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1600GTO German Equatorial Mount with Standard Temperature Absolute Encoders - Includes APCC-PRO and PEMPro


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If this product is not in stock we will dropship it directly from the manufacturer.

Astro-Physics Mount AP Mount Price:
Price may vary depending on manufacturer's current production run.

Why a 1600GTO?

Thirty plus years of mount design and building expertise has been employed to engineer and manufacture our new 1600GTO mount into the most robust, high-precision mount in its class. We have enhanced its design and utility by incorporating additional optional features like absolute encoders and a precision polar scope to meet the needs of even the most demanding astro-imager or visual enthusiast. 

We offer three versions: 1600GTO, 1600GTO-AE and 1600GTO-AEL. The latter two versions include the Standard Temperature Absolute Encoders or the Extended Temperature Absolute Encoders, respectively. If you order the 1G00GTO without the absolute encoders, you will be able to purchase them at a later date to install yourself. 

This 1600GTO-AE version includes Standard Temperature absolute encoders installed at Astro-Physics prior to shipment.

The 1600GTO mount is built from the ground up to be a precision imaging platform while still remaining totally user-friendly. Consider these advantages and features:

Features to Enhance your Observing or Imaging Sessions


Extremely solid, rugged, high payload mount, yet the equatorial head comes apart into two components – a true advantage for a mount of this class.

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 15 amp filtered, regulated power supply like our 13.8-volt, 15-amp Power Supply (PS138V15A). For a heavy payload in cold conditions, we offer a 25 Amp Variable Volt Power Supply (PSVPW25A)

Azimuth and Altitude Adjustment is convenient and quick

  • Major altitude adjustments are extremely easy to make. Simply shift the position of the bar into a new slot without having to line up obscure holes referenced in the manual. The large "captain's wheel" knob is also very easy to grasp and turn. If you travel to a star party at a different latitude, you can make changes to your setup very quickly. This also allows you to transport the RA assembly in a more compact, zero degree latitude configuration.
  • Azimuth adjusters are positioned 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 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.
  • Altitude range now extends from 0-78 degrees, which makes it suitable for most anyone except the extreme polar locations.

Through-the-mount cabling

  • Motor cables are built into the mount and routed internally 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.


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 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 (KEYVFK2, optional), 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
  • Inherent very low backlash gear train eliminates Dec reversal delays and provides high position accuracy during guiding. The Absolute Encoders remove any residual backlash for effortless guiding. 


Absolute Encoders

Absolute Encoders on both axes provide error-free tracking, software readable absolute position, and 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 1600GTO is straightforward and easy to maintain. We provide information in the 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

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. These parts are manufactured and assembled at our facility and individually tested to meet or exceed our periodic error specification of 5 arc seconds (+/- 2.5 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 5 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 5 arc seconds (+/- 2.5 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 mount's 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 software updates will be available via downloads from the Software Updates 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 1600GTO uses the same GTOCP4 Control Box as 1100GTO and Mach1GTO. In fact, the control boxes for all three 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. 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.

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. 10.3" (262 mm), 225 tooth aluminum
Worm gear - R.A. & Dec. 1.22" (31 mm) diameter special low-wear alloy
Axis shaft - R.A. & Dec. 3.74" (95 mm) diameter
Shaft axis bearings - R.A. & Dec. 5.71" (145 mm) diameter
Latitude range 0 to 78 degrees
Azimuth adjustment Approximately 13 degrees (+/- 6.5 degrees from center)
Counterweight shaft 1.875" (47.6 mm) diameter x 22" (559 mm) useable length, incl. large machined safety stop knob. Optional 8.675" (220 mm) shaft extension available. Weight 17.2 lb. (7.8 kg)
Weight of mount

R.A. axis/polar fork: 63.7 lb. (28.9 kg)
Dec. axis: 40.0 lb. (18.1 kg)
Dec. top plate 3.0 lb. (1.4 kg)

Capacity Approximately 220 lb. (100 kg) of scope and accessories, depending on length. Recommended for refractors up to 250 mm, 18-20" 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 Suitable mounting plates
Pier adapter base diameter

9.775" (248.3 mm) Base. The base is an integral part of the mount and azimuth adjuster.


GTOCP4 Servo Drive System Specifications

Electronic components Rated for industrial and automotive applications
Motors High-torque, zero-cogging Swiss DC servo motors, enclosed in machined aluminum housing
Motor encoder 2000 tic quadrature yielding an effective resolution of 0.050 arc seconds 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

+/- 2.5 arc seconds or less in one worm cycle (6.4 minutes); native, prior to any error correction

Maximum slew speed 5 degrees / second


Control Options

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

As this chart 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.

You will be able to link to a full-sized view 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

Absolute Encoders for Your 1600GTO

The 1600GTO mount has been designed and engineered to accommodate the use of extremely precise Absolute Encoders. We invite you to review the technical information regarding the encoders and 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 arc seconds in our tests.

If you order the 1600GTO-AE or 1600GTO-AEL, the R.A. and Dec. encoders will be installed and fully tested with the mount prior to shipment. However, if you purchase the 1600GTO without encoders, you may purchase the Absolute Encoder Kit at some point in the future and install them yourself. 

What's Included

1600GTO-AE: 1600GTO 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
  • GTOCP4 Servo Control Box (GTOCP4)
  • 23” Stainless Counterweight Shaft, 1.875" diameter (M12601-E) 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)
  • 15' Straight-through Serial Cable (CABSER15)
  • Allenhead wrench set
  • Astro-Physics Command Center, Pro version (APCC-PRO) Software license key
  • ASCOM V2 Driver
  • USB thumb drive containing: PEMPro v3 Software written by Ray Gralak of Sirius Imaging. Also, PDF of 1600GTO and GTO Keypad instruction manuals
  • Manual: 1600GTO German Equatorial
  • Manual: GTOCP4 Servo Motor Drive System
  • All required fasteners
  • Registration Card

Items that You will Need for Your Mount

  • Counterweight: Stainless Steel Counterweights - (5SCWT, 10SCWT, 18SCWT, 30SCWT188)
  • Saddle Plate: DOVELM162, DOVEPW
  • D-Style (3") Dovetail Plate: Check out our wide selection of D-Style Dovetail Plates, 13" and 16" Side-by-Side Plates (SBD13SS and SBD16SS)
  • P-Style (7.65") Dovetail Plate: 23" PlaneWave Style Dovetail Plate (SBPW23)
  • Pier: Astro-Physics Portable Pier - 10" diameter, heights 24",32",42",48",54",62", Advanced Telescope Systems (ATS) Portable Pier or build your own permanent pier
  • Regulated Power Supply: 13.8V 15 Amp Power Supply (PS138V15A) or 25 Amp Variable Volt Power Supply (PSVPW25A) with Digital Readout
  • 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.

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)
  • Losmandy Polar Alignment Scope with LED Cable for 1100GTO and 1600GTO (PASILL4L-179)
  • Losmandy Polar Alignment Scope Adapter for 1100GTO and 1600GTO (Q16030)
  • 8.67" Counterweight Shaft Extension (M12675)
  • Flat Surface Adapter (1612FSA)
  • Flat Surface Adapter with Flat Pier Plate for 1600GTO and all 1200 Mounts - For 10" ATS and other non-Astro-Physics piers (1612FSA-FP)
  • Pier Accessory Trays and Support Bar 
  • Powerwerx In-line Watt Meter shows volts, amps, watts, amp-hours, watt-hours. (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). 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, the 10 x 60 Vario-Finder with Quick Release Guider Bracket and the Astro-Physics Command Center (APCC) software.


The 1600GTO is currently in production with anticipated delivery starting in the fall 2023.  If you would like to order this mount, please complete the 1600GTO Notification Request Form. We will contact you when a mount is available for you to order.