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Astro-Physics Model 400 GTO Mount with 13cm f6 EDF Telescope, and GTO CPU/Control Panel (Hand Control Box not shown)


A discontinued product, information posted for information purposes only

Right: Astro-Physics Model 400 GTO Mount with optional 13cm f6 EDF Telescope, and GTO CPU/Control Panel (Hand Control Box not shown).

The two most important considerations in mount design and construction are maximum strength/rigidity for a given size and accuracy of the drive system. Without this basic foundation, all other features of a mount are just superfluous frills. The Astro-Physics 400 GTO Equatorial mount is designed to be a compact, firm, precise tracking platform for your high resolution instrument. This handy mount head can be lifted easily into your backyard, packed conveniently into your car, or carried aboard an airliner for travel to another hemisphere. When coupled with the options described separately, the 400 GTO German Equatorial mount system will be your portable observatory.

This mount has been engineered to work seamlessly with the included Servo "DigitalSky Voice" Go-To Computer Control System. The furnished Keypad controller permits access and control of most desired functions, while the "DigitalSky Voice" software is a terrific observing companion offering many observing ideas and information, and a new level of ease of use for the beginner or the more experienced observer. If you plan to use an IBM-compatible personal computer to control your GTO mount, then you will have lots of fun with this accompanying software.

Below: Astro-Physics Model 400 GTO Mount Head with optional counterweight and telescope. GTO CPU/Control Panel and Hand Control Box not shown (182,658 bytes) Astro-Physics Model 400 GTO Mount Head with optional counterweight and telescope. GTO CPU/Control Panel and Hand Control Box not shown (182,658 bytes)

Over the years, Astro-Physics mounts and drive systems have functioned reliably in the coldest environments of Canada, Norway and remote northern Alaska. The circuitry of our controller designs has been proven since the mid-1970's and is comprised of the highest-quality Military Spec. and Aircraft Grade components. Astro-Physics avoids the cost cutting techniques employed in most competing controllers: construction with flimsy, hygroscopic (water absorbing) circuit boards, components rated for indoor use, and poor solder connections. Astro-Physics controllers will stand up to the humidity and temperature extremes common to many observing locations.

Whether your interests are purely visual or include astrophotography, a steady image in the eyepiece or camera viewfinder is extremely important; and yet both axes respond to fingertip pressure with unparalleled smoothness. Built-in clutches can be disengaged for ultra-smooth sweeping or locked for astrophotography. The worm gears, motors and drive components are enclosed to protect them from dirt and dust. With a telescope such as the 105 Traveler, the 400 GTO mount damps out in one second when mounted on the optional lightweight aluminum tripod.

Your 400GTO mount can grow with your skills and interests in astronomy. You can enjoy the visual pursuits of astronomy using the hand held "go-to" keypad controller, and/or the DigitalSky Voice software (running on a common PC computer) to direct the mount to many fascinating objects. If you plan to become engaged in astrophotography, then you will be pleased how this is facilitated with the solid stability and inherent accurate tracking capability of the drive system. The GTO CPU Control Box contains a plug-in for use with the optional CCD auto-guiding and imaging systems such as those we offer developed by Santa Barbara Instruments Group; these CCD systems will permit you to automatically guide astronomical photos with film cameras, or explore CCD imaging.

The 400 is constructed of the highest quality components to provide you with years of observing pleasure. All parts are precisely machined on Astro-Physics computerized CNC lathe and machining center using solid or thick wall aluminum and stainless steel. Machining tolerances are very high to achieve a tight, solid fit of all components. There are no thin wall, weak, porous die castings as in most other mounts of comparable size. Astro-Physics avoids the use of any carbon steel shafts or plated steel fasteners because they will deteriorate with time. This mount will not rust or bind up and will retain its appearance and function throughout the years.


  • Precision machined aluminum with radiused edges
  • Gears and motors are fully enclosed
  • Gear in declination axis allows full 360 degree continuous rotation; a telescope can move through zenith in the course of long exposure astrophotography
  • 2.5" (6.4cm) diameter hollow right-ascension and declination shafts maximize strength at minimum weight
  • Large thrust bearings form ultra-stable thrust surfaces for tremendous rigidity in a small package
  • Right-ascension shaft threaded for optional polar scope allows quick, accurate polar alignment in the field
  • Removable stainless steel counterweight shaft for compact storage
  • R.A. Setting Circle Porter Slip Ring design so when mount is moved manually, or driven electronically it follows the stars with no need to be reset
  • Fine altitude and azimuth adjustments for quickly and accurately zeroing in on the pole in the field
  • Black anodized finish will retain its lustrous beauty for years
  • Base fits into 6" diameter pier with 0.083" wall thickness

Below Right: Diagram of 400 GTO dimensions commonly requested. If the telescope is horizontal and pointing to west or south, then the measurement from the top of the pier to the middle of the cradle plate is 9.25 inches (23.5cm); these dimensions will vary somewhat depending on your latitude. We quote thus for 42 degrees because that is the latitude of the factory, it is also a good average value (155,796 bytes).

Diagram of 400 GTO dimensions (155,796 bytes).
Worm wheel: 3", 192 teeth fine pitched bronze wheel
Worm gear: stainless steel
Latitude range: 10 to 64 degrees*
Azimuth adjustment: approximately 25 degrees
Azimuth adjustment: Porter Slip Ring design
Right ascension: 10 minute increments, pointer engraved both Northern/Southern
Declination: 1 degree increments, pointer
Capacity: will accommodate refractors
up to 5", reflectors to 6", Cassegrains to 9.25"
Weight of equatorial head: 20 lbs (9.1 kg)
*Low Latitude wedge available.


The drive system employs a high-quality, DC servo motor controlled by a microprocessor. The tracking is very smooth, noticeably better than any production stepper motor drive. The system can be accurately controlled over a wide speed range of 4800:1 (0.25x sidereal for guiding to 1200x sidereal for 5 degree per second slewing). The servo drive will satisfy the requirements of the sophisticated, advanced astrophotographer, yet is easy for the casual, visual observer to use. Please refer to the separate section entitled "GTO Control Box and Keypad for Servo Drive" section of our Internet Site for more details about this revolutionary development.

  • Each axis has a fully enclosed, industrial quality zero-cogging DC Servo motor
  • Motors are microprocessor controlled to an accuracy of +-0.05 arc seconds
  • Power requirements: 12 Volt D.C.
  • Current draw: only 0.3 amps when tracking or up to 1.2 amps with both motors slewing at 1200x
  • Electronic components meet industrial and aircraft application standards
  • Push button selection of drive rates for lunar, solar, or sidereal tracking
  • PEM permanently stored Periodic Error Memory correction
  • TVC Time Variable Constant Declination backlash control
  • R.A. and Declination reversing switches for correct object orientation and movement in eyepiece
  • TIC Interface for optional SBIG Autoguider/Star Tracker controller
  • Adjustable brightness control for optional guiding or measuring reticle illuminator
  • Locking plug connections for all control and power cables


    Please see the accompanying information sheets for descriptions:
    • Sturdy, adjustable Hardwood Field Tripod with shelf and carrying case
    • Lightweight aluminum adjustable field tripod
    • Heavy Duty aluminum adjustable field tripod (by Company Seven)
    • Mounting Plates, and Dovetail Quick Release Hardware
    • Low Latitude wedge
    • SBIG ST-4 or other Star Tracker/Imaging System
    • Portable Pier - 6 inch diameter, in heights of 48", 54" or 62"
    • 12 Amp-hour, 12 Volt Rechargeable Battery Pack
    • Stainless Steel Counterweights of 6 lbs., or 9 lbs.
    • Astro-Physics Encoders for Digital Setting Circles
    • Integral 5X Polar Axis Finder Scope with Illuminator
    • Mounting Rings for telescope
    • Carrying Cases (up to ATA - Airline Transport Assoc. approved)

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