1600GTO German Equatorial Mount (1600GTO)
with GTOCP3 Control Box
Includes CDs with PulseGuide and PEMPro (full version) software


NEW PRICE: $9,890 - 4 Weeks

Why a 1600GTO?

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. We have 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 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:

Improved Features Compared to the 1200GTO, its Predecessor

Although we believe that the 1200GTO will continue to provide years of excellent performance, we felt that the time had come to improve the ease of use and add new features to take it into the future. We listened to your suggestions and added a few of our 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 mount if you build an observatory for near (backyard) or remote (halfway across the world) imaging.

We 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, we 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:


Our customers say it best:
1600GTO without encoders:

"As you know I am a huge fan of AP products and think that they are the ultimate in quality and customer support. Having used two of the AP1200 GTO mounts for many years now at two of the observatories, with never so much as a glitch in complete robotic/remote use, they have been completely dependable and trouble-free. Never a glitch, not one.

I expected the same out of the 1600GTO and my personal use observatory made room for this mount with great anticipation. Never in my wildest dreams did I expect such absolute perfect performance and quality right out of the box . . .

This mount is absolutely the finest piece of equipment that I have ever used; the through-the-mount cabling makes remote use trouble free and worry-free without exception. I am carrying a load of about 120 pounds on the mount (a Meade 16" f/8 ACF, with piggybacked 110mm APO, both equipped with heavy ST2000XM cameras for photometric research) and the mount never complains. In just this first week, after moonset, I have been able to easily get down to below magnitude 20.5 in unguided 120 second exposures with NO PEC applied.....just the excellent and steady tracking of the 1600GTO at work. This is adding tremendous horizons for our NEO research and leading way to extending the ASO exo-planet searches.

The precision of this mount and the quality that has obviously gone into building it is extraordinary, truly. In my 47 years of running observatories I have had much larger, and more expensive, mounts....but never in my days have I seen anything to compare to this AP1600GTO. Without exception, it is the finest piece of astronomical equipment I have ever put into use."
Dr. C.S., AR

1600GTO without encoders:

"I highly recommend an AP mount and it is a very well engineered and thought out piece of astro equipment that basically disappears into the background when you are imaging. You can concentrate on the imaging and just depend on the mount to do its job once setup. Exactly what you want and somewhat rare in this astrophotography world where fixing up and modifying gear to make it work is too often the norm.

As the mount is the most important component of the astrophotography setup its well worth considering investing that bit extra to get a reliable fussfree mount that will give many years of round star imaging.
G.B. Australia


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 1600GTO 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:

The 1200GTO's ability to continue tracking when past the meridian is an absolute winner for me. It avoids meridian flips (=imaging time) and reduces the need for expensive rotators. Jan Rek.

. . . I love the ability to place the OTA on the "wrong side" of the mount when starting an imaging session ("premature meridian flip") and which I have used extensively. This feature is pure INGENUITY! Anthony Ayiomamitis.
Easy alignment for non-critical viewing.
You can align the 1600GTO 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 1600GTO 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.

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 brass
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 19.5" (495 mm) long [18.5" (470 mm) useable length], incl. large machined safety stop knob. Optional 9" (229 mm) shaft extension available.
Weight of mount

Total: 114.0 lb. (51.8 kg)
R.A. axis/polar fork: 58.5 lb. (26.6 kg)
Dec. axis: 38.5 lb. (17.5 kg)
Dec. top plate 3.0 lb. (1.4 kg)
Counterweight shaft: 14 lb. (6.4 kg)

Capacity Approximately 220 lb. (100 kg) scope and accessories (not including counterweights), 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. Maximum capacity may require the use of the 9" extension (M12675)
Instrument mounting interface Refer to list of suitable mounting plates below
Pier adapter base diameter 9.775" (248.3 mm) Base. The base is an integral part of the mount and azimuth adjuster.

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.

GTOCP3 Control Box
The GTOCP3 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 1600GTO uses the same GTOCP3 Control Box as the 1100GTO 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. Extensive information regarding the GTOCP3 can be found here.

GTO Keypad (optional purchase)
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. 

GTO 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 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 GTOCP3 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

5 arc seconds peak-to-peak (+/- 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

Absolute Encoders (optional)

10 minute unguided exposure

The 1600GTO mount has been designed and engineered to accomodate 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. Check out the 10 minute (600 seconds) unguided exposure by clicking on the thumbnail to the left.

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 powerful Windows software application that allows you to correct your mount's periodic error, polar alignment and backlash using your CCD Camera or Webcam 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.

Price and Delivery Information

1600GTO$9,890.00 4 weeksAdd 1600GTO To My Cart

On October 16, 2015, we introduced a change in our pricing structure and the "Best Deal Ever" promotion, which provides significant savings on all of our mounts, while quantities last.

Pricing structure changes:

Additional $500 off mounts in stock with GTOCP3 !
On the eve of the GTOCP4 control box introduction, we realized that we have made too many GTOCP3 control boxes . So, we decided to discount them deeply and then pass the savings onto you. This is a great chance to own this mount and pocket the savings OR you can upgrade to the GTOCP4 at a special introductory price when it becomes available.

Upgrade to GTOCP4 for only $700 !
The retail price for the GTOCP4 will be $1,195 after the promotion.

Doing the math
For those who are wondering "what's the catch", there isn't one. Check it out.
$11,700 Pre-Oct 16 price
- 1,060 Price of Keypad
-  500 Special savings during our "Best Deal Ever" promotion
-  250 Shipping that had been included
$9,890 1600GTO price, remember that you will have to add back the shipping.

If you purchase a GTOCP4 Control Box during the introductory period, add $700. This will be equivalent to the new retail price of the 1600GTO once it is released with the GTOCP4.

So, in reality, you will be getting a mount with two control boxes for the price of one! And, you can enjoy your 1600GTO during the time we are in production with the GTOCP4!

What a deal!

Absolute Encoders
Please note that the Absolute Encoder option will not be available again until after the GTOCP4 is released. The good news is that all the functions of the GTOAE will be integrated into the GTOCP4 control box. There will be fewer cables and a more attractive price due to these savings. So, hold on for a while longer. You will not be disappointed!

1600GTO - What's Included?

Items that You will Need for Your Mount

Additional Accessories to Consider

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This page was last modified: November 24, 2015

Astro-Physics, Inc.
11250 Forest Hills Road, Machesney Park, IL  61115, U.S.A.
Phone: 815-282-1513   Fax: 815-282-9847