Sunday, August 15, 2010
The Sky on His Shoulders
The Atlas has been around for quite some time now, beginning life as a non-computerized German equatorial about a decade ago. Frankly, it was the first Chinese-made mount to impress western amateurs. It wasn’t perfect, suffering from less than good gears, but it was big and it was cheap and it was clear Synta intended to keep improving it, just as they had their smaller EQ-4/CG5 mounts.
In a remarkably short time, the Atlas was given a complete makeover, which included go-to via a new motor control board and a “SynScan” computer hand controller. Many of its former faux pas were corrected, too. The gears on the go-to version were much higher in quality than the old ones, and the weasel fat-based glue-grease slathered on ‘em had been replaced by a decent lubricant.
We amateurs noticed what Synta was doing with this mount, and before you could say “Jack Horkheimer” err… “Robinson,” the EQ-6 had become the choice for budget-conscious astrophotographers the world over. The EQ-6/Atlas developed a reputation for being one of the most trouble-free go-to GEMs available at any price for use in any amateur application. That’s what everybody said, anyhow. What did I think about the Atlas?
I didn’t think anything about it. I was perfectly happy with the Celestron CG5 I’d bought to replace the fork mount of my beloved 1995 Ultima C8 SCT, Celeste. That decision is a story in itself, but, to summarize, I was tired of not having go-to for my C8, I was tired of wrestling with an equatorial wedge for visual observing, and I was tired of contorting my middle-aged bod to find objects and view them with the wedge-mounted Celestron.
The CG5 worked out splendidly. I was gobsmacked at how good its pointing accuracy was, almost as good as that of my NexStar 11. No, it wasn’t in the Astro-Physics or even Losmandy league, but it was able to bring back some long-exposure deep sky images that made me happy. Why would I need another mount? That became clear one windy early spring night at the Chiefland Astronomy Village.
My usual astro-camera is not a long exposure CCD rig, but a deep sky videocam, my Stellacam II. It lets the C8 go insanely deep, and is pretty forgiving when it comes to tracking errors. I’ve been using the CG5 with the C8/Stellacam ever since I got the mount, and it’s proven to be quite adequate for that combo of scope and camera. “Adequate”? It’s usually fantastic. Not on the run in question, though. What started as a mild breeze wound itself up into genuine gusts of wind, and afore long my images were dancing all over the monitor. Removing the dew shield, which was acting like a sail, helped some, but not enough. Worse, even with the dew heater cranked up to ten, I had to shut down due to a soggy corrector long before I was ready.
Also, while I generally do my imaging with video, there are times I want to use a DSLR or my SBIG CCD, and three years ago was one of those times. I was finishing up a book, Choosing and Using a New CAT, and I needed pictures. Not just pictures, either, but my pictures. I’d sworn every astrophoto in the new book would be a genuine SCT shot, preferably done by me. While I’d got some OK images with the CG5 and my still CCD cameras, I decided a new GEM mount was in order in the interest of More Better Gooder.
Course, switching from the NexStar way of doing things to the SynScan way wasn’t all gravy. A lot of the features in the NexStar I’d come to take for granted are lacking in the SynScan. The Celestron HC, for example, includes an effective polar alignment routine. With the Atlas, you use the mount’s built-in polar alignment scope, just like the bad old days. Oh, well. I’d get used to it, I reckoned. The reduced feature set as compared to my CG5’s computer seemed worthwhile for such a solid mount.
So I was happy. Till I heard about the CGEM. It seemed Synta was putting together a new “EQ-6” for its Celestron brand. Not only was the EQ-6’s old Takahashi-EM-200-clone external appearance radically updated, the mount’s innards were changed, too. Synta swapped the EQ-6 stepper motors for servo motors, which allowed the SynScan hand control to be replaced by the fancier NexStar HC.
REacquainted? I hadn’t used the Atlas much since I put Choosing and Using a New CAT to bed. Why not? The CG5. It’s gone through numerous software revisions in the five years I’ve had it, and Celestron has turned it into one of the best working mounts it’s ever been my pleasure to use. Yes, I knew it could be a mite shaky under the wrong conditions, but it was so nice and light and easy to load and unload that that didn’t seem a bad trade-off for the longest time.
Then came a blustery eve on the PSAS (Possum Swamp Astronomical Society, natch) observing field, windy enough that I had to forget about imaging with the Stellacam and go visual, which was annoying. I got to thinking, “Maybe it’s time to give the Atlas another shot. Shame not to use the bigun. Sure woulda come in handy on a night like this.” I resolved the CG5 would stay home in favor of the Atlas for the next dark-site run.
When that night came, just a couple of weeks back, conditions were not encouraging. It was clear it was gonna be a sucker-hole-ridden hazy one at best. I decided to forget the Stellacam. It would have been tempting just to lug Charity Hope Valentine, my ETX125, out to the club site, but I’d resolved to get the Atlas going again, and that I would do. But not with a computer and EQMOD. I’d keep it simple. I wanted to try out the SynScan HC, anyway. I’d never used it under a decent sky, and despite updating its firmware as new releases had come out, I’d used it exactly twice in the near three years I’d had the mount.
I always hope to be pleasantly surprised on these iffy evenings: “Hell, all of a sudden, the clouds blew off and the Milky Way started burning.” Sometimes that actually happens. Not on this night. It started out cloudy, hazy, and humid and stayed that way. Until it got worse. At sundown it did look good enough to get the Atlas and C8 aligned, so I proceeded to do so.
With dark coming and the sky looking at least passable, I fired Atlas up. Not that I was ready to start the go-to alignment yet. I’d have to polar align the thing first. Turning on the Atlas illuminates the polar scope crosshairs and (after some data entry) displays the current Polaris Hour Angle on the SynScan.
The wha? Unlike the NexStar, there’s no polar alignment routine in software to help get the GEM’s right ascension axis pointed at the North Celestial Pole. So, you’ll use the mount’s polar alignment borescope. There are a couple of ways to do that. Easiest, though least accurate, is to just move the mount in R.A. till the pictures of the Big Dipper/Plough and Cassiopeia on the polar scope reticle match the approximate positions of the constellations in the sky. After that, you move the mount in altitude and azimuth to put Polaris in a little circle on the reticle and you are polar aligned. Sort of, anyhow. Almost as easy, and considerably more accurate is using Polaris’ Hour Angle.
The rest is easy. Look through the polar scope and adjust the Atlas in altitude and azimuth (not R.A. and declination) using the bolts and knobs on the mount head until Polaris is centered in its circle. Voila! You are decently polar aligned. Not as easy, maybe, as the computerized Nexstar procedure, but not bad, and good enough for me.
Possible complications? If you use a long-tube scope, you may want to remove it during the polar alignment procedure, as positioning the reticle properly may put the tube in positions where it will bump into a tripod leg (you must keep the tube perpendicular to the polar axis, at declination 90, to use the polar borescope). Also, some folks worry about the altitude and azimuth adjusters, as they seem awfully hard and sticky on some mounts.
Then there is altitude, which, as is the case with most GEMs, is adjusted by alternately tightening and loosening forward and aft “latitude” bolts on the mount head. The secret to moving the mount in altitude without busting a gut? Loosen the forward bolt and adjust only with the aft bolt. If the mount doesn’t want to go down when you need to go down, just a little downward pressure on the counterweight bar will ease things along. Apply firm, even pressure when raising the scope in altitude and don’t use a cotton pickin’ pair of vice grips. Too much force and you can bend the bolt. It’s not needed anyway. If “up” seems too hard, remove scope and counterweights (in that order) during polar alignment and you will be in like Flynn.
So you are polar aligned with the polar scope. Do you need to drift align? Probably not. Not unless you are a much more serious astrophotographer than I am. An alignment with the Atlas’ polar scope allows me to do 3-minute integrations with my CCD camera and my C8 at f/6.3, and that is all I need. If you are just observing visually, don’t even worry about adjusting the polar scope’s reticle and figuring out hour angles. Just center Polaris in the borescope. Admittedly, the closer you are to the pole, the closer the mount will come to the first go-to alignment star, but that’s all. Oh, if you insist on doing a one or two star go-to alignment instead of a three-star, a close polar alignment will help with pointing accuracy.
How about go-to alignments? In this area, the Atlas is, again, a little more primitive than the NexStar, but is completely adequate. These days, you align a Celestron GEM on as many as six stars, which ensures excellent accuracy all across the sky. SynScan? It is where the NexStar was several years ago. Unless you have a dead-nuts-on polar alignment, you do a three star go-to alignment, which consists of two stars on one side of the Local Meridian and one on the other. This third star is the “cone alignment” star. Centering it up allows the computer to take any mechanical misalignments present into account.
One thing I’d been told and had found out for myself in my two outings with the SynScan HC was that, unlike with the NexStar, you are wise not to blindly accept the first alignment stars the HC comes up with. Instead, use the SynScan’s up and down keys to select the best candidates. The first two stars should be fairly far apart in azimuth, up to 60-degrees apart, and not too close to the horizon. Certainly no closer than 15 degrees or so. MOST importantly, star 1 and star 2 should be separated by several hours of right ascension. That appears to be critical for go-to accuracy. Star 3 should be between either declination +30 and +70 or between declination -30 and -70--in other words, not too close to the poles or the celestial equator. Like stars 1 and 2, it should not be close to the horizon, either. The Atlas manual does a good job of explaining the requirements for alignment stars, so read it. A couple of times.
My problem on this poor night in Tanner – Williams, Alabama was finding three stars in the clear that fit these requirements. The number of possible alignment stars the SynScan allows you is fairly limited, too. I just did the best I could. Star one was about a degree out when the slew stopped; stars two and three were right on the edge of the center ring of Celeste’s Telrad, which I habitually use for alignment instead of her 50mm finder. “Alignment Success” Atlas said. We’d see about that.
M13, which was close to culmination, almost straight overhead, would be a good test, as many go-to systems tend to have trouble with stuff up in Dobson’s hole. I punched in “M13” (at least SynScan doesn’t demand you enter “M 013” like the NexStar). In due time, the HC beeped and I stuck a 20mm Expanse eyepiece in the diagonal—yeah, I was really going minimalist on this evening. There was M13, on the edge of the field at f/6.3, but in the field nevertheless. I then essayed a walkabout of the midsummer sky, visiting everything from Lyra in the east to Virgo in the west. Anything I requested was somewhere in the field of the 20mm, and often in the field of a 9mm Expanse.
Just as I was contemplating having a look at Ursa Major’s Messiers, the sky began to close down. It was pretty clear it was time to start thinking about packing up, even though it wasn’t quite 11pm. The sky wasn’t going to get any better any time soon, and had the look of incipient “much worse.” An old Moon would be on the rise before long, anyhow.
Alrighty, then. I lugged Atlas’ head back to the Toyota. It is, at close to 40-pounds, considerably heavier than the CG5. It didn’t feel that way, though, and packing up for the drive home was a breeze. Maybe because the Atlas is less awkward than the CG5. You can retract the counterweight shaft into the body of the mount, and there’s no external declination cable to snag on anything or cheesy plastic motor covers to worry about. For good or ill, the tripod is almost identical to the one shipped with the CG5, so that is not a factor.
Verdict on the mount’s go-to capability with the hand control? If you choose alignment stars carefully, the SynScan’s accuracy is on a par with that of the NexStar HC, despite the fact that it is limited to a three-star alignment. While the extra cone stars the NexStar HC allows you to use supposedly improve pointing accuracy, the SynScan seems just as good at object finding. Need more better gooder? Use the EQMOD program instead of the SynScan controller, and you can center on as many alignment stars as you need, which can, potentially at least, deliver arc second level pointing accuracy.
OK, then. It sounds like the SynScan is good but EQMOD is better. How does EQMOD fit into the Atlas story? I’d intended to tell y’all, but we are utterly out of space for this morning, and that will have to be a story for another Sunday. Cain’t wait? I did a pretty complete review of EQMOD in the December 2008 issue of Astronomy Technology Today magazine. Don't have that one? Individual back issues are not available at this time, but a mere 30 bucks will get you ALL the back numbers, which I call a b-a-r-g-a-i-n.
Anyhoo, where things stand with the Atlas now is that I have at least provisionally demoted my CG5 to “backup GEM” status. We will see how the Atlas/EQMOD does with the Stellacam II and the Herschel Project when I finally get some clear and dark skies, but I think I am gonna be one happy camper with the combination. You’ll know how that went soon after I do, muchachos.