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Celestron 8" Rowe-Ackermann Schmidt Astrograph Optical Tube Assembly - 91073

Celestron   ——   SKU: CEL-91073
$2,210.00 CAD
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Celestron 8" Rowe-Ackermann Schmidt Astrograph
Optical Tube Assembly

  • Flat image field free of optical aberrations like field curvature, coma, astigmatism, and chromatic aberration across an entire APS-C sensor
  • NEW Ultra-Stable Focus System – six precision sealed ball bearings virtually eliminate image shift
  • Integrated air cooling system –12V DC MagLev fan reduces cooldown time and provides optimal air flow while filtering out dust
  • Internal filter mount – seamlessly accommodates a Light Pollution Imaging Filter into the optical path
  • CGE dovetail mounting rail
  • Performs over a wider spectral range than most telescopes, from 390-800 nm, so more of the light passing through the astrograph is in sharp focus
  • Wider spectral range means brighter image results with your digital camera

The 8" Rowe-Ackermann Schmidt Astrograph (RASA) from Celestron, is a cost-effective optical system for wide field astroimaging. It offers unprecedented value in aperture, speed, field of view, and optical performance. The RASA design has a convenient external prime-focus image capture location with a flat focal plane, providing small spot sizes to the edge of a wide field. The result is images that are free of optical defects like field curvature, off-axis coma, or astigmatism. RASA 8" has an ample back-focus distance of 25 mm which accommodates a wide variety of imaging sensors.

Some Information About the RASA Technology:

Celestron's 8" Rowe-Ackermann Schmidt Astrograph (RASA’s) optical design is patented (US 2016/0299331 A1). The design consists of a Schmidt corrector, spherical 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 nm-700 nm), the 8” RASA’s optics are designed to perform over a wider spectral range, from 390 nm-800 nm. This allows more of the light emitted from the astronomical object to be sharply focused in the image. Also better spectral matching to silicon array sensors.

With many imaging systems, adding an extra piece of flat glass such as a filter may not affect the optical performance. However, that is not the case with super-fast optical systems like the RASA. Celestron's engineers addressed this concern by designing the RASA with a removeable optical window. This means you can maintain peak optical performance if a filter is added or if a camera has its own optical window. Simply remove the flat window and replace it with a Celestron filter. Celestron offers a Light Pollution Imaging Filter designed specifically for the 8” RASA, which replaces that optical window.

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. When compared with a “Hyperstar SCT” system, the RASA 8 provides better optical performance and field illumination.

8" Astrograph Scope Description:

Capture spectacular wide-field deep sky images in seconds with Celestron’s new portable astrograph, the 8” Rowe-Ackermann Schmidt Astrograph (RASA). 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 often, you can eliminate the need for using an autoguider completely because of the fast exposures. Weighing in at just 17 pounds, it’s easy to transport your 8” RASA from Celestron to the most remote dark sky locations.

The 8” RASA is an imaging telescope that delivers a flat field without optical aberrations for razor sharp stars across a wide field of view. This astrograph 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. The latest addition to the RASA family, this 8” version has many of the same thoughtfully designed features as its “big brother” the RASA 11", including the integrated air-cooling system, internal filter mount, and sturdy CGE dovetail mounting bar.

As a typical astrograph design, this scope was purely designed for imaging, hence the 8” RASA cannot be used visually. The prime focus focal plane is located near the front aperture of the optical system, so it cannot accommodate a traditional eyepiece. Since it is an F/2.0 optical system, imagers can use shorter exposure times to capture detail in faint objects. With sensitive cameras and the proper “live stacking” software, the 8” 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. The 8” RASA’s relatively short 400 mm focal length also lessens the demand for equatorial tracking accuracy. In many cases, autoguiding will not be required. Weighing only 17 lb, this optical tube pairs perfectly with a wide variety of mounts. Celestron has unveiled 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. This Ultra-Stable Focus System uses two sets of precision bearings that are precisely aligned and tested during the assembly process to ensure optimal focus results.

Note that the 8” model RASA 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 which have up to a 22 mm diagonal, but performs well with sensors up to 32 mm in diagonal. The APS-C sized sensors used in many mirrorless cameras are a good choice. 42 mm full frame sensors will also work, but performance will be poor at the edges of the sensor and field illumination will be reduced. Additionally, it is not recommended to pair RASA 8 with any camera body more than 4” in diameter. See the chart below to determine if your camera is compatible with RASA 8.

Camera Compatible with RASA 8? Adapter required
Astronomical CMOS/CCD camera with C-mount Yes C-mount adapter (included)
Astronomical CMOS/CCD camera with M42-thread mount Yes M42 adapter (included) with M42 extension tubes (not included)
Astronomical CMOS/CCD camera with other mount Yes Custom camera adapter
Canon mirrorless with APS-C sensor Yes
Canon mirrorless adapter
(sold separately)
Sony mirrorless with APS-C sensor Yes
Sony mirrorless adapter
(sold separately)
Canon mirrorless with full frame (42mm) sensor Yes, but not optimized across the full sensor
Canon mirrorless adapter
(sold separately)
Sony mirrorless with full frame (42mm) sensor Yes, but not optimized across the full sensor
Sony mirrorless adapter
(sold separately)
DSLR No --

 

Specifications:

Optical Design Rowe-Ackermann Schmidt Astrograph (RASA)
Aperture 203 mm (8")
Focal Length 400 mm (15.74")
Focal Ratio f/2.0
Central obstruction diameter 93 mm (3.66") (46% of aperture diameter)
Light Gathering Power (Compared to human eye) 843X
Resolution (Rayleigh) 0.68 arcsecond
Resolution (Dawes) 0.57 arcsecond
Image circle 22 mm (.86") Ø, 3.15°
Useable field 32 mm (1.26") Ø, 4.6°, only minimal performance loss at edge
Wavelength range 390 nm – 800 nm
Spot size < 4.6 μm RMS across image circle
Optical coatings XLT multi-coatings used throughout
Off-axis Illumination 93% at 11 mm (0.43") off-axis
Optical window 46 mm (1.81") Ø
Back focus with included camera adapter 25 mm (0.98")
Back focus from top of threaded collar 29 mm (1.14")
Optical Tube Aluminum
Optical Tube Dims. 628 mm (24.7") length | 235 mm (9.3") diameter
Focuser New focuser design, minimizes focus shift
Finderscope Not included
Optical Tube Weight 17 lb (7.7 kg)
Other features Ventilation fan, built in filter mount
Included items M42 camera adapter, C-Thread camera adapter, fan battery pack
Dovetail Mount CGE Dovetail Bar
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