This package combines Celestron's 8” Rowe-Ackermann Schmidt Astrograph (RASA) with the CGEM II EQ mount, offering all the essential components to capture stunning wide-field deep-sky images.

Unlocking RASA Performance for All

Celestron presents the 8” Rowe-Ackermann Schmidt Astrograph (RASA), an exceptional tool for swiftly capturing wide-field deep-sky images. This remarkable f/2.0 system perfectly complements contemporary color astronomical CMOS cameras, compact CCD cameras, and mirrorless cameras. Its rapid focal ratio and patented optical design allow you to generate crisp, intricate images, often eliminating the need for an autoguider. Weighing a mere 17 pounds, the 8” RASA is highly portable, facilitating transport to remote dark sky locations.

The 8” RASA serves as an imaging telescope that yields a flat field devoid of optical aberrations, resulting in pinpoint stars across an expansive field of view. It can produce breathtaking deep-sky astrophotographs without the typical challenges associated with longer focal length instruments, all at a fraction of the cost.

Expanding the RASA Family

The 8” RASA joins the esteemed RASA family as a more portable and budget-friendly alternative to the renowned RASA 11, which earned accolades upon its introduction in 2014. Sharing many of the thoughtful features of its larger counterpart, including the integrated air-cooling system, internal filter mount, and robust CGE dovetail mounting bar, the 8” RASA opens up the benefits of the RASA design to a broader audience. It is worth noting that the 8” RASA is exclusively designed for imaging and cannot be used for visual observation due to the prime focus focal plane's positioning at the front of the optical system.

Reduced Exposure Times and Near Real-Time Observing

The F/2.0 optical system of the 8” RASA enables astrophotographers to employ shorter exposure times for capturing intricate details in faint celestial objects. Coupled with sensitive cameras and suitable "live stacking" software, this telescope offers an almost real-time observing experience, delivering brighter and more detailed images than what can be perceived with the naked eye through much larger telescopes.

Ultra-Stable Focus System

Celestron introduces a new focuser design with the 8” RASA, mitigating lateral movement of the primary mirror during focusing, slewing, or tracking. This results in smoother, more precise, and more stable focusing. The Ultra-Stable Focus System relies on a precision linear ball bearing, meticulously tested during assembly to ensure optimal performance.

Tailored for Modern Cameras

Unlike its larger RASA counterparts designed for DSLR and sizable CCD cameras, the 8” model is engineered with color astronomical CMOS cameras, compact CCD cameras, and mirrorless cameras in mind. It is not compatible with standard DSLR cameras. Optimized for sensors up to 22mm diagonal, it also performs well with sensors up to 32mm diagonal. APS-C sized sensors commonly found in mirrorless cameras are a suitable choice. While 42mm full-frame sensors can be used, performance may diminish at the sensor's edges, and field illumination will be reduced. Additionally, it is not recommended to pair the RASA 8 with a camera body exceeding 4 inches in diameter. Refer to the chart below to verify your camera's compatibility with the RASA 8.

 Innovative Optical Design

Celestron's RASA boasts a patented optical design (US 2016/0299331 A1) that incorporates a Schmidt corrector, primary mirror, lens group, and optical window. Within the lens group, four elements, including rare-earth elements, are employed. Unlike many telescopes optimized solely for the visible spectrum (400-700nm), the 8” RASA's optics are engineered to perform across a broader spectral range, spanning from 400-800nm. This extended range ensures sharp focus for more of the light emitted by celestial objects in your images.

When dealing with super-fast optical systems like the RASA, the addition of extra flat glass, such as a filter, can significantly impact optical performance. To address this, the RASA features a removable optical window, allowing you to maintain peak optical performance when using a filter or when your camera possesses its optical window. Celestron offers a Light Pollution Imaging Filter tailored specifically for the 8” RASA, which can be mounted in place of the optical window.

All refractive optical surfaces are coated with StarBright XLT coatings, while the primary mirror benefits from enhanced aluminum coatings, ensuring high light transmission throughout the entire optical system. In comparison to "Hyperstar SCT" systems, the RASA 8 delivers superior optical performance and field illumination.

CGEM II: An Ideal Platform for RASA

The CGEM II equatorial mount provides robust support for the 8” RASA, with its 40 lb load capacity effortlessly accommodating the 17 lb optical tube, leaving ample capacity for your camera and accessories. The sturdy adjustable height tripod is equipped with 2” diameter steel legs featuring graduated markings, simplifying leg extension to achieve equal heights. The 8” RASA connects directly to the CGEM II via its CGE dovetail mounting bar.

Designed with imaging in mind, the CGEM II motor drive system ensures accurate tracking during exposures. This system employs low cog DC servo motors with integrated optical encoders at its core. The low cog design ensures smooth motor operation, while the integrated optical encoders deliver precision. Steel worm gears turn against brass worm wheels, further enhancing the motor drive system's smooth and precise performance.

To accurately track celestial objects, polar alignment is a prerequisite. Celestron simplifies this process with the innovative All-Star Polar Alignment procedure, eliminating the need for additional equipment such as a polar finder scope (though an optional polar alignment finder scope is available if desired). This alignment procedure typically takes about 15 minutes to complete, even when Polaris is not visible.

All mounts exhibit some degree of "periodic tracking error" due to tiny gear imperfections. To mitigate this, the CGEM II incorporates Permanent Periodic Error Correction (PPEC), which allows you to record periodic errors just once, with subsequent corrections based on this recording, enhancing tracking accuracy. For even higher tracking precision, the CGEM II features a dedicated autoguider port for connecting an autoguiding camera directly to the mount, compensating for any residual tracking errors.

Imaging conditions are optimal when celestial objects are at their zenith with a dark background, a condition known as the meridian. However, some German equatorial mounts require a "meridian flip" to avoid the telescope tube striking the mount. The CGEM II overcomes this limitation by easily imaging through the meridian without requiring a flip until the object is a full 20° past the meridian.

The NexStar+ hand controller provides an array of functions to control various aspects of the mount's behavior. These include:

• Multiple alignment methods for syncing with the night sky.
• Adjustable slew rates of up to 5° per second.
• Compatibility with both Northern and Southern hemispheres.
• Adjustable autoguiding rates.
• Hibernate mode for powering down the mount without losing alignment.
• Ongoing firmware development, regularly introducing new features.

In addition to the autoguider port, the CGEM II offers other ports to expand the mount's capabilities. The hand controller includes a USB 2.0 port for external computer control using optional third-party software. An AUX port on the mount can support optional accessories like StarSense AutoAlign.

When it comes to imaging, cable management can be a challenge with various cables involved, including those for the camera, mount power source, computer connection, and autoguider. To simplify cable management and reduce the risk of unwanted snags, all cabling for the mount is internal. This eliminates the need to connect or disconnect an external Dec. motor cable during setup or breakdown.

Transporting the entire system to a dark sky location poses no issue. The optical tube, mount head, tripod, counterweight bar, and counterweight can all be disassembled with ease, without the need for tools.

In summary, the CGEM II and RASA 8 combine seamlessly to achieve remarkable imaging results with minimal complications. This kit is an excellent choice for those seeking to elevate their deep-sky astrophotography endeavors.

Specifications

Software and Documentation