INTRODUCTION
The 900GTO German equatorial was designed to meet the needs of the advanced observer who requires a mount with
maximum strength and rigidity and minimum weight. The excess material in both axes has been carved out while retaining a
heavily ribbed structure for internal strength and rigidity. A unique dovetail was machined into the mating surfaces of the R.A.
and Dec axes. This feature allows quick and easy assembly in the field without any tools.
The DC servo motor drive with GTO computer system, the keypad with its digital display screen, and the included
PulseGuide™ and PEMPro™ v.2 software all combine to offer extraordinary sophistication for today’s observer. Whether
you enjoy visual astronomy exclusively or plan an aggressive astrophotography or CCD imaging program, this mount will
allow you to maximize your night out under the stars.
The advanced keypad features allow you to slew automatically to objects in a wide range of databases as well as any
R.A./Dec coordinate. A large selection of common names for stars and other objects makes your selection a snap. The rapid
slew rate of 5 degrees per second (1200x) allows you to locate objects very quickly and accurately. You will be very pleased
with the intuitive operation of this keypad. 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.
PulseGuide™ is a stand-alone Windows (98, ME, 2000, NT4, XP, Vista) utility that provides complete remote control of all
Astro-Physics GTO 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. PulseGuide™ was written by Ray Gralak of Sirius-
Imaging. Please refer to his website http://www.pulseguide.com for further developments and enhancements.
PEMPro™ (Periodic Error Management Professional) is a Windows software application that makes it easy to characterize
and reduce periodic error. PEMPro™ will analyze the performance of any mount that is equipped with a CCD camera and
compatible camera control software. PEMPro™ gives you powerful tools to program your mount's periodic error correction
firmware to achieve the best possible performance for your mount. PEMPro™ dramatically improves guided and unguided
imaging resulting in better images and fewer lost exposures. PEMPro™ v.2 Full Version also adds a Polar Alignment Wizard
and a video interface for using many webcams. PEMPro™ v. 2 Full Version began shipping with 900GTO mounts in May,
2008.
The periodic error of your 900GTO will be 7 arc seconds or less (before correction). We have already loaded the PEMPro
curve that was generated during your mount’s testing into the servo to reduce the error even further, and to give you a head
start right out of the box. See additional information under “Servo Motor Drive.”
The 900 is equally at home in a permanent observatory or as a portable mounting for remote star parties thanks to the ease
with which the two axes come apart. This is the perfect mount for a mid-size refractor, Newtonian, Cassegrain or astrograph.
In order to maximize your pleasure on your first night out,
we recommend that you familiarize yourself with the
assembly and basic operation of the mount indoors. The
temperature will be comfortable, the mosquitoes at bay,
and you'll have enough light to see the illustrations and
read the manual. Please take particular note of counter-
balancing, use of the clutches and operation of the
keypad controller.
Why Polar Alignment is Important
Polar alignment compensates for the Earth’s rotation.
If you were to take a long exposure photograph with
Polaris (often called the North Star) in the center of the
field, you would discover that all stars seem to revolve
around Polaris. This effect is due to the rotation of the
earth on its axis. Motor driven equatorial mounts were
designed to compensate for the earth's rotation by
moving the telescope at the same rate and opposite to
the earth's rotation. When the polar axis of the telescope
is pointed at the celestial pole (polar aligned) as shown
in the diagram, the mount will follow (track) the motions
of the sun, moon, planets and stars. As a result, the
object that you are observing will appear motionless as
you observe through the eyepiece or take astrophotos.
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