traditional eyepiece.

Shorter Exposure Times and Virtual Real-Time Observing

Since it is an F/2.0 optical system, imagers can use shorter exposure times to capture detail in faint objects. When combined with sensitive cameras and the proper live stacking software, the 8-inch RASA 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.

Because shorter exposure times are possible, your equatorial mount won’t need to accurately track over extended periods. This astrograph is relatively short 400mm focal length and also lessens equatorial tracking demands. In many cases, autoguiding will not be required. Weighing only 17 lb, this optical tube pairs perfectly with a wide variety of mounts.

Unique Optical Design

RASA’s optical design is patented (US 2016/0299331 A1) consisting of a Schmidt corrector, primary mirror, lens group, and optical window. The lens group contains 4 elements and utilizes rare-earth elements. Unlike many telescopes that only perform well over the visible spectrum (400-700nm), the optic is designed to perform over a wider spectral range, from 390-800nm. This allows more of the light emitted from the astronomical object to be sharply focused in the image. All refractive optical surfaces are coated with StarBright XLT coatings, while the primary mirror uses enhanced aluminum coatings. This maintains high light transmission through the entire optical system and provides better optical performance and field illumination.

Ultra-Stable Focus System

With the launch of the 8-inch RASA, Celestron is unveiling a new focuser design that mitigates lateral movement of the primary mirror when focusing, slewing, or tracking with the astrograph. Focusing is easier, more accurate, and more stable than ever. The key to the Ultra-Stable Focus System is two sets of precision bearings that are precisely aligned and tested during assembly to ensure optimal results.

Built for Today’s Latest Cameras

Unlike the larger RASAs that work with DSLR and large CCD cameras, the 8-inch model was designed with color astronomical CMOS cameras, smaller CCD cameras, and mirrorless cameras in mind. The telescope does not work with standard DSLR cameras. It is optimized for sensors with up to a 22mm diagonal, but performs well with sensors up to 32mm diagonal. The APS-C sized sensors used in many mirrorless cameras are a good choice. The 42mm full frame sensors will also work, but performance will be poor at the edges of the sensor and field illumination will be reduced.

Product Highlights
  • Incredibly fast f/2.0 system
  • Flat field free of optical aberrations
  • Patented optical design
  • Designed for use with CMOS, smaller CCD, and mirrorless cameras
  • Ultra-Stable Focus System – six precision sealed ball bearings
  • Integrated air cooling system and filter mount
  • CGE dovetail mounting rail
  • Weighs just 17 pounds making it portable
  • Performs over a wider spectral range from 390-800 nm
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