The C8N Optical Tube
The Celestron C8-N Newtonian VX GOTO Telescope uses the “C8N” optical tube, a generic 8” (203mm) f/5 Newtonian reflector with a focal length of 1000mm. At f/5 with any Newtonian, collimation tolerances are fairly important, and you will get coma at the edges of the field of view with most cameras and 2” eyepieces. You’ll also notice edge-of-field aberrations with cheaper wide-angle oculars thanks to the steeper light cone of an f/5 system.
Collimating the C8N requires the use of a screwdriver to adjust the primary mirror and a hex key for the secondary mirror. The optics of the C8N are usually decent, though the occasional defective unit slips past quality control. It is usually not quite as good as 8” f/6 Dobsonians optically and has a slightly larger secondary mirror, inhibiting contrast on high-resolution targets. A collimation tool of some sort will be needed as Celestron doesn’t provide one, and precise collimation is critical for both visual and imaging use at a fast focal ratio.
The C8N uses a simple 2” rack-and-pinion focuser. This focuser is made entirely out of metal and works okay, but it lacks the smoothness or fine adjustment offered by a dual-speed Crayford focuser while also suffering from some mild play/wobble, which can interfere with astrophotography use. However, with a motor focus attachment, it will suffice for the task, though it’s a bit of a disappointment.
To attach to a mount, the C8N includes a pair of standard tube rings, which let you rotate and slide the tube back and forth for balance. The rings are attached to a Vixen-style dovetail bar, which allows you to easily interchange the scope between most astronomical mounts without tools.
The Celestron C8-N Newtonian VX GOTO telescope includes one eyepiece: a 20mm Plossl providing 50x magnification with an approximately 50-degree apparent field of view, which translates to a true field of 1 degree with the C8N’s 1000mm focal length. It’s an acceptable eyepiece, though hardly the only one you’ll need for the widest field option available.
Celestron provides their standard 9×50 finder scope with the C8N, attached with a standard Synta/Vixen-style shoe for easy interchangeability with others finders, such as a red dot unit. The 9×50 reveals stars a few magnitudes fainter than your eyes can see alone, along with the brightest deep-sky objects, such as star clusters, with an upside-down field of view about 5 degrees across and non-illuminated crosshairs. It works fine for the purposes of aligning the Advanced VX mount on the sky.
The Advanced VX Equatorial Mount
The Celestron C8-N Newtonian VX GOTO is the smallest and lightest of Celestron’s computerized, GoTo German equatorial mount line. It features many of the features of other Celestron computerized mounts, such as the NexStar+ hand controller and compatibility with Celestron’s accessories like the StarSense AutoAlign, SkySync GPS, and the SkyPortal WiFi adapter for control via your smartphone/tablet and an app like SkySafari Pro. The Advanced VX can be controlled with your PC and an astrophotography program like NINA or Sequence Generator Pro thanks to its ASCOM drivers; however, due to the way the hand controller is required for the PC to interface with the mount, it will not work with EQMOD and consequently is not as responsive, as well as requiring you to use the issue-prone and outdated ST4 port for autoguiding. These software issues make the Advanced VX mount problematic for astrophotography to begin with, but they are exacerbated by the mount’s use of servo motors, which reduce tracking accuracy.
For holding the C8N and other telescopes, the Advanced VX comes with two 11-lb counterweights, and the C8N’s dovetail bar slides into the VX’s Vixen/CGE-style dovetail saddle. Unlike most high-quality dovetail saddles, the Celestron C8-N’s dovetail saddle uses screws rather than a clamp to grip the dovetail, and this consequently digs into the dovetail bar and requires you to remove and re-install the screws depending on which size bar you are using. It also will not provide as tight or parallel a grip as a clamping-type saddle and is just a few millimeters too thin to hold a true Losmandy D-style dovetail bar, which is otherwise basically the same as the far less commonly used CGE bar.
The Celestron C8-N has a stated payload capacity of 30 lbs, and the standard rule of thumb is to exceed no more than half of that for imaging purposes. The C8N optical tube weighs 14 lbs before you count the rings or finder scope, and with a camera, motor focuser, coma corrector, and autoguiding equipment, you will easily exceed 20 lbs, if not 25 lbs. This would be too much for the C8-N to handle even if it were made to better standards. As such, deep-sky images, even with good alignment and ideal guiding, balance, etc., will often be inconsistent in quality, with trailing issues appearing even with fairly short exposure times. You really need both a bigger and better mount for deep-sky astrophotography with an 8” Newtonian, such as a Sky-Watcher EQ6R, Celestron CGX, Losmandy G11, or one of the larger new harmonic drive mounts on the market.
For visual use, the Celestron C8-N works fine and is fairly easy to set up. After balancing the optical tube by sliding it in its rings and adjusting the counterweights, as well as leveling the tripod, you can polar align with a polar scope or Celestron’s All-Star Polar Align method. Once polar alignment is complete, the Celestron C8-N is aligned on the sky the same way as any other Celestron GoTo mount with its NexStar+ hand controller. You slew to several alignment stars, center them in the eyepiece, and confirm them, after which the mount can automatically slew to and track anything in its 40,000 object catalog (or whatever you select in an app like SkySafari or the SkyPortal app if you’re using a WiFi adapter). The weight of the 9×50 finder scope and 2” eyepieces will inevitably not be in line with either axis of the mount for visual use and thus cause torque at strange angles, which builds up inaccuracies in the mount’s GoTo and tracking as you go back and forth across the sky. As such, you’ll be thankful for the inclusion of the Sync feature in the NexStar+ controller, which allows you to update the telescope’s alignment using whatever you’re currently aimed at as an additional reference to compensate for such errors.
The Celestron C8-N comes with a DC power cable by default and can be run off any sufficient 12-volt battery or with a separately sold AC adapter.
Should I buy a Used Celestron C8-N Newtonian VX GOTO?
A used, complete Celestron C8-N Newtonian VX GOTO telescope can make for a decent package if it’s available at a low enough price; a smaller scope can be swapped for use on the Celestron C8-N for imaging and you could build a DIY Dobsonian mount for the tube (or just get rid of it). As with any used telescope and mount, however, make sure that the mirrors in the C8N are free of corrosion, the Celestron C8-N powers up, and so forth. Missing counterweights or knobs, a missing or broken hand controller, or a missing finder can be replaced fairly easily and cheaply.
The Celestron C8-N Newtonian VX GOTO package isn’t ideal for astrophotography or visual use. As such, we would recommend looking at a separate optical tube and mount for deep-sky astrophotography purposes or considering one of the following if you are looking for a telescope suitable for visual observation or planetary imaging.
- The StellaLyra 10”/Zhumell Z10/Orion SkyLine 10 offers more aperture, more accessories, and of course, a much simpler mount than the Celestron C8-N Newtonian at a fraction of the price.
- The Celestron StarSense Explorer 8” Dobsonian offers similar views to the Celestron C8-N Newtonian but with a better focuser, lightweight and portable mount, and aided by Celestron’s StarSense Explorer technology to help you navigate around the night sky.
- The Sky-Watcher Virtuoso GTi 150P has fully motorized tracking and GoTo, excellent optics, and an ultra-compact collapsible tube and tabletop Dobsonian mount, which combined take up less space than the C8N optical tube when disassembled. The manual Heritage 150P is identical apart from its lack of GoTo/tracking and you can also choose from a 130mm Heritage or 130mm Virtuoso GTi model.
- The StellaLyra 12”/Zhumell Z12/Orion SkyLine 12 offers significantly better views than the Celestron C8-N Newtonian, with over double the light-gathering power and 50% more resolution along with the same great accessories and features of the smaller AD10/Z10. However, it is a little bit bulky thanks to its massive solid tube.
- The Celestron StarSense Explorer 10” Dobsonian has the same well-designed lightweight Dobsonian mount and StarSense Explorer technology as the 8” model and essentially takes up the same amount of space, but has significantly more light gathering and resolution ability on account of its larger primary mirror.
- The Celestron NexStar 6SE is compact, portable, and makes for an ideal planetary instrument thanks to its f/10 focal ratio and motorized tracking/GoTo. Atop a different mount, the C6 XLT optical tube can be used for deep-sky imaging at f/2 with the addition of a Starizona HyperStar.
- The Celestron NexStar Evolution 6” is similar to the NexStar 6SE with an identical C6 XLT optical tube (also HyperStar compatible) and a GoTo mount and tripod, though you get the bonuses of a built-in battery and WiFi adapter.
- The Sky-Watcher 12” Collapsible Dobsonian is more compact than a standard 12” Dob but offers the same great views without the complexity of a full truss setup, and includes decent accessories to get you started. A GoTo version is also available, which can be used manually too in conjunction with its electronics.
- The Explore Scientific 12″ Truss Tube Dobsonian offers an extremely compact form factor when disassembled thanks to its truss tube, along with a well-designed all-metal frame, though assembly can be time-consuming and it lacks accessories.
- The Celestron NexStar Evolution 8” offers many of the same features as the 6” Evolution but with larger aperture, offering better performance for visual use and ideal as a planetary imaging setup.
- The Sky-Watcher 10” GoTo Collapsible Dobsonian can be controlled via your smartphone/tablet but also features Sky-Watcher’s FreedomFind technology to allow for manual use even when the scope is powered on and aligned. The collapsible tube makes it easier to transport, and the included accessories are acceptable too.
Aftermarket Accessory Recommendations
For slightly increased magnification and a more immersive view than the provided 25mm Plossl eyepiece, a 16mm UWA (41x) is an excellent choice, while a 15mm redline/goldline (43x) serves as a decent budget alternative. A 10mm UWA (65x), or a 9mm redline/goldline (72x), is ideal for medium-high magnification, while for higher magnification, a 4mm planetary eyepiece or 4mm UWA (163x) is a suitable selection. A Cheshire collimation tool is also a valuable item to keep nearby to ensure precise collimation for the sharpest possible views with the C8N.
Incorporating a narrowband Ultra High Contrast (UHC)/OIII nebula filter into your collection of accessories for the C8N is a smart choice, as it can significantly enhance your views of nebulae, such as the Orion Nebula, when used with nearly any telescope, including the Advanced VX C8N. You can also, of course, utilise this filter with a larger telescope in the future, so it’s certainly worth acquiring one. Additionally, it provides substantial contrast improvement to reveal the faint, wispy Veil Nebula supernova remnant and other low surface brightness nebulae with the Advanced VX C8N under suitably dark sky conditions.
The Advanced VX equatorial mount doesn’t include a polar scope by default, which can make rough polar alignment using just the hole in the polar axis both inaccurate and frustrating, especially when it leads to your telescope straying off-course midway through an imaging session. To address this problem, the standard polar scope available from Celestron is sufficient. Furthermore, a DC power supply, such as the Celestron PowerTank Lithium, is essential.
What can you see?
The C8N can be extremely uncomfortable to use atop the Advanced VX, or any equatorial mount, for visual use. The eyepiece will frequently be put in awkward positions, requiring you to rotate the tube in its rings to make viewing comfortable—though this can easily ruin your balance and the alignment of the Advanced VX mount. A pair of DIY Wilcox rotating rings usually improves the situation but still isn’t ideal compared to the simple ergonomics of a Dobsonian. This is a common feature of any equatorially mounted Newtonian that worsens with size.
Thanks to its wide field of view with a 2” eyepiece — slightly wider than what’s achievable with a typical 8” f/6 Dobsonian — the C8N excels at observing large open star clusters, such as the Double Cluster, Wild Ducks Cluster (M11), and Pleiades (M45). These will show up well under almost any viewing conditions, and many of the stars will appear quite colorful owing to the C8N’s aperture and their brightness. The C8N is also capable of resolving the individual stars in many globular clusters, including almost all of the globulars in the Messier catalog and many others. However, magnifications of 80x or more are recommended to resolve globulars clearly, along with dark skies.
Under moderately light-polluted skies, the C8N can easily reveal intricate details in bright nebulae such as M42 and M8. However, for the best viewing experience, it is highly recommended that you observe these objects under darker skies and/or a high-quality UHC nebula filter. With suitably dark skies and a good UHC filter, you can see fainter nebulae like the Veil and North America Nebula, and easily observe details in larger planetary nebulae like the Dumbbell and Helix Nebula. The C8N’s 8″ aperture also allows you to observe fine details, along with obvious azure, turquoise, and emerald colors in planetary nebulae like the Blue Snowball, the Ghost of Jupiter, or the Cat’s Eye.
With any 8” telescope, you can start to observe details in galaxies under dark skies, though light pollution washes most of them out. Galaxies such as Andromeda (M31), M82, M64, M65, and M101 show dust lanes, while traces of spiral arms in galaxies like M51, M33, and M101 can be detected, and you can observe many galaxy groups and clusters such as those in Virgo, Leo, and Coma Berenices.
Compared to a typical 8” f/6 Dobsonian, the C8N is slightly inferior for planetary viewing, as focusing is made more difficult by the mediocre single-speed rack-and-pinion focuser coupled with the shallower depth of field at f/5 versus f/6. Collimation is also more critical, and you need shorter focal length eyepieces to achieve the same power. However, decent planetary and lunar views are still possible. Expect to see plenty of detail on the Moon, the phases of Mercury and Venus, and a few dark markings on Mars, along with its polar ice caps. The moons of Jupiter are clear disks along with their shadows during transits, and Jupiter shows plenty of colorful cloud belts and storms, including the Great Red Spot. You can also resolve Saturn’s cloud bands, the Cassini Division in Saturn’s rings, and a handful of Saturn’s moons. Uranus’ teal disk is somewhat resolved, and a couple of moons are faintly visible next to it to the discerning eye under dark skies, while Neptune is often difficult to distinguish from a star, but its moon Triton is fairly obvious. Pluto requires a bigger telescope to see.
Deep-sky astrophotography with the Celestron C8-N Newtonian VX GOTO telescope can still be done, albeit only with shorter exposures, and you can expect to throw out a fair amount of frames that may be trailed. You are also going to need a motor focuser and almost certainly a coma corrector, as mentioned above. Smaller objects like galaxies, star clusters, and nebulae like Orion are an ideal fit for a 1000mm focal length, and the f/5 speed allows a decent signal-to-noise ratio even with the short exposures you’re limited to by the Advanced VX mount.
Planetary astrophotography is also possible with the Celestron C8-N Newtonian VX GOTO, though achieving a large enough image scale requires a 4-5x Barlow lens, which can be somewhat difficult to find a good example of (an f/10 SCT, on the other hand, only needs a 2-3x Barlow, which is more common). You can get great shots of the surface of the Moon, or sunspots with a solar filter. You can also image the phases of Venus and Mercury, various surface details and dust storms on Mars, resolve atmospheric details of Jupiter and Saturn along with the disks of Io, Europa, Ganymede, Callisto, and Titan, and possibly even reveal hints of atmospheric detail on Uranus; longer exposures/high gains will allow you to pick up the faint moons of Mars, Uranus, and Neptune.