Company Seven.

  C-7 Home Page C-7 News Consignment Library Products & Services Product Lines Order Search

Availability Distribution News Notes Overview Pricing Products

Accessories and Options Mounts Mount Control Systems Telescopes



Astro-Physics GTO Mount R.A. Axis showing current production GTO CPU/Control Panel. Hand Control Box not shown (181,659 bytes) Right: Astro-Physics Model 900 GTO Mount R.A. Axis housing showing current production GTO CPU/Control Panel. Hand Control Box not shown (181,659 bytes)

Introduction Astro-Physics is one of only a few companies that makes industrial quality Go-To products characterized by high degrees of reliability and precision, to the consumer as well as for industry and government. The two most important considerations in telescope mount design and construction are:

    1. maximum strength and rigidity for a given size, and
    2. the tracking accuracy (smoothness of motion, and moderation of any deviation or amplitude of mechanical errors) of the drive and load bearing system.

Once a mount does incorporate those features, then the operator is free to consider aids to celestial navigation which culminate in true "Go-To" computer control systems. These are electronic mount control systems which incorporate an extensive database "knowledge" of the sky whereby the user, or a predefined sequencing program direct the mount to rapidly move from one position to another with repeatable precision. The importance of the "Go-To" options has increased particularly with the advent of CCD imaging systems pioneered by companies including SBIG. For CCD applications, the telescope may need to be very precisely pointed onto a target, covered by a CCD detector that may be only a fraction of the size of 35mm (24 x36mm) or medium format (60mm x 70mm) film camera formats. And, these objects that must be found in centered in the field of view are often invisible to the naked eye, or visually through the telescope. CCD imagers and astrophotographers will set up their shots quickly to maximize the number of images that can be captured in a single night. You can even program a sequence of objects that you intend to observe or photograph.

New and experienced visual observers too will appreciate the many advantages of the Astro-Physics GTO computer system. It allows you to locate objects easily in light-polluted areas where star hopping is very difficult. Even if you only recognize a few of the major stars in the night sky, then you can explore the beauty of the universe. You can even polar align in the daytime, this may facilitate solar observing with our white light or DayStar Hydrogen-Alpha systems, or you may find bright stars and planets! The system also serves as a powerful educational tool, providing descriptive information regarding the object you are observing. don't forget your favorites or new objects that you wish to explore.

Features of the System The Astro-Physics GTO controller has been developed for those:

  • who have limited observing time, and wish to locate and observe the most objects quickly
    • organizations (such as educational and research) where a variety of casual or inexperienced users benefit from such ease of use
    • organizations where limited time per user of the equipment mandates the most time efficient finding techniques
  • in suburban settings where the sky glow renders traditional finding techniques impractical
  • with limited knowledge of what is in the sky within the reach of their telescope, and wish to have the telescope automatically tour the sky
  • who wish to employ the GTO repeatable centering precision to acquire otherwise invisible objects for imaging or other research with devices such as CCD cameras
  • requiring a programmable mount system that can operate by remote control, or completely independent of real time human control
  • who have simply acquired all the other gizmos, and now seek a new "Gee Whiz" factor

Compatibility The current Astro-Physics mounts are compatible with either the discontinued Servo Micro-Drive Control (SMD), or with the production Astro-Physics "GTO" computer keypad (and with optional DigitalSky Voice software) control electronics. These systems have been engineered incorporating the advantages of years of experience and design of synchronous and stepper electronics with geared drive systems, combined with the latest innovations in servo motor and controller circuitry.

The change from the prior QMD Stepper Motor System (discontinued in 1997) to the current Servo motors was made because:

  • Zero-cogging servo drive motors are more accurate than steppers, even when steppers are in the "micro step" mode
  • Servo motors require less power to run, and therefore extend battery operating times
  • Servo motors offer improved torque at high slewing rates.
Astro-Physics GTO Keypad hand-held control (169,134 bytes).


Over the recent years a host of new software and hardware products have been released that facilitate the integration of these mounts into complete observatory systems, with control of imaging systems and other accessories. The control of the Astro-Physics GTO system by the provided Keypad, or by provided or third party software, and even by Smart Phones is explained in our article Control Of Astro-Physics GTO Systems. We urge our customers to read that article and to explore the links for the latest updates on these rapidly evolving technologies.

The input commands to the "GTO" system are entered either by the furnished industrial quality keypad (illustrated at right), or by an optional personal computer (Macintosh or PC compatible), or even by spoken command with the optional DigitalSky Voice control software. With the optional DigitalSky Voice control software. If the computer is equipped with a speaker and microphone, then all control functions can be done simply by speaking the commands; these are then "spoken" by the computer to acknowledge what it "understood"! The keypad is routinely the communication center for the operation of your GTO mount; it has been designed to be as intuitive and easy to use as possible while filling it with terrific features to make your observing sessions productive and pleasurable.

Right: Astro-Physics GTO Keypad hand-held control with "Keypro" Rubber Bumper (standard with 2002 models and later) 169,134 bytes.

The keypad allows you to control all the essential telescope functions such as selection of tracking and guiding/centering or slewing rates, PEM (permanent error memory), declination backlash control, RA/Dec reversal, polar alignment, brightness of the cross hair of your illuminated guiding eyepiece and movement of N-S-E-W directional keys.

Most buttons are assigned to one function only. You do not have to remember shift key patterns or complex keystroke sequences. The directional buttons are shaped like arrows to help you find them in the dark without looking at your keypad. The stop button is readily accessible if you need to cancel any slewing request immediately.

The menu system is very easy to navigate. Each 4-line screen will display several choices which correspond to a number button. Simply press the number button to initiate the command, e.g. "1=M, 2=NGC." When you press "1" the Messier entry screen will display and you can enter the number of the object that you wish to see. Press GOTO which will cause the mount to slew. The buttons will allow you to scroll quickly through the lists of common names or from one menu to another.

The advanced keypad features allow you to slew automatically to objects in the Messier, NGC, IC, ADS double star and Abell galaxy cluster databases; bright stars; all planets; the Moon; Sun; as well as any RA/Dec coordinate. The search function locates objects based on type and magnitude. The tour function guides you on a tour of interesting objects by constellation. Both the search and tour features provide you with lots of observing ideas. You will be very pleased with the intuitive operation of this controller. There are no complicated sequences of keystrokes to remember. It is so easy to use that even if you don't use it for a few months, you will feel at home with the keypad very quickly.


  • Handheld keypad controller with red backlit alphanumeric keypad and red 4-line by 20-character data display.
  • Vacuum fluorescent display rated to -40 degrees F or C (F and C are are equivalent at this temperature) allows hardy observers to view or image on cold winter nights. Normal computers or PDA units cannot be used at these temperatures.
  • Directional N-S-E-W keys provide immediate response when you wish to center an object or cruise the surface of the moon.
  • R.A. and declination reversal for correct object orientation and movement in eyepiece.
  • PEM - Permanent Error Memory correction. Make your correction just once, remains in memory permanently.
  • R.A. and declination backlash control.
  • Stores 3 observing site locations.
  • Specify safety zone so that tripod does not interfere with telescope during slewing operation.
  • Quick and easy polar alignment routines, even during daylight!
  • Adjust brightness of the reticle output for your illuminated guiding eyepiece or polar alignment scope.
  • Automatic meridian swapping in go-to slewing mode.
  • Continues to track at sidereal rate, even while slewing so that your position is always accurate.
  • More than 17,000 objects in extensive databases: Messier (110), NGC (7840), IC (5,386), ADS double stars (215), Abell galaxy clusters (2,712), calibration stars by common name (200), Greek star names by constellation (1053), common objects (100), planets (8) , Moon and Sun.
  • Enter catalog or common star number, solar system object, RA/Dec coordinates or common name of object; press GO TO and your telescope will automatically slew to the object.
  • Search and tour functions assist you to plan observing session.
  • Display will indicate if object is below horizon and cancel slewing request.
  • STOP button to cancel your slewing request when the telescope is already moving.
  • Display information about objects (object type and magnitude) before slewing.
  • Timer will let you know when the exposure time of your astrophoto is complete.
  • Continuous readout of current position.
  • Park in any position you choose or select one of three preprogrammed park positions.
  • Meridian swap delay function allows astrophographers to take a series of images for a mosaic near the meridian without the mount swapping sides.
  • Retractable hanger.
Astro-Physics GTO CPU/Control Panel arrangement (35,940 bytes).
Above: Astro-Physics Control Panel, model GTOCPU2, arrangement (35,940 bytes)

Basic functions that are included are: selection of tracking and guiding (or centering) rates between 0.25x and 1200x Sidereal (5 degrees per second!), PEM (Permanent Error Memory) to reduce periodic errors typical of worm gears to virtually an imperceptible amplitude, declination backlash control, N-S-W-E directional control buttons with control switch reversal, user selectable ability to operate in either North or Southern hemispheres, adjustable power output for accessories such as guiding eyepiece illuminators. The hand controller contains a Telescope Interface Connector ("TIC") socket for CCD Star Tracker/Imaging Camera Systems such as our Santa Barbara Instrument Group (SBIG) "ST" series. Most of the SBIG CCD systems will allow you to auto-guide astronomical film photos, and explore CCD imaging thereby rendering the invisible - obvious.

Astro-Physics DigitalSky Voice software logo (181,644 bytes). The Astro-Physics GTO electronics feature a new low current draw, reversible servo motor drive system on both the Right Ascension (R.A.) and the Declination axes. These motors and gears systems are the same as those furnished with the "SMD" control system with the SMD hand held controller. The GTO version of a mount head with the furnished keypad hand controller can operate in most climates due to its new low temperature display independent of a personal computer. With either an optional Macintosh (using optional PC emulator software such as "Virtual PC"), or with a PC compatible personal computer, then operation all control functions are accessible. Most control functions may be accessed using suitable software on a hand held "Windows CE" Pocket PC computer too!

At your convenience can upgrade and SMD to the GTO full computer control with keypad hand control (for use in the field independent of a personal computer) and also employ the "DigitalSky Voice" two-way voice control system (furnished with the GTO systems) all without the need to return the mount head to Company Seven or to Astro-Physics for any modifications.

It is possible to retrofit the QMD stepper motor driven mounts with the "SMD" and "GTO" motors and electronics however, it is cost effective to trade in or to sell the older mounts and then use the proceeds to buy the new mount. We suggest those with and SMD system who become interested in adding optional encoder (or employing furnished encoders) with digital displays such as our JMI "Max" series CPU's, then you might find the cost and performance differences may favor upgrading your choice of the "SMD" mount to the "GTO" system at the outset.



  • Extensive object database includes: Messier, IC, NGC, ADS (Aitkens Double Star) and planets.
  • Voice control as easy as saying "M1", or "Find the Cocoon Nebula".
  • Voice control preserves night vision by eliminating need to view a computer screen.
  • Remote transmitting microphone can be employed thereby permitting PC to remain in warm location.


  • Guides you through polar alignment and all functions of the program.
  • Provides extensive information about the object you are viewing.
  • Timer: lets you know the time remaining during an exposure.
  • Advises when the object that you selected has reached the desired position in the sky.
  • Informs you of favorite objects that are visible within constellations that have risen.


  • Easy two star polar alignment.
  • User can add objects to the database.
  • User can store up to three observing site locations in memory to facilitate future set up.
  • GTO will advise you when you ask to go to an object that is below the horizon.
  • Search for objects based on criterion you select:
    • within current constellation
    • across entire sky
    • database type
    • object type (galaxy, globular cluster, open cluster, planetary nebulae, cluster w/nebula, etc.)
    • within specified magnitude limit
    • Tour - follow a predefined sequence of objects that you can select; the telescope automatically moves from one object to another
    • Tour Builder - prepare your own tours before your viewing session
  • Intuitive computer interface - very easy to learn and use.
  • Night Vision Mode display
  • Can use with Software Bisque astronomy planetarium program "TheSky" version 4.0 or later, and Pocket PC versions too!


  • Machined aluminum housing provides robust protection for electronics.
  • Gears and motors are fully enclosed.
  • Directional N-S-E-W control buttons.
  • Tracking for North or South hemispheres selected by switch on panel.
  • User selectable fine guiding or slewing speeds.
  • Hand held push-button keypad controller with low temperature (VFD) display.
  • Periodic Error Memory correction; user programmable to correct for worm induced periodic errors.
  • Periodic Error Memory correction retains correction data - no need to reprogram each night out.
  • User select able Declination Backlash control.
  • The servo is digitally controlled, and the shaft position is updated at a rate of 2000 times per second.
  • Adjustable voltage output up to 12 v for accessories such as a guiding eyepiece illuminator.
  • Voltage output of 6 volt accepts 2.5mm phono plug to power Pentax 6x7 camera directly from the mount.
  • Meets FCC requirements for home and office use.

Controller Dimensions 4.9" x 4.9" x 1.8" (12.5 x12.5 x 3.4cm)
Weight 8 ounces (227 grams)
Display Type Red LED backlit alphanumeric
Display Screen Vacuum Fluorescent Display (VFD)
Display Arrangement 4 line, 20 character display
Drive Rates King, Lunar, Sidereal, Solar
Guide/Slew rates 0.25x, 0.5x, 1x, 8x, 64x Sidereal
Maximum Slew Rate 5 Deg./Sec. (1200x Sidereal)
Hemisphere North or South (user selectable)
Power Consumption 0.4 amps at Sidereal rate
Power Requirements 12 to 16* volts, DC
Power Supplies AC to 15 vdc Converter (5 amp minimum) regulated and well-filtered to prevent spikes
Portable Power Packs 12 to 16 vdc (6 amp hr. or larger suggested)

* 2011 and later production 1200GTO and 3600GTO can use up to 18 volt DC.


Please see the linked information sheets for descriptions:
  • Models 400GTO, 600E GTO, Mach1GTO, 900GTO, 1200GTO, and 3600GTO series German Equatorial Mounts
  • Sturdy adjustable hardwood Field Tripod with shelf and carrying bag for 400/600E/Mach1 series mounts
  • Particle Wave Technology lightweight alloy field tripods
  • Pier Tech observatories, fixed or adjustable height piers
  • Mounting Plates, and Dovetail Quick Release Hardware
  • SBIG CCD Star Tracker/Imaging System
  • Regulated AC to 12 to 18 Volt Power Supply
  • Portable 12 to 18 Volt Rechargeable Battery Packs
  • Stainless Steel Counterweights
  • Astro-Physics Encoders for optional Digital Setting Circles of earlier model mounts
  • Integral 5X Polar Axis Finder Scope with Illuminator
  • Mounting Rings
  • Company Seven ATA Approved or Mil Spec. Carrying and Shipping Cases


Contents Copyright 1994-2002 Company Seven - All Rights Reserved