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 51 years. It is an 8” Schmidt-Cassegrain with a focal ratio of f/10 and a focal length of approximately 2032 mm. Its 8” of aperture is enough to show you deep-sky objects and planets with a fair amount of detail without being too unwieldy, and while 2032mm is a bit of a long focal length for larger objects, it’s not claustrophobic like the larger Schmidt-Cassegrains in Celestron’s lineup. The current generation of C8 OTAs also includes secondary assemblies that are Fastar or HyperStar compatible. Since the C8 is a Schmidt-Cassegrain, it needs to be collimated every so often, but not nearly as often as most Newtonian reflectors.
Altogether, the C8 weighs about 13 pounds and is about 17 inches long. This means it’ll work on a variety of different mounts and fit in a very small space, such as a large backpack, suitcase, or dedicated carrying case. It uses a standard Vixen-style dovetail bar to attach to mounts.
Using the Advanced VX Mount for Visual and Imaging
The Advanced VX is Celestron’s cheapest GoTo equatorial mount. It has a 30-pound stated payload capacity, and roughly 40,000 objects in its internal database (most of which are either stars or simply invisible to most telescopes). Setting it up and polar aligning it is a slightly more involved process than setting up and polar aligning a standard alt-azimuth GoTo mount. However, the Advanced VX’s equatorial design allows one to do long-exposure astrophotography. 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.
The AVX can take advantage of nearly all of Celestron’s advanced technologies, 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.
The Advanced VX mounting saddle is designed to handle two different styles of dovetail plates. Celestron refers to these as CG-5 and CGE. The CG-5 dovetail plate is pretty much identical to the Vixen-style dovetail, while the CGE dovetail is basically identical to the Losmandy style dovetail plate.
At about 35 pounds altogether, the Advanced VX may sound a little heavy, but it does break into plenty of smaller pieces (the heaviest being the tripod at 17 pounds).
RECOMMENDED BUY FOR VISUAL AND BASIC IMAGING
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, the AVX does pretty well.
When properly set up and aligned, the GoTo’s performance and tracking are accurate and reliable. Put an object in the eyepiece, and you can expect it to stay there for as long as you intend to look at it. Slew to another object, and assuming you 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 two areas, the AVX is a bit of a disappointment.
The first is backlash, particularly on the declination axis. One of the chief reasons the CG-5 was never a great performer for imaging was the backlash, which could be pretty significant.
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 is usually not a problem (though it can decrease the accuracy of GoTo performance). It can cause visible problems in the stars when imaging.
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. The backlash on the declination axis, however, is a common complaint among users. There are some ways of reducing it, but it’s disappointing that Celestron wouldn’t have done more in design and manufacture, particularly since this mount is designed with imaging in mind.
The Celestron AVX 8 SCT 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.
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.
- 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 Explore Scientific 10” Hybrid Dobsonian offers more light gathering and resolving power than the Advanced VX 8” with the ability to collapse and fold up into an ultra-compact package, thanks to its easy-to-assemble truss tube and all-metal aluminum frame. As with any Dobsonian, finding and tracking objects manually is a breeze, and the Explore Scientific Dobsonians are particularly renowned for their buttery-smooth motions and ease of balancing with heavier accessories. You don’t get a lot of accessories, and the focuser is only a single-speed, however, so some TLC and additional investment are required to get this telescope to perform at its best – though the effort is surely rewarding.
- 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.
- 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 Explore Scientific 10” Truss Tube Dobsonian is quite compact compared to solid tubed offerings and occupies a similar amount of space to the C8 XLT and Advanced VX mount head when disassembled. Compared to the 10” Hybrid, the upper tube assembly is more compact and features a dual-speed rather than a single-speed 2” Crayford focuser – otherwise the two telescopes are largely identical with many of the same benefits and drawbacks.
- 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.
- 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.
- The Sky-Watcher 8”, 10”, or 12” FlexTube GoTo models feature collapsible tubes to increase portability (though the 8” and 10” are no less heavy than a solid-tubed counterpart) and full motorized GoTo and tracking, with the ability to push the telescope around the sky manually with or without being powered on. The Dobsonian mount is easy to set up and use, as well as align on the night sky with the SynScan GoTo setup, you get a decent pair of eyepieces to start out with, and overall the mechanical quality of these scopes is fairly sound. However, any model will need a shroud to keep light out of the open tube and the GoTo base is fairly heavy and hard to move around by yourself on the 12” model.
- The Explore Scientific 12” Truss Tube Dobsonian is a monster when assembled, but dismantles into a fairly compact package in minutes. Its massive 12” of aperture blows away smaller scopes like the Advanced VX 8” SCT in brightness and sharpness on almost any target. Like many other Explore Scientific offerings, you don’t get a lot of good accessories provided, but the mechanical design is rock-solid, the structure is entirely aluminum and the performance is spectacular.
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. 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. 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.
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.