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LOSMANDY GM-8 AND G-11 GERMAN EQUATORIAL MOUNTS
Since its introduction in the Spring of 1992 the Losmandy Model G-11 German Equatorial mount has come to represent the best value in its class and a particularly attractive choice for those who require a high degree of tracking precision and reliability. Learning by experience and responding to increasing demands from demanding astrophotographers the G-11 was improved over the years so that it presently provides payload capacities of up to 6 inch refractors, or up to 12 inch aperture Schmidt Cassegrain telescopes. In order to compete in the marketplace for lighter weight precision mounts, Losmandy reduced the bearing and gear set dimensions of the G-11 and developed a more compact folding tripod to produce the GM-8. And on the other side of the G-11, for people who seek a platform engineered for telescopes such as the Celestron C-14, and Astro-Physics 10" Mak, Losmandy developed the HGM Titan mount.
These mounts are fully machined from virgin metals stock on precision Computer numerical control (CNC) milling machines in California. In spite of other mount encroaching the market that may resemble these, or that claim similar payload capacities, no other mounts in this price class provides this balance of payload capacity, low periodic error control, reliability, serviceability; Company Seven views these mounts as being among the least expensive truly precision-made tracking platforms of their class. Furthermore, the Losmandy mounts and their operating systems have been so popular for nearly two decades that there is a large installed user base of accomplished users; we are confident there will many sources of parts and advice for years to come.
"Yes Virginia, there really is something great left being made in the USA"
While the smaller GM-8 remains very popular, the G-11 mount is a particularly attractive choice for those who require a high degree of performance and reliability. And for users who require utmost reliability, who find it inconvenient to obtain repair assistance at remote locations the GM-8 and G-11 mounts are a high performance platform whose components are modular, symmetrical, and fairly simple to service or replace in the field. In fact these mounts are available with either the proven Losmandy Model 492 stepper motor drive and control system or with the Gemini 'Go To' computer control system; either can be installed or replaced in the field! Our experience is that there is rarely a need to return a head to the USA for service more so since Company Seven technicians put in several man hours checking through and fine tuning each new mount which we receive. You are not likely to encounter any defect that would require a return of the head sold by Company Seven for service.
An equatorial mount is judged by it payload capacity and tracking accuracy. Payload ratings of mounts vary in the manner with which the manufacturer judges their product, so this number alone may not be a consistent predictor of capacity. What is most important to the user of the product is how rigidly the mount holds the payload, how smoothly it tracks (amplitude and smoothness of the periodic error of a gear), and how it overcomes the moment imparted by the load. The weight put onto the mount will vary depending how the instrument is to be used too for example one telescope used for visual work only may be as much as fifty percent lighter in weight than another employed for imaging (with guide scopes, cameras, filter wheel, etc.). The potential loading on the mount may also vary with local winds so even a mild wind accross the "sail" area of a large reflecting telescope can dramatically increase the effective load imparted to the mount. So a small mount operating from within a shelter (such as a dome or shed) with a short and narrow telescope might perform as well or better than a larger mount outside a sheltered environment. Indeed, some people elect to buy a smaller mount and then put the balance saved by not buying a larger mount into a shelter.
A mount in this performance class tracks very well making it suitable for the most demanding astrographic applications. This is quantified by measuring the amplitude and smoothness of the periodic error of a gear. The period of the GM-8 Worm Gear is 8 minutes, that of the G-11 is 4 minutes. By measuring the up and down motion of a star being tacked over this period we can measure this error. The typical GM-8 delivered by Company Seven will have something under 20 Arc. Secs. of periodic error (peak to peak). While the recent production G-11 mounts that leave Company Seven will average about 10 Arc. Secs. So the unguided tracking precision of these mounts are among the best in their price class. The amplitude is reached over a broad smooth period, not jerky or rapid. When one employs the Periodic Error Control circuit (of the Gemini), specialized software ("PemPro" for example), or guides the mount with an automatic CCD system then this error can be reduced to much less. Note when using the mount with an autoguiding CCD we teach our customers to turn off the PEC.
Read Company Seven's Review of the original Losmandy G-11 Mount with Celestron C-11 telescope. This was a revolutionary departure from the previous traditional fork mounted arrangements being the first large SCT optical tube assembly sold mated to a German Equatorial platform. The CG-11 became the most successful mid aperture Schmidt Cassegrain telescope system ever sold by Company Seven.
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Common Features of both GM-8 and G-11 Mounts:
- All machined mountings made from stainless steel and aluminum barstock
- Hollow R.A. axis with detachable polar scope for quick, accurate
alignment in the field
- Removable precision ground 1.25" diameter stainless steel
counterweight shaft
- Fine altitude and azimuth adjustments for quickly and accurately
zeroing in on the Celestial pole in the field
- Setting circles with Porter Slip Ring Design; polar-axis ring is
driven; it follows the stars without needing to be reset each time
you look at a new object
- Both axes machined to accept optional high-resolution encoders for
use with popular digital setting circles
- Customer's choice of control electronics:
- Model 492 Dual Axis Drive Corrector, or
- Losmandy Gemini Computer Controlled "Go-to" System
Right: Losmandy Model G-11 German Equtorial Mount Head shown without furnished tripod, counterweight shaft.
Clutch adjustment handles shown are optional. Click on image to see enlarged view.
| SPECIFICATIONS OF G-11 MOUNT SYSTEM* |
| R.A. Gear Wheel: |
5.625", 360 tooth 7075 T35 aluminum |
| DEC. Gear Wheel: |
5.625", 360 tooth 7075 T35 aluminum |
| DEC. and R.A. Worm gear: |
440C Stainless (54 Rockwell hardness) |
| Worm gear support: |
Dual supported ball bearings |
| Worm gear coupling: |
Oldham |
| Laser Engraved Setting Circles: |
Porter Slip Ring design, 5" DEC. and R.A., |
| Right ascension resolution: |
4 minute increments, pointer |
| Declination circle resolution: |
1 degree increments, pointer |
| R.A. Axis Needle Thrust Bearings: |
one 3.75", one 2", and two 1.625" |
| DEC. Axis Needle Thrust Bearings: |
one 3.75", one 2", and two 1.625" |
| DEC. and R.A. Clutches: |
Slip clutch, variable friction, one knob ea. axis |
| Latitude Tangent Arm range: |
12 to 64 degrees with polar scope, 8 to 68 with minor modification |
| Azimuth adjustment range: |
+-8.5 degrees |
| Dovetail Saddle Plate: |
"D" Series Standard |
| Weight of Mount Head |
Approximately 31 lbs. |
| Weight of Field Tripod |
approximately 20 lbs. |
| Semi-Pier Tripod Height |
34 to 48 inch |
| Load Capacity: |
Approximately 60 lbs. |
G-11 Instruction Manuals
-
 "Losmandy™ Model G-11 Instruction Manual". Complete 12 page instruction manual as furnished with our Losmandy Model G-11 German Equatorial Mount. Publication content by Losmandy Hollywood General Machining, all rights reserved. From Company Seven's Library. 180,349 bytes (in Acrobat Reader ".pdf" format).
- "Losmandy Pole Finder Instructions" Illustrated instruction manual as written by David A. Kodama for Losmandy, with slight reformatting by Company Seven. This document covers the older Losmandy reticle (with the errant pattern), as well as the current model. Furthermore, it provides assistance for our Southern Hemisphere neighbors. Provided in support of customers who buy the optional Losmandy German Equatorial Mount Pole Finder.
| SPECIFICATIONS OF MODEL 492 DIGITAL DUAL AXIS ELECTRONICS* |
| Power Requirements:
| 12 Volt D.C., 500 MA* |
| R.A. and DEC. Geared Motors: |
SAIA 48mm Stepper Drive Motors |
| Motor MTBF: |
2.5 years of continuous operation |
| Hand Control: |
Diamond Pattern Push Botton Switches, DEC. &
R.A. Reversing, |
| Quartz Tracking Rates: |
Sidereal, Lunar, Solar, King |
| Fine Movement Rates: |
4x, 8x, 16x Sidereal |
| Photo-Guide Setting Rates: |
+-30%, 50%, and 2x Sidereal |
| R.A. Drive Gear Correction: |
user programmable Periodic Error Control |
| DEC. Drive Backlash Correction: |
user programmable Time Variable Correction |
| North/South Hemisphere Operation |
selectable by user |
| Miscellaneous: |
Compatible with our SBIG CCD Star Tracker & Imaging CCD Systems such as our ST series including the original Model ST-4 |
* Power Source Notes we suggest the user consider one of the following options:
- operate from wall current (with GFCI outlet) with an AC/DC inverter. Ideally this should be through a Line Conditioner/Surge Suppresssor (contact us to discuss what we offer).
- If you intend to use a 12 VDC power supply then please ensure that it is noise free, and regulated to +/- 5%. It must have a current supply of at least 2.5 amps with no appreciable voltage drop. Be especially careful when using an instrument with running vehicles as a supply source since a malfunctioning alternator or voltage regulator as well as vehicle power demands, can produce power surges and appreciable amounts of AC power which can easily damage the micro controller in your instrument.
- For simple observing, use a portable rechargeable 12 Amp hour (or greater capacity) 12 Volt D.C. rechargeable battery pack.
- For higher current demands use a sealed, Deep Cycle/Marine/R.V. battery. These are readily available at automotive service and parts centers. This does not have to be the most immense battery, one designed for a golf cart for example may be adequate for your needs.
Right: Losmandy Model GM-8 German Equtorial Mount Head shown without furnished tripod, counterweight shaft.
Click on image to see an enlarged view.
| SPECIFICATIONS OF GM-8 MOUNT* |
| R.A. Gear Wheel: |
2.8", 180 tooth 7075 T35 aluminum |
| DEC. Gear Wheel: |
2.8", 180 tooth 7075 T35 aluminum |
| DEC. and R.A. Worm gear: |
440C Stainless (54 Rockwell hardness) |
| Worm gear support: |
Dual supported ball bearings |
| Worm gear coupling: |
Oldham |
| Laser Engraved Setting Circles: |
Porter Slip Ring design, 3.5" DEC. and R.A., |
| Right ascension resolution: |
6-minute increments, pointer |
| Declination circle resolution: |
2 degree increments, pointer |
| R.A. Axis Thrust Bearings: |
one 2.1", one 2"; two 1.5" needle |
| DEC. Axis Needle Thrust Bearings: |
one 2.1", one 2"; two 1.5" needle |
| DEC. and R.A. Clutches: |
Slip clutch, variable friction, one knob ea. axis |
| Latitude Tangent Arm range: |
0-64 degrees with polar scope, lower latitude wedge available |
| Azimuth adjustment range: |
+-8.5 degrees |
| Dovetail Saddle Plate: |
Optional "C" or "D" Series |
| Weight of Mount Head |
Approximately 17 lbs. |
| Weight of Field Tripod |
Approximately 15 lbs. |
| Semi-Pier Tripod Height |
36" to 48" |
| Load Capacity: |
Approximately 30 lbs. |
| GM-8 MOUNT TYPICAL SHIPPING ARRANGEMENT* |
| Head Box Dimension |
20 x 15 x 15 inches / 50 x 38 x 38 cm |
| Head Box Weight |
43 lbs. / 19.6 kg |
| Tripod Box Dimension |
33 x 12 x 13 inches / 84 x 31 x 33 cm |
| Head Box Weight |
19 lbs. / 8.6 kg |
| Standard Counterweight |
8 x 8 x 4 inches / 20 x 20 x 10 cm |
| Head Box Weight |
9 lbs. / 4.1 kg |
* Specifications subject to change.
GM-8 Instruction Manuals
- "Losmandy™ Model GM-8 Instruction Manual". Complete 12 page instruction manual as furnished with our Losmandy Model GM-8 German Equatorial Mount. Publication content by Losmandy Hollywood General Machining, all rights reserved. From Company Seven's Library. 180,304 bytes (in Acrobat Reader ".pdf" format).
- "Losmandy Pole Finder Instructions" Illustrated instruction manual as written by David A. Kodama for Losmandy, with slight reformatting by Company Seven. This document covers the older Losmandy reticle (with the errant pattern), as well as the current model. Furthermore, it provides assistance for our Southern Hemisphere neighbors. Provided in support of customers who buy the optional Losmandy German Equatorial Mount Pole Finder.
POPULAR AVAILABLE OPTIONS FOR THESE MOUNTS
Accessories Section for illustrations and descriptions
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Right: Losmandy Model G-11 German Equtorial Mount Head shown without furnished tripod, counterweight shaft.
