3600GTO German Equatorial Mount (3600GTO)
" el Capitan "
with GTOCP3 Control Box
Includes GTO Keypad and CD with PulseGuide and full PEMPro v.2 software

Solid as a rock!
El Capitan is the ultimate imaging platform for large instruments like the 20" or 24" Ritchey-Cretiens by RC Optical, PlaneWave CDK17 or CDK20, RC20 or RC24 by Optical Guidance Systems or instruments of similar size. Setups that employ smaller multiple instruments would also be ideal.

Why a 3600GTO ?

The 3600GTO is the culmination of over 30 years of experience designing and building mounts at Astro-Physics for the amateur and professional astrophotographer .

Mechanical Features

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.

. . . 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., More… (commenting on his 1200GTO that uses the same control system. All A-P mounts have this feature!)

Full 360 degree rotation of both axes.
The full 360 degree rotation of both of the 3600GTO's axes also allows this mounting to be placed onto an astrographic pier for complete freedom from movement restrictions.

Through-the-mount cabling capability.
We designed this mount to allow cabling to be run through the axis shafts for tangle and clutter free operation. Cables from cameras, guiders, dew heaters and the mount's own servo drive cables can all be run through the mount's cavernous 4" hollow shafts where they are out of the way and where they won't ever get caught or tangled during your imaging session. Ports have been included for the mount's servo cables. Additional ports can be added by the user, as needed.

Components are modular and easy to maintain.
The design of the 3600GTO is straightforward with modular construction and no complicated internal wiring. 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. The mechanical design of the mount is extremely simple and straightforward, allowing easy adjustment by anyone - no need to have a mechanical engineering degree to service the mount. We will provide information in the Technical Support section of our website pertaining to typical adjustment issues.

Integrated Pier Adapter
The pier adapter for the 3600GTO has been integrated into the mount's design and incorporates the design principles of the Precision Adjust Rotating Pier Adapters and, in an innovative twist, puts the Super Heav-Duty Azimuth Adjuster UNDER the BACK of the mount where it is both conveniently located for fine polar alignment and remains out of the way. Polar alignment is smooth and easy, and the system locks down tight with no unintended movement.

Easy to Adjust and Polar Align.

Precise polar alignment can be achieved easily using the precision adjusters for both altitude and azimuth. The system locks down with zero alignment shift for an unprecedented ability to achieve that "perfect dead on" polar alignment that is so critical to the best imaging and the most accurate go-to slews.

The PEMPRo Software program (included with the mount)includes the "Polar Alignment Wizard," a powerful feature that allow you to dial in on the pole quickly.

Extremely solid, rugged, high payload mount, yet the equatorial head comes apart in two components for transport and field setup. Because of this mount's size and weight, we recommend that field assembly be done by at least two people working together. The RA axis and base assembly alone weighs just over 120 lbs. You wouldn't want to transport it as your regular mode of operation, but it can certainly be done for special occasions.

The 3600GTO is shown in the photo on the right with a 12" x 30" portable pier developed by ATS (Advanced Telescope Systems). Unfortunately, as of August 2008, ATS is no longer accepting orders. However, Astro-Physics has ordered a limited number of 12" x 30" portable piers that we make available to customers who purchase a 3600GTO.

Precise Mechanical Fabrication.

Highly accurate mechanics.
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.

Our machinists are among the most skilled available anywhere, attending to the smallest detail to ensure a precision instrument. The finishing department assures that all parts are deburred, sanded, polished and painted to provide an exceptional aesthetic appearance. Our mount assembly is directed by a life-long astronomer with almost 20 years of experience here at Astro-Physics! All of our production personnel take great pride in their work and are true craftsmen and women.

Worm gear accuracy.
Critical worm gear accuracy is maintained by special machining techniques developed at Astro-Physics after extensive studies, actual field operation and many years of experience making precision mounts. Our worm accuracies are second to none and are guaranteed to be 5 arc seconds or less, peak-to-peak. The periodic error of each mount is verified during our intensive testing procedures. We optimize performance further by characterizing the error using a special version of PEMProAP and downloading the appropriate correction into the mount's GTOCP3 before it leaves Astro-Physics. With good alignment and PEM training with the Keypad or PEMPro, it is quite practical now to achieve unguided CCD images with today's hi-resolution cameras coupled to a large telescope.

If your application requires the highest possible levels of tracking accuracy, you may want to consider the Precision Encoder System described with the options below.

Specifications of Equatorial Head

Worm Wheels-RA & Dec Aluminum - 13" (330mm), 256 tooth
Worm Gears Brass - 1.41" (35.8 mm) diameter
Axis Shafts 4.72" (120mm) diameter with 4.02" (102mm) clear inside diameter
Axis Bearings 7.09 " (180mm) diameter deep groove ball bearings
Worm gear bearings 1.57" (40mm) angular contact ball bearings
Latitude range 15 to 70 degrees
Azimuth adjustment Approximately 14 degrees (+/- 7 deg.)
Motors Swiss DC servo controlled - 2 motors per axis
Capacity Conservatively rated for 300 lbs (not including counterweights). Please feel free to call and discuss your application with our staff.
Counterweight Shaft 2.5" (6.35 cm) diameter, 31.5" (80 cm) total length, 30" (76 cm) useable, 42 lbs. (19kg). Twelve of the optional 30# counterweights will fit onto this shaft. Includes large, machined safety stop.
Diameter of Base 11.480" (29.16 cm), fits into 12 " outside diameter pier with 0.25" wall thickness.
Weight Equatorial head (without counterweight shaft or counterweights): 205 lbs. (93 kg), Dec axis is 84 lbs. (38kg), RA axis and base assembly is 121 lbs. (55kg)
Counterweight shaft: 42 lbs. (19kg)

Servo Motor Drive

The drive system uses TWO high-quality Swiss DC servo motors for EACH axis 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 drive. The dual motor system smoothes out the drives even further by applying an averaged power curve to the drive system. In preliminary testing this has resulted in PE curves that are noticeably smoother than the already phenomenal curves on our 1200GTO mounts. The system can be accurately controlled over a speed range of 4800:1 which allows 0.25x sidereal for manual guiding to roughly 720x sidereal for 3 degrees per second maximum slew rate. The circuit draws well under an amp when tracking the stars, 3 to 5 amps with both axes slewing and requires only 12 volts to operate (15-18 volts is recommended). This servo drive will satisfy the requirements of the sophisticated, advanced astrophotographer, yet is easy for the casual, visual observer to use. Please refer to GTOCP3 Control Box and Keypad for Servo Drive for additional information.

For reliable operation in your observatory, we recommend that you use a a minimum 10 amp filtered, regulated power supply like our 15V, 10 amp power supply (PS15V10AC). We may also offer an 18V power supply, please call for information. For lighter, well-balanced loads, you can use a commonly available heavy-duty, deep-cycle marine 12V battery.

Flexible Control with either Keypad or Personal Computer

Keypad Operation
The keypad is a handheld computer with all of the features, functions and databases you need to tour the universe night after night. The vacuum-fluorescent display with a temperature range down to -40 degrees F (and C, they are the same in this instance), allows hardy observers to use this mount on cold winter nights.

As new firmware versions are released in the future, you can upgrade your keypad directly from the download section of our website - free of charge!

Remote Control with personal computer, if desired.
All functions of the servo drive can be commanded from a laptop or desktop computer using PulseGuide or popular planetarium software. Depending on the features of the program, you can position your telescope, center your image and control tracking rate, remote focusing, reticle brightness and park at the end of your observing session. The GTOCP3 control box provides two RS-232 inputs so that you can operate the mount with two programs simultaneously. For instance, you can control most mount functions with PulseGuide, which takes full advantage of our firmware protocol, and use TheSky as your planetarium program. Serial to USB connectivity has been simplified by the addition of Keyspan Serial-to-USB devices to our product line. Please review the products on this page to determine which one will work best for your set-up. Examples of currently available software:
Write your own computer program.
The Astro-Physics GTO protocol for the GTOCP3 Control Box is freely available to those who would like to write their own computer program for controlling the mount.

PulseGuide™ Software

Please note: Ray Gralak, the author of PulseGuide, is currently working on a new software program that will combine the Astro-Physics ASCOM driver, all the features of PulseGuide, plus additional features. The new software will have a new name befitting its vastly increased capabilities (tentatively the Astro-Physics Command Center), and will replace PulseGuide when it becomes available. In the mean time, here's the lowdown on the existing PulseGuide software:

PulseGuide is a stand-alone Windows (98, ME, 2000, NT4, XP and Vista) utility that provides complete remote control of Astro-Physics 400GTO, 600EGTO, 900GTO, 1200GTO and 3600GTO mounts. It derives its name from its most distinctive feature, pulse guiding, which can improve unguided tracking. Specifically, it can help correct tracking errors caused by polar misalignment and atmospheric refraction. You can also train PulseGuide to track objects moving relative to the stars, such as asteroids, comets, and the moon. In addition to pulse guiding, PulseGuide also has many useful utility features. With just a few exceptions, it supports the entire serial Astro-Physics command protocol. More ....

PEMPro v. 2.0 Software - FULL Version!

PEMPro (Periodic Error Management Professional) is a Windows software application developed by Ray Gralak that makes it easy to characterize and reduce periodic error. While the periodic error of your 3600GTO will be 5 arc seconds or less, you can reduce it even further to maximize performance without auto-guiding. PEMPro v. 2.0 is the latest version of PEMPro and includes exciting new features like the "Polar Alignment Wizard" to quickly, accurately and easily dial in your polar alignment. The software will be included with all new 3600GTO mounts. More ...

Optional Accessories To Enhance the Performance of Your Mount
Limit Switch System for the 3600GTO (36LSS)
Optional switches can be installed to control operation and for homing past the meridian. The final details of hardware are still under development. However, we are optimistic that this option will be available for mounts in this first production run. All mounts will be drilled and tapped to accept this option, which can be added as an upgrade later and installed by the customer. The price has not been determined.
36LSS$530.00 in stockAdd 36LSS To My Cart

Precision Encoder System for the 3600GTO (36PES)
A precision encoder installed in the RA axis provides feedback to the servo to eliminate periodic error to a level below 1/2 arc second for long period exposures. Test results on the new 3600 mount with optional feedback encoder have exceeded all our expectations. The measured periodic error was 0.05 arc seconds peak to peak for a 12 minute test period. To further refine the unguided error of the mount, we are adding an all-sky tracking rate to the software, which will minimize RA drift everywhere in the sky. This will allow significant unguided exposure times with a well polar-aligned mount. The final details of hardware and software are still under development, however we are optimistic that this option will be available for mounts in this first production run. Please note that this option must be installed when the mount is assembled and cannot be added as an upgrade later. Although it is not possible to finalize the price, we anticipate that it will fall in the range of $5,500 to $7,000.

The Precision Encoder System is considered a custom option, since we must purchase and/or manufacture very expensive hardware components for your order and install them early in the assembly process. A deposit of $2,750 will be required when you place your order. If you must cancel for any reason, your deposit refund will be limited to $1,000.

30 lb. (13.6 kg) Counterweight for the 3600GTO (30SCWT)
This stainless steel counterweight was designed to fit onto the 2.5" diameter shaft of the 3600GTO. It features a spring-loaded, recessed lock knob and measures 7.9" in diameter by 2.5" thick.
30SCWT$365.00 in stockAdd 30SCWT To My Cart

22" Dovetail Saddle Plate (DOVE3622) and 22" Dovetail Sliding Bar (SB3622) for the 3600GTO

The massive and sturdy two-part telescope mounting system provides the convenience of a dovetail with the security of a fixed mounting plate. It was custom designed for strength, rigidity and versatility.

The saddle plate (shown in the photo to the right) was designed as a female dovetail and features four spring-loaded clamps that will grip the largest instrument solidly. It can be attached to the mount in three possible positions – centered, forward or back depending on the balance point of your instruments.

The robust male dovetail plate (photo will be added soon) features a myriad of holes throughout the entire length that can accommodate a variety of instrument configurations at various balance points. Instruments include the Planewave CDK telescopes and any mounting rings that have the Astro-Physics hole spacing of 3.2” . We also offer hole spacing of 3.5”, 5.5” and 7.5” from one end of the plate to the other. You can also use two (or even three, depending on instrument size) DOVELM16S mounting plates in a side by side configuration for multiple instruments (we will drill the appropriate holes into your DOVELM16S at no charge).

The dovetail system can be set up for tip-in or slide-in of the dovetail sliding bar. Safety slots on the saddle plate coupled with the sliding bar's safety stop will help keep accidents from happening.

For permanent installations, a series of matching through-holes in the saddle and tapped holes in the sliding dovetail plate allow the setup to be bolted into its final position through both plates once adequate balance is achieved. As an added feature, the dovetail plate is drilled on the eyepiece end so that you can attach a plate that can be customized as a cabling port.

22" Dovetail Saddle Plate for the 3600GTO (DOVE3622)
12.9" x 22" (328 x 559mm), 15 lbs. (7kg)
DOVE3622$720.00 in stockAdd DOVE3622 To My Cart

22" Dovetail Sliding Bar (SB3622)
9.9" x 22" (251 x 559mm), 9 lbs. (4kg)
SB3622$335.00 NO LONGER AVAILABLEAdd SB3622 To My Cart

Flat Surface Adapter for the 3600GTO (3600FSA)
If you plan to install your 3600GTO onto a pier with a flat plate, we suggest our flat surface adapter. The 3600GTO fits into the ID of the adapter; eight bolts hold the mount in place. This adapter is machined from a solid plate and is ribbed in the base for strength and reduced weight. It is 12" OD, 1 7/8" tall and weighs 5.75 lbs.

Bolt circle:

3600FSA$325.00 in stockAdd 3600FSA To My Cart

11.5" Counterweight Shaft Extension for the 3600GTO (M3655)

This 2.5" diameter extension is beautifully machined from the same 303 stainless stock as the full counterweight shaft of the 3600GTO and adds another 10" of usable length. The fit of the extension on the primary counterweight shaft is virtually seamless, so your weights will slide up and down smoothly. The large machined counterweight safety stop knob threads into the end to protect your toes. The shaft weighs 13.5 lbs. (6.1kg)
M3655$160.00 in stockAdd M3655 To My Cart

ATS 12" x 30" Portable Pier (ATS12X30)
Astro-Physics has purchased a limited number of 12" x 30" Portable Piers from Advanced Telescope Systems (ATS). These piers will only be sold with 3600GTO mounts. Since ATS has decided that they will no longer accept orders, these will be the last piers made. Please contact Astro-Physics for additional information.

Current Installations
The first two mounts have been in service since the Fall of 2007.

Antarctica The very first 3600GTO was installed at Dome C at Concordia Station in Antarctica in the Fall of 2007. It was designed to carry a large telescope that will be used for scientific studies by the Laboratoire Universitaire d'Astrophysique de Nice (LUAN). As you can imagine, the Antarctic is the most severe environment on the planet. Maintainance is extremely difficult due to the extreme low temperatures and dangerous wind conditions that prevent technicians from working outdoors. The mount must be a reliable performer and function flawlessly 24 hours per day for the entire polar night lasting 6 months..

Our smaller mounts have proven themselves in these frigid Antarctic conditions since 2003. We have had a number of 900GTO and 1200GTO mounts running continuously at Dome C in Antarctica, and they have shown themselves to be winners. In fact, they are some of the few things that actually work under those conditions, where the temperature is so cold that optics shatter and paint falls off tube assemblies like skin shed from a molting snake. The same design philosophy that has overcome these harsh conditions has made the 3600GTO the finest large mounting available.

Here are some links that you may wish to check out:
Collection of photos showing the production of the first 3600GTO and subsequent installation at Dome C in Antarctica.

Video of an Astro-Physics 1200GTO operating at -73 degrees Celcius (-99 degrees Fahrenheit)!!! This video was recorded by Erick Bondoux and posted on the website August 23, 2008 (copyright by Erick Bondoux). We have prepared an English translation of Erick's comments for your convenience.

Video provides a tour of the Astro-Physics mounts based at dome C. This 3:50 minute video was was filmed May 30, 2008 by Erick Bondoux and is posted on the website. You will need to be a little patient with this video since it was filmed with only a faint light on the horizon and all installations had to be lit. You can also hear wind noise. (copyright by Erick Bondoux)

Video entitled: DC4 - Concordia 2008, The Winterover in Antarctica in Dome C Antarctica. This 3:25 minute video will provide a glimpse into the French and Italian Concordia team members, their living environment and equipment used during their 2008 research session. Very entertaining (musical overlay) and informative.

Blog/Journal by Erick Bondoux, which includes additional videos and observations of research and life in Antartica.

Photos from 2003 installation at Dome C. On the linked page click on Photo Gallery and then scroll down to Astro-Physics place; click on Turbulence Monitoring; and click on Summer 2003: First Seeing . . .

Astro-Physics and Laboratoire Universitaire d'Astrophysique de Nice (LUAN)
The 3600GTO was introduced to astro-imagers at the Advanced Imaging Conference in San Jose, CA in late October 2007. As imaging trends lean towards larger scopes requiring sturdier mounts, we felt this was an excellent venue to introduce the 3600 and get some initial feedback from the astronomers most likely to use it. Pictures of this informative event are available here. The mount was under test in our observatory at Astro-Physics. Walter Piorkowski, head of our mount department, generously allowed us to use his large 16 inch f/5 Newtonian-Cassegrain to which we added some additional stainless steel stock on the mounting plate to reach 250 lbs. We feel that the mount can handle additional weight quite easily.

This second prototype shipped to the Laboratoire Universitaire d'Astrophysique de Nice (LUAN) in Nice, France in early June 2008. It was recently installed in a rolloff observatory on the grounds of the Nice Observatory on Mont Gros overlooking Nice and the Meditteranean. It will be used to test software and large professional imaging telescopes.
Click to enlarge


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-gto user groups in the Yahoogroups forum. The user group is comprised of 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.

Additional Recommended Accessories

Introductory Price
3600GTOTBD click here
Contact Astro-Physics about 3600GTO

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This page was last modified: August 26, 2008

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