Celestron CGEM II 800 RASA 8" Telescope

• Flat field free of optical aberrations like field curvature, coma, astigmatism and chromatic aberration across an entire APS-C sensor.
• Unlike the larger RASAs that work with DSLR and large CCD cameras, the 8” 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.
• NEW Ultra-Stable Focus System – six precision sealed ball bearings virtually eliminate image shift.
• Internal filter mount – seamlessly accommodates a Light Pollution Imaging Filter into the optical path.
• 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.
• The CGEM II, with its 40 lbs load capacity, is the latest update to the venerable CGEM mount and provides a sturdy and rigid platform for the fully-loaded RASA 8.
• The drive system, consisting of low cog DC Servo motors with integrated optical encoders, steel worm gears supported by precision sealed bearings, and brass worm wheels, ensures smooth and accurate slewing and tracking.
• Proven NexStar+ computerized telescope control technology supports functions to address imagers’ needs, such as All-Star Polar Alignment, Permanent Periodic Error Correction (PPEC), and adjustable tracking through meridian.

This Celestron 8" f/2 Rowe-Ackermann Schmidt Astrograph (RASA) optical tube has:

Very fast 8" f/2 Rowe-Ackermann Schmidt optics 
StarBright XLT optical multicoatings for the highest possible light transmission
MagLev DC cooling fan and cooling vents 
Built-in corrector lens
Mirror locks
42mm T-thread and C Thread camera adapters
CGE (Losmandy-style "D-plate") dovetails 
2-year warranty

"I don't get it. What do you look through?"

This might be the most common question people ask when you unpack your new Celestron Rowe-Ackermann Schmidt Astrograph (RASA). It's not only missing something that comes with virtually every telescope ever produced . . . an eyepiece . . . it doesn't even have a place to put an eyepiece. That's because the 400mm focal length f/2 Celestron 8" RASA is strictly a deep space imaging scope and cannot be used visually.

But what an imaging scope! It has a 22mm image circle that can handle CMOS cameras, smaller CCD cameras, and mirrorless cameras.  The telescope does not work with standard DSLR cameras. It provides a proven Schmidt corrector optical system with a built-in corrector lens that keeps the images free of coma, field curvature, and false color. 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.

Its fast, wide field, f/2 optics give you two huge advantages over traditional f/10 catadioptric imaging scopes (even those using an optional f/6.3 or f/7 focal reducer). Those advantages? Better apparent tracking due to the image scale, plus shorter exposure times due to the speed of the optics. That means you can create better-looking deep space images in a fraction of the time it used to take, even without using an autoguider.

The Celestron RASA concept was to modernize the Celestron Schmidt camera, an instrument that had a loyal following, as its very fast focal ratio allowed amateur astrophotographers to produce wide field deep space images in the 1970s. Schmidt cameras could produce great images, but they wre and imaging scope only a really hard-core astrophotographer could love.

Those Schmidt cameras used a single frame of 35mm film, cut from a roll of film. You flexed the chip of film in total darkness (being careful not to touch the emulsion side) to fit snugly into a curved holder that matched the camera's curved focal plane, then loaded it into the camera by feel inside a black cloth bag to avoid image-spoiling stray light. You manually guided your scope during the entire exposure, keeping your eye glued to the crosshairs of an illuminated reticle eyepiece so your stars wouldn't turn into elongated squiggles. Finally, after a sometimes multiple hour single exposure, you tediously processed the small chip of film in your own darkroom before you could even begin to see if you had captured a usable image.

No more. Telescope mount drive accuracy has improved tremendously, electronic eyeballs have taken over guiding, and fast digital photography has taken the place of slow 35mm film.

Today's CCD camera can have sensors as large, if not larger, than film. To compensate for the new large sensors Celestron had to push the boundaries of the Schmidt camera design and make an entirely new type of instrument. The Celestron Rowe-Ackermann Schmidt Astrograph has provided that advance in the performance of deep space imaging scopes. With it, today's amateur astrophotographers can produce results rivaling that of the best professional observatory photos of only a few short years ago.

As with most advances in optics, the Celestron Rowe-Ackermann Schmidt Astrograph was designed not by committee, but by two dedicated optical experts who believed things could be done better - Dave Rowe and Mark Ackermann.

Dave Rowe - amateur astronomer, telescope maker, and optical designer - studied astronomy and astrophysics at Caltech, has published more than 50 papers, and holds 15 patents. Rowe has designed and fabricated many telescopes for Celestron and PlaneWave Instruments, including PlaneWave's corrected Dall-Kirkham and CDK700 telescope. He also worked closely with Celestron engineers in the development of the unique StarSense technology.

Mark Ackermann - amateur astronomer and experienced optical designer - earned a BS in mathematics and physics from the United States Air Force Academy, an MS in solid state physics, and a PhD in nonlinear optics from the University of New Mexico. He has published dozens of papers on optical telescope design and holds six US patents related to optical systems.

Engineered as a complete astroimaging system, every component of the Celestron Rowe-Ackermann Schmidt Astrograph is optimized for peak performance with CMOS, smaller CCD camers, and mirrorless cameras. Every component of the system has been designed to work together seamlessly, right down to the thickness of the glass used in the scope's fully-multicoated optical window.

Some of the advanced features of the Celestron 8" RASA includes mirror locks hold your precise focus. A quiet high-output 12V internal MagLev fan on the rear cell reduces cooldown time and provides optimal airflow through the dust filtered 24.7" long optical tube. Naturally, industry leading StarBright XLT optical multicoatings are standard equipment for the highest possible light throughput. A Losmandy-style "D-plate" dovetail is standard. The back focus with the included camera adapters is 25mm.

The Celestron #93614 RASA LPR (Imaging Filter is highly recommended with the RASA. The scope's incredibly fast f/2 focal ratio gathers so much light so quickly that even modest amounts of sky glow at a dark sky site can brighten the sky background and reduce the contrast in your images. In light-polluted city and suburban locations, the RASA Light Pollution Reduction (LPR) Imaging Filter is a must.

The Celestron CGEM II is an upgraded heavy-duty computerized go-to German equatorial moun. The ergonomically-designed CGEM II has a fresh, attractive, bold appearance – and a 40 pound payload capacity. This allows it to carry Celestron SCT optical tubes up to 11" in aperture, plus a full load of imaging accessories, as well as virtually any other optical tube and accessory payload less than 40 pounds in weight.

The CGEM II mount head contains dual-axis slewing/tracking motors on each axis for go-to computer control. Steel worm gears and 90mm diameter brass worm wheels assure long-term reliability and high accuracy performance. The use of low cog DC Servo motors with integrated optical positioning encoders offers smooth, quiet operation and precision slewing and tracking. The motor armatures are skewed to minimize cogging for precise jitter-free low speed tracking. The motor drives and their wiring are all internal, keeping them snag-free and free from dust and debris.

The mount requires a minimum 1.5 amp 12 VDC power supply to operate. The maximum 1.5 amp power draw happens only briefly when accelerating to, or decelerating from, the high speed slewing mode from a standing start with a small payload (8" SCT OTA or similar). Normal power draw with a well-balanced payload is generally less than half the maximum draw.

The mount comes with a car battery cord to operate from the cigarette lighter plug of your car or from a rechargeable 12V battery pack. The 17 amp hour capacity Celestron Power Tank #4517V is recommended and will operate the mount all night long without danger of running out of power. An optional Celestron #2338PRO 5 amp ac adapter is available to run the CGEM II all night from household AC in backyard or observatory.

To make a casual polar alignment for visual use quick and easy, there's a latitude scale with large ergonomically-friendly altitude and azimuth adjustment knobs. No polar alignment finderscope is available to aid in the precise polar alignment required for long exposure astrophotography, nor is any needed. A unique Celestron All-Star Polar Alignment program built into the NexStar hand control helps you do a very precise computerized polar alignment in mere minutes, using any bright star, even when Polaris is hidden by trees or buildings. It works in both northern and southern hemispheres.

The supplied 17 pound counterweight is locked in place on the steel counterweight shaft with a single hand-tighten knob, making it easy to rebalance a scope if you add heavy photographic accessories. If needed, optional counterweights are available to balance very heavy loads.

For observing or imaging objects near the meridian (the imaginary line passing directly overhead from North to South), the CGEM II is designed to track well past the meridian for uninterrupted imaging through the most ideal part of the sky.

There are nine motor drive speeds: 0.5x and 1x sidereal for guiding; 4x, 8x, 16x, and 64x for centering; and 1°, 2°, and a fast 5° per second for slewing. Preset tracking rates include sidereal, solar, and lunar. Equatorial tracking modes are available for both northern and southern hemispheres.

The supplied NexStar computer hand control has a built-in database of more than 40,000 stars and objects. These include the complete RNGC, Messier, Caldwell, IC, and Abell catalogs; selected SAO stars; the planets, the Moon, and others. The custom database lists of all the most famous deep-sky objects by name and catalog number; the most beautiful double, triple and quadruple stars; selected variable stars; non-planetary solar system objects; and asterisms.

You can also store and edit the right ascension and declination of 400 additional user-defined objects of your own choosing, such as the comet and asteroid coordinates published monthly in Astronomy and Sky & Telescope magazines. The computer control can find any of those objects with only a few keystrokes, and track them with high accuracy for visual or photographic applications. There is enhanced information on over 200 of the most note-worthy objects.

The NexStar computer control of the smooth and precise CGEM II go-to mount makes finding over 40,000 stars and objects easy and automatic, so you can spend more time looking at them, rather than looking for them.

New for the CGEM II mount, a USB 2.0 communication port on the hand control allows you to operate the telescope via a personal computer using a USB cable and NexRemote software CD-ROM. The hand control and motor control software is flash-upgradeable to allow you to download the latest product updates over the Internet to keep your CGEM II mount always at the cutting edge of technology. An autoguider port is located on the electronic pier for guided, but unattended, long exposure astrophotography.

The NexStar hand control provides a constant digital r. a. and dec readout of the scope's position on the sky. This provides much greater accuracy than conventional manual setting circles for star-hopping or locating objects by their celestial coordinates alone, should you want to observe the old-fashioned way without using the computer to find objects for you.

The software built into the NexStar hand control includes mount calibration, database filter limits, hibernate, five alignment procedures, user-defined slew limits, a new "All-Star" polar alignment routine that uses any bright star for a quick and accurate polar alignment, and more. Built-in adjustable backlash compensation permits precise corrections during astrophotography and when observing visually at high powers. A high precision pointing subroutine in the computer lets you point accurately at objects that you want to photograph that are too dim to be seen though the scope.

The software includes permanent programmable periodic error correction (PEC) to correct for the minor periodic tracking errors inherent to all worm drives that might otherwise mar your long exposure photographs. The CGEM II mount retains the PEC recordings when it is powered down. The hand control and motor control software is flash-upgradeable to allow you to download the latest product updates over the Internet to keep your CGEM II mount always at the cutting edge of technology.

An autoguider port is located on the electronic pier for long exposure astrophotography. The autoguider port can use a six-pin RJ-12 modular jack ST-4 compatible CCD autoguider to automatically control the drive motors during long exposure astrophotography.

Five different alignment methods are built into the NexStar computer - 2-star align, quick align, 1-star align, last alignment, and solar system align - allowing you to choose a level of computer accuracy in automatically finding objects with which you are comfortable. Alignment is easily accomplished in only a few short minutes. You can be observing in less than 15 minutes after you first take your CGEM II-mounted scope outdoors.

In addition, the NexStar computer hand control is GPS-compatible (using an optional inexpensive SkySync GPS module) for full GPS (Global Positioning System) satellite accuracy. Adding GPS to the computer is something no competitively-priced mount can do. Once the scope is approximately polar aligned, the 16-channel SkySync GPS system uses signals from government satellites to calculate the scope's location on earth with an accuracy measured in meters. The system also calculates the current time based on the split second accuracy of the GPS time signals.

After the SkySync quickly completes these calculations and enters the information into the computer control for you automatically, the computer can then orient the scope with the sky, slew to a pair of guide stars, ask you to confirm that the stars are in the center of the field (and center them if they're not precisely aligned), and then start finding and tracking over 40,000 objects for you at your command. With the CGEM II go-to mount and the SkySync, orienting your scope in time and space on earth and aligning it on the sky becomes almost as easy a task as simply turning the mount on.

The adjustable height tripod has 2" diameter stainless steel legs with a metal center leg brace for rigidity to provide excellent damping characteristics. The center leg brace is drilled to form a convenient accessory tray that holds 1.25" and 2" eyepiece to keep them up out of the dew-soaked grass.

New for the CGEM II mount is a dual saddle plate. The saddle plate will now accept both the CGE/Losmandy wide dovetail plate as well as the AVX/Vixen style dovetail plate. The dovetail slot on the top of the mount holds the long dovetail slide bar mounted under the optical tube. This allows you to slide the optical tube fore and aft in the dovetail slot to quickly and precisely balance the optical tube in declination when you add or subtract accessories, eliminating the need for an extra counterweight to balance a camera or other accessories. Setup and takedown times are exceptionally fast, as a single large hand-tighten knob holds the optical tube in place. A second lock knob prevents the tube from sliding off the mount should the hand-tighten knob loosen. The oversized dovetail mounting platform assures secure vibration-free tube attachment.