The EdgeHD 8 Optical Tube
The Celestron Advanced VX 8” EdgeHD telescope features the Celestron 8” EdgeHD optical tube, an 8” (203mm) f/10 aplanatic Schmidt-Cassegrain telescope with a focal length of 2032mm, which can be reduced to 1422mm and f/7 with Celestron’s optional reducer or to an f/2 400mm system with a Starizona HyperStar kit (resembling the 8” RASA).
The EdgeHD design is a type of Schmidt-Cassegrain telescope that uses corrector lenses inside the baffle tube to eliminate edge-of-field aberrations. This design is similar to Meade’s ACF line, but has a wider range of focal reducer options and other accessories to choose from, such as the HyperStar system. The EdgeHD 8 otherwise functions like any other Schmidt-Cassegrain telescope, like the C8 XLT, with Starbright XLT multi-coated optics and no loss of light-gathering ability to any of its internal corrector lenses. However, the EdgeHD’s correction of coma and field flattening are only noticeable with a camera, as most wide-angle eyepieces have their own aberrations towards the edge of the field of view anyway that negate the field curvature found in a normal SCT (which is fairly subtle to begin with).
Besides the flattened field, another major optical difference I noticed between the EdgeHD 8 and a regular 8” Schmidt-Cassegrain was that the baffle tube of the EdgeHD is 2” in diameter, allowing for the use of wide 2” eyepieces or large format camera sensors without vignetting. Mechanically, the EdgeHD 8 features some other improvements, such as mirror locks to maintain focus during long exposures and HEPA-filtered vents to accelerate the cooldown of the telescope.
As with any Schmidt-Cassegrain, you collimate the EdgeHD 8 by adjusting three screws to tip and tilt the secondary mirror, which is a fairly seldom required process and not nearly as difficult as some would make it out to be; you can do it yourself in just a few minutes by following our collimation guide. The EdgeHD’s focus is achieved by adjusting a knob at the back of the telescope, which moves the primary mirror inside the tube and adjusts the position of the focal plane. You attach accessories such as the provided visual back, a focal reducer, or a camera adapter directly to the back of the EdgeHD 8’s standard SCT threaded port.
The EdgeHD 8 is supplied with a CGE-style dovetail rail, which fits the Advanced VX or any mount capable of fitting a Losmandy D-style plate (which is slightly larger). The top of the tube allows for easy attachment of a second dovetail of Vixen, CGE, or Losmandy design to piggyback a guide scope or other imaging accessories. The back of the tube also has a small carrying handle.
Accessories
The Celestron Advanced VX 8” EdgeHD telescope comes with a 1.25” visual back, 1.25” prism star diagonal, and a Celestron E-Lux 1.25” 40mm Plossl eyepiece, which provides 51x magnification with the EdgeHD 8 at its native 2032mm focal length. The visual back is a little longer than the one provided with normal SCTs to provide optimal spacing. The provided diagonal is the same unit supplied with many of the better Celestron telescopes and works well. The 40mm E-Lux has a rather narrow 43-degree apparent field of view due to the limitations of the 1.25” barrel size, leading to a true field of only about 0.85 degrees. A wider true field can be achieved with a 2” diagonal and eyepiece or the f/7 EdgeHD 8 reducer. You’ll want to use additional eyepieces anyway for higher magnifications.
The Advanced VX 8” EdgeHD includes a standard 9×50 straight-through, upside-down view finderscope with a true field of around 5 degrees. This finder shows stars and deep-sky objects fainter than your eyes alone. For aligning the Advanced VX mount, it is somewhat overkill, but the magnification and crosshairs make it easier to be sure you’ve got your target stars centered in the telescope’s field of view. For deep-sky imaging, you should remove it due to its weight, which exacerbates that of the already-heavy EdgeHD 8 optical tube; you won’t need it for plate solving anyway.
The Advanced VX Equatorial Mount
I found the Advanced VX to be the smallest, lightest, and lowest-quality of the Celestron computerized German equatorial mounts, borrowing from many of the other scopes and mounts I am familiar with; it uses the NexStar + hand controller and is compatible with the StarSense AutoAlign, SkySync GPS, and SkyPortal WiFi adapter accessories. The dovetail saddle on the Advanced VX accepts the EdgeHD 8’s CGE dovetail bar as well as smaller Vixen-style bars, but doesn’t quite fit a Losmandy D-style bar despite the CGE’s similar dimensions and uses cheap thumb screws instead of a clamping saddle that won’t mar your dovetail’s anodized finish.
On the surface, the VX’s 30 lb weight capacity and various features seem like a bargain, and it’s rock solid for holding the 8” EdgeHD optical tube for short exposure/planetary imaging as well as visual use. However, for imagers, it presents various concessions due to its cost-cutting measures in the design, and even in the best-case scenario, it would be inadequate for deep-sky astrophotography with the EdgeHD 8” optical tube anyway.
The Advanced VX is rated to a payload capacity of 30 lbs for visual use. Generally, even with a good mount, it is advised not to exceed half that amount for deep-sky astrophotography. The EdgeHD 8 weighs 14 lbs before you add any accessories to it, so it is pound to exceed the Advanced VX’s limitations. The EdgeHD 8’s 1425mm focal length with an f/7 reducer is extremely demanding on any mount, and the Advanced VX’s cheap servo motors and flaws in the design of the mount’s declination axis make tracking errors common. An autoguider can only compensate for so much thanks to the inherent inferior design of servo motors compared to good stepper-driven mounts.
The Advanced VX has ASCOM drivers for control via a computer, but the mount requires you to connect your PC through the hand controller to it to control the mount directly for imaging with NINA or SGP, and as a byproduct of this decision, you can only use an autoguider through the Advanced VX’s ST-4 autoguider port, which makes for more cables and a more error-prone setup. You also cannot use the popular EQMOD program to control tracking or guiding.
As such, for imaging with the EdgeHD 8, the Advanced VX is going to limit you to shorter exposure times and require you to throw out your frames or reduce exposure time if tracking/guiding errors persist. A larger, stepper-driven equatorial mount such as the Sky-Watcher EQ6R or Celestron’s own CGX would be a much better choice for this telescope.
Despite its flaws if you try to use it for deep-sky imaging, for visual use with the EdgeHD 8, the Advanced VX is just fine. After balancing the EdgeHD optical tube and leveling the tripod, you can perform polar alignment using a polar scope or the mount’s built-in All-Star Polar Align method. Once polar alignment is complete, the Advanced VX mount can be aligned to the sky using the NexStar+ hand controller. To align the mount, you need to slew to several alignment stars, center them in the finder, center them again in the EdgeHD 8’s eyepiece, and press a few buttons for confirmation on each. After alignment, the mount can automatically slew to and track any object in the hand controller’s 40,000 object catalog or however else you choose to control it. A single 11 lb counterweight is provided to balance the EdgeHD 8 optical tube for visual use; imagers will need a second counterweight.
Should I buy a Used Celestron Advanced VX 8″ EdgeHD?
A used Celestron Advanced VX 8” EdgeHD can be a decent package, though the same caveats for deep-sky imaging apply. Make sure that the mount powers on and the scope is free of obvious damage. The optics need to be clean and free of any fungus or corrosion, as well as debris inside the tube. Servicing an EdgeHD has to be done by Celestron if there is any debris or other issue inside the telescope due to the complex optical design of the scope compared to a regular Schmidt-Cassegrain. Missing parts such as adapters, a finder, counterweights, and knobs are thankfully fairly easy and inexpensive to replace, as is a missing or non-functional hand controller.
Alternative Recommendations
The Celestron Advanced VX 8” EdgeHD is not the best option for a visual or astrophotography telescope in its price range for the reasons we’ve outlined. You should consider one of the telescopes below – or pick out a separate high-quality optical tube and equatorial mount for deep-sky astrophotography.
Under $1200
- The Apertura AD10/Zhumell Z10/Orion SkyLine 10 offers slightly more resolving and light-gathering power than the EdgeHD 8, along with a plethora of accessories and a wider field of view, at an astonishingly low price.
- The Celestron StarSense Explorer 10” Dobsonian isn’t as well-accessorized as the AD10/Z10 but has a significantly lighter and more portable Dobsonian base as well as Celestron’s StarSense Explorer technology to help you navigate the night sky with your smartphone.
- The Celestron NexStar 6SE is lightweight, compact, and delivers sharp views of brighter targets with a fully motorized GoTo mount.
$1200-$2200
- The Apertura AD12/Zhumell Z12/Orion SkyLine 12 is significantly more capable than an 8” or 10” scope and offers a variety of high-quality features and accessories with a sturdy and easy-to-use Dobsonian mount.
- The Sky-Watcher 12” Collapsible Dobsonian is available in both manual and GoTo configurations, the latter offering the ability to be aimed by hand thanks to its FreedomFind encoders. The collapsible tube is easy to set up but helps a lot with storage and portability.
- The Celestron NexStar Evolution 6” features high-quality Schmidt-Cassegrain optics with the improved NexStar Evolution mount, which has a sturdier tripod than the 6SE as well as a built-in WiFi adapter and lithium battery for convenience.
$2200+
- The Celestron NexStar Evolution 8” offers identical viewing capabilities to the EdgeHD 8 with the conveniences of its lightweight fork mount and tripod, built-in WiFi and lithium battery, and the option of an EdgeHD version with StarSense auto-align technology too.
- The Celestron Advanced VX RASA 800 is essentially an EdgeHD 8 with a built-in Hyperstar f/2 conversion kit; it’s not usable with every camera, but it’s a decent setup as the 400mm focal length exposes fewer of the Advanced VX mount’s flaws.
- The Celestron Advanced VX 9.25” SCT is more capable than the EdgeHD 8 for visual use or planetary imaging while remaining essentially the same with regard to portability and cost.
Aftermarket Accessory Recommendations
The EdgeHD 8 benefits from the use of a dew shield to prevent condensation from forming on the front Schmidt corrector plate. Dew, of course, fogs up your views and images, but it also contains trace acids, chemicals, and pollen, which can chemically attack the coatings on the scope’s front corrector plate and even etch the glass itself. A basic flexible dew shield is usually sufficient, but heated plastic or metal dew shields may be necessary in very humid climates. A dew shield also helps to prevent stray light from entering the telescope, improving contrast like a lens shade, and protecting the corrector plate from accidental touches.
The EdgeHD 8’s specially designed 0.7x focal reducer is a must for deep-sky imaging. It screws onto the back and brings the scope down to f/7 and a focal length of 1425mm. You can use the reducer for visual astronomy as well, though a 2” star diagonal and 2” eyepieces may be more effective for the job. If you are interested in using 2” accessories, the Apertura 38mm SWA (53x) and 2” dielectric screw-on diagonal also from Apertura, are an ideal fit; the 0.7x reducer and 40mm E-Lux suffice as an equal, albeit less immersive, alternative. Higher powers up to 300-400x can be achieved with additional 1.25” oculars; our top picks would be a medium-power eyepiece such as a 15mm SWA (135x) or Explore Scientific 14mm 82-degree (145x), and a higher power eyepiece like the Explore Scientific 8.5mm 82-degree (239x) or a 9mm redline/goldline (226x). A good Barlow lens can also be used to achieve higher powers and doubles as an accessory for planetary imaging use. You will also want an Orion UltraBlock or similar UHC nebula filter to improve views of nebulae; choose the 2” version if you are getting a 2” diagonal as it can be used with either size eyepiece with a threaded 2” to 1.25” adapter.
For imaging purposes with the EdgeHD 8, a motor focuser and Bahtinov mask are highly recommended. And as previously mentioned, a Starizona HyperStar f/2 kit turns the EdgeHD 8 into an f/2 Schmidt camera, which can be used with the Advanced VX. However, the 8” RASA has this conversion essentially permanently built in and is cheaper.
If you’re planning on imaging, in addition to a large guide scope or off-axis guider for the EdgeHD 8, along with an autoguider camera, you’ll need a polar scope or PoleMaster to accurately polar align the Advanced VX (a polar scope is also good for visual use). Lastly, either an AC adapter or a power supply such as the Celestron PowerTank Lithium Pro.
What can you see?
The EdgeHD 8 can achieve a maximum field of view of around 1.3 degrees with a 2” wide-angle eyepiece or a 1.25” eyepiece and its f/7 reducer. This is rather small when you consider most 8-10” Dobsonians can reach a true field of around 2 degrees; a narrower field limits your options in viewing open star clusters and the largest nebulae. However, many of the smaller open clusters, such as M11 or M35, are still a delight with the EdgeHD 8 and you can resolve many of the brighter globular star clusters from the Messier catalog into their individual components too. Small, colorful planetary nebulae like the Blinking Planetary or the Saturn Nebula show tiny details and an array of bluish and greenish colors, while larger emission nebulae such as Orion (M42), the Lagoon (M8) and the Swan (M17) are fantastic even under so-so conditions, though a UHC filter enhances the view.
Galaxies through the EdgeHD 8 will be washed-out smudges under light-polluted skies. Transport the telescope to a suitably dark location, however, and you’ll be able to resolve details such as hints of spiral arms, H-II regions, and high-contrast dust lanes in many of the brighter galaxies from the Messier and NGC catalogs, as well as groups of dozens or even hundreds of galaxies like the Virgo Cluster or Fornax cluster.
The EdgeHD 8 is also superb for viewing the Moon and planets, as is any optically decent telescope of its aperture. The phases of Mercury and Venus, as well as dark markings and polar ice caps on Mars, can be seen when the three inner planets are well-placed for viewing. The Moon shows stunning details merely miles across on a night of steady seeing. Jupiter’s cloud belts and the Great Red Spot, along with other atmospheric features, are sharp and colorful, and the four Galilean moons can be seen as tiny disks with round inky shadows moving across the planet’s cloud belts during their frequent transits. The EdgeHD 8 also reveals the Cassini Division in Saturn’s rings, along with possibly even the Encke gap on an extraordinary night, along with the brown to beige cloud belts in Saturn’s atmosphere and a half dozen moons. Uranus’ teal disk can be resolved as a fuzzy dot, with one or two moons faintly accompanying the planet. Neptune’s tiny angular size makes resolving it difficult without very high power and good seeing, but the EdgeHD 8 can pick up Triton next to it. Pluto is too dim to be seen with an 8” telescope under all but the best viewing conditions and to the well-trained eye.
Astrophotography Capabilities
Deep-sky astrophotography with the Advanced VX 8” EdgeHD can be done, but don’t expect exposures longer than a minute and be sure to use the 0.7x reducer and a sufficient autoguider. Galaxies and smaller star clusters or nebulae are ideal targets. However, expect plenty of even fairly short subframes to have to be discarded due to trailing from tracking errors, as the 1425mm focal length is very sensitive to these problems.
The Advanced VX 8” EdgeHD is ideal for planetary imaging, coupled with a 2x, 2.5x, or 3x Barlow lens to boost it to f/20 to f/30, along with a high-speed planetary video camera like the ZWO ASI224MC (which can also do double duty as a guide camera for deep-sky astrophotography). Mars, Jupiter, Saturn, and the Moon all make excellent targets under good seeing conditions, and you can also get recognizable shots of Mercury, Venus, Uranus, and Neptune. The moons of the ice giants can be brought out with a high gain setting or properly timed exposures.
