Astro-Physics - 1100GTO German Equatorial Mount with GTOCP4 Servo Drive

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Please Note: We cannot ship Astro-Physics products to customers in Germany, Switzerland, Austria, France and Japan.

The Astro Physics 1100GTO mount offers the same precision tracking and pointing accuracy but in a lighter option to the 1600GTO. Instrument capacity of 110lbs.

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Product Description


Please Note: We cannot ship Astro-Physics products to customers in Germany, Switzerland, Austria, France and Japan.

The Astro-Physics 1100GTO GEM telescope mount includes all of the features in the 1600GTO mount, but is smaller to accommodate for certain needs. For instance, it is easier to transport to star parties and kept running with the 12V battery, further making observing and imaging sessions easier and more exciting.  The Astro-Physics 1100GTO was introduced at the NEAF 2013 event in Suffern, NY. In the video below, George Whitney, from the Astro-Physics Technical Support staff, explains key features of the 1100GTO in an interview conducted by Dennis DiCicco, Sky & Telescope editor


Improved Features Compared to the 900GTO, its Predecessor

Since the introduction of the 900 German Equatorial Mount in the mid 1990s, it has evolved several times to meet the increasingly greater technological requirements of our customers. The new 1100GTO German EQ mount is the next step in that evolutionary process offering increased capacity, ease of setup and use and enhancements to make your imaging sessions more productive and enjoyable. The modular design allows you to easily upgrade your mount with limit switches or absolute encoders sometime in the future.

Here are some changes that you may find useful:

  • Dec. axis gear increased to 7.2" (183mm) for higher payloads and more stability.
  • Azimuth adjusters have been repositioned to the rear of mount which allows you to make minor corrections quite easily without reaching or moving around the mount. Since the knobs are now in front of you as you look through the polar scope, the graduations can be more easily seen as you dial in your position.
  • Built-in precision-rotating pier adapter is now included and not purchased as a separate item.
  • Major altitude adjustments are extremely quick and easy to make by simply shifting the position of the altitude adjustment bar into a new slot. The large "captain's wheel" knob, convenient to grasp and turn, performs the fine adjustments. If you travel to a star party at a different latitude, the changes to your setup are quickly made and allow you to transport the RA assembly in a more compact, zero degree latitude configuration.
  • Altitude range has expanded on both ends and now extends from 0-78 degrees in its normal configuration. The Hi-Low Wedge is no longer necessary.
  • Right-Angle Polar Alignment Scope (optional) can be used without the need for an additional adapter. 
  • Unobstructed Dec. opening for Polar Alignment Scope allows greater field of view for both the Astro-Physics Right-Angle or the Losmandy Style Polar Alignment Scopes.
  • Internal routing of motor cables to remove the possibility of snagging.
  • Easily route additional cables through the large openings in the R.A. and Dec. axes. The top of the Dec. axis separates so that you can add cables with large connectors.
  • Right-angle connectors are used where applicable to reduce strain on the cables.
  • Automatic worm gear mesh is quick and easy. Produces the best settings on the worm teeth and repeatable settings.
  • Improved clutch system with NO clutch plugs that can potentially deform over time if they are overtightened. This issue has been eliminated.
  • Clutch can be set to any amount of engagement up to complete locking of the axes so nothing can slip.
  • Control box mounted vertically rather than on the top to reduce the possibility of moisture getting into the electronics in damp environments.
  • Precision bubble level built into mount base.
  • Stainless steel lanyard post on either side of base to hang your keypad.
  • Greater capacity to provide a rigid platform for fairly large instruments or side-by-side setups. 
  • Limit/Homing Switch option to provide home and limit functions using a mechanical switch (does not use the absolute encoders). This option will be available in the future.


Extremely solid, rugged, high payload mount, yet the equatorial head comes apart into two components for hassle-free field setup.


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 13.8-volt, 5-amp Power Supply (PS138V5A). For a heavy payload in cold conditions, we offer a 15-volt, 12-amp power supply (PS15V12AC).



Allow manual operation if power is not available. Use the clutches to easily balance your setup, then lock the R.A. and Dec. axes so that they cannot move when the motors are engaged.


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 critical viewing.

You can align the 1100GTO using setup routines in the keypad for most non-critical observing. Our optional Right-Angle Polar Alignment Scope will allow you to quickly zero in on the pole or the polar alignment routine in PEMPro (included) will guide you through the process. You can even align the mount during the day with our clever Daytime Polar Alignment Routine (outlined in the Keypad Manual) for solar observing, viewing the planets at twilight, or just getting a jump start on a long night.


Multiple Options for Controlling your Mount in the Field or in Your Observatory

You have your choice of the GTO Keypad (SOLD SEPERATELY), which is a full-featured handheld computer, PC computers using a wide variety of software with or without our ASCOM driver, Mac computers or even your mobile smart device (like your iPhone or iPad). The Astro-Physics command language is available to those who need to write their own software.


Mechanical Features:


Precise Mechanical Fabrication

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. Massive thrust bearings and preloaded shaft bearings provide excellent stability under all imaging situations. 


Easy to Adjust and Maintain

The design of the 1100GTO is straightforward with modular construction. We provide information in the Technical Support section of our website pertaining to typical adjustment issues.


Components are modular. 

All electronics including the GTOCP4 control box, motors, gearbox or cables can be removed for servicing. The RA and Dec axes can be shipped separately, if needed.


GTO Servo Drive System

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 motor. The system can be accurately controlled over a speed range of 4800:1, which allows 0.25x sidereal for manual guiding to 1200x sidereal for 5 degree per second slewing. The circuit draws approximately 0.5 amps when tracking the stars, 2.5 amps with both motors slewing and requires only 12 volts to operate. The servo drive will satisfy the requirements of the sophisticated, advanced astro-imager, yet is easy for the casual, visual observer to use.


Gear Accuracy and PE Performance

The heart of this mount is a precision gearbox using custom high-quality fine-pitch gears, coupled to a highly accurate worm and worm wheel. These parts are manufactured and assembled at our facility and individually tested to meet or exceed our periodic error specification of 7 arc seconds (+/- 3.5 arc sec.) before introducing any periodic error correction. The PE is smoothly variant with extremely low ripple or moment to moment error. In contrast, mounts that use integral gearboxes have very small spur gears with tiny teeth and too few of them. This generally causes ripples in the tracking rate which are difficult to guide out.

Each mount is rigorously tested on our specialized periodic error tester. Only mounts that provide an accuracy of 7 arc seconds or better will pass this inspection. If the mount exhibits greater error, the substandard part is identified, replaced and the mount is retested.


Pre-loaded PEMPro Curve

As mentioned above, the spec of 7 arc seconds (+/- 3.5 arc sec.) is the maximum native mechanical error inherent in the mount's RA axis WITHOUT any software correction. In order to optimize performance even further, we use a special version of Ray Gralak's PEMPro developed specifically for our test equipment. We generate a unique PE curve for each mount that we program into each GTOCP4 Control Box. Simply use the Keypad or your Astro-Physics software (ASCOM V2 driver, PulseGuide or APCC) to turn the PE Correction "on" and you will see results significantly better than our published 7 arc second spec without additional PEMPro runs! However, you may use PEMPro to further refine your PE, if you chose to do so.

1100GTO-AE or 1100GTO-AEL: If you purchase either of these versions with absolute encoders, the final in-house PEMPro run will utilize the corrections of the absolute encoders and the values will be stored in the GTOCP3 Control Box.


GTOCP4 Control Box

The GTOCP4 Control Box contains all of the circuitry to drive the two servo motors and the logic required to navigate the sky. It can be easily removed from the mount, if required. The 1100GTO uses the same GTOCP4 Control Box as the 1600GTO and Mach1GTO (the control box is black-anodized for the latter mount). In fact, the control boxes for all three mounts are interchangeable with one another in an emergency.



The Keypad is a self-contained computer that allows you to control all essential telescope functions and includes an extensive database of objects. We have designed the interface and firmware to be as intuitive and easy to use as possible, while filling it with terrific features to make your observing session productive and pleasurable. Click here for detailed information regarding features and functions of the Keypad.


Optimized for Astronomy

Astro-Physics mounts and the Astro-Physics GTO Servo Control System are designed from the outset as tools for celestial observing and imaging.  These mounts do not have any military or defense applications. Applications like missile, airplane, or very low earth orbit satellite tracking require faster tracking rates and more rapid changes to those tracking rates than our mounts allow.   Note that the ISS is generally within the mount’s tracking rate capabilities for casual observation.


Dimension Calculator:

Horizontal Dimensions:

  • Center of pier to back of mount - 11.2cm
  • Center of pier to centerline of Dec. axis - Park 1 - 22.2cm
  • Center of pier to front of mount (CWS and Dec. axis) - 28.2cm
  • Center of pier to end of counterweight shaft - 22.2cm
  • Front of Mount to back of Mount - 39.4cm
  • End of counterweight shaft to back of mount - 33.3cm
Vertical Dimensions:
  • Bottom of baseplate to centerline of Dec. Axis - Park 1 - 19.2cm
  • Bottom of baseplate to highest point on mount - Park 2/3 - 36.3cm
  • Bottom of baseplate to end of counterweight shaft - -26.4cm
  • Bottom of baseplate to highest point on mount - 31.5cm
  • Bottom of base to center of Dec. mounting surface - Park 2/3 - 36.3cm
  • Bottom of baseplate to top of Polar Axis (for case design) - 31.5cm
Newtonian balance to rear point to rear end of OTA:
  • Lowest eyepiece position - pointing @ horizon N or S - Newtonian - 19.2cm
  • High eyepiece position - pointing @ zenith - Newtonian - 19.2cm
  • High eyepiece position - pointing @ pole - Newtonian - 36.3cm
  • Bottom of OTA when pointing at Zenith - Newtonian - 19.2cm
Dimensions that do not change with latitude:
  • Length of Dec Axis - Dec Mounting surface to end of CW shaft adapter - 28.3cm
  • Center of RA axis to end of CW shaft adapter - 11.1cm
  • Center of RA axis to DEC Mounting Surface - 17.2cm
  • Standard CW shaft including safety stop - 34.5cm
  • Polar Fork Base width at widest point (includes azimuth adjusters) - 24.4cm





Name Astro-Physics - 1100GTO German Equatorial Mount with GTOCP4 Servo Drive
Manufacturer Astro-Physics
Model ASP-1100GTO
In The Box Astro Physics 1100GTO Mount Head GTOCP4 Servo Drive CD PulseGuide PEMPro
Azimuth Adjustment Approximately 18 degrees (+/- 9 degrees from center)
Latitude Range 0 to 78 degrees
Payload Capacity Approximately 110 lb. (50 kg) scope and accessories (not including counterweights), depending on length. Recommended for refractors up to 200 mm, 14-16" Cassegrains, Ritchey-Chretiens and CDKs. These are only guidelines. Some telescopes are very long for


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In the Box

Astro Physics 1100GTO Mount Head
GTOCP4 Servo Drive