Celestron Advanced VX 8″ SCT Reviewed: Recommended Scope

The C8 Optical Tube

The C8 is Celestron’s oldest mass-produced telescope, having debuted in 1970. Other than small changes to the manufacturing and coating processes, the C8 has hardly changed in the past 50+ years.

C8 is an 8” Schmidt-Cassegrain with an aperture of 203.2 mm (8″) and a focal length of 2,032 mm, giving it a focal ratio of f/10. Its 8” of aperture is enough to show me deep-sky objects and planets with a fair amount of detail without being too unwieldy. While 2032mm is a bit long of a focal length for larger objects, it doesn’t make me feel as claustrophobic as the larger Schmidt-Cassegrains in Celestron’s lineup.

The secondary mirror obstruction in the front of the optical tube is 64 mm wide, accounting for 31% of the aperture diameter but slightly less than 10% when we calculate in terms of aperture area. This secondary assembly of the current generation of C8 OTAs are also Fastar or HyperStar compatible.

Since the C8 is a Schmidt-Cassegrain, I need to collimate it every so often, but not nearly as often as most Newtonian reflectors.

Altogether, the C8 optical tube weighs about 13 pounds and is about 17 inches long. This means it’ll fit in a very small space, such as a large backpack, suitcase, or dedicated carrying case.

Simply put, the C8 is one of the best amateur scopes on the market that put Celestron on the map. While there are better and cheaper scopes out there, there aren’t many, and the C8 continues to be a classic.

The Advanced VX Mount

The Advanced VX is Celestron’s cheapest GoTo German Equatorial Mount (GEM).

At about 35 pounds altogether, the Advanced VX may sound a little heavy, but we can break it into plenty of smaller pieces. The heaviest is the tripod at 18 pounds and the mount head weighs 17 pounds.

The tripod has 2-inch diameter stainless steel legs, and the legs spreader has fairly standard holes drilled for keeping 1.25 and 2-inch eyepieces.

The AVX comes with Celestron’s standard NexStar+ hand controller (the variant for equatorial mounts). The NexStar+ hand control has a database of over 40,000 objects, including the entire Messier, Caldwell, NGC, and IC catalogs.

I can take advantage of nearly all of Celestron’s advanced technologies with the AVX, such as SkyAlign and CPWI (their new software developed in conjunction with PlaneWave), as well as their StarSense AutoAlign, SkySynch GPS, and SkyPortal WiFi add-ons.

My Take on AVX’s Payload Weight Capacity Rating

The AVX has a 30-pound stated payload capacity. This does not include counterweights: just the weight of anything attached to the dovetail saddle, and generally including the telescope, mounting rail, rings (if needed), eyepiece, finder scope, camera, autoguider, additional mounting hardware, and anything else riding on the mount.

Every company has their own method of rating mount capacity. In my experience, Celestron tends to be a bit liberal with the number. So, when they say 30 lbs., I wouldn’t recommend putting any more than 30 on it. I’m sure doing so would put you in jeopardy of voiding the warranty.

If I load the AVX up close to 30 lbs., I can well notice some performance problems, such as less accurate tracking and GoTo performance. I could also hear it straining to move the load. With this in mind, I find it odd that Celestron actually offers the mount with the C11 as an option, which weighs in at 27.5 lbs—just shy of the mount’s maximum. When you add in a diagonal, eyepiece, finder scope, and dew shield to the C11 package, you may easily find yourself over 30 lbs.

It’s also good to keep in mind that a common rule of thumb for astrophotography says that our total payload weight for imaging should be kept to one-half the mount’s rated maximum or less. So, for imaging, the C11 would be right out.

But with a tube weight of only 12.5 lbs., however, the C8 rides the mount fairly well. For visual use, I have plenty of room in the weight budget to add on heavy eyepieces and a better finder.

For imaging use, it comes pretty close to the recommended limit of 15 lbs, but a lightweight camera, along with a focal reducer and auto guider, while likely to be over the 50% mark, probably won’t be too bad for casual imaging use. And for planetary imaging, which uses short exposures or, more often, video capture, which puts less emphasis on the mount, there should be no problem here.

The Adaptability of AVX’s Mounting Saddle

The AVX’s mounting saddle is designed to handle two different styles of dovetail plate. Celestron refers to these as CG-5 and CGE. The CG-5 dovetail plate is pretty much identical to the Vixen-style dovetail. Both a Celestron CG-5 Dovetail and a standard Vixen style should work equally well.

The Celestron CGE style dovetail, on the other hand, while being similar to the Losmandy D plate, is not quite the same, and because of this, the AVX cannot accept an actual Losmandy D. The actual Losmandy standard is slightly wider than the Celestron variant and doesn’t fit in the saddle properly. Additionally, I’ve noticed that the height of the dovetail portion itself, what is called the undercut, on the CGE is somewhat higher than the Losmandy D plate.

If the width wasn’t a problem, I could probably attach a Losmandy D, but I’m not sure I’d recommend it as it may not clamp down tightly and may not provide a stable attachment.

Celestron does make an optional universal mounting plate for use with other scopes, but this is another cost. If you want a mount to handle multiple payloads and you’re not entirely brand-loyal, you may end up spending more on additional mounting plates.

The CG-5/Vixen style variant is probably the best option if you do want to handle multiple payload options. It works just fine for most uses. It may be a little less stable for heavier payloads, particularly for imaging. Personally, I find the Vixen style much easier to mount, however.

The AVX’s Performance

The AVX was designed to be a mount both for imaging and visual observing. For visual observing, the requirements are far less than those needed for imaging. And here, I can state with confidence that the AVX does pretty well.

When properly set up and aligned, the GoTo’s performance and tracking are accurate and reliable. If I put an object in the eyepiece, I can expect it to stay there for as long as I intend to look at it. If I slew to another object, and assuming I did a good star alignment, the object should be in the center of the eyepiece.

Though heavier loads may make it strain and may decrease accuracy, it still generally performs well, making it definitely good enough for visual use.

But in one main area, the AVX is a bit of a disappointment. That’s backlash, particularly on the declination axis.

One of the chief reasons the discontinued CG-5 mount was never a great performer for imaging was the backlash, which could be pretty significant. The AVX’s backlash on the right ascension axis is definitely better than that of previous CG-5 models, but it may still appear a little high to some users, particularly those who require high precision for imaging.

Backlash is a problem caused by gears that don’t mesh together as closely as they should. This can be due to gears that aren’t being held tightly together or gears that aren’t properly sized to fit each other. The key symptom is some give in the axis.

While properly meshed gears should remain in contact with each other at all times, when gears aren’t properly meshed, there may be some looseness, which can result in back and forth wobbling. For visual use, this can be a nuisance but I don’t usually consider it to be a problem (though it can decrease the accuracy of GoTo performance). But when imaging, it causes visible problems in the stars.

The AVX’s backlash on the declination axis, however, is a common complaint among users. There are some ways of reducing it, but it’s disappointing to me that Celestron didn’t do more in design and manufacture, particularly since this mount is designed with imaging in mind.

Overall, as designed, the performance of the AVX is hard to beat in its price class. But, again, that’s as-designed.

But All Is Not Well

If you do a little digging around on astronomy forums, you may find a higher than average number of complaints about the AVX. And while some of those complaints are about issues such as backlash, there are some bigger problems out there.

I’ve seen some users reporting significant problems with the mount’s electronic components. And here, it appears, is where Celestron has really dropped the ball. The horror stories are mostly regarding poor wiring and lower-quality electronic components in the mount itself—the hand control seems to be just fine here, unless problems in the mount lead to damage.

When a mount such as this stops working, for whatever reason, it becomes a high-priced doorstop.

The core of the problem may be traceable to quality control on the production line. While some of Celestron’s higher-end equipment, such as their more recently released mount, the CGX, appears to be well manufactured, AVX, at its lower price-point, appears to not get as much attention and care in the assembly process. As a result, many owners have had to send theirs back for warranty work or replacement. This can be frustrating, especially to those newer in the hobby.

Accessories

The Celestron AVX 8″ Schmidt-Cassegrain comes with a 1.25” 25mm Plossl eyepiece providing 81x, along with a 1.25” prism star diagonal. You’ll probably want at least one more eyepiece for higher magnification and, ideally, a 2″ diagonal and one or two 2″ wide-angle eyepieces for the widest possible field of view and lowest useful magnification.

The Advanced VX 8 SCT is supplied with a standard 6×30 finderscope. While a red dot finder would probably be easier to use and is all that is really required, the 6×30 doesn’t have any batteries to worry about draining and works fine for the simple task of aligning the GoTo mount.

Alternative Recommendations

The Celestron Advanced VX 8” SCT is a decent telescope, but those looking for a more convenient and portable package might want to consider something else, and for visual astronomy an 8” SCT is hardly the most capable or easy-to-use option you can get for the money.

Under $1000

• The Apertura AD10/Zhumell Z10/Orion SkyLine 10 offers a wider field of view, better accessories, more light gathering and resolving power, and a drastically simpler setup compared to the Advanced VX 8” SCT – think seconds vs. nearly an hour of assembly and setup time. The Dobsonian mount is steady and easy to aim, and you get a wide variety of included features and accessories like a 2” dual-speed Crayford focuser, wide-angle low-power 2” eyepiece, and a built-in cooling fan for the primary mirror.
• The Apertura AD8/Zhumell Z8/Orion SkyLine 8 offers the same great features as the AD10/Z10, but with less aperture and a lower price tag. Given the similar form factor and minimal difference in weight/bulk between the two aperture sizes, however, we would recommend going with the larger 10” on account of its better capabilities and overall value for the money.
• The Sky-Watcher Virtuoso GTi 150P is smaller than the Advanced VX 8” SCT and thus less capable in light gathering and resolving ability, but offers a considerably wider maximum field of view and is vastly more compact and easy to set up, despite still featuring motorized tracking and GoTo. The mount is controlled via your smartphone or tablet and can be aimed manually without impairing the accuracy of its tracking or GoTo, or causing any damage to the internal gears. You can also get a manual version, available as the Heritage 150P, or a smaller 130mm model in either GoTo or manual configuration as the Virtuoso GTI 130P or Heritage 130P respectively.

$1000-$1400

• The Apertura AD12/Zhumell Z12/Orion SkyLine 12 offers significantly more light gathering and resolving power than the Advanced VX 8” SCT or similar 8” telescopes. You get a plethora of high-quality features and accessories supplied with this scope by default like a 2” dual-speed Crayford focuser, 9×50 right-angle finder scope, 2” wide-angle eyepiece and a built in cooling fan. The downside is that the tube is monstrous and may not fit across the back of a car, the base is heavy and awkward, and overall these telescopes are monsters. However, the views are more than worth it if you can put up with this beast of a telescope.
• The Celestron StarSense Explorer 10” Dobsonian doesn’t have motorized slewing and tracking, but it features Celestron’s StarSense Explorer technology to help you navigate the night sky with the assistance of your smartphone. It’s easy to set up in just minutes and is quite lightweight and easy to carry thanks to its weight-optimized base and carry handles. You don’t get a lot of accessories or other features for the money – just one eyepiece, a red dot finder and a single-speed 2” Crayford focuser – so if those are important to you, one of the other 10” Dobsonians on our list might be a better option. An 8” StarSense Explorer model is available at a lower price but with many of the same caveats, and given the near-identical weight, volume, and general ease of use we’d recommend a 10” over an 8” if you can afford it.
• The Celestron NexStar 6SE is smaller than the C8 XLT, and the SE mount can’t do nearly as much as the Advanced VX can, but it’s a portable setup that’s small enough to even fly with and easily fit in a large backpack (minus the tripod). You can still do some deep-sky astrophotography with a HyperStar f/2 conversion kit, and planetary astrophotography is dead simple; views of brighter targets are spectacular thanks to the sharp optics of the C6 XLT optical tube, but you are of course limited with only 6” of aperture.

$1400-$2600

• The Celestron NexStar Evolution 8” is easier to set up and assemble than the Advanced VX 8” and is basically a superior 1:1 alternative if you don’t plan on doing serious deep-sky astrophotography. The alt-azimuth nature of the mount eliminates polar alignment or 2-axis balancing from the equation, you can control it via your smartphone/tablet or with the provided hand controller, and there’s much less weight or parts to assemble. The mount also features a built-in lithium battery and you get a bonus medium-power eyhepiece thrown in to start with. The smaller, cheaper NexStar Evolution 6” model is also a great choice, though it features less in the way of useful improvements over the cheaper 6SE and isn’t as good value for the money.

What can you see with the Advanced VX 8″ SCT?

The large aperture and moderately long focal length of the C8 make it great for viewing the Moon, planets, double stars, and smaller deep-sky objects.

It’ll also have no trouble showing you details as small as a mile on the Moon, Mars’ dark shading and ice caps, Mercury and Venus’ phases, Jupiter’s cloud belts, the Great Red Spot, and, of course, Saturn’s rings with the Cassini division in them. Uranus and Neptune are star-like dots, and Neptune’s moon Triton can be faintly seen. A plethora of moons surround Jupiter and Saturn.

Large open clusters and nebulae won’t fit in the field of view, but the C8 is great for viewing smaller galaxies like M82 and M51, globular clusters like M13, and planetary nebulae like the Cat’s Eye.

Astrophotography Capabilities

It’s also good to keep in mind that a common rule of thumb for astrophotography says that your total payload weight for imaging should be kept to one-half the mount’s rated maximum or less. At 13 pounds bare, by the time you load up the C8 with a camera, autoguiding, etc., it is going to be above 15 pounds, which is the most you can really load onto the Advanced VX and expect consistently good performance, especially at a 2032mm focal length. But it will suffice if you keep your exposures short and do a good job with polar alignment and autoguiding.

Overall, the C8 works pretty well for deep-sky astrophotography with a DSLR or dedicated astronomy camera if you add an aftermarket f/6.3 reducer to it to shorten your exposure times—and, of course, use an autoguider. You can also convert the C8 to an f/2 system using a Starizona Hyperstar, which will allow you to get more detail with much shorter exposure times and a wider field of view.

When used with a Barlow lens and a high-speed planetary camera, the C8 is also great for taking pictures of planets and the moon.