400GTO German Equatorial Mount
Includes Go-to Keypad Controller and DigitalSky Voice™ software

The 400GTO is not available to purchase and we do not have any plans to produce this particular model in the future. A new mount in this size range is in development with planned introduction in 2005. This information is presented for present owners and those who are curious about its history.

400GTO with 8" Dovetail Plate, 9 lb. Counterweight, and Adjustable Aluminum Tripod
Additional photos to view:
400GTO with 105mm f6 Traveler, 8" Dovetail Plate, 9 lb. Counterweight, Adjustable Aluminum Tripod, and other accessories
400GTO with 130mm f6 StarFire EDFS, 8" Dovetail Plate, 6 and 9 lb. Counterweights, Adjustable Wood Tripod and other accessories

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 400GTO was engineered to be a compact, firm platform for your high-resolution instrument. Whether your interests are purely visual or include astro-photography, a steady image in the eyepiece or camera viewfinder is extremely important.

The 400GTO is constructed of the highest quality components to provide you with years of observing pleasure. All parts are precisely machined on our 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. These are not thin-wall, weak, porous die castings as in most other mounts of comparable size. We avoid 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.

Both axes respond to fingertip pressure with unparalleled smoothness. Built-in clutches can be disengaged for smooth sweeping or locked for astrophotography. The worm gears, motors and drive components are enclosed to protect them from dirt and dust. With the 105 Traveler, the 400 mount damps out in one second when mounted on the lightweight aluminum tripod.

Your 400GTO mount can grow with your skills and interests in astronomy. You can enjoy the visual pursuits using the go-to Keypad controller and/or DigitalSky Voice software to help you find many fascinating objects. If you plan to take astro-photos, you will be pleased with the solid stability and inherent accurate tracking capability of the drive system. The GTO Control Box contains a plug-in for the CCD auto-guiding and imaging systems. These units will allow you to auto-guide astronomical photos and explore CCD imaging.

Features Specifications of the Equatorial Head

Worm wheel

3" (7.6cm), 192 teeth, fine-pitched bronze wheel

Worm gear

Stainless steel

Latitude range

10 to 64 degrees

Azimuth adjustment

Approximately 25 degrees

Setting circles

Porter Slip Ring design

Right ascension

10 minute increments, pointer engraved both Northern/Southern


1 degree increments, pointer


Approximately 18 lbs. (8.2 kg) scope and accessories, depending on length. Will accommodate many refractors up to 5" f8;, reflectors to 6", Cassegrains to 8"
Note: Some telescopes are very heavy for their size and will require a larger mount.

Weight of equatorial head 21 lbs. (9.5 kg)

Servo Motor Drive

The drive system uses a high-quality, zero-cogging DC servo motor controlled by a microprocessor to an accuracy of 0.2 arc seconds per step. Tracking is very smooth, noticeably smoother than any stepper motor drive. The system can be accurately controlled over a speed range of 4800:1 (0.25x sidereal for guiding to 1200x sidereal for 5 degree per second slewing). The circuit draws only 0.3 amps when tracking the stars, 1.2 amps with both motors slewing and requires 12 volts to operate. The servo drive will satisfy the requirements of the sophisticated, advanced astrophotographer, yet is easy for the casual, visual observer to use.


The diagram shows several dimensions that are commonly requested. In addition, if the scope is horizontal and pointing west or south, the measurement from the top of the pier to the middle of the cradle plate is 9.25." Please note that these dimensions will vary somewhat depending on your latitude. We quote them for 42 degrees because that is the latitude of Astro-Physics and all of our equipment is set up that way. It is also a good average value.


We have prepared some pertinent support documents relating to this mount and many of our other products on our Technical Support page. Please check there first to find the information that you need.

Upgrades and Spare Parts

Check out our websiteto find accessories, replacement parts or learn about possible upgrades for your mount.

Copyright 2004-2019 Astro-Physics Inc. All rights reserved.
Last modified: March 11, 2019

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