1100GTO German Equatorial Mount with Standard Temperature Absolute Encoders. Includes APCC-PRO and PEMPro. (1100GTO-AE)

Brand :

Refer to Availability tab below
U.S. Packing, shipping & insurance:
$ 330
International Packing:
$ 220 plus shipping & insurance

Why an 1100GTO?

The 1100GTO is a mid-sized observatory-class mount that will provide reliable operation in your distant, remote observatory *** or *** eagerly travel to star parties where your 12V battery will keep it running all night.

We offer three versions: 1100GTO, 1100GTO-AE and 1100GTO-AEL. The latter two versions include the Standard Temperature Absolute Encoders or the Extended Temperature Absolute Encoders, respectively. If you order the 1100GTO without the absolute encoders, you will be able to purchase them at a later date to install yourself. (11AE-4-KIT or 11AE-4L-KIT)

This web page specifically discusses the 1100GTO-AE, though many features that are common to all three mount versions.

Features to Enhance your Observing or Imaging Sessions


Extremely solid, rugged, high payload mount, yet the equatorial head comes apart easily into two components for hassle-free field setup. The heaviest component is about 27 lbs (12.5kg).

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 the 25 Amp Variable Volt Power Supply from Powerwerx (PSVPW25A),  This variable supply can be boosted to 15V if you observe in cold climates or are at the upper end of the capacity recommendations.

Azimuth and Altitude Adjustments are convenient and quick

  • Major altitude adjustments are extremely 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.
  • Azimuth adjusters are located at the rear of mount which allows you to make minor corrections quite easily. Since the knobs are 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 for smooth azimuth adjustments.

Through-the-mount cabling

The RA and Dec motor cables are routed internally to reduce the possibility of snagging. Additional cables can pass 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.


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. Manual operation is possible 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 so 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. This feature of our GTO mounts has been a real customer favorite for many years.

Easy polar alignment for critical viewing

Our optional Right-Angle Polar Alignment Scope (RAPAS) 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 optional GTO Keypad (KEYVFK2), 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).

Auto-Adjusting Motor/Gearboxes

Our motor/gearboxes were designed to be responsive for precision astro-photography, while at the same time making it super easy to use and adjust.

  • Spring-loaded worms maintain full contact under all guiding and slewing conditions
  • Automatic setting for worm mesh requires no adjustments over long time periods
  • Precision balance mechanism allows full backing off the worm from the worm wheel
  • Very low backlash gear train eliminates Dec reversal delays and provides high position accuracy during guiding


Absolute Encoders

Absolute Encoders on both axes provide error-free tracking, software readable absolute position, customizable home and limit functions for robotic imaging. 

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-AE 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.

Gear Accuracy and PE Performance

The GTOCP4 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 and repeatable from one worm cycle to the next, which enables PE correction to be very accurate. The system can be precisely 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.

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. Each mount is 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 commercial 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.

Continual PEM Correction with the Absolute Encoders

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. The absolute encoders eliminate any remaining periodic error to continually optimize your mounts performance. You will not have to do periodic PEMPro runs like you would with non-encoder mounts. However, we include PEMPro so that you can utilize the polar alignment feature. 

GTOCP4 Control Box

The GTOCP4 Control Box offers multiple connection options to suit your requirements including Wi-Fi, Ethernet, USB and serial ports. In addition to all the features carried forward from previous control boxes, the GTOCP4 applies safety slew logic to all slew commands. Future firmware updates will be available via downloads from the Software Update tab of our website.

The GTOCP4 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-AEL uses the same GTOCP4 Control Box as the 1600GTO as well as these previously produced mounts: 900GTO, 1200GTO and Mach1GTO. In fact, the control boxes for all of these mounts are interchangeable with one another in an emergency. However, the absolute encoder function is only available in the control boxes sold with those mounts.

Be sure to review extensive information regarding the GTOCP4.

GTO Keypad (optional purchase)

The Keypad (KEYVFK2) is a self-contained computer that allows you to control all essential telescope functions and includes an extensive database of objects. Many people do not want to bother with a computer in the field and like the handiness of the Keypad and its ability to operate in very cold temperatures while wearing gloves. The Keypad is an ideal choice for these users.

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.

Be sure to review extensive information regarding 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. 

Dimension Calculator

To determine the appropriate pier height for your system and to calculate many of the dimensions that vary with your latitude setting, please try this Excel spreadsheet Latitude Dimension Calculator.

Mechanical Specifications

Construction All CNC machined aluminum bar stock, stainless steel, brass; stainless steel fasteners
Finishing and Assembly Every part is hand-finished and inspected. All assembly is done by hand, by highly skilled mount assembly staff.
Worm wheel - R.A. & Dec. 7.2" (183 mm), 225 tooth aluminum
Worm gear - R.A. & Dec. 0.71" (18 mm) diameter
Axis shaft - R.A. & Dec. 3.15" (80 mm) diameter
Shaft axis bearings - R.A. & Dec. 3.94" (100 mm) diameter
Latitude range 0 to 78 degrees
Azimuth adjustment Approximately 18 degrees (+/- 9 degrees from center)
Counterweight shaft 1.875" (47.6 mm) diameter x 16.5" (419 mm) usable length, incl. large machined safety stop knob. Optional 8.675" (220 mm) shaft extension available. Weight 13 lb. (5.9 kg)
Weight of mount

R.A. axis/polar fork: 27.6 lb. (12.5 kg)
Dec. axis: 15.6 lb. (7.1 kg)
Dec. top plate 1.5 lb. (0.7 kg)

Capacity Approximately 110 lb. (50 kg) of scope and accessories, 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 their weight or heavy for their size and will require a larger mount. Remember also that imaging requirements are more rigid than visual observation.
Instrument mounting interface Refer to list of suitable mounting plates
Pier adapter base diameter 7.730" (196.3 mm) Base. The base is an integral part of the mount and azimuth adjuster.

GTO Servo Drive Specifications

Electronic components Rated for industrial and automotive applications
Motors Zero-cogging Swiss DC servo motors, enclosed in machined aluminum housing
Motor encoder 2000 tic quadrature yielding an effective resolution of 0.050 arcseconds per tic
Motor reduction gear train 57.6:1 gear reduction through a custom built set of large diameter, fine-toothed, precision, spur gears for vastly superior performance
Servo Motor Control Box GTOCP4 Control Box, removable
Hand-held computer (optional) GTO Keypad to control all mount functions. Includes extensive databases and tour features in a simple, intuitive interface. Firmware updates via the internet
Power consumption ~ 0.3 to 0.6 amps at 13.8 volts - tracking
~ 1.3 to 2.5 amps at 13.8 volts - both motors slewing at 1200x
Power requirements Nominal 12 volt DC supply at minimum of 5 amps continuous
Periodic error

+/- 3.5 arc seconds or less in one worm cycle (6.4 minutes); native, prior to any error correction

Maximum slew speed 5 degrees / second

Flexible Control with Your Keypad, Computer or even your Mobile Smart Device!

As the chart below shows, there are many options available for controlling your mount. Take a few minutes to link to descriptions of the varied software and devices that are available and see a full size version of this chart.


Included Software:

Astro-Physics Command Center, Pro Version (APCC-PRO) 

APCC-PRO provides advanced mount control features useful for local or remote operation of your Astro-Physics GTO mount. It was developed by Ray Gralak, the author of PulseGuide and PEMPro, in collaboration with Astro-Physics.  This software package features a dual-pointing model for both normal and counterweight UP orientation, dual-axis tracking rate correction for RA and Dec, APPM application to acquire pointing and tracking model data, many safety features and much, much more. Please refer to the APCC-PRO webpage for more information. 

PEMPro Software, Version 3

PEMPro (Periodic Error Management Professional), Version 3, by Sirius Imaging is included with this mount. You will not need it to correct this mount's periodic error since the Absolute Encoders will do that on a continual basis. However, the polar alignment wizard is quite useful. 

Absolute Encoders for your 1100GTO-AE

The 1100GTO-AE mount has been designed and engineered to accommodate extremely precise Absolute Encoders. These are the same encoders that are used on the 1600GTO. We invite you to review the technical information regarding the encoders to find out what they can do for you.  

Absolute Encoders allow the mount to know its exact location regardless of accidental software errors and will allow its recovery. This is particularly important in remote setups. Furthermore, they virtually eliminate periodic error, reducing it below 0.2 arcseconds in our tests.

If you order the 1100GTO-AE or 1100GTO-AEL, the R.A. and Dec. encoders will be installed and fully tested with the mount prior to shipment. However, if you purchase the 1100GTO without encoders, you may purchase the Absolute Encoder Kit (11AE-4-KIT or 11AE-4L-KIT) at some point in the future and install them yourself.  Please note that the price and availability of these encoders may change over time. 

1100GTO: 1100GTO German Equatorial Mount with Absolute Encoders (Standard Temperature Range)

  • Polar Fork / Right Ascension Axis (R.A.) Assembly
  • Declination Axis (Dec.) Assembly
  • R.A. and Dec. Renishaw Absolute Encoders, standard temperature version, installed
  • Junction Box and Cables
  • GTOCP4 Servo Control Box  (GTOCP4)
  • Control Box Adapter (CBAPT)
  • 16.675" Stainless Counterweight Shaft, 1.875" diameter (M9404-B) and Safety Stop (M12676)
  • Power Cable Set for GTOCP4, includes 6' Cable with PowerPole Connector, 18" Cable with Cigarette Lighter Plug and 18" Cable with Ring Terminals (CABPP4SET)
  • Allenhead wrench set
  • USB thumb drive containing: PEMPro v3 Software written by Ray Gralak of Sirius Imaging. Also, PDFs of 1100GTO and GTO Keypad instruction manuals.
  • Manual: 1100GTO German Equatorial
  • Manual: GTOCP4 Servo Motor Drive System
  • Registration Card
  • Astro-Physics Command Center (APCC) Pro version software is included (APCC-PRO)

Items that You will Need for Your Mount

  • Counterweights: Stainless Steel Counterweights - 5, 10, 18 and 30 lb. (5SCWT, 10SCWT, 18SCWT, 30SCWT188)
  • Saddle Plate: DOVELM162, DOVEDV10, 900RP
  • D-Style (3") Dovetail Plate: Check out our wide selection of D-Style Dovetail Plates, 13" and 16" Side-by-Side Plates (SBD13SS and SBD18SS
  • Pier: Astro-Physics Portable Pier - 8" diameter, heights 24",32",42",48",54",62", Advanced Telescope Systems (ATS) Portable or Permanent Pier (order directly from ATS) or build your own permanent pier
  • Regulated Power Supply: 25 Amp Variable Volt Power Supply (PSVPW25A) Regulated Power Supply
  • Portable Rechargeable 12-volt Battery Pack: Several sizes and types are available from a variety of vendors. Be sure that your battery pack can supply adequate power for an entire observing session! We recommend having separate batteries - one for the mount and another for all other accessories: camera, dew removers, etc. We do not offer any battery packs at this time.
  • Alligator Clips with APC Fuse to PowerPole Connector (CABPPAL). 

Additional Accessories to Consider

  • GTO Keypad with 15' Coiled Cable and Keypad Protector (KEYVFK2)
  • Right-Angle Polar Alignment Scope with LED Illuminator - 1600GTO, 1100GTO, Mach1GTO and all 900 and 1200 Mounts (RAPAS)
  • 8.675" Counterweight Shaft Extension (M12675)
  • Flat Surface Adapter (119FSA)
  • Flat Surface Adapter with Flat Pier Plate for 1100GTO and all 900 Mounts - For 8" ATS and other non-Astro-Physics piers (119FSA-FP)
  • 8" Pier Accessory Trays (TRAY08 and TRAY08H) and Support Bar(s) (TRAYSB and TRAYSB1)
  • Powerwerx DC Inline Watt Meter and Power Analyzer (CABPPWM) 

Northeast Astronomy Forum (NEAF) 2016

During the 2016 Northeast Astronomy Forum (NEAF),Roland Christen of Astro-Physics demonstrated some of the functions of the Auto-Adjusting Motor/Gearboxes, the Absolute Encoders and GTOCP4 Control Box (begins at 4:14). Although the 1600GTO mount is shown, these same features are available for the 1100GTO. Dennis DiCicco, editor of Sky & Telescope magazine, opens the interview with a discussion of the 17" f8 Flat Field Astrograph.

Northeast Astronomy Forum (NEAF) 2013

The 1100GTO was introduced at the Northeast Astronomy Forum (NEAF) in Suffern, NY in April 2013. 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. We also invite you to view the entire video for demonstrations of these additional exciting products: 1600GTO German Equatorial mounts with discussion of the Absolute Encoder System used in both the 1100GTO and 1600GTO mounts, Right-Angle Polar Alignment Scope (RAPAS), the 10 x 60 Vario Finder with Quick Release Guider Bracket (1060VGKIT) and the Astro-Physics Command Center (APCC-PRO) software.

Click on the link below to read the Sky & Telescope July 2017 review by Jerry Lodriguss.
The Astro-Physics 1100GTO


"The 1100GTO offers superlative craftsmanship, design, and execution, but when you buy an Astro-Physics product you’re also getting industry-leading support. . . When I used the 1100GTO mount, I had to say that I felt, like Oscar Wilde,“always satisfied with the very best.”


The most recent production run of the 1100GTO is sold out. If you would like to order the mount in the future, please complete the 1100GTO Notification Request Form . We will contact you when this mount is available for you to order.