1200GTO German Equatorial Mount (1200GTO)

Includes Go-to Keypad Controller and DigitalSky Voice™ software

With the advent of the CCD camera, amateurs are exploring the skies to an ever increasing level of precision, easily exceeding the image quality of large observatories using film techniques decades ago. This new level puts a higher demand on the precision of the equatorial mounting. Many of the finest imagers today have been using our GTO mounts as a solid platform for a wide variety of instruments. The largest of these is our 1200GTO.

Since its introduction in 1998, the 1200GTO has gained a reputation for both tracking and pointing accuracy, essential to casual visual observation as well as advanced imaging. Quite a few 1200GTO and 900GTO mounts can be found at Mount Pinos in California, favorite observing site of many advanced photographers and imagers.

These mounts are truly a marvel of engineering - maximum strength and rigidity with minimum weight. Our CNC lathes and mills carve out the excess material in both axes of the 1200 and 900 German Equatorials while retaining a heavily ribbed structure for internal strength and rigidity. A unique dovetail was machined into the mating surfaces of the R.A. and Dec axes. This feature allows quick and easy assembly in the field without any tools.

The 1200 equatorial is equally at home in a permanent observatory or as a portable mounting for remote star parties thanks to the ease with which the two axes come apart. You CAN have it all. This is the perfect mount for a large refractor, Newtonian, Cassegrain or astrograph. Telescopes commonly used include Astro-Physics 155-206mm refractors, 12-14" Schmidt-Cassegrains and 10-16" Ritchey-Chretiens.

The 1200GTO mount is built from the ground up to be a precision imaging platform while still remaining totally user friendly. Consider these advantages and features:


Extremely solid, rugged, high payload mount, yet comes apart in two reasonably light-weight components for hassle-free field setup. No tools needed to assemble the mount in the field.

Operate with 12V battery.
You can take it to the darkest skies and power it with a commonly available 12V battery. In the observatory, we suggest a minimum 5 amp filtered, regulated power supply.

External computer not needed.
The keypad is a handheld computer with all of the features, functions and databases you need to tour the universe night after night. The unique software allows you to precisely polar align your mount in the field, even in broad daylight! The vacuum-fluorescent display with a temperature range of -40 degrees F (and C, they are the same in this instance), allows hardy observers to use this mount on cold winter nights. You can't do that with a PC!

Separate computer control.
All functions of the servo drive can be commanded from a laptop or desktop computer using popular planetarium software. Depending on the features of the program, you can position your telescope, center your image and control tracking rate, remote focusing, reticle brightness and park at the end of your observing session. Examples of currently available software: Write your own computer program.
The Astro-Physics GTO protocol is freely available to those who would like to write their own computer program for controlling the mount. While based on the Meade protocol, it has many more features and enhanced precision level which allows pointing and tracking to the 1 arc second level.

Precise Mechanical Fabrication.

Highly accurate mechanics.
Using modern CNC machining techniques, we make all components to a high precision level which results in a final package that is solid and accurate in all respects. The critical angles are accurately machined so that the mount is orthogonal to a very high degree. This results in pointing accuracies well below 1 arc minute for a properly aligned mount.

Worm gear accuracy.
Critical worm gear accuracy is maintained by special machining techniques developed at Astro-Physics after extensive studies and actual field operation. Our worm accuracies are second to none. With good alignment and PEM training, it is quite practical now to achieve unguided CCD images with today's hi-resolution cameras coupled to a 6" to 16" telescope.

Mechanical Features

Specifications of Equatorial Head

R.A. worm wheel

10.3" (26.2cm), 225 tooth aluminum

Declination worm wheel

7.2" (18.3cm), 225 tooth aluminum

Worm gears


R.A. shaft

3.35" (8.5cm) diameter

R.A. thrust bearings

9.5" (24.1cm) diameter

Dec. shaft

2.36" (6.0cm)diameter

Dec. thrust bearings

6.5" (16.5cm) diameter

Latitude range

20 to 68 degrees

Azimuth adjustment

Approximately 14 degrees

Right ascension

4-minute increments, pointer, engraved both


1 degree increments, engraved, pointer

Setting circles

Porter Slip Ring design, engraved, pointer


Approximately 140 lb. (63.6kg) scope and accessories depending on length. Will accommodate Astro-Physics and similar refractors up to 206mm f8, 16" Cassegrains and Ritchey-Chretiens
Some telescopes are very heavy for their size and will require a larger mount.

Weight of equatorial head

91 lbs. (41.4kg), Dec axis is 30 lbs. (13.6kg), RA axis is 47 lbs. (21.4kg), counterweight shaft is 14 lbs. (6.4kg)

Servo Motor Drive

The drive system uses a high-quality Swiss DC servo motor controlled by a microprocessor to an accuracy of 0.05 arc seconds per step. Tracking is very smooth, noticeably smoother than any stepper motor drive or inexpensive servo drive. The system can be accurately controlled over a speed range of 4800:1 which allows 0.25x sidereal for guiding to 1200x sidereal for 5 degree per second. The circuit draws only 0.4 amps when tracking the stars, 2 amps with both motors slewing and requires only 12 volts to operate. This servo drive will satisfy the requirements of the sophisticated, advanced astrophotographer, yet is easy for the casual, visual observer to use. Please refer to GTO Control Box and Keypad for Servo Drive for additional information.

Mount Base/Pier Adapter (S1200PA)

This component is included with your 1200GTO mount. However if you plan to have two pier installations, perhaps one permanent and another portable, you may wish to purchase an extra adapter to install on the the second pier. This will make your setup and switchover much quicker. Please refer to Mount Base/Pier Adapter for additional information.

If we ship an Astro-Physics or ATS pier to you at the same time your mount is shipped, the Mount Base/Pier Adapter will be installed already on the pier.

DigitalSkyVoice™ Software

DigitalSky Voice is a terrific observing companion offering lots of observing ideas and information. If you plan to use an IBM-compatible personal computer to control your telescope, you will have lots of fun with this program. The software is included with the mount. Please refer to DigitalSky Voice Software for additional information.


The diagram shows several dimensions that are commonly requested. In addition, if the scope is horizontal and pointing west or south, the measurement from the top of the pier to the middle of the cradle plate is 11.25." Please note that these dimensions will vary somewhat depending on your latitude. We quote them for 42 degrees because that is the latitude of Astro-Physics and all of our equipment is set up that way. It is also a good average value.

Recommended Accessories

Santa Barbara Instrument Group
ST-4, ST-6, ST-7 and ST-8 CCD Star Tracker/Imaging Systems
Jim Kendrick Studio Kendrick Power Supply and 18 Amp-hr. 12 Volt Rechargeable Battery Pack
Portable Pier - 10" diameter, heights 24",32",42",48",54",62
Mounting Plates- FP1800, DOVELM, 1200RP,1200RP15
Advanced Telescope Systems (ATS) Portable Piers
Cable for SBIG ST-4, ST-6, ST-7, ST-8, ST-10
Stainless Steel Counterweights - 10, 18 lbs
Special 27" Counterweight Shaft (M12661)
Pier Accessory Trays and Support Bar
Jim's Mobile Inc. Digital Setting Circles
Mount Base/Pier Adapter (S1200PA)
Encoders for Digital Setting Circles
Cord for Pentax 6x7 Camera
Polar Alignment Scope
Mounting Rings

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This page was last modified: May 1, 2002

Astro-Physics, Inc.
11250 Forest Hills Road, Rockford, IL  61115, U.S.A.
Phone: 815-282-1513   Fax: 815-282-9847