Celestron 11" Rowe-Ackermann Schmidt Astrograph (RASA 11) Optical Tube Assembly (CGE Dovetail) - 91076

Highlights

• Fast, wide-field 11 f/2.2 optical design with rare-earth glass for images free of false color, coma, and field curvature
• Large 43.3mm optimized image circle maintains pinpoint stars to the far corners of even the largest astroimaging sensors, while the usable field extends even further to 52mm for larger format sensors
• New Ultra-Stable Focus System (USFS) minimizes focus shift and mirror flop
• Integrated air-cooling system features a quiet, high-output 12V MagLev fan and vents with mesh filters to prevent dust ingress
• Common camera adapters (T-thread and M48) included for easy attachment to popular CCD and DSLR cameras
• RASA scopes are for imaging only and cannot be used for visual observation.

Capturing impressive deep-sky astro images is easier than ever with Celestron's Rowe-Ackermann Schmidt Astrograph (RASA) V2, the perfect companion to today's top DSLR or astronomical CCD cameras. This fast, wide-field f/2.2 system allows for shorter exposure times compared to traditional f/10 astroimaging, without sacrificing resolution. Because shorter sub-exposure times are possible, your equatorial mount won't need to accurately track over extended periods. The short focal length also lessens equatorial tracking demands. In many cases, autoguiding will not be required.

RASA 11 V2 builds on the legacy of Celestron's Schmidt Cameras, which allowed astrophotographers to produce images with much shorter exposure times on film in the 1970s.

Today, with CCD sensor sizes as large as film or larger, the RASA 11 V2 offers a 43.3mm optimized image circle to capture pinpoint stars on the largest imaging chips. Optical performance for huge sensors with diagonals of up to 52mm wide is still excellent.

Combine this large image circle with a focal length of just 620mm and you have an instrument suitable for wide-field imaging, creating huge mosaics of the night sky, surveying, and even comet hunting.

Optical Performance
The RASA 11 V2 features optics with 4-element rare-earth glass for images free of false color and aberrations like coma and field curvature. The optical quality and spot size across the entire image circle are unprecedented for an astrograph in this price range-or even that of a much more expensive instrument. The design also provides minimal vignetting.

Advanced Features
RASA 11 V2 utilizes the new Ultra-Stable Focus System (USFS). At the heart of this system is a precision linear ball bearing. The bearing serves to minimize focus shift (unwanted lateral motion of the primary mirror during focusing which causes shifting of the image) and mirror flop (movement of the primary mirror when the telescope is pointing to different positions in the sky). The USFS is also compatible with the optional Celestron Focus Motor (#94155-A). The integrated 12V DC MagLev fan reduces cool-down time and provides optimal airflow through the dust filtered optical tube.

Engineered as a complete astroimaging system, every component of the RASA 11 V2 is optimized for peak performance with DSLR and astronomical CCD cameras. Down to the thickness of the glass used in the included fully-multi-coated optical window or optional imaging filter, every component of the system has been taken into careful consideration to work together seamlessly. The Dovetail CGE bars on the top of the optical tube provides a connection for use of optional accessories like a guide scope.

Unique Optical Design

RASA's optical design is patented (US 2016/0299331 A1). The design consists 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 8 RASA's optics are 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. With many imaging systems, adding an extra piece of flat glass such as a filter does not change optical performance. However, that is not the case with super-fast optical systems like the RASA. Our engineers addressed this by designing the RASA with a removable optical window, so you can maintain peak optical performance if a filter is added or if a camera has its own optical window. Celestron offers a Light Pollution Imaging Filter designed specifically for the 8 RASA, which mounts in place of the 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 Hyperstar SCT systems, the RASA 8 provides better optical performance and field illumination.

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