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Astro-Physics 1200GTO German Equatorial Mount

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Product Description

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. Until the introduction of the 3600GTO at the Advanced Imaging Conferrence in 2007, the largest of these was 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 (smaller cousin) mounts can be found at Mount Pinos in California, favorite observing site of many advanced photographers and imagers. You will find them at star parties and in observatories throughout the world.

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.

Over the years, a number of improvements have been incorporated into the design of the 1200GTO, among these are smoother azimuth adjusters; increased height of the polar forks to allow more room for your hand when making altitude adjustments; rounded profile of the base to prevent cords from catching; improved gear profiles in the motor gearbox for quieter operation and reduced backlash; motor bracket with built-in spring-action to keep the worms loaded at the proper setting; verifiable worm gear accuracy of 5 arc seconds or less; internal changes to improve overall accuracy; several pier adapter options; updated GTOCP3 control box with additional capability; updated keypad with larger memory capacity and LED fiber optic backlit panel; inclued PulseGuide and PEMPro software as described below. Each time we begin a production run, we ask ourselves what improvements we can make to improve the accuracy and functionality of the 1200GTO. As a result, the 1200GTO has evolved over the years to meet the needs of the advanced imager or visual observer.

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 and other instruments of similar size.

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 the equatorial head 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 like our 13.8V, 5 amp Power Supply (PS13V5A). For a heavy payload in cold conditions, we offer a 15V, 10 amp power supply (PS15V10AC).

Clutches and setting circles.
Allow manual operation if power is not available.

Image past the meridian.
The mount will track and guide well past the meridian in either direction if the object is located such that the telescope will clear the pier. This allows the user to set up the mount for a long series of exposures without stopping in the middle to flip sides. One can start the telescope under the mount while pointing at an object in the eastern part of the sky and track it all the way deep into the western sky. This is very useful for long exposure H-alpha or in cases where a large number of individual exposures are needed for stacking.

Easy alignment for non-critical viewing.
Can align with a polar alignment scope to quickly zero in on the pole for most non-critical observing or to get close before tweaking in for CCD. You can even align in the daytime for solar observing or viewing planets at twilight.

Components are modular.
All electronics including the GTOCP3 control box, motors, gearbox or cables can be removed for servicing. The RA and Dec axes can be shipped separately, if needed.

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 firmware 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 or PDA!

Free Keypad Firmware Updates
All functions of the servo drive can be commanded from a laptop or desktop computer using PulseGuide or 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. The GTOCP3 control box provides two RS-232 inputs so that you can operate the mount with two programs simultaneously. For instance, you can control most mount functions with PulseGuide, which takes full advantage of our firmware protocol, and use TheSky as your planetarium program. Examples of currently available software:

  • PulseGuide by Ray Gralak (included with the 1200GTO)
  • Software Bisque's suite which includes TheSky Astronomy Software, CCDSoft CCD Astronomy Software, TPoint Telescope Pointing Analysis Software and Orchestrate Scripting Software.
  • Starry Night Pro by Simulation Curriculum Corp.
  • Earth Centered Universe (ECU) by David Lane of Nova Astronomics
  • SkyMap Pro by Chris Marriot
  • Any software that is ASCOM compliant.

If your computer does not have serial port inputs, there are many USB to serial port adapters available on the market. Serial to USB connectivity has been simplified by the addition of Keyspan Serial-to-USB devices to our product line.

Write your own computer program.
The Astro-Physics GTO protocol for the GTOCP3 Control Box is freely available to those who would like to write their own computer program for controlling the mount.

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, actual field operation and many years of experience making precision mounts. Our worm accuracies are second to none and are guaranteed to be 5 arc seconds (+-2.5 arc sec.) or less, peak-to-peak. Since late March 2002, all 1200 mounts have been tested on our specialized periodic error tester. Only RA worm gears that provide an accuracy of 5 arc seconds or better will pass this inspection. Any worm gears with greater errors are removed from the mount and are scrapped. Another worm gear is installed and the mount is retested.

Pre-programmed with PEMPro.
Beginning in 2007, all 1200GTOs have been pre-programmed with a special version of PEMPro to reduce the periodic error even further before it leaves Astro-Physics. This information is stored in the control box so that the mount performs optimally out-of-the-box without further PEMPro runs. We will continue to provide a CD with the PEMPro program so that you can tweak the performance further after your worm gear has run in over time.

Easy to Adjust and Maintain.
The design of the 1200GTO is straightforward with modular construction and no complicated internal wiring. If the electronics ever need servicing, the GTOCP3 control box can be easily removed and returned.

Mechanical Features

  • All machined mounting made from aluminum bar stock and stainless steel. All fasteners are stainless steel.
  • Motors and all electronic components are enclosed.
  • Each shaft is supported by 5 bearing elements, two preloaded ball bearings and 3 sets of massive thrust bearings. The result is very low friction, which is constant with the load.
  • 19.5" (18.5" useable length) removable 1.875" diameter counterweight shaft can hold up to six 18 lb. counterweights and one 10 lb. counterweight. An optional 9" Extension is also available.
  • Polar and declination axes come apart quickly without tools for light-weight, easy handling and ease of transport.
  • Fine altitude and azimuth adjustments for quickly and accurately zeroing in on the pole in the field.
  • Engraved setting circles are Porter Slip Ring Design. If your battery runs out of power, you can still find objects.
  • Lead-free electronic components rated for industrial and automotive applications.
  • Base fits into 10" diameter pier with 0.094" wall thickness.


 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 Brass
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 22 to 69 degrees
Azimuth adjustment Approximately 14 degrees
Setting circles Porter Slip Ring design, engraved, pointer
Right ascension 4-minute increments, pointer, engraved both Northern/Southern
Declination 1 degree increments, engraved, pointer
Instrument Mounting  

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
These are only guidelines. Some telescopes are very long for their weight or heavy for their size and will require a larger mount.

Weight Equatorial head: 81 lbs. (36.7 kg), Dec axis is 31 lbs. (14.1kg), RA axis is 50 lbs. (22.7kg)
Counterweight shaft: 14 lbs. (6.4kg)

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