11" f/2.2 Rowe-Ackermann Schmidt Astrograph (RASA) on CGEM DX Mount

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This Celestron 11” f/2.2 Rowe-Ackermann Schmidt Astrograph (RASA) CGEM DX mount combination has:
  • Very fast 11" f/2.2 Rowe-Ackermann Schmidt optics 
  • StarBright XLT optical multicoatings for the highest possible light transmission
  • MagLev DC cooling fan and cooling vents 
  • Built-in four-element rare earth corrector lens
  • 42mm T-thread and 48mm camera adapters
  • CGEM DX go-to German equatorial mount
  • 2-year warranty
Details on the Celestron 11” RASA optical tube . . .

The Celestron Rowe-Ackermann Schmidt Astrograph (RASA) updates and improves the Celestron Schmidt camera, a premium wide-field imaging instrument of the 1970s that had a loyal following, but a difficult instrument to use that only a really hard-core 35mm film astrophotographer could love.
 
Today, fast DSLR and CCD electronic imaging has taken the place of slow 35mm film. Home computers can manipulate and improve DSLR and CCD images in ways that 35mm imagers could only dream of. DSLRs and CCD cameras can have sensors as large as (and in some cases larger than) 35mm film. 

To compensate for these new large sensors Celestron had to push the boundaries of the Schmidt camera design and make an entirely new type of instrument, the RASA. The Celestron RASA provides an advance in the performance of deep space imaging scopes that lets today’s amateur astrophotographers produce wide field results rivaling those of the best professional observatory photos of only a few short years ago.

The 11” 620mm focal length f/2.22 Celestron Rowe-Ackermann Schmidt Astrograph imaging-only optical tube has a huge 70mm image circle that can handle full frame DSLRs and the largest sensor size CCD cameras with minimal vignetting. It combines a proven Schmidt corrector optical system with a built-in 4-element rare earth 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/2.22 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). You get 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 and mosaics in a fraction of the time it used to take, even without using an autoguider.

With a Rayleigh Limit (photographic resolution) of 0.50 arc seconds, the Celestron 11" RASA is capable of revealing much finer deep space detail than a similar focal length 4" apo refractor (a scope type often used for wide field imaging), which has a Rayleigh Limit of 1.36 arc seconds. And the RASA will record those more detailed images in a fraction the time of that 4" apo. 

The Celestron 11” RASA optical tube includes a custom-engineered linear brass focuser bearing to reduce image shift It is combined with a FeatherTouch Micro Focus Knob to allow you to make the precise fine adjustments you need to capture the perfect image. 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 33” long optical tube. 

Naturally, industry leading StarBright XLT optical multicoatings are standard for the highest possible light throughput. 42mm T-thread DSLR and 48mm CCD camera adapters are standard equipment. Two Losmandy-style “D-plate” dovetails are standard, one on the bottom of the RASA for installing it on the CGEM DX mount, and one on top for installing accessories (such as on optional photoguide scope). The back focus from the included camera adapters is 55mm. 

Naturally, an astrograph as good as the RASA demands an equally good mount. The Celestron CGEM DX is that mount.

Details on the Celestron CGEM DX go-to German equatorial mount . . .

The Celestron CGEM DX mount is light enough to transport to a dark sky imaging site, yet stable and accurate enough for serious imaging. The CGEM DX 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 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 AC adapter is also available for backyard or observatory use.

No polar alignment finderscope is needed for the precise polar alignment required for long exposure astrophotography. A unique Celestron “All-Star Polar Alignment” program built into the mount’s 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 two supplied 22-pound counterweights are 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. The two standard counterweights will balance any load up to the full 50-pound payload capacity of the CGEM DX mount.

For observing or imaging objects near the meridian (the imaginary line passing directly overhead from North to South), the CGEM DX 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 easily add 100 of your own favorite objects to the list.

All of the database and mount operation information is displayed on a double line, 16-character, liquid crystal display on the hand control. There are 19 fiber optic backlit LED buttons to make it easy for you to control the NexStar computer without affecting your dark-adapted vision. An RS-232 communication port on the hand control allows you to operate the telescope via a personal computer using the supplied RS-232 cable and NexRemote software CD-ROM.

The software built into the NexStar hand control includes mount calibration, database filter limits, hibernate, five alignment procedures, user-defined slew limits, the new "All-Star" polar alignment routine, and more. Adjustable backlash compensation is standard. 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 images. The CGEM DX mount retains the PEC recordings when it is powered down. The hand control and motor control software can be flash upgraded over the Internet to keep your CGEM DX 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 Celestron mount’s NexStar computer – 2-star align, quick align, 1-star align, last alignment, and solar system align. This allows you to choose a level of computer accuracy in automatically finding objects with which you are comfortable. Alignment takes only a few short minutes. You can be observing in less than 15 minutes after you first take your CGEM DX-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) 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.

The adjustable height tripod (the same as used on the Celestron CGE Pro mount) has 3” diameter stainless steel legs with a center leg brace for rigidity to provide excellent damping characteristics. The center leg brace forms a convenient accessory tray that holds 1.25” and 2” eyepieces to keep them up out of the dew-soaked grass. Setup and takedown times are exceptionally fast, as a single large hand-tighten knob holds the 11" optical tube in place. A second lock knob prevents the tube from sliding off the mount should the hand-tighten knob loosen.

The complete RASA/CGEM DX mount combination weighs 143 pounds (64.1 kg). The tripod is the heaviest component, at 45 pounds (20.5 kg). The equatorial head weighs 41 pounds (18.6kg). The two supplied counterweights weigh 22 pounds (10 kg) each. The 11” RASA optical tube weighs 35 pounds (15.9 kg). The image shown above includes an optional CCD camera mounted on the RASA OTA.


Focal Length:
This is the length of the effective optical path of a telescopeor eyepiece (the distance from the main mirror or lens where the lightis gathered to the point where the prime focus image is formed). Focallength is typically expressed in millimeters.

The longer the focallength, the higher the magnification and the narrower the field of viewwith any given eyepiece. The shorter the focal length, the lower themagnification and the wider the field of view with the same eyepiece.

620mm
Focal Ratio:
This is the ‘speed’ of a telescope’s optics, found by dividing the focal length by the aperture. The smaller the f/number, the lower the magnification, the wider the field, and the brighter the image with any given eyepiece or camera.

Fast f/4 to f/5 focal ratios are generally best for lower power wide field observing and deep space photography. Slow f/11 to f/15 focal ratios are usually better suited to higher power lunar, planetary, and binary star observing and high power photography. Medium f/6 to f/10 focal ratios work well with either.

An f/5 system can photograph a nebula or other faint extended deep space object in one-fourth the time of an f/10 system, but the image will be only one-half as large. Point sources, such as stars, are recorded based on the aperture, however, rather than the focal ratio – so that the larger the aperture, the fainter the star you can see or photograph, no matter what the focal ratio.

f/2.22
Resolution:
This is the ability of a telescope to separate closely-spaced binary stars into two distinct objects, measured in seconds of arc. One arc second equals 1/3600th of a degree and is about the width of a 25-cent coin at a distance of three miles! In essence, resolution is a measure of how much detail a telescope can reveal. The resolution values on our website are derived using the Dawes’ limit formula.

Dawes’ limit only applies to point sources of light (stars). Smaller separations can be resolved in extended objects, such as the planets. For example, Cassini’s Division in the rings of Saturn (0.5 arc seconds across), was discovered using a 2.5” telescope – which has a Dawes’ limit of 1.8 arc seconds!

The ability of a telescope to resolve to Dawes’ limit is usually much more affected by seeing conditions, by the difference in brightness between the binary star components, and by the observer’s visual acuity, than it is by the optical quality of the telescope.

0.50 arc seconds
Aperture:
This is the diameter of the light-gathering main mirror or objective lens of a telescope. In general, the larger the aperture, the better the resolution and the fainter the objects you can see.
11"
Weight:
The weight of this product.
145 lbs.
Heaviest Single Component:
The weight of the heaviest component in this package.
45 lbs.
Warranty:
2 years
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11" f/2.2 Rowe-Ackermann Schmidt Astrograph (RASA) on CGEM DX Mount

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11" f/2.2 Rowe-Ackermann Schmidt Astrograph (RASA) on CGEM DX MountClose-up of the 11" RASA rear cell, showing the focuser, mirror locks, cooling fan, and one of the cooling ventsGraph of the field illumination of the 11" Celestron RASA, showing the minimal falloff.Graph of the ray trace of the complete 11" Celestron RASA optical system.Graph showing the image circle of the 11" Celestron RASA, relative to the chip size of various cameras.Graph of the spot matrix of the 11" Celestron RASA optical tube.11" Celestron RASA image of Markarian's Galaxy Chain (a 900x900 pixel portion of the 2136x1752 pixel original.A closer 11" Celestron RASA image of Markarian's Galaxy Chain (a 900x900 pixel portion of the 2136x1752 pixel original.11" Celestron RASA image by John Davis of the Propeller Nebula (a 900x900 pixel portion of the 1600x1153 pixel original.
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Our Product #: CRA-DX
Manufacturer Product #: 11006
Price: $4,999.00  FREE ground shipping - Click for more info
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Combine the exceptional wide-field imaging optics of the Celestron 11" f/2.22 Rowe-Ackermann Schmidt Astrograph (RASA) with the proven excellence of the Celestron CGEM DX go-to equatorial mount and you have an imaging scope that is equally at home in your backyard, in your observatory, or in the field at a dark sky site.





. . . our 36th year