| The heavy duty Orion Atlas-GT is a high precision 40 lb. payload capacity go-to German equatorial mount with computerized object locating and tracking. It is the ideal step between the low price/small payload mounts that can’t handle a large optical tube and the big payload mounts at budget-busting prices that may be more mount than you need and more money than you can afford. It has periodic error correction and an autoguider input for precision astrophotography, a go-to computer with a database of over 13,400 celestial objects (one you can calibrate to find objects with 1 arc minute accuracy!), and all the performance you need to keep you happily observing and imaging for years to come.
The Atlas-GT mount is fabricated of die-cast and CNC machined aluminum and stainless steel. Its stepper-type dual-axis drive motors are completely enclosed for safety. The microstep motors work through reduction gears that result in an ultra-precise drive rate of over 9,000,000 steps per revolution – a visually imperceptible 0.144 arc seconds of telescope motion per motor step. The motors have integrated encoders that constantly relay the mount’s orientation to the computer hand control. This allows the computer to direct the mount to find objects and move around the sky at your command.
To make a casual polar alignment for visual use quick and easy, there’s a latitude scale and fine adjustment controls in both altitude and azimuth. The mount is usable over a latitude range of 10° to 65° in both northern and southern hemispheres. For increased computer go-to accuracy, and for long exposure astrophotography, a standard equipment illuminated polar finder is built into the mount to increase the accuracy of your polar alignment.
A supplied 13" long x 1.75" wide dovetail slide bar allows your optical tube to be quickly and precisely balanced fore and aft on the mount, often eliminating the need for an extra tube counterweight to balance a camera or other accessories. Optical axis offset adjustment screws are provided on the dovetail to permit the cone error calibration you can use to achieve 1 arc minute pointing accuracy. Setup and takedown times are fast. Two large hand-tighten knobs hold the dovetail and its attached optical tube in place. The dovetail mounting system makes it easy to adapt the Atlas-GT mount to virtually any optical tube weighing up to 40 lbs. In addition, any Celestron CG-5, Vixen Great Polaris, or Meade LXD75 style 1.75" wide dovetail will work with the Atlas-GT mount.
Two 11 lb. counterweights are supplied with the scope, allowing you to install optical tubes up to 30 lbs. in weight in the standard mount configuration. An optional additional 11 lb. Orion counterweight (#9863) is available to allow balancing payloads up to 40 lbs. in weight. Each counterweight is locked in place with a single hand-tighten knob, making it easy to rebalance the scope if you add heavy photographic accessories.
A car battery cord is supplied to power the scope from the cigarette lighter plug of a car or a rechargeable battery pack. The mount requires 12VDC power at 2 amps for slewing (about 750 milliamps for tracking). The optional #4517V Celestron Power Tank 12VDC 17 amp-hour multipurpose rechargeable battery pack will power the scope for a full night’s observing and longer. An optional #7728 AC adapter is available for backyard or observatory dome operation.
The mount’s adjustable height heavy-duty tripod has 2" diameter stainless steel outer legs, with extendable stainless steel inner legs. A single hand-tighten lever locks each inner leg in place. The levers are located on the inner sides of the legs, where they won’t snag clothing at night in the dark. A die-cast spreader bar/tripod tray locks the legs firmly in place. The spreader bar/tripod tray has pre-drilled holes that will hold five 1.25" eyepieces and two 2" eyepieces. A mounting bracket for storing the computer hand control snaps into place in a notch in the side of the tripod tray.
The mount head has a CCD autoguider port, a serial jack for connecting the hand control, a 12VDC power input jack, a power switch, and a power indicator light. The computer hand control contains an RS-232 serial port for connecting to a laptop or PC for remote operation using the supplied RS-232 to DB-9 serial cable and for updating the hand control’s firmware from the Orion website. It also has a serial jack for connecting the hand control to the mount head using the supplied coiled cord.
The go-to computer hand control has a two-line backlit LCD screen and a red LED back-lluminated pushbutton keypad. The hand control’s back-lit display will dim and the pushbutton illumination will turn off if left idle for 30 seconds. Pressing any button will re-illuminate the display. You can adjust the LCD contrast, the LCD brightness, and the LED brightness to suit your personal preferences. Navigating the menu buttons is very intuitive and takes little time to master. The mount’s computerized hand control can lead your telescope optics to the planets and thousands of deep space objects the very first night you use your scope – even if you’ve never used a telescope before!
The computer’s memory contains the coordinates of, and basic information about, the following objects: 7840 of the brightest deep space objects from the entire NGC 2000.0 database from Sky Publishing; 5386 objects from the IC (Index Catalog) of nebulas, galaxies, and star clusters; the Messier Catalog of the 110 best known deep sky objects; the Caldwell Catalog of the 109 best deep sky objects that Messier missed; eight planets (or seven planets and dwarf planet #134340 if you want to demote Pluto as the International Astronomical Union did on August 24, 2006); 212 named stars; 55 of the best double stars; 20 of the best-known variable stars; and 25 user-defined objects. It’s a total of well over 13,000 objects the computer can find for you.
You can scroll through lists of the celestial objects organized by object type instead of catalog designation. These type-specific catalogs include: single stars; double stars; globular clusters; uncertain stars; galaxies; clusters and nebulas; reflection nebulas; planetary nebulas; open star clusters; and user-defined objects (the right ascension and declination of 25 user-defined objects of your own choosing, such as the comet and asteroid coordinates published monthly in Astronomy and Sky & Telescope magazines) or the position of an object you come across in the sky to which you’d like to return. The hand control has a 12VDC power input jack that allows you to browse the computer’s database and add your user-defined objects without having to set up the mount and connect the hand control to the mount. The hand control can also identify unknown objects you may come across when moving around the sky manually, if those objects are in its database. At any given time, you can have the hand control display the RA and dec coordinates at which the telescope on your mount is pointing.
Once the mount is set up and polar aligned, enter your latitude and longitude and the date and time into the computer hand control. The hand control has three different set-up procedures for aligning the mount on the sky to permit computerized go-to and tracking. The three-star alignment method will generally provide the highest pointing accuracy and is usually best for critical observing and long exposure astrophotography. The two-star alignment method will provide more than sufficient accuracy for visual observing. The one-star alignment method provides less accuracy and will generally suffice for casual visual observing. For optimum performance with a one-star alignment, the polar alignment should be very accurate and the cone error should be minimized. This alignment method is perhaps best suited for use with scopes that are permanently mounted and polar-aligned in an observatory building.
The computer hand control can find and center objects with up to 15 arc minute accuracy as it comes out of the box. This level of pointing accuracy is sufficient for most general observing applications and imaging. Once an object is found, the mount can track it with high accuracy for visual or photographic application. If you need higher accuracy, for example for astrophotography of objects too dim to be seen through your scope, 1 arc minute pointing accuracy can be achieved by calibrating the mount for cone error. Cone error is common with German equatorial mounts and results from the optical axis of the telescope not being precisely aligned with the right ascension axis of the mount. Full instructions for the procedure are in the 24-page 8.5" x 11" instruction manual.
The hand-held computer programs include backlash compensation and programmable periodic error correction to provide the responsiveness needed for visual guiding and the tracking accuracy needed for astrophotography. There are four user-selected tracking rates: the default sidereal rate, a lunar rate, a solar rate, and sidereal rate with PEC (periodic Error Correction) for long exposure astrophotography. Once you have trained the PEC system, the drive train error corrections are retained in the computer’s memory, even when the scope is turned off.
You have your choice of four guide speeds when using an autoguider for astrophotography: 1.25x, 1.5x, 1.75x, and 2x the sidereal rate. You have your choice of northern (default) or southern hemisphere operation. The default northern hemisphere RA and dec directional buttons can be reversed for southern hemisphere use. There are ten user-selected slewing rates available for manually moving your scope around the sky: 1.5x sidereal, 2x, 8x, 16x, 32x, 64x, 400x, 500x, 600x, and 800x sidereal (3.4° per second).
The Atlas-GT mount weighs 54 lbs. without counterweights. One person can transport and set up the mount, but this is best done in sections (with tripod, equatorial head, counterweights, and optical tube carried separately).
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