GM-8 Equatorial Mount with Gemini II go-to computer


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The Losmandy GM-8 with a Gemini II go-to computer is a well made high-precision go-to mount that is ideal for the serious visual observer/astrophotographer who needs a highly portable mount with a 30 lb payload capacity.

Our Product #: GM8GT
Losmandy Product #: GM8G
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Product Description

The Losmandy GM-8 mount with a Gemini II computer system is a well-made, high-precision German equatorial mount that is very portable, but can still hold a respectable payload. It is rated at a 30 pound payload capacity, making it an excellent choice for almost every 4" refractor, most 6" Maksutov-Cassegrains and Maksutov-Newtonians, and even some 5" refractors. It comes standard with a Gemini II computer and dual axis drive system whose built-in drive corrector includes periodic error correction, making it an excellent photographic platform for the serious astrophotographer.

The Losmandy GM-8 equatorial head:

All parts are machined from stainless steel or aluminum. All aluminum parts are black anodized. All hardware is stainless steel for rust-free long life.

Bearings include one 2.100" diameter needle thrust bearing, one 2.000" diameter needle thrust bearing, and two 1.500" diameter needle bearings. Right ascension and declination shafts are precision-machined of 1.250" diameter aluminum. The 180 tooth main drive gear is machined of 2.812" diameter 7075 aluminum. The heat-treated and ground stainless steel worm is in a dual supported ball bearing housing. There is a one-knob design variable slip clutch on each axis. The drive uses a 160 oz/in stepper motor, with 1.0 arc second steps.

The unique fully-locking tangent arm design altitude adjustment allows use over a 0-64 degree latitude range. There is a single large adjustment knob for easy alignment. The latitude scale is laser engraved in 2 degree increments. The two-knob azimuth control provides a +/- 8.5 degree adjustment range and positive locking.
3.500" diameter laser engraved setting circles are marked in 6 minute increments in right ascension and 2 degree increments in declination. The right ascension circle is engraved for both Northern and Southern Hemisphere use. The r. a. circle is a Porter slip ring design, so that when the mount is moved manually, or driven electronically, the r. a. circle follows the stars with no need to be reset periodically.

A dovetail saddle that can accept both Losmandy D-plate and Vixen-style OTA dovetails allows for the fast interchanging of tube assemblies. Its range of fore and aft adjustment reduces the need for declination weights. The stainless steel counter weight shaft is removable and has a safety knob. The payload capacity is 30 lbs. The equatorial head weighs 21 lbs., exclusive of counterweight(s). The mount comes with one 7 lb. counterweight standard. Additional 11 lb. and 21 lb. counterweights are available to balance heavy payloads.

An optional illuminated through-the-axis polar alignment scope works in both Northern and Southern Hemispheres.

The Losmandy GM-8 tripod:

The tripod is made of all machined aluminum, black anodized. Fold-up design for easy transporting. The tripod height is adjustable from 27" to 43". All heights are to the top of the tripod. Add 15" (at a latitude of 34 degrees) to account for the distance from the top of the tripod to the top of the saddle. This total will give you the distance from the ground to the underside of the telescope optical tube. The tripod weighs 15 lbs.

The Losmandy GM-8 Gemini II go-to dual-axis electronics:

The Losmandy Gemini 2 system is a DC servo motor-based go-to computerized positioning system. The upgraded Maxon DC servo motors supplied with the Gemini 2 have higher torque through their entire range of tracking and slewing speeds than the motors on standard Losmandy mounts that don’t have a go-to capability. The drive system has a dual 12~18V DC input/output and draws 3.0A maximum.

The servo motors used in the Gemini 2 have two main advantages over the stepper motors normally used in scopes. First, servo motors run with a continuous smooth rotation, rather than the discrete short steps taken by stepper motors. This results in less image “jitter” in extremely high magnification planetary observing and stars that are tighter and more point-like in critical astrophotography applications. Second, servo motors have very high torque, even at high slewing speeds. As a result, the Gemini 2 system can deliver a maximum slew rate of approximately 6 degrees per second with the GM-8 mount.

The Gemini 2 computer is a stand-alone system, with no PC required for operation in the field. A full-color graphic touch screen on the hand control of the Gemini 2 system clearly displays all functions. There is a classic four-button diamond pattern for guiding, centering, moving, and slewing on both the touch screen on the front of the computer and on a tactile four-button membrane on the rear. There is also support for the original Gemini four-button controller.

The Gemini 2 has 0.5 arc second positioning accuracy during go-to operation. It is GPS-compatible with an optional #LGPSG2 receiver. It has Ethernet 10/100 with full IP function to permit operation from anywhere using a browser, ASCOM, or an application over the web or serial port. There is also custom mount support using a programmable gear rate function.

The more than 40,000 object memory of the Gemini 2 is non-volatile and the system contains a real-time clock. You can select from English, French, Spanish, and German language displays. There are two USB ports; one for virtual COM to PC, and one for an ASCOM or planetarium program. There is PEC correction built in and an auto-guider port. The firmware can be upgraded via the internet. There are ports for future high-resolution encoders and a multi-function A/D I/O serial port.

The following databases, comprising about 41,000 stars and objects, are built into the Gemini 2 system, more than enough to keep even the most avid observer busy for some time! You get the Messier catalog (110 objects), the revised NGC catalog (7840 objects), the revised IC catalog (5386 objects), the Sh2 Sharpless 2 catalog (313 objects), a catalog of 167 bright stars, and a 17,635 star catalog of SAO stars.

Tech Details

Warranty 1 year


Review by:
I have had three (!) of these mounts over the years, and all have been rock solid mounts. A great mount for DSLR and widefield small Ritchie-Chretain and refractors for astrophotography. And MADE IN USA! (Posted on 7/22/2019)
Review by:
Review by:
The Losmandy GM8 has been around for many years, why simple it is an extremely well made mount, is dead simple to use, it's accurate, and the support is second to none. The GM8 is the standard for 30lb capacity mounts, you can buy one today and 15-20 years from now with reasonable care it will operate just like new. Losmandy has parts available for 25 year old mounts, working on them only requires hand tools in the rare event it does need a service.

If you are looking for a bullet proof mount that easily handle 30lbs of capacity for visual and AP work, this mount is EXTREMELY difficult to beat. (Posted on 10/6/2018)
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