Uncle Rod's Astro Blog

Tiger guarding the  new mount...

I come not to praise Celestron, but neither do I come to bury them. I used to be a Celestron fanboy. For years, I bought only Celestron's gear and praised the company to high heaven. In recent times, things have changed. For one thing, Celestron ain’t the Celestron it used to be. It’s long since been bought out by Chinese telescope giant Synta. I’ve changed too; maybe I’ve grown a little more cynical and skeptical than I was in my salad days.

However, I still like a good bargain if it’s a good bargain, and I’m not afraid to give praise where praise is due. Or criticism when that’s warranted. So, where does one of Celestron’s more popular and inexpensive mount offerings, the Advanced VX German equatorial mount (GEM), fall in the spectrum from damnation to salvation?

About four years ago, I began thinking about a replacement for my then most used rig, a 1995 Celestron Ultima 8 SCT tube riding on the company’s Advanced GT (CG5) telescope mount, a medium-light, computer-equipped GEM. Why? I wanted a new mount mostly because my CG5 was approaching ten years old, and I wasn’t quite sure how much longer the inexpensive rig would go. With early retirement in the offing in 2013, I also wanted to ensure any necessary astronomical gear purchases were taken care of while I was still working full-time, if possible.

I initially considered a wide range of mounts, especially to include the Losmandy G11 and the iOptron CEM60. Eventually, after worrying myself into a tizzy over the choices, I decided the best thing for me would be to get a mount as similar to the CG5 both in weight and capability (and price) as possible. I was also addicted to the Celestron NexStar hand control and didn’t want to give that up. Before spring 2013 was out I ordered the new successor to the CG5, the Advanced VX. Actually I ordered Celestron’s Edge 800 SCT/ AVX pairing.

Why did I buy a new telescope to go with the new mount? At the time, I had three freaking C8s, and my most used one, Celeste, the Ultima 8 OTA, who you’ve read about many times if you frequent this blog, had always been a good performer. There were, a couple of reasons. For one, I was attracted by the better field edge offered by Celestron’s corrected Edge SCTs. For another, Celestron always gives you a real good deal if you buy a telescope/mount combo. The Edge 800 with its off-white tube was just so pretty, too. And I just felt like I deserved a retirement telescope, e’en at the somewhat young retirement age of 59.

What a pretty scope!

This story is not the story of the Edge 800, however. I may talk about her, "Mrs. Emma Peel," again someday. My switch (for the most part) to refractors means she doesn’t get used as much as she used to, but she’s still a good telescope and  I still like her and use her when I need a long focal length large(er) aperture instrument. What does get used all the time? The Advanced VX mount.

As is sometimes the case in modern amateur astronomy, my experience in obtaining the AVX wasn’t smooth. While it arrived promptly from my astro-dealer of choice, Bob Black at Skies Unlimited, it had to be shipped to Celestron for replacement shortly thereafter because of two problems. One was that the hole on the declination counterweight bar for the “toe saver” bolt was mis-threaded. The safety bolt, which is intended to prevent the 11-pound counterweight(s) from smashing your toes if the counterweight locking bolt should come undone, would only thread in a few threads.

That was not a huge deal. What was was the other problem, that the hole in the underside of the mount head that the tripod’s threaded rod screws into to secure mount to tripod was also mis-threaded. I screwed the rod into the mount when I set the AVX up for the first time, and found out to my dismay that there was no way I would ever be able to unthread it again. I had to destroy the rod and the hole in order to get the mount and tripod apart and back in the box for return to Celestron.

Celestron replaced the AVX promptly with a mount that was perfect (you can see a video of the replacement mount immediately after its unboxing here), but there’s no use denying that receiving a bad mount is not an uncommon experience for buyers at the low end of the astro-market. When you are talking Chinese gear at this price level, there will be lemons. That knowledge didn’t make me feel a bit better, however. While the AVX is considered a bargain mount by some of the folks in our game, to me 900 dollars, which is what it cost, is a not inconsiderable sum.

My first AVX. Bummer!

While most people will not have a problem with their new AVX, my experience and the experiences of more than a few other purchasers show Celestron's QA can be spotty to the point of nonexistent. Be prepared. Above all, if you receive a mount that is bad out of the box, don’t agree to have Celestron fix it for you. Insist on a replacement, an immediate replacement, from them or your dealer. If you bought a big screen TV at BestBuy or HH Gregg and it was dead out of the box, you wouldn’t agree to ship it to LG or Panasonic and let them keep it for a month or so while they fixed it, would you?

Be that as it may, things began looking up after the second AVX arrived. I missed taking the mount to the Spring 2013 Deep South Star Gaze Spring Scrimmage—the replacement arrived just a little too late—and I used good old reliable CG5 with the Edge 800 instead. I was shortly able to get the AVX and Edge down to Chiefland, Florida, to the Chiefland Astronomy Village for a Chiefland 4th of July and a good shakedown cruise, though.

That’s what I intended, anyhow; the weather gods had other ideas. All me and Mrs. Peel, saw was the undersides of clouds. Thick rain clouds. That turned out to be the story for much of the summer of 2013, and I didn’t get a chance to see what my new rig could do under dark skies for quite a while.

The Specs

Before I talk more about how the AVX performed, I suppose it’s a good idea to summarize the mount’s basic specs. The Celestron Advanced VX is a computerized goto GEM mount that uses Celestron’s NexStar + (plus) computer hand controller. It is powered by two servo motors (with encoders) that are similar to those that were used on the CG5.

While Celestron doesn’t publish a figure for the weight of the mount’s EQ head, it’s about 18-pounds. The 2-inch steel-legged tripod comes in at 18 pounds as well, and is the same basic model (with a slightly different head) that is shipped with the CGEM, the EQ-6, and several other Synta-made mounts. The AVX is light enough when separated into components—mount, tripod, and counterweight(s)—that most people will have no trouble transporting it and setting it up.

Celestron Plus Controller...

The mount comes with a single 11-pound counterweight, a DC power cord, a short serial cable, and (usually) a DVD containing a telescope control program—the First Light Edition of TheSky X at the time I bought my mount.

How about payload capacity? Celestron says 30-pounds. That is actually, surprisingly, a downgrade from the figure they published for the CG5, 35-pounds. Is the AVX less sturdy than the CG5? No. Either the company decided to be more realistic about the weight this mount can handle, or they just forgot the figure they quoted for the CG5. The capacity of the two mounts is pretty much identical. That is, around 30-pounds for visual, and maybe 15 – 20-pounds for the more demanding task of imaging.

What’s New

Are the CG5 and AVX identical save for appearance, then? No. The new mount is an improvement on the CG5 in several ways. The CG5 was nothing more than a non-goto Vixen Great Polaris mount clone with goto motors pasted on, and it looked it. While the mount worked well, it definitely had rough edges. The CG5’s plastic motor housings could, for example, interfere with movement in R.A. If you lived at 30-degrees latitude or south of that, you’d find you’d have to remove the mount’s forward altitude adjustment bolt or the R.A. motor housing would bump into said bolt and prevent you from reaching 30-degrees altitude during polar alignment.

The internals of the AVX are much the same as those of the CG5, though the motor control board has supposedly been somewhat improved. However, the mount head has been completely redesigned. The motor housings now look like they are actually part of the GEM and don’t interfere with any of its movements. The R.A. shaft housing is more sleek looking, and the CG5’s pitiful polar scope eyepiece cover, which was always falling off and getting lost, has been replaced with a nice thread-on job.

Perhaps the most important redesign was of the control panel, though it’s taken Celestron a couple of tries to get it exactly right. A bug-a-boo with the CG5 was the connection for the declination motor’s cable was right there with the rest of the mount’s identical RJ-11 receptacles. Plug the declination cable into the hand control port or vice versa and you could do real damage to the mount. The initial VXes improved upon that somewhat, putting the dec receptacle on the top lip of the control panel, which extends out from the R.A. housing. Some folks still managed to plug the declination cable into the wrong receptacle, though. In the most recent production runs, Celestron has finally given the declination cable a connector that can’t be plugged into an RJ receptacle.

AVX Control Panel...

What else? The mount now features Permanent Periodic Error Correction (PPEC). The CG5 didn’t have PEC at all, permanent or otherwise. Another, more important, improvement is that the altitude and azimuth adjustment knobs are larger and better on the AVX and make polar alignment easier. Also helpful is that the new mount, like the CGEM, features an internal battery that keeps time and date current when the power is turned off. Finally, the too loose power connector of the CG5 has been replaced by one with a thread on collar that ensures a firm power connection, again like the one on the CGEM.

The AVX mount has shipped with Celestron’s Plus HC from the beginning, and will soon be equipped with the new USB HC, which includes a built-in USB-serial converter for control with a PC without an add-on serial converter. All you'll have to do is run a USB cable from PC to mount HC, a pretty substantial improvement if'n you ask me. Well,  unless  you need to control the scope from more than a few feet away. Then, you'll be dealing with USB extensions and boosters. So it goes, I reckon.

What’s Not New

That’s a pretty impressive line-up of improvements. What didn’t get fixed, though? Mainly, the declination axis. Unlike the right ascension axis, which features ball bearings, the declination axis uses a thrust bearing. The axis rides on plastic. Some people have expressed concerns about that, and it’s true the declination axis doesn’t move as freely as the R.A. axis, but I’ve never had a problem balancing even lighter scopes in declination. My mount also auto-guides reasonably well in dec, so I’ve pronounced this a non-issue. How about the mount’s sound? The CG5 is a notoriously noisy mount when it is slewing at high speed. That is caused in part by the motor housings resonating. The AVX is noticeably and substantially quieter than the CG5 and at least slightly less noisy than my CGEM.

In Use

The AVX is identical to all the other Celestron GEMs in most respects when it comes to alignment. The only exception is the more expensive Celestron mounts’ homing/limit switches. The Advanced VX doesn’t have them. Instead, as with the CGEM and CG5, you set the mount to a home position manually using marks on the R.A. and declination axes. The marks are improved over the CG5’s stick on labels, at least. The AVX has engraved R.A. and declination home position marks that are easy to see with a dim red light.

It's a modern looking mount.

Once you are in home position, it’s the same old story as with other Celestron GEMs. You do a 2+4 alignment for best goto accuracy. You align on two stars the hand control chooses for you. When they are centered in finder and eyepiece, you go on to add as many as four “calibration” stars. These stars allow the mount’s computer to take cone error—misalignment between the telescope and the AVX’s R.A. axis—into account, and are what is mostly responsible for the mount’s excellent goto accuracy.

And the mount's goto accuracy is outstanding. I’ve never worried about getting objects in the field of view of a medium power eyepiece, even with the f/10 SCT, or in the frame of fairly small camera chips. Any object you request, from horizon to horizon is just there assuming you’ve been careful in your goto alignment—used a medium power reticle eyepiece and done final star centering with the mount’s up and right keys only.

Polar alignment? A GEM mount must be accurately polar aligned for good tracking. Like the CG5 and CGEM, the AVX is amazingly immune to goto accuracy problems caused by polar misalignment. If you are just observing visually, it’s usually enough to merely point the mount north and raise the R.A. axis’ altitude to a value equal to your latitude. If you are taking pictures, however, you need a good polar alignment.

The VX doesn’t come with a polar alignment borescope (a rather poor one, if you ask me, is available as an option), but you don’t really need a polar scope. Like the other NexStars, you can employ the hand control’s built-in polar alignment routine, AllStar. Once you’ve done a good 2+4 alignment, AllStar will have you center a star using the mount’s altitude and azimuth adjusters. Allstar is more than adequate for most imaging purposes and is decidedly more accurate than the polar scope.

Making Alignments Simpler

The alignment process, centering up to six stars, can be something of a hassle, but Celestron’s optional StarSense alignment camera takes all the pain out of that. The StarSense easily and accurately performs a goto alignment with the VX without user intervention—other than to set the mount to home position and start the procedure. Since you don’t have to do a second 2+4 alignment following the ASPA—StarSense does it for you—it’s painless to do two ASPA iterations and really dial in polar alignment. In my opinion, StarSense is almost a must-buy for Celestron GEM owners.

In the Field

Since my mount came with the Edge 800 OTA, that was the scope I used with it initially and for about a year and a half thereafter. I was mostly imaging with deep sky video cameras like the Mallincam, and, for video, the setup was a dream. While there was some backlash in the AVX’s declination axis, there was little in R.A., pointing was excellent, and my results were everything I expected and more. While the tracking quality of the Advanced VX was not worlds better than that of the CG5, it was somewhat better and more than good enough for unguided video imaging with short (usually around 15-seconds) exposures.

The replacement AVX was perfect.

However, my purchase of the AVX came at a time when changes were in the offing for me. One of those changes was that after using nothing but video for picture taking for the previous several years, I was turning away from that and back to using CCD and DSLR cams. Oh, I’d had a ball with video, but I suddenly wanted prettier, more finished looking pictures than what my Xtreme or Stellacam could deliver. How would the Advanced VX cope with the longer, guided exposures demanded by my DSLRs?

The answer was “surprisingly well,” though my initial images with the Edge 800 (reduced to f/7) weren't quite perfect. The stars were a little off-round if you were zoomed-in far enough on the picture. Mostly, I think that was my fault. For one thing, I was using a fast 50mm guide scope. Most people will tell you these can work OK up to about 1500mm of focal length, but I was almost there at 1400mm and pushing it. Also, I often forgot to lock the telescope’s primary mirror down. Finally, me being me, I sometimes (usually) wasn’t as exacting with the AllStar polar alignment as I could have been. When you get up around 1400 - 1500mm, everything becomes critical.

I could have tightened things up with a better guide scope or an off-axis guider and a better polar alignment, but as 2014 wound down, another thing that began to change for me was my choice in telescopes. One day, I began wondering how the combination of my 80mm Megrez II Fluorite refractor and my Canon 60D DSLR would do with the AVX. I just happened to be heading out to my club dark site that evening, and decided to take the William Optics APO rather than the SCT. I was bowled over by the wide field shots I got.

And it wasn’t just that the smaller scope’s wider field was cool. It was eye-opening how darned easy it was to get perfectly guided shots at 550mm. The 50mm guide scope was more than adequate at this image scale. And sometimes it wasn’t even needed. One night I was shooting with the Megrez and Advanced VX in the backyard, where I really need to keep exposures down to two minutes or so because of the bright sky background. Watching the subs coming in, I thought to myself, “Man, PHD 2 (my auto-guiding program) sure is guiding well tonight.” Then, I realized I’d forgotten to start PHD 2. While I do usually guide for exposures of a minute or more, you can get away with a lot at 550mm, that you can’t at 1400mm.

There were more changes ahead for me as 2015 began, including changes in my approach to astronomy. I sold my 12-inch Dobsonian (the fabled Old Betsy), three C8s, an RV6, and some other gear (including my CG5) I wasn’t using, and applied part of the proceeds to a 120mm APO refractor. As I’d expected, it was easier to manage for imaging than my SCTs had been, even with its fairly substantial focal length of 900mm. If nothing else, there was none of the SCTs’ dratted focus shift to annoy me. And, yeah, I gotta admit I found myself becoming addicted to the refractor visual experience, that certain-special look of images in a lens scopes.

How did the Advanced VX do with the 120mm? Until recently, I didn’t know. I only used it on that mount for visual, moving it to the CGEM for imaging. The other day, however, as I was preparing to test a new camera, I got lazy. I like the CGEM a lot. In some ways, the mount gets a bum rap on Cloudy Nights (ya think?), but one thing I don’t like about it is its weight. Lifting over 40-pounds onto a tripod just ain’t my bag these days. I was not convinced the AVX would handle the longer focal length for imaging, though. But, on the night in question I was, yeah, feeling lazy and also more than a little sore from working in the yard, and thought I’d give the Advanced VX a try with the 120mm.

NGC 253 with 80mm APO and AVX...

I wasn’t in the mood to set up for guiding, either. I just wanted to figure out how to operate the camera and its software. So, what I did was limit my exposures to 30-seconds. If I had to throw out every other sub-frame at 900mm I would just do that. Surprise! I didn’t have to toss a single sub all night. I did take pains with balancing the scope, and I did do two iterations of the ASPA polar alignment, but other than that I just let the VX do its thing and it performed admirably.

In retrospect, I suppose I shouldn’t have been surprised. The VX handles large payloads well for visual use. My 6-inch f/8 achromatic refractor, which approaches 30-pounds with a 2-inch diagonal and a heavy 100-degree AFOV eyepiece onboard, is good on the VX. It would actually be very good for visual with the VX if Celestron just sold a half-pier extension for the tripod. As is, the 6-incher’s tube is a little too long and can crash into the tripod if you are not careful. With that experience in mind, the idea that it can handle the 11-pound 120mm refractor, including for imaging, shouldn’t be a surprise.

One of the great advantages of the VX for me is that I am willing to set it up even on iffy nights. Lately, the sky has to look darned near perfect before I’m going to wrestle with the CGEM or my old EQ-6. The mount is also robust. I’ve never worried about leaving the VX set up in my backyard under a Desert Storm Cover for three or four days.

That’s good, but how has the mount held-up over nearly four years of fairly frequent use? No complaints. It’s never done anything crazy. It is working as well today as the day I got it out of its box. Heck, I haven’t even had to replace the little button cell battery that keeps time and date current yet.

The greatest complement I can give Celestron’s "bargain" goto mount? I’ve often speculated as to what I would replace the VX with if it went up in smoke one night (not that I expect that). It would be a similar size mount, and I’ve been attracted to some of the newcomers in this class like the iOptron CEM25 and the Exos PMC-8 from Explore Scientific. But I would probably just get another VX. It’s never been a hassle, has never irritated me, and has never failed to do what I want done on the observing field. What greater praise can you give a mount than that?

Postscript...

The good news? I still have my Advanced VX and still use it frequently. The better news? The mount is actually better for imaging than it ever was. What I did, first of all, was buckle down and get the settings for the mount in PHD2 Guiding dialed in. I also abandoned AllStar for the much more precise polar alignment offered by Sharpcap (if you ask me, it's also easier to do than AllStar) finally, I did a PPEC run on the mount. The combination of these three things brought my RMS guide error down into the 1" range on a night of average seeing. I could no doubt get it better than that with some more fiddling with PHD, but why? 1" results in round stars with my scopes, which is good enough for me.

Still the best thing about the mount? While I love my GM811G, there's no denying that lazy ol' me is almost always more willing to drag the light AVX into the backyard.