The Sky-Watcher EQ6 Mount.
IT WAS ALMOST 400 YEARS AGO THAT Galileo first aimed a telescope skyward, and ever since, observers have been devising imaginative ways of mounting astronomical telescopes. In 1824 German instrument maker Joseph Fraunhofer introduced what is now known as the German equatorial mount, which allowed telescopes turning on a single axis to track the motion of stars and planets across the sky. By the early 20th century equatorial mounts dominated. Then came the Dobsonian revolution of the 1980s and the revival of the long-neglected altazimuth mount, which was elegant in its simplicity though it required motion on two axes to follow stars. The equatorial's dominance further eroded in the 1990s with the introduction of computer-controlled telescopes that gave altazimuth mounts motorized tracking, once the exclusive domain of the equatorial mount.
While many observers, both serious and casual, have succumbed to the obvious delights of computerized telescopes, there remains a significant demand for the workhorse German equatorial mount. This is especially true among amateurs who are pursuing astrophotography, since altazimuth mounts are incompatible with long-exposure imaging because the field of view rotates as the telescope tracks across the sky.
Finding myself in the market for a new mount, I was very interested to hear that Synta, the Chinese manufacturer of the Sky-Watcher EQ5 mount supplied with many imported telescopes, was bringing a considerably more substantial German equatorial mount to the marketplace. When word spread that this new Sky-Watcher EQ6 mount could handle telescope tubes weighing about 55 pounds (25 kilograms), came with dual-axis motor drives, and was going to cost about US$1,000, I became even more interested. But the obvious question was: Would it live up to expectations?
The Sky-Watcher EQ6 is currently available from several suppliers in the United States and Canada, but for this review I borrowed one from Astronomy World, a telescope retailer based here in the United Kingdom. The mount arrived last January, and I quickly discovered that the right-ascension drive was faulty. At first I thought I was doing something silly, so I checked that the manual clutch engaging the drive to the telescope's polar axis was firm. I also removed the side cover on the declination-axis housing, which revealed a tidy circuit board, two motors, and two gears. These motors and gears rotated and changed speed as I pressed buttons on the hand controller, so I surmised that the drive's main worm gear was not engaging. Unable to proceed further, I contacted the people at Astronomy World, who quickly arranged to get me a replacement unit. The new EQ6 worked fine.
After this unfortunate start, my first impressions were otherwise favorable. Assembling the mount proved to be very simple. The extendable tripod is robust, weighing 17 lb (7.5 kg) with legs made of 2-inch-diameter stainless-steel tubing. The legs are held rigidly in place by a tray that doubles as an eyepiece holder with openings for five 1 1/4- and two 2-inch eyepieces. With the legs retracted the tripod is 29 inches (74 centimeters) tall, which puts the EQ6 head at a good working height for a Newtonian telescope. It also affords maximum stability. With the legs fully extended the height is 50 inches (127 cm).
The EQ6 head weighs 36 lb (16 kg) and fits into a circular recess on the tripod. It can be positioned with the declination housing either directly over a tripod leg or between two legs, depending on the observer's preference, and it is fixed to the tripod with a single hand bolt. After attaching the head to the tripod I roughly adjusted the elevation of the polar axis using the latitude scale on the side of the mount as a guide, extended the counterweight shaft (which stows neatly inside the hollow declination shaft when not in use), and added the two 12-lb (5.3-kg) counterweights. I then plugged cables for the hand controller and power source into their respective sockets on the side panel. Last, I attached an 8-inch f/6 Newtonian reflector, which I had previously fitted with a dovetail plate that comes with the mount. I was up and running in 15 minutes. Furthermore, I found the EQ6 to be very comfortable to lift, even complete with its counterweights and my telescope attached--I had no trouble maneuvering the whole lot around my garden without once straying into the pond! Anyone who is reasonably fit and has suitable storage space could leave the mount set up and simply carry it outside for use.
It was at this point that I noticed there was no bubble level on the mount. Its absence led to the obvious quandary of how to polar align without a level mount. I dismantled everything and started again, this time using a small spirit level and adjusting the individual legs until the top of the tripod was level before I placed the EQ6 head on it. While not ideal, the procedure worked fairly well.
Heading Toward the Pole
The EQ6 has a polar-alignment scope inside its hollow polar shaft. This small scope has a reticle with etched crosshairs indicating the shaft's axis of rotation and a small circle for Polaris (for use in the Southern Hemisphere there are circles for four stars in Octans). In principle you achieve polar alignment by positioning the mount so that Polaris falls within its circle. Before attempting this, however, I decided to check the centering of the reticle by aiming the mount so that the crosshairs were pointed at a distant tree and rotating the polar shaft. The crosshairs should have remained fixed on the tree, but instead they traced a small circle about 15 to 20 arcminutes in diameter. Fortunately, I could adjust the reticle's centering via three small Allenhead screws, but another problem then arose.
Many mounts that use polar-alignment scopes, such as the Vixen Super Polaris or the Sky-Watcher EQ5, have dials that help you set the proper rotation of the polar shaft, depending on the date, time, and your longitude. This is so that the reticle circle for Polaris will be correctly positioned relative to the celestial pole. Normally this is an elegantly simple procedure, but not so with the EQ6. The mount I tested had a small dial on the polar scope with 12 marks (months?), but the only other "dial" was the right-ascension setting circle at the opposite end of the housing. I looked to the mount's instruction sheets for guidance, but they appear to be a work in progress and make reference only to polar alignment for "casual" observing, which isn't as rigorous as that needed for imaging.
After a little experimentation I managed to work out a method for rotating the polar shaft to have the reticle oriented with reasonable accuracy. One solution involves attaching an additional scale to the mount, and there are instructions for doing this on the EQ6 discussion forum of Yahoo! Groups (http:// groups.yahoo.com/).
With the reticle positioned, I iteratively adjusted the altitude and azimuth of the polar shaft using four fine-motion bolts on the EQ6's head until Polaris was in the center of the reticle's circle. This process would have been considerably easier with an illuminated reticle, which the EQ6 does not include. You can work around this by aiming a flashlight into the objective of the polar-alignment scope, but holding a flashlight while trying to look through the polar scope and adjust the alignment bolts is not fun. Given the space and electrical power available inside the mount's declination housing, a do-it-yourselfer could illuminate the reticle by mounting a small light-emitting diode (LED) in front of the polar scope's objective.
With the scope polar-aligned, I engaged the conveniently located clutches on the right-ascension and declination axes and powered up the mount. The EQ6 comes with a flimsy plastic battery holder made for eight D cells. I chose instead to supply the 12-volt DC power by means of a small wall transformer with a current rating of 500 milliamperes.
The hand controller has a power switch that you use to select Northern or Southern Hemisphere operation. Another switch selects the speed for the four direction buttons--2x (for guiding) and 8x and 16x (for slewing). There is a small LED that glows green when the mount is tracking but changes to red when you push any of the direction buttons. The hand controller is connected to the mount with a telephone-style jack that locks in place with a satisfying click.
Go Silently Into the Night
The great surprise of my first night with the mount was the wonderful quietness of the drives. They are all but inaudible. I heard the occasional click of a relay when the motors stopped, changed direction, or started, but otherwise the drive betrayed itself only by a muted whirring when slewing at 16x. This was a far cry from the coffee-grinder impressions done by some popular Go To mounts.
Gear backlash in the EQ6 was taken up in less than a second at 16x, and the response to button presses on the hand controller was smooth and prompt. To test the drive's accuracy, I pointed the telescope at a moderately bright star and used a CCD camera to make a series of seventy-five 1-second exposures separated by 10-second intervals. Later, I measured the star's apparent position on each of the frames and determined that the drive's periodic error was between 10 and 18 arcseconds. This error took the form of a sharp change in star position followed by a slow and bumpy return to the original position over a period of roughly 125 seconds.
For another test I took twenty 20-second exposures with a Starlight Xpress CCD and the 8-inch f/6 reflector. Of these, only eight frames were untrailed at an image scale of 2.1 arcseconds per pixel, and several of the frames clearly showed evidence of sharp movements during the exposure. With 12 of the 20 frames trailed, the failure rate was three times what I typically encountered with a Vixen Super Polaris mount used in similar circumstances. This level of drive error generally would not affect casual visual observing or piggyback astrophotography with camera lenses. But CCD users shooting unguided exposures through telescopes would need to be prepared to throw away a good fraction of their images.
Although the EQ6 is new, there are already several third-party companies producing drive controllers for the mount. Several of them, including one from Baader Planetarium in Germany, are advertised as offering periodic-error correction as well as compatibility with CCD autoguiders (which the standard controller for the EQ6 does not support). Even so, a far better solution would be if Synta simply improved the smoothness and accuracy of the EQ6's drive.
So what do I think? Realistically, the EQ6 doesn't quite hit the mark. The axes move nicely on the ball and roller bearings, the tripod is very rigid, the construction satisfyingly robust, and the mount is easy to use. I suspect it is stable enough to cope with all but the heaviest 12-inch telescopes. But to realize the full potential of the EQ6, Synta will need to improve the drive gears, add a bubble level, and sort out the issues with the polar-alignment scope. If that is done, then I suspect the mount will become a great success. I would certainly be happy to pay an additional $50 for an EQ6 that tracks more reliably than the model I tested. In the meantime, I classify the EQ6 as a German equatorial mount that is entirely usable for visual observing and wide-angle photography but probably not the mount of choice for astrophotographers who enjoy shooting with long-focal-length instruments.
What we liked:
* Robust but portable mount can support telescopes weighing up to 55 pounds
* Ball- and roller-bearing construction throughout
* Dual-axis drives are standard
What we disliked:
* Periodic error too jumpy for unguided CCD imaging
* Drive controller does not accept autoguider input
Sky-Watcher EQ6 German equatorial mount
U.S. Price: Around $1,000
Sold through dealers worldwide; for one near you contact:
<ADD> Pacific Telescope Corp. 160-11880 Hammersmith Way Richmond, BC V7A 5C8, Canada Phone: 604-241-7027 www.skywatchertelescope.com </ADD>
GRANT PRIVETT is generally found observing (or bemoaning the lousy weather) near his home in Herefordshire, England. He can be contacted at email@example.com.
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|Title Annotation:||Synta's new Sky-Watcher EQ6 German equatorial mount; S&T test report|
|Publication:||Sky & Telescope|
|Article Type:||Product/Service Evaluation|
|Date:||Oct 1, 2002|
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