Sunday, June 22, 2014


Good Old CG5 (and a Little RSpecing)

Plenty of y’all liked the Celestron CG5, muchachos; even members of the “An A-P Mach 1 is the minimum mount for astrophotography” crowd admit it was a pretty good little GEM (German Equatorial Mount) for very little money. But it still doesn't get all the credit it deserves. Mainly for being the mount that gave plenty of near-cast-off 1980s and 1990s SCTs a second lease on life.

Howsomeever, I come here not just to praise the CG5. No matter how fondly we remember Celestron’s first popularly priced go-to GEM—it was superseded last year by the new VX—it was not perfect. Not hardly. And reviewing some of those imperfections may help elucidate the situation regarding the VX, which—surprise—ain’t perfect either.

The GEM we know and love as the CG5 wasn’t actually Celestron’s first CG5. By the mid 1990s, the company was selling Chinese clone copies of the Vixen mount formerly sold with the Great Polaris C8, which was the follow-on from the company’s earlier C8 + GEM configuration, the Super Polaris C8. The GP C8 was popular, but it was only popular at a price point around 1000 dineros. With Vixen gaining popularity at the time and increasing prices out of all reason, that price point was impossible for Celestron to maintain.

Enter the CG5. The initial CG5 looked a lot like what we think of as a CG5 today sans motor housings and an electronic control panel. No go-to for this 90s GEM. You could, however, order it with a pair of bolt on Chinese motors that provided tracking and slow motion/guiding via a dual axis HC that ran off D batteries. Superficially, it looked a lot like a Great Polaris down to the D battery bag with its silly little “purse” handle.

Appearances often deceive in the import scope biz, however, and the CG5 was no exception. It was OK, mind you, especially if you took the time to clean out the Chinese glue-grease (made of ground up weasels, apparently) and relube it. Unfortunately, though, it didn’t have ball bearings. Plastic sleeve “bearings” were on both axes and that limited the mount’s performance potential. My long-time observing companion Pat Rochford had one of these proto CG5s for a while, which he rigged up with the Mel Bartels home-brew go-to system, and while his mount  worked, it just barely worked.

When Celestron announced a go-to configurated CG5, the “ASGT” CG5 (Advanced Series Go To), I was appalled. Given my experiences with Pat’s CG5, I couldn’t believe this would work reliably, not unless major improvements were made to the mount.

Celestron (and Synta, the mount’s Chinese maker, who was soon to own Celestron) knew that, too, and had made improvements. The glue grease was gone. While the bearing situation on the declination axis was unchanged, there were now ball bearings on RA. The mount was also somewhat (if not a whole lot) better finished. The bolt-on motors had been replaced by servos in plastic housings. The non-goto CG5’s dreadful extruded aluminum tripod was trashed in favor of a hefty 2-inch diameter tubular steel-legged job. Maybe most importantly, go-to was furnished with a standard Celestron NexStar HC, which was getting better all the time.

Unk was still skeptical but not immune to the ASGT’s charms. I had been spoiled by the goto on my NexStar 11 GPS, which I got in 2002, and it was getting ever harder to make myself use my old fork mount Ultima C8, Celeste. Which was a shame. She had good optics, especially by the standards of the mid 1990s. Didn't matter. I was over polar-aligned fork mounts. I had had enough of navigating the sky with finder, Telrad, analog setting circles, and freaking Sky Atlas 2000.

Anyhow, it sure would have been nice to have a go-to rig a little lighter than the NS11. There was the non-GPS NexStar 8, but that telescope and the similar NexStar 5s I’d tried left me cold regarding their so-so go-to accuracy. Howzabout a NexStar 8 GPS? Unk, stingy then as now, didn’t want to pony up that much cash.

Hokay, I’d get me a cotton-picking ASGT CG5.  Just the mount. I’d defork the Ultima 8 OTA, and give it a whirl. If I decided I liked using a C8 on a goto GEM, I’d put the CG5 on Astromart and get a good goto GEM. A Vixen or a Losmandy or sumpin’. I was sure the CG5 wouldn’t have the go-to chops to keep me happy.

My purchase of a CG5 was not without incident—Unk’s astro-gear purchases never are. On its way to me from Anacortes, Washington in the spring of ought five, the UPS truck it was in crashed and burned on the Interstate--or so I was told, anyhow. Anacortes Telescope and Wild Bird got another one on its way to me promptly, however, and the delay gave me time to figger out how to get the C8 off her fork and equipped with a dovetail. It turned out that wasn’t much of a task. Removed some screws, and the Ultima 8, Celeste, was free of her old-timey mount. A few dollars to Scopestuff for a dovetail and maybe 15-minutes attaching it to the tube and we was ready to go.

As I have told y’all before, I was gobsmacked when I got the C8/CG5 combo into the backyard. I hadn’t expected much in the way of goto accuracy; nevertheless, after a simple three-star alignment, the mount placed anything I requested smack in the field of my 12mm Nagler. The hand control operation was identical to that of the 11 GPS, and Unk just fracking zoomed around the sky. The first night, anyway.

The second night? That was testimony to the split personality of the CG5. After my success at first light, I was anxious to give the mount a second night in Chaos Manor South’s backyard (which in the early spring of 2005 still had enough openings among the trees to allow me to see a few things). Started the alignment, the scope headed for star one, and kept right on going past it till I killed the power. “Well, hot damn. Dadgum thing lasted all of one night!”

The declination axis seemed to be the problem, so I opened up the motor housing. All seemed well. I put it back together and hit Chaos Manor South’s kitchen computer for a look through the archives of the (already burgeoning) ASGT Yahoogroup, which I’d joined when I first ordered the CG5. I was swiftly edumacated about one of the mount’s Achilles’ heels, POWER.

Seemed as this was one power hungry sucka. I was accustomed to getting two nights (partial nights, anyway) out of the NS11’s battery without charging it. That, I read, was not going to be the case with the CG5. If you didn’t start each evening with a fully charged batt’ry you was in for t-r-o-u-b-l-e. There was also the mount-side power connector. The center pin of which was composed of two halves that apparently never made good contact with the power cord’s connector.

The simple solutions, I read, were to charge your battery, natch, and use a knife or jeweler’s screwdriver to gently spread the pin halves a mite. I did both things and hoped for the best on night three. I was rewarded with sterling, nearly unbelievably good, performance. It is no exaggeration to say I saw more with the C8 in the first year it was on the CG5 than I had with it the previous ten years. Celeste went from being a bench warmer to being my most used scope again.

So the goto was good. How about tracking? Not bad, not bad at all. Now that I had a manageable C8 on a go-to mount, I decided it was time to try that electronic imaging bidness again via the inexpensive Meade DSI. When I used the NexStar HC’s built in polar alignment procedure (the old pre-AllStar one that had you center Polaris), I could easily get decent unguided 30-second sub frames I was able to stack into nice finished shots. When I moved up to a big-boy cam, an SBIG ST2000, I could do 10-minute self guided shots without much hassle.

DSI Dumbbell
As always, when it came to the CG5’s nature there was a good angel and a bad angel, however. Yes, the scope could guide well (some users had problems with stiction in dec guiding, but I never did). BUT… only if you were properly balanced, a little east heavy that is. Ignore that and you would get trailed stars. Move to a different position in the sky, maybe closer to the horizon, where your balance was not so hot? You’d get star trails again if you didn't re-balance. A pain in the butt, yeah, but manageable considering the mount’s 800 buck price tag.

I loved doing visual observing with the help of the CG5’s wonderful goto system, but that wasn’t perfect either. Those of y’all used to Celestron’s current GEM mounts, the VX, the CGEM, etc., are more than familiar with the 2+4 alignment method. Align on two stars, add (up to) four calibration stars, and your gotos are crazy good all over the sky. But did you know ‘twarn’t always so? That the original CG5 didn’t have no calibration stars?

What it had was a three-star alignment like the current SynScan mounts. That was OK, but, as with the SynScans, you had to be damned careful about your alignment star choices. As I found out during the mount’s first visit to the Chiefland Astronomy Village. That was, I recall, in the spring of 2006, and on the first night, things didn’t go as I’d hoped. As usual, I just accepted the three stars the alignment routine offered. Now for some Virgo galaxies! Alas, anything I slewed to was on the hairy edge of a low power eyepiece or just outside the field.

Standing on the crowded observing field looking up at the rising Realm of the Nebulae (Galaxies) with Pat Rochford, I thunk and I thunk. “Hmmm…the first two alignment stars shore were low on the horizon.” I powered down, did another three-star, and rejected the first stars the HC offered, selecting a pair a little higher up. BAM! Anything in the Virgo cluster was well within the field of my 12mm Nagler eyepiece again.

These were early days for the CG5, and Celestron was continuing to work on its HC code, so I figgered there would be improvements. I also knew those improvements would come at a cost. The original CG5 HC, you see, just like the original NS11 HC, was not upgradeable. Want improved firmware? That meant a new HC at worst or sending the controller back to California at best. Luckily, by the time I got my mount, Celestron had fixed the worst faux pas in the CG5 code—which caused runaway slewing during gotos and guiding.

A cold CAV January, 2009...
As I’d hoped, Celestron soon came out with a user-programmable hand control, and the improvements in the CG5 firmware began to come thick and fast. Some were a godsend, like the 2+4 alignment routine, others, like AllStar, took a while to catch on with me. While I usually ran the mount with NexRemote, I nevertheless bought a new “Version 4” programmable hand control for those times when I didn’t want to tote a computer. The 2+4 alignment was so good that after that firmware upgrade (version 4.10), I never used the original hand control again.

Finally, about five years in, another notorious CG5 problem bit Unk. The mount’s control panel was small and the power switch was correspondingly tiny. It was also crappily made. I have never heard of a CG5 switch that’s lasted more than five years.

Luckily, I knew what to do when the switch failed on me. Power light wouldn’t come on. HC was dead. I unplugged from the battery and exercised the switch mucho times. Plugged the power cord back in, turned the switch on and the power came up.  I knew it wouldn’t last, though. Once that little switch went, it was a gone pecan. The answer—if you were lazy like Unk and didn’t want to replace the switch—was to leave it in the on position and turn power on and off by plugging and unplugging the cord. Not elegant, but it worked and still does.

Yeah, the CG5 was a great mount but it wasn’t perfect now matter what old timers like Unk “remember.” The new VX is considerably better in comparison. The CG5’s corners have mostly been rounded off. That nasty little power switch and iffy connector have been replaced. The finish of the mount is mucho bettero. It’s even a little quieter than the CG5, which as I have said more’n once sounds like a weasel with tuberculosis when slewing at high speed.

None of which makes me or the other folks who’ve received a bum VX feel much better, of course. As I related here, my initial mount head had improperly threaded holes for the declination shaft’s toe-saver and, fatally, for the tripod’s threaded rod. Bolted mount to tripod and that central bolt locked forever.

The up side, however, is not just that my replacement mount was perfect, but that us VXers didn't have to live through the travails of the CG5’s early adopters:  runaway slews, punk alignments, slow boat gotos to nowhere, and more. The VX has had a few problems, but its introduction has been a helluva lot smoother than that of the old reliable CG5.

The CG5 did mature, however, at least vis-à-vis the hand control and its firmware (mechanically the mount never changed much over its lifetime). In the end, the CG5 became a SOLID performer. But what’s it like to use one today, in this day of the VX and the innovative mounts coming out of places like iOptron? Unk thought he would find after not giving the CG5 a real workout in over a year. I’d had it out a few weeks back for some casual videoing, but I didn't take much care with the alignment or try to determine how it compares to the Victor X-ray. I also thought I might kill two chirpers with one rock.

I last reported on RSpec and the Star Analyser diffraction grating in January. Your old Unk was just on the crux, he thought, of learning the difficult art of astronomical spectroscopy using these excellent tools. RSpec is the software that allows you to acquire and analyze stellar spectra ; the Star Analyser is the 1.25-inch filter-like diffraction grating you screw onto your camera to turn stars into rainbows.

I was beginning to make progress, but then some things intervened. Mostly, the weather. As I don’t have to tell my fellow Southrons, it was a crazy-cloudy winter and early spring south of the Mason Dixon line. I got out a few times, but only a few, and the only really successful outing over those long months was at the 2014 Deep South Regional Star Gaze Spring Scrimmage, where I was busy wrapping up the reimaging of some Herschel Project objects.

Now that June’s here, the skies have improved, though they are not perfect—that would be a lot to ask for on the Gulf Coast with summer coming in—and at the New Manse I can now observe from my backyard. There’s light pollution, and, worse, it’s been continually hazy, but that didn't hurt my lunar imaging none, and I didn't expect it would stop me from RSpecing either.

Setup last Saturday night was a leetle different. As I’ve mentioned previously, my best view of the sky is near the deck. I plunked the CG5 tripod down there, positioned a little table on the deck for my laptop, and put all the pieces together:  Celeste on CG5, flip mirror in rear port, ZWO camera on flip mirror. Hooked the mount to the laptop via the NexRemote cable and got ready to rumble.

Need it be said that Uncle Rod’s observing runs do not usually go smoothly? My problems on this evening had nothing to do with the CG5, howsomeever. I had to pick a few alternate alignment and calibration stars due to trees, but that was it. Last cal star was near the center of my old Meade 12mm reticle eyepiece when the slew stopped. Polar alignment (via Polaris; stars to the south that would be good for AllStar are currently blocked by a tree) was a breeze. My last calibration star was Vega, so I left the mount sitting there. RSpec’s author, the talented Tom Field, advises you to begin with Vega when you are just learning, since it has a very prominent h-beta line, and is easy to “calibrate.”

I had used RSpec several times before, so I shouldn't still be “just learning,” but I had a sneaking suspicion I would be anyway. Too many months without using the program left me foundering. “How do I get it to connect to the ZWO camera? How do I set the exposure? Where do the files go?” I fooled around and fooled around, locked things up a time or two, restarted a few times and finally got back in the swing of things. Did a couple of .avi sequences of Vega, and moved on to Arcturus, Spica, and Aldebaran.

What’s it like using the CG5 in lieu of the VX? It ain’t that much different, y’all. Certainly the CG5’s goto is every bit as good. It was routinely placing stars on the tiny chip of the ZWO planet cam at f-freaking-10. Otherwise, about all I noted was that the mount does have more declination backlash than the VX. Reverse declination directions, and it can take quite a while for the mount to start moving. Not at all unmanageable, but worse than in the newer mount. Oh, and it’s definitely louder than the Victor X-ray. My new next-door neighbor stuck his head out mid-evening, no doubt wondering what that weird whining noise was.

Last star in the can, I retired to the den to watch the remainder of Svengoolie, who was showing a good one—Evil of Frankenstein—after a long dry spell.  A little Yell and a little Hammer horror and it was soon well after midnight and time for some shut-eye. As always, I didn't even peek at my images; that would wait for morning.

Sunday morning, I did yet more fumbling on the way to getting my spectra calibrated (converting pixels to angstroms, that is), but I got ‘er done despite the fact that during our move I lost the RSpec cheat-sheet I’d made up. I still have a long way to go with spectroscopy and I am starting all over, but Vega, from what silly old Unk can tell, is my best spectrogram yet. RSpec was great. The Star Analyser was great. The ZWO was great. But what was the greatest despite its few blemishes was my wonderful old CG5. Long may she wave, muchachos, long may she wave.

Next Time: Revenge of the Return of the Denkmeier… 

nice article Rod, I still use my old Super polaris mount. its not goto but the setting circles work well with a level mount [imagine that ], the polar scope gives decent alighnment adjusting for the present date and the tracking unguided is good for first 4-5 minutes.... no computer, no xs cables , just plain old analog technology at its best. regards Howard
Thanks to your books and blogs, I bought a CG5 for an early 2080, added a set of wheels, and am very pleased. Thanks for your expertise and writing style.pp
I really enjoyed the information on how the CG mounts evolved. Sometimes "deals" come up on the resale market. This information is helpful in evaluating these mounts.

Tom Wall
I bought a CG5-ASGT last October. I never knew about your blogs until this past spring. I went on the assumption that is was a good goto mount based on some CN reviews. I like my CG5. I always do 2+4 stars for aligning and calibration. Most of my slews bring the object into the field of a low power ep. I know the sky very well and if the object is out of the fov, I can usually find it without too much trouble.

I like your blogs, just wish they were more frequent.

Waltham, MA
Great entry as usual. Question for you...your go to dealer (and my local shop) has a used CG5 ASGT for 349 clams. Should I jump on it or save my dollars for th AVX?
What kind of shape is it in? That's a damned sweet price...
I'm going up tomorrow and talk to señor black. It looked pretty good but I didn't play with it. Bob might let me take it home and try it out
Hi - I am looking at a used $500.00 Advanced CG5 vs a Celestron VX at $719.00

Any suggestions?
Get the VX...think it's worth the extra money.
There is not much difference between the ASGT and the AVX, I have owned both.

The AVX has a USB port instead of serial port, is just slightly quieter, and has some extra aux ports which probably won't get used. The fit and finish is a lot nicer than the ASGT and the plastic covers feel a lot more solid. For $350 the ASGT is a great deal. If you can swing the price of the AVX go for it, it IS a bit nicer, but there is not really much difference in performance. I would not feel bad for choosing a $350 ASGT over a $800 AVX.

I definitely would not pay $500 for an ASGT though... $400 max if it's in perfect condition.

ASGT and AVX are light and reliable.

Here are the differences:

AVX has a nice screw on polar scope cover. The ASGT version always falls off.

AVX has nice large dovetail and latitude adjusters bolts vs small ones on the ASGT

AVX finish is nicer, plastic housings are thicker.

AVX dec motor housing does NOT rotate with the scope like the ASGT.

AVX locking levers are 1/4 turn. I actually liked the ASGT locks better.

AVX is a bit quieter when slewing.

AVX has USB instead of requiring an additional USB->RS232 converter. This is convenient but actually sort a downside because serial cables can be run much longer than USB cables, and you are stuck with the dreaded PL2303 driver instead of being able to use a more mac friendly driver. It does work tho.

More ports on the AVX for additional accessories

AVX power cord is in a dumb location and gets pulled out easily.

AVX has no bubble level and nowhere to stick one. I miss this from the ASGT.

AVX dec port points straight UP... and gravity pulls dew straight down. Guess where the dew goes?

AVX dec bearing/bushing is very sticky. The ASGT is better in this regard, but not sure why since the internals are almost identical.

Hope this helps.

Both mounts are amazing with an 8" SCT. Build an adjustable observing chair and you are all set.
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