Losmandy's Gemini system.
MY DECADE-OLD LOSMANDY G-11 German equatorial mount has been a great investment. I purchased it along with an 11-inch Celestron Schmidt-Cassegrain telescope after reviewing the pair in this magazine's May 1993 issue (page 43). The G-11's quick setup, rock-solid stability, precise tracking, and highly accurate polar-alignment scope make it my mount of choice for a half dozen different instruments. Through the years I've used it in my backyard and on road trips to image Comets Hyakutake and Hale-Bopp and scores of deep-sky objects. It has traveled to eclipses and helped show schoolchildren the Moon and planets through the 11-inch Celestron.
But my 1993 G-11 was dumb.
Dumb, that is, by today's standards, since it lacked Go To pointing--the ability to automatically slew itself to objects at the press of a few buttons. This wasn't a big deal in 1993, since Go To wasn't widely available on amateur telescopes. Nowadays, however, we have come to expect Go To with any high-end telescope mount.
Although my G-11 carries the Celestron name, it was manufactured by Scott Losmandy and his company, Hollywood General Machining. Celestron eventually began making its own German equatorial mounts, at which point Losmandy started selling the G-11 under his own Losmandy brand. Recently he added some high-tech brains to this workhorse mount and named it the Gemini System.
The Losmandy Gemini System provides Go To functions and a host of additional features for the company's current line of mounts, and it's also available as a retrofit for older Losmandy G-8, G-11, and HGM-200 mounts. Gemini transforms these mounts from utility tracking platforms into impressive Go To instruments with an onboard database of 41,000 objects, selectable and trainable tracking rates, and slew speeds of up to 10??per second on the smaller G-8 mount and about 6[degrees] per second on the larger G-11 and HGM models. I tested a retrofit kit loaned by the manufacturer for this review.
Converting to Gemini
Any mount retrofitted with Gemini should be in sound mechanical shape. Its motions should be smooth without any binding or sloppiness in its bearings. The Gemini retrofit uses the mount's original worms and gears; only the drive motors and electronics are changed. The stock stepper motors are replaced with high-torque DC servomotors.
Switching my mount's motors took me less than an hour. All the necessary Allen wrenches are supplied with the retrofit kit, and the only other tool I needed was pliers. While the retrofit works with the mount's standard worms, I took this opportunity to install optional precision worms (a $50-per-worm upgrade), which offer even greater tracking accuracy than the originals. The Gemini system has small gearboxes sandwiched between the mount's worm shafts and the new servomotors. Anodized aluminum covers give a finished look to the installation.
The new servomotors offer smoother tracking than the stepper motors, since they rotate in a continuous motion, while the steppers, as the name implies, turn in small, discrete steps. In the past when observing at very high magnification, I could easily see the start-and-stop stepping of the original drive.
The servomotors weigh less than the old stepper motors, but they protrude about 2 1/2 inches from the motor-mounting surface, which is 1 1/4 inches more than the originals. This wasn't a concern until I tried to fit the equatorial head back into its carrying case. The case lacks sufficient depth to seat the head with the servomotors attached. During the past decade my G-11 case has proved to be a rugged and convenient way to carry and protect the mount. It's too bad that it can't be used with the retrofit.
After installing the servomotors, I needed only to swap the electronic control panels to complete the retrofit. The Gemini panel is bigger, but not by much. It's the same width and thickness as the original but 2 3/4 inches taller. Nevertheless, it still fits in the original panel bracket on the tripod's center column. Gemini's control panel, like the one it replaces, is handsomely made from a milled, black-anodized block of aluminum. While the original motor cords used modular RJ-type plugs, Gemini has cords with DIN-type connectors on each end. Although Gemini can be controlled through a connection with a personal computer, all of its features are accessible through the supplied hand box without any additional accessories.
Powerful Features, Powerful Needs
Gemini's extensive software controls and Go To capabilities are powerful features, but they also require power, and lots of it. Gemini needs more juice than the original G-11 drives. It requires 12 to 18 volts DC from a source capable of providing a continuous current of 3 amperes. The original needed only 12 volts at 1/2 ampere.
During my field tests I found that it is the high-speed slewing that demands the most power, and this fails when there isn't sufficient power available. I suspected the hefty requirements when I unpacked Gemini's hardware and found the power cord to be a thick, 1/4-inch-diameter cable extending from a cigarette-lighter adapter. Gemini does not come with an AC power supply, though Losmandy does offer one as a $40 option.
My usual source of electricity in the field is an old lawn-mower battery, but it couldn't meet the demands of Gemini. More surprising, however, was that I couldn't get sufficient power from my car's cigarette lighter unless the engine was left running. With the engine off, Gemini's motors ran fine while tracking, centering objects in the eyepiece, and guiding, but they stalled whenever the mount attempted a Go To move. This wasn't an isolated problem with my car, since I had the same result with three different vehicles, one with a battery less than a month old. The problem was a voltage drop when there was high current draw through the cigarette lighter. With the car's engine running, the alternator kept the voltage high enough to allow Go To slewing.
The first solution I found turned out to be rather simple. I removed the cigarette-lighter plug from the power cord, substituted a pair of car-battery clips, and connected these directly to the battery terminals under the hood. Powered this way, Gemini ran fine. Another solution is to lower the slewing speed for the Go To operation, which is a separate setting than the one used to adjust the slewing rate for the hand-control buttons. By decreasing the slewing speed I was able to power the unit from the cigarette lighter without problems.
When observing in my backyard, where house current is available, I ran Gemini with a Radio Shack 3-ampere power supply that I purchased locally for about $40. It is the same unit that Losmandy sells for Gemini, and it delivers a regulated 13.8 volts DC. The motors never stalled during high-speed slewing while I was using this device.
A Gemini Test Drive
Gemini's list of features and operations is too extensive to cover in detail here. That's best left to the instruction manual, which is available to anyone for free as a downloadable PDF file from the Losmandy Web site, www.losmandy.com. Even when you purchase Gemini you must download the 106-page manual (a 838-kilobyte file). Without it, or at least the downloadable three-page "Quick Start" guide, a new Gemini user will be very frustrated trying to set up and operate the system. I printed out the manual and referred to it frequently as I learned Gemini's operation. It is very complete and gives detailed information about everything from Gemini's databases to fundamental explanations of the celestial-coordinate system of right ascension and declination.
When Gemini is powered up, the mount should be in its home position with the counterweight shaft pointed down and the scope aimed at the celestial pole. The most challenging aspect of setting up Gemini for the first time is using the hand control to navigate the system's extensive setup and feature menus. All functions are accessed with only five buttons. Frustrating is the best way to describe my first attempts at navigating the menus--so many features, so few buttons.
You access the menus by pressing the Menu and RA+ buttons, while their options are selected with the Dec+ and Dec- buttons. The RA- button serves as a back function, sort of like the Escape key on a computer. As I became more familiar with the system, the process of entering data and accessing information became quite easy and intuitive.
The Gemini control fits comfortably in your hand and has membrane-type buttons that help protect the electronics from dirt and moisture. The hand control is connected to the electronics panel by a 6-foot-long cable with 15-pin connectors at each end. The one-line LED display can be dimmed to a comfortable level for night use, but even at its brightest setting it's tough to read in daylight. The display is 16 characters wide, and any information that exceeds this scrolls across the display. The first and last characters are so near the edges of the display window that you sometimes need to tilt the hand control to read them.
The secret to Gemini's precision pointing capability is "teaching" it well. During the setup process it is very important that you center several alignment stars carefully in a telescope's reticle eyepiece (and make sure you identify the stars correctly!). Stars with at least several hours' difference in right ascension should be used, since alignment stars with similar right ascensions won't provide the alignment accuracy Gemini needs for optimum pointing. While you initially use alignment stars on one side of your local meridian, using additional stars on the other side of the meridian allows Gemini's software to reconcile any misalignments between the optical and mechanical axes and provides better Go To pointing accuracy.
The mount should be properly balanced. The Gemini servomotors have high torque and quickly accelerate to their maximum slewing speed, but any substantial imbalance can lead to motor stalling. Special attention should also be given to any wires attached to equipment on the telescope. If a wire becomes tangled and tugs on the mount, Gemini will stop slewing and report "motor stalled" on the hand-controller display.
There are several options for starting Gemini each night. A Cold Start is the method you use the first time you power up Gemini or when you move the mount to a new observing site. Cold Start prompts you to enter the Universal Time and the mount's longitude and latitude. You then work through a set of alignment stars. Once you're familiar with Gemini, the whole process takes about 15 minutes on average.
The Warm Restart option is selected when the mount has not been moved since the last time it was used, as would be the case for a telescope housed in an observatory. Gemini keeps track of the time with its internal battery-powered clock and retains in memory the mount's positional information of when it was last turned off. On many nights when I was finished observing I would simply switch off the power and put a waterproof cover over the scope and mount. By using Warm Restart the next night I could begin using Gemini right away without having to do a star alignment. Indeed, one afternoon I simply switched the power on, selected the Warm Restart option, and slewed directly to Jupiter in a daytime sky.
The third start-up option is called Warm Start, and it is for times when the mount has been stored since its last use but then set up in roughly the same location as before and polar aligned. In such cases a one-star alignment is all that's needed to get Gemini in sync with the sky again. Even so, if you use additional stars you'll further improve the accuracy of the Go To pointing.
Gemini has a nice feature if you just want to use the mount quickly without its Go To functions. You simply power up Gemini as an ordinary sidereal drive. The tracking, guiding, and centering motions still operate normally when you press the buttons on the hand control. Used this way there is virtually no learning curve. Furthermore, since you aren't using the Go To slewing with its high power demands, the mount will run off a small 12-volt battery. I used the mount this way to photograph a lunar eclipse, to make deep-sky exposures, and to show a group of kids Saturn's rings. This aspect of the Gemini system will be a welcome feature for longtime G-11 owners who want to use their mount continuously after a retrofit without substantial time lost while learning Gemini's features.
Gemini's stated pointing accuracy is 1 arcminute, and my experience showed that this is true for short Go To slews with objects on the same side of the meridian, but not for long slews from one side of the sky to the other, which typically had a pointing accuracy of 3 or 4 arcminutes. The best results came after I aligned the mount using a high-power reticle eyepiece and carefully centered alignment stars on both sides of the meridian. Having done this, I found that Gemini could point anywhere in the sky and always place my target within the 28'-diameter field of a 107x eyepiece on my 11-inch Celestron.
Other Smart Features
Gemini offers several drive rates, including sidereal, solar, lunar, terrestrial (drives off), trainable, and King rate, which is the best tracking rate for stars since it factors in the effects of atmospheric refraction. The trainable rate is for following moving objects such as comets and asteroids, and it is set either by short sessions of manual guiding on the specific object or by entering positional data and letting Gemini calculate the proper tracking motions.
There's also an Object Search feature for finding a target that does not appear in the eyepiece after a Go To slew. Gemini will initiate a search with an outward spiraling motion. Deep-sky observers may find the Wobble Object feature useful. It moves the telescope in a small Z-shaped motion on both axes, which often helps the eye perceive a faint object barely brighter than the background sky.
Gemini's onboard database includes the complete Messier catalog; 7,840 NGC objects; 5,386 IC objects; and nearly 18,000 stars. You can also enter additional objects into the database.
Gemini will work with the original G-11 hand controller, which is smaller and lighter than the Gemini controller, for manual guiding. The new electronics are also plug-and-play ready for SBIG's ST-4 and STV autoguiders, and they even use the same interface cord I had for the old G-11 drive. But you'll get an "autoguider" error if you try connecting directly to any of SBIG's autoguiding CCD cameras, such as the ST-7, -8, -9, or -10. These cameras require an optional relay box available from SBIG or a similar device sold by Losmandy. I tested Gemini with my ST-4 and found it very responsive. Calibration runs were more precise, and tracking generated fewer errors than I was accustomed to getting with the mount's old stepper-motor drives.
While Gemini's internal electronics keep track of where it's pointed, if you have separate shaft encoders on your mount (such as those used with various digital setting circles) Gemini will benefit from them. Just plug them into the encoder port on Gemini's panel and the electronics will automatically detect them. With encoders you can manually aim the telescope without Gemini losing track of its position. Without encoders, Gemini works only when you move the scope using the drive motors.
Gemini links to personal and handheld computers (via an RS232 serial port), which you can use to direct the mount to point at objects. I had no difficulties using Gemini with a desktop computer running Software Bisque's TheSky, but it also works with Guide 7.0 and Palm Planetarium. Gemini is compatible with Software Bisque's T-point, which is useful for refining polar alignment and providing precision Go To pointing.
The Gemini Niche
Should everyone using a Losmandy mount consider adding Gemini? That's a tough question to answer, and it depends on how you use your mount and whether it's hauled around or permanently installed. Go To pointing is certainly a big advantage for observers who spend the night moving from one object to another. The precision pointing is also a plus for astro imagers working with CCD cameras, since the system's accuracy will easily place faint objects on small CCD chips.
Although a Gemini-equipped mount is as portable as a standard G-11, the system is especially attractive for a permanent observatory where abundant electrical power is available. Gemini's accurate pointing and large onboard databases make the G-11 an impressive Go To performer. Those with permanent installations can easily take advantage of Gemini's quick Warm Restart routine.
As an amateur with only limited experience using Go To instruments, I was amazed by Gemini's capabilities and accuracy. Watching my old reliable German equatorial mount think for itself and cruise from one side of the sky to the other was something I never dreamed about when I bought the mount 10 years ago. I wouldn't have imagined that I could push a few buttons and watch my scope spend 40 seconds whirring from the galaxy M65 in the west and pointing directly at the Ring Nebula, M57, in the northeast.
Losmandy German equatorial mounts have a well-earned reputation for quality and performance. Couple that with Gemini's state-of-the-art electronics and you have a system that is ready to meet the 21st-century demands of observers and astro imagers.
Losmandy's Gemini System provides enhanced Go To performance for the company's line of time-tested German equatorial mounts. Gemini is available as a pre-installed upgrade with new mounts and as a retrofit kit for older mounts.
US Price: $1,595 (retrofit kit) $1,000 (upgrade cost when purchased with new mount)
<ADD> Hollywood General Machining, Inc. 1033 N. Sycamore Ave. Los Angeles, CA 90038 phone 323-462-2855 www.losmandy.com </ADD>
Losmandy's Gemini System
What we liked:
* Precision Go To pointing
* Easy retrofit
What we disliked:
* High power requirement
* Original storage case doesn't accommodate retrofit
After learning to navigate Gemini's menus, JOHNNY HORNE says that he is no longer intimidated by setting his VCR, digital watch, or any other high-tech device that has numerous features but few buttons.
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|Publication:||Sky & Telescope|
|Date:||Oct 1, 2003|
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