Astro-Physics - 1600GTO German Equatorial Mount (Keypad NOT Included, Sold Separately)

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

Thirty plus years of mount design and building expertise plus actually using the equipment has been employed to engineer and build the new Astro Physics 1600GTO German equatorial telescope mount into the most robust, high-precision mount in its class.

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Product Description

The Astro Physics 1600GTO German equatorial telescope mount now ships with the new GTOCP4 Control Box

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

Thirty plus years of mount design and building expertise plus actually using the equipment has been employed to engineer and build our new 1600GTO mount into the most robust, high-precision mount in its class. Astro-Physics has enhanced its design and utility by incorporating additional optional features like absolute encoders, sophisticated control systems and a new precision polar scope to exceed the needs of even the most demanding astro-imager or visual enthusiast.

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


Improved Features Compared to the 1200GTO, its Predecessor

Although Astro-Physics believes that the 1200GTO will continue to provide years of excellent performance, they felt that the time had come to improve the ease of use and add new features to take it into the future. They've listened to your suggestions and added a few of their own. Some of them make the mount easier to set up for portable use, others set the standard for remote imaging. The modular design allows you to easily upgrade your GEM telescope mount if you build an observatory for near (backyard) or remote (halfway across the world) imaging.

They also felt that we needed to increase the size differences between the Mach1GTO, 900GTO and the 1200GTO, which were too close together and overlapping. Since the "new 1200" has greater capacity than the original 1200, they felt that it should have another name and selected 1600GTO "Sweet 16". Nevertheless, it maintains the heart of the 1200. Here are some changes that you may find useful:

  • Dec. axis gear increased to 10.3" 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 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.
  • Altitude range has expanded on both ends and now extends from 0-78 degrees, which makes it suitable for most anyone except the extreme polar locations. The Hi-Low Wedge is no longer necessary on the Astro Physics 1600GTO German equatorial telescope mount.
  • New 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 in most locations to reduce strain on the cables.

  • The Astro Physics 1600GTO German equatorial telescope mount features larger motors for increased torque in cold temperatures. These are the same motors as used in the current 3600GTO mount. Note: The 1200GTO mounts produced in 2011 also have these motors.

  • 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 on the side rather than the top to reduce the possibility of moisture getting into the electronics in damp environments.

  • Greater capacity to provide a rigid platform for fairly large instruments or side-by-side setups.

  • The Astro Physics 1600GTO German equatorial telescope mount features an Absolute Encoder option to provide error-free tracking, software readable absolute positioning, customizable home and limit functioning for robotic imaging. This option can be installed whenever you are ready to take advantage of its capabilities.




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 (PS13V5A). 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. One of the truly unique features of the Astro Physics 1600GTO German equatorial telescope mount is the ability to use the clutches to help you balance your setup, then you can bolt the R.A. and Dec. axes in place so that they do not move for clutchless operation.


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. This feature of our GTO mounts has been a real customer favorite:


Easy alignment for non-critical viewing.

You can align the Astro Physics 1600GTO German equatorial telescope mount using setup routines in the keypad, or 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 imaging (polar scope not included). 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 Your Observatory

You have your choice of the GTO Keypad (included), 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. GTO control options are discussed in detail at this link.


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 Astro Physics 1600GTO German equatorial telescope mount is straightforward with modular construction and no complicated internal wiring. We provide information in the Technical Support section of our website pertaining to typical adjustment issues.


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.


GTO Servo Drive System

The drive system uses a high-quality, heavy-duty 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 astroimager, 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 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 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 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.


Pre-loaded PEMPro Curve

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. In order optimize performance even further, we use a special version of Ray Gralak's PEMPro (described below) developed specifically for our test equipment. We generate a unique PE curve for each mount that we program into each GTOCP3 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 5 arc second spec without additional PEMPro runs! However, you may use PEMPro to further refine your PE, if you chose to do so.


GTOCP4 Control Box

The GTOCP4 Control Box offers multiple connection options to suit your requirements including wifi, 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 available via direct downloads.


GTO Keypad

The Keypad is a self-contained computer that allows you to control all essential telescope functions and includes an extensive database of objects. Astro-Physics 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.


Absolute Encoders (optional)

The Astro Physics 1600GTO German equatorial telescope mount has been designed and engineered to accommodate the use of extremely precise Absolute Encoders. Absolute Encoders allow the mount to know its exact location regardless of accidental software errors and will allow it's recovery. This is particularly important in remote setups. Furthermore, they virtually eliminate periodic error, reducing it below 0.2 arcseconds in our tests. The encoders can be user installed on both axes, or on just the RA axis based upon the user's need. This frees the user from having to make the decision to include the encoders at the time of the mount's purchase; rather, they can be added later as need arises.


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 further link to a full size view of this chart and discover more about each method.









PEMPro Software, Version 2

PEMPro (Periodic Error Management Professional), Version 2, by Sirius Imaging is a very poAstro-Physicsrful Windows software application that allows you to correct your mount's periodic error, polar alignment and backlash using your CCD Camera or Astro-Physicsbcam to dramatically improve tracking and guiding. As mentioned previously, our extensive testing procedures include several PEMPro runs so that your new mount will perform with optimum PE correction out of the box. Simply use the Keypad or the PulseGuide software to turn PE Correction "on." Although you will not need to use PEMPro when you receive your mount, you may wish to do a PEMPro run at a later date after the worm gear has run in. Depending on usage, re-measuring error and re-loading periodic error correction from one to four times a year is a good practice, especially if you do some unguided images from time to time.


Pier Mounting Options 

The 1600GTO mount integrates a precision rotating pier adapter and azimuth adjuster as part of its base. The mount's base will directly attach to the Astro-Physics pier, or it can be attached to any flat surface using the Flat Surface Adapter for 1600GTO and all 1200 Mounts (1612FSA). When choosing the Advanced Telescope System's (ATS) Pier, you will need to order our Flat Surface Adapter with Flat Pier Plate 1612FSA-FP that will fit into the top of their pier. The 1600GTO's large adjustable 0 to 78 degree latitude range (which spans from Antarctica to the arctic circle) makes the use of a wedge unnecesary.



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.



All Astro-Physics mounts are supported by a dedicated staff who will assist with any issues that may arise. You can talk to a real person in a timely manner. Astro-Physics staff also participate in the ap-ug and ap-gto user groups in the Yahoogroups forum. The user groups are comprised of scope and GTO owners who are willing to share their wealth of experience using their mounts as well as imaging strategies and other concerns of advanced amateurs.


Included Items:

  • Polar Fork / Right Ascension Axis (R.A.) Assembly
  • Declination Axis (Dec.) Assembly
  • GTO Servo Control Box (GTOCP4)
  • GTO Keypad with 15' Coiled Cable and Keypad Protector (KEYVFK)
  • 19.5" Stainless Counterweight Shaft, 1.875" diameter (M12601-D) and Safety Stop (M12676)
  • R.A. / Dec. Y-cable
  • 8' Power Cable (CABLPF)
  • 15' Straight-through Serial Cable (CABSER15)
  • Allenhead wrench set
  • Astro-Physics Keystrap and Velcro Cable Ties
  • CD containing: PEMPro v2 Software and PulseGuide Software, both written by Ray Gralak of Sirius Imaging. Also, PDF of 1600GTO and GTO Keypad instruction manuals
  • Manual: 1600GTO German Equatorial
  • Manual: GTO Keypad
  • Registration Card


 Dimension Calculator

 Horizontal Dimensions:

  • Center of Pier to back of mount - 18.7cm
  • Center of pier to centerline of Dec. axis - Park 1 - 27.6cm
  • Center of pier to front of mount (CWS end of Dec. Axis) - 35.7cm
  • Center of pier to end of counterweight shaft - 27.6cm
  • Front of Mount to Back of Mount - 54.4cm
  • End of counterweight shaft to back mount - 46.3cm
Vertical Dimensions:
  • Bottom of baseplate to centerline of Dec. axis - Park 1 - 22.6cm
  • Bottom of baseplate to highest point on mount - Park 2/3 - 46.2cm
  • Bottom of baseplate to end of counterweight shaft - -41.7cm
  • Bottom of baseplate to highest point on mount - 39.5cm
  • Bottom of base to center of Dec. mounting surface - 46.2cm
Newtonian Balance point to rear end of OTA:
  • Lowest eyepiece position - pointing at Horizon N or S - Newtonian - 22.6cm
  • Highest eyepiece position - pointing at Zenith - Newtonian - 22.6cm
  • Highest eyepiece position - pointing at Pole - Newtonian 46.2cm
  • Bottom of OTA when pointing at Zenith - Newtonian  - 22.6cm



Name Astro-Physics - 1600GTO German Equatorial Mount (Keypad NOT Included, Sold Separately)
Manufacturer Astro-Physics
Model ASP-1600GTO
Periodic Error Correction ~ 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 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
Slew Speeds 5 degrees / second maximum


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