Why a 900GTO?
Stability ... accuracy ... ease of setup ... friendly go-to control interface - these were the primary design goals of the 900GTO. Amateurs today demand a precise mount that will allow them to pursue all aspects of astronomy whether it be observing visually, CCD imaging or photographing with 35mm or 6x7 camera. Many of the finest imagers today have been using our GTO mounts as a solid platform for a wide variety of instruments. Astro-Physics now offers four German Equatorial mounts listed in order of size from largest to smallest: 3600GTO German Equatorial, also known as El Capitan, 1200GTO, 900GTO and the most compact is the Mach1GTO. If your instrument of choice is a medium-sized refractor, Cassegrain, Ritchey-Chretien, Newtonian or astrograph, the 900GTO may be the ideal choice for you.
Since its introduction in 1998, the 900GTO has gained a reputation for both tracking and pointing accuracy, essential to casual visual observation as well as advanced imaging. Quite a few 900GTO and 1200GTO mounts can be found at major star parties throughout the country and the world. It is a favorite of many advanced photographers and imagers.
These mounts are truly a marvel of engineering - maximum strength and rigidity with minimum weight. Our CNC lathes and mills carve out the excess material in both axes of the 900GTO German Equatorial 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.
Over the years, a number of improvements have been incorporated into the design of the 900GTO, among these are smoother azimuth adjusters; increased height of the polar forks to allow more room for your hand when making altitude adjustments; improved gear profiles in the motor gearbox for quieter operation and reduced backlash; motor bracket with built-in spring-action to keep the worms loaded at the proper setting; verifiable worm gear accuracy of 7 arc seconds (+-3.5 arc sec.) or less; internal changes to improve overall accuracy; additional pier adapter options; updated GTOCP3 control box with additional capability; updated keypad with larger memory capacity and LED fiber optic backlit panel; included PulseGuide and PEMPro software as described below. Each time we begin a production run, we ask ourselves what improvements we can make to improve the accuracy and functionality of the 900GTO. As a result, the 900GTO has evolved over the years to meet the needs of the advanced imager or visual observer.
Gilles Cohen, of France, has been using his 900GTO for several years and has documented its impressive performance. He not only prepared a beautiful French page to show off the mount, but he also was inspired to prepare a second page in English for the rest of us. Gilles is a rising star imager who does his work from a major urban site with lots of light pollution and not always the best seeing, but has managed to take some excellent astrophotos - some of which are posted on his Gallery Page.
The 900GTO mount is built from the ground up to be a precision imaging platform while still being totally user friendly. Consider these advantages and features:Versatility
|Construction||All CNC machined aluminum bar stock, stainless steel, brass; stainless steel fasteners|
|Finishing and Assembly||Every part is hand-finished and inspected. All assembly is done by hand, by highly skilled mount assembly staff.|
|Worm wheel - R.A.||7.2" (183 mm), 225 tooth aluminum|
|Worm wheel - Dec.||6.0" (152 mm), 225 tooth aluminum|
|Worm gear - R.A.||Brass, 0.710" (18 mm) diameter|
|Worm gear - Dec.||Brass, 0.705" (17.9 mm) diameter|
|Thrust Bearing - R.A.||7.0" (178 mm) diameter|
|Thrust bearing - Dec.||6.0" (152 mm) diameter|
|Axis shaft - R.A.||2.20" (56 mm) diameter|
|Axis shaft - Dec.||1.75" (44 mm) diameter|
|Shaft axis bearings - R.A./Dec.||Each shaft is supported by 5 bearing elements, two preloaded ball bearings and 3 sets of massive thrust bearings|
|Latitude range|| 20 to 68 degrees with or without the polar scope attached.
0-20 or 68-88 degrees when using Hi-Lo Latitude Wedge (900WDG or 900WDGA)
|Azimuth adjustment||Approximately 15 degrees (+/- 7.5 degrees from center)|
|Setting circle - R.A.||4-minute increments, pointer, engraved both Northern/Southern, Porter Slip Ring|
|Setting circle - Dec.||1 degree increments, pointer, engraved, Porter Slip Ring|
|Counterweight shaft||1.875" (48 mm) diameter x 14" (356 mm) long [12.875" (327 mm) useable length], incl. large machined safety stop knob. Optional 9" (229 mm) shaft extension available.|
|Weight of mount||Total: 54 lb. (24.5 kg)
R.A. axis/polar fork: 26.5 lb. (12.0 kg)
Dec. axis: 17 lb. (7.7 kg)
Counterweight shaft: 10.5 lb. (4.8 kg)
Approximately 70 lb. (31.8 kg) scope and accessories (not including counterweights), depending on length. Recommended for: Astro-Physics and similar fast refractors up to
|Instrument mounting interface||Refer to list of suitable mounting plates below|
|Pier adapter base||7.730" (196.34 mm) diameter. The base is part of the chosen pier adapter - either the Rotating Pier Adapter (900RPA), the Standard Pier Adapter (900SPA), or the Hi-Lo Latitude Wedge (900WDGA or 900WDG). The desired pier adapter must be purchased separately.|
GTO Servo Drive System
The drive system uses a high-quality Swiss DC servo motor 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 motor. The system can be accurately controlled over a speed range of 4800:1, which allows 0.25x sidereal for manual guiding to 1200x sidereal for 5 degree per second slewing. The circuit draws approximately 0.4 amps when tracking the stars and 2 amps with both motors slewing and requires only 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.Gear Accuracy and PE Performance
GTO Servo Drive System Specifications
|Electronic components||Rated for industrial and automotive applications|
|Motors||Zero-cogging Swiss DC servo motors, enclosed in machined aluminum housing|
|Motor encoder||2000 tic quadrature yielding an effective resolution of 0.050 arcseconds per tic|
|Motor reduction gear train||57.6:1 gear reduction through a custom built set of large diameter, fine-toothed, precision, spur gears for vastly superior performance|
|Servo Motor Control Box||GTOCP3 Control Box, removeable|
|Hand-held computer||GTO Keypad to control all mount functions. Includes extensive databases and tour features in a simple, intuitive interface. Firmware updates via the internet|
|Power consumption||~ 0.3 to 0.5 amps at 13.8 volts - tracking; ~ 1.0 to 2.3 amps at 13.8 volts - both motors slewing at 1200x|
|Power requirements||Nominal 12 volt DC supply at minimum of 5 amps continuous|
7 arc seconds peak-to-peak (+/- 3.5 arc seconds) or less in one worm cycle (6.4 minutes); native, prior to any error correction
|Maximum slew speed||5 degrees / second|
Flexible Control with Your Keypad, Computer or even your Mobile Smart Device!
|As this chart shows, there are many options available for controlling your mount. Take a few minutes to link to descriptions of the varied software and devices that are available. You will be able to further link to a full size view of this chart and discover more about each method.|
The 900 Standard Pier Adapter (900SPA) was included with 900 mounts sold in the past. However, in 2005, we decided to offer several choices to meet a variety of needs. We ask that you add one of these options to your mount order. If you plan to have multiple pier installations, perhaps one permanent and another portable, you may wish to purchase an extra adapter to install on the the second pier. This will make your setup and switchover much quicker. Many customers have found this to be advantageous.
If you do not purchase one of our pier adapters described below, for instance, if you purchase the Monolith Pier from Particle Wave Technologies, you will need to purchase the Pier Adapter Knob Kit (part# 9KBKIT) in order to attach your mount to the Monolith.
Complete descriptions and photos are available at the links below.
People often ask us what the 900GTO's dimensions are. The answer is: It depends. Different latitude settings can drastically affect the shape and dimensions of the mount. To answer this question we have prepared the following PDF document: 900GTO Dimension Sheet and this Excel spreadsheet Latitude Dimension Calculator.
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 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.
We have prepared some pertinent support documents relating to this mount and many of our other products on our Technical Support page. You may find the information that you need simply by clicking here.
Price and Delivery Information
The 900GTO German Equatorial Mount with the GTOCP3 Control Box is no longer available to purchase. We are excited to introduce our new mid-size German Equatorial Mount. This mount will be debuted at the Northeast Imaging Conference (NEAIC) and the Northeast Astronomy Forum (NEAF) in a few weeks. It incorporates the design features of the 1600GTO in a smaller, more portable package. For your first peek at this full-featured mount and its specifications, please check out this link: 1100GTO German Equatorial Mount . You can sign up to be notified when this mount is available for you to order using our Online Notification Request Form.
900GTO - What's Included?
Items that You will Need for Your Mount
Additional Accessories To Consider
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This page was last modified: April 4, 2013
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