Celestron Telescope RASA CGEM II 800, f/2.0 Review

My Experience with the Celestron Telescope RASA CGEM II 800, f/2.0: Here’s the Truth

For years, the pursuit of capturing faint deep-sky nebulae and galaxies in stunning detail felt like an exclusive club, often requiring significant investment in bulky, slow optical systems and complex guiding setups. When I first heard about the Celestron Telescope RASA CGEM II 800, f/2.0, a fast f/2.0 astrograph designed to bring wide-field imaging to a more accessible level, my interest was immediately piqued. I needed a solution that could deliver impressive results without the astronomical cost and complexity of larger imaging trains. This particular setup promised a revolution in portability and speed, aiming to democratize astrophotography for enthusiasts like myself who juggle limited space, time, and budget. My previous experiences with longer focal length telescopes often meant agonizingly long exposure times and constant fussing with autoguiders. Compared to those cumbersome setups, the RASA 8’s promise of rapid data acquisition and simplified operation was incredibly appealing, almost too good to be true. My first impression upon unboxing was one of solid engineering; the mount felt substantial, and the optical tube, though compact, exuded a sense of precision.

Real-World Testing: Putting Celestron Telescope RASA CGEM II 800, f/2.0 to the Test

First Use Experience

My initial foray with the Celestron Telescope RASA CGEM II 800, f/2.0 took place under the relatively clear skies of my suburban backyard, a far cry from the pristine darkness I usually crave. Setting up the CGEM II mount was straightforward, thanks to its clear markings and sturdy legs that adjusted easily. The RASA 8 optical tube attached securely via its CGE dovetail bar. The included NexStar+ hand controller made the GoTo alignment process surprisingly painless, even with some light pollution obscuring fainter stars. My first target was the Andromeda Galaxy, and within minutes of alignment, the mount had centered it precisely in the field of view of my ZWO ASI294MC Pro camera. The speed of the f/2.0 system was immediately apparent; even short exposures of 30 seconds revealed impressive detail and color that would have taken minutes with my previous setup. I encountered a minor quirk with cable management, as the various power and data cables from the camera and mount required careful routing to avoid snagging during slews, but a few zip ties and Velcro straps quickly resolved this.

Extended Use & Reliability

After several months of consistent use, spanning multiple observing sessions and even a trip to a designated dark sky site, the Celestron Telescope RASA CGEM II 800, f/2.0 has proven to be a remarkably reliable imaging companion. The CGEM II mount, with its low cog DC servo motors and integrated optical encoders, has consistently provided smooth tracking, even during extended exposures of several minutes. I’ve noticed virtually no star trailing, which significantly reduces the need for recalibration. The optical tube itself has held its collimation exceptionally well, a testament to its robust design and the Ultra-Stable Focus System. Cleaning the corrector plate is simple, requiring only a puff of air and a microfiber lens cloth; I’ve found no issue with dust accumulation inside the tube, likely due to the sealed design. Compared to my old SCT, which often required frequent collimation and suffered from image shift, this RASA system is a dream. It’s handled moderate dew without issue, though I always use a dew shield and occasionally a dew heater on damp nights.

Breaking Down the Features of Celestron Telescope RASA CGEM II 800, f/2.0

Specifications

The Celestron Telescope RASA CGEM II 800, f/2.0 is engineered for dedicated deep-sky imaging. It boasts a 203mm (8″) aperture with a 400mm focal length, resulting in an incredibly fast f/2.0 focal ratio. This system employs a Rowe-Ackermann Schmidt Astrograph optical design, renowned for its ability to produce a flat field free of optical aberrations such as field curvature, coma, astigmatism, and chromatic aberration, even across an entire APS-C sensor. The central obstruction is 93mm (3.66″), representing 46% of the aperture diameter. Light gathering power is listed at 843x compared to the human eye, with theoretical resolution limits of 0.68 arc seconds (Rayleigh) and 0.57 arc seconds (Dawes). The optical system is optimized for a wide wavelength range from 390-800 nm, capturing more of the light emitted by celestial objects. The usable field of view is quoted at 32mm (1.26″), providing a 4.6-degree angle.

The included CGEM II Equatorial Mount provides a stable platform with a 40 lb load capacity, easily handling the 17 lb optical tube and camera. Its heavy-duty adjustable height tripod features 2-inch diameter steel legs. The mount utilizes low cog DC servo motors with integrated optical encoders, driving steel worm gears against brass worm wheels, all supported by precision sealed bearings for smooth and accurate slewing and tracking. The NexStar+ hand controller offers a database of over 40,000 celestial objects and advanced features like All-Star Polar Alignment and Permanent Periodic Error Correction (PPEC). Cable management is integrated internally, and the entire system disassembles tool-free for transport.

Performance & Functionality

The core function of the Celestron Telescope RASA CGEM II 800, f/2.0 is deep-sky astrophotography, and it excels at this. The f/2.0 focal ratio is its standout feature, drastically reducing exposure times. For instance, capturing the Horsehead Nebula, which might take hours with an f/6 or f/10 scope, can be achieved in a fraction of that time with the RASA 8. This speed also makes it a fantastic partner for sensitive CMOS and mirrorless cameras, offering an almost “real-time” observing experience through live stacking software. The flat field performance is exceptional; stars remain sharp points of light all the way to the edge of my camera’s sensor, a significant improvement over many other designs I’ve used. The Ultra-Stable Focus System is genuinely impressive, providing fine, repeatable focusing without any hint of image shift, even when adjusting the focus knob. The CGEM II mount’s tracking is accurate enough that for many targets, autoguiding is truly optional, a huge boon for beginners and those seeking a simpler workflow.

However, it’s crucial to understand its limitations. This is purely an imaging instrument; it cannot be used visually because the focal plane is at the front of the telescope. Also, the central obstruction is substantial (46%), which does impact contrast compared to a refractor or Newtonian of similar aperture, though for deep-sky objects, the speed advantage far outweighs this. The image circle is specified for up to 22mm, but it performs well with larger sensors up to 32mm, meaning some vignetting might be present on larger APS-C or full-frame sensors without a field flattener or careful processing, though Celestron offers options for this.

Design & Ergonomics

The Celestron Telescope RASA CGEM II 800, f/2.0 presents a cohesive and thoughtfully designed package. The RASA 8 optical tube is compact and surprisingly lightweight at just 17 pounds, making it manageable for single-person setup. Its white finish is classic Celestron, and the matte black interior of the tube minimizes stray light. The integrated air-cooling system is a subtle but effective design choice, helping the optics reach thermal equilibrium faster. The mounting bar is robust, and the focuser, with its internal bearing system, feels incredibly precise and smooth. The CGEM II mount itself is a workhorse; its heavy-duty steel tripod provides excellent stability, and the adjustment knobs are easy to grip and operate, even with gloves on. The internal cable management is a clever touch that significantly tidies up the setup, preventing tangles and snags that can ruin an imaging session.

Durability & Maintenance

From my experience, the Celestron Telescope RASA CGEM II 800, f/2.0 is built for longevity and the rigors of astrophotography. The optical surfaces are protected by Celestron’s StarBright XLT coatings on refractive elements and enhanced aluminum coatings on the primary mirror, which have shown no signs of degradation. The CGEM II mount, with its steel worm gears and precision bearings, feels robust and designed for sustained operation. Routine maintenance primarily involves keeping the optics clean and ensuring the mount’s internal gears are properly lubricated (though this is a task for advanced users or service centers). The lack of external motor cables reduces points of failure and wear. Given its construction and the quality of its components, this system should provide many years of dedicated service for an active imager.

Accessories and Customization Options

The included accessories with the Celestron Telescope RASA CGEM II 800, f/2.0 are essential for its function. You receive the CGEM II Equatorial Head, the Tripod, an Accessory Tray, one 17 lb counterweight, the NexStar+ Hand Control, and a DC Power Cable (cigarette lighter adapter type). Crucially, camera connection adapters for M42 threads are included, and Celestron offers optional adapters for specific mirrorless cameras like Sony and Canon. The internal filter mount is a significant accessory, allowing seamless integration of a filter, such as the Celestron Light Pollution Imaging Filter, directly into the optical path without degrading performance. While the RASA 8 is designed for specific cameras, its compatibility with common adapters makes it versatile. The CGEM II mount also features an autoguider port for those seeking even finer tracking precision, and a USB 2.0 port on the hand controller enables computer control with third-party software.

Pros and Cons of Celestron Telescope RASA CGEM II 800, f/2.0

Who Should Buy Celestron Telescope RASA CGEM II 800, f/2.0?

The Celestron Telescope RASA CGEM II 800, f/2.0 is an outstanding choice for dedicated deep-sky astrophotographers who want to maximize image acquisition time and capture stunning wide-field images with minimal fuss. It’s perfect for those who are frustrated by long exposure times and the complexities of traditional imaging setups. This astrograph is particularly well-suited for users employing modern CMOS, smaller CCD, or mirrorless cameras with sensors up to APS-C size. If you’re looking to upgrade from a more basic telescope for imaging or want to invest in a dedicated imaging rig that prioritizes speed and optical quality, this system is a compelling option.

Conversely, anyone looking for a versatile visual telescope should look elsewhere, as the RASA 8 is exclusively an imager. Those who primarily photograph planets or the Moon will also find its wide field and low magnification less suitable. If budget is a primary concern and deep-sky imaging is not your sole focus, more affordable and versatile options might exist. For those who do purchase it, investing in a good dedicated astronomy camera with a suitable sensor size (up to 32mm diagonal) and a reliable astronomy software suite for stacking and processing will unlock its full potential. A dew heater is also a wise accessory for humid environments.

Conclusion on Celestron Telescope RASA CGEM II 800, f/2.0

The Celestron Telescope RASA CGEM II 800, f/2.0 represents a significant leap forward in accessible, high-performance astrophotography. Its combination of a blazing fast f/2.0 optical system with a stable and intelligent equatorial mount delivers on its promise of spectacular wide-field imaging with reduced complexity and exposure times. The optical quality is superb, providing sharp stars across a wide field, and the focusing system is a joy to use. While the price is certainly an investment, the value proposition lies in the time saved, the quality of data acquired, and the simplified workflow it offers to dedicated imagers. I wholeheartedly recommend this system to any serious amateur astrophotographer looking to elevate their deep-sky imaging capabilities, especially those who value speed, portability, and optical precision.