The Celestron CGEM – a Sky & Telescope Hot Product for 2010
– is a newly-designed heavy-duty computerized go-to German equatorial mount. The ergonomically-designed CGEM has a fresh, attractive, bold appearance. It has 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 payload capacity, performance, features, and price of the Celestron CGEM mount place it squarely between the Celestron Advanced Series and the premium CGE and CGE Pro Series mounts. It combines the portability of the Advanced Series with the precision of the CGE Pro mount at a price that is closer to the Advanced Series mount than it is to the CGE Pro.
The CGEM 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.
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 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 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.
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 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 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 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-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 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.
Optical tubes are installed on the CGEM mount using a slot on the mount head that accepts a Celestron CGE-style or Losmandy D-plate dovetail slide bar. This allows the optical tube to be quickly and precisely balanced fore and aft on the mount, 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 CGEM mount weighs 75 pounds. The equatorial head is the heaviest component, at 41 pounds. The tripod weighs 17 pounds, as does the single supplied counterweight. Optional 11 lb. and 17 lb. counterweights are available to balance heavy payloads.