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. I can reduce it to 1422mm and f/7 with Celestron’s optional 0.7x focal reducer or to an f/2 400mm system with a Starizona HyperStar kit (resembling the 8” RASA).
Difference Between Regular and EdgeHD 8″ SCT
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 the now-defunct Meade’s ACF line but has a wider range of focal reducer options and other accessories to choose from, such as the aforementioned HyperStar system. The EdgeHD 8 otherwise functions like any other 8″ 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, I expect EdgeHD’s correction of coma and field flattening to be noticeable only 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 and a regular 8” Schmidt-Cassegrain is that the baffle tube of the EdgeHD is 2” in diameter, allowing me to use 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 exposure astrophotography and HEPA-filtered vents to accelerate the cooldown of the telescope.
Doing the Collimation
As with any Schmidt-Cassegrain, I collimate the EdgeHD 8 by adjusting three screws to tip and tilt the secondary mirror, which is a fairly seldom required process. It’s also not nearly as difficult as some would make it out to be. You can do it yourself in just a few minutes by following my collimation guide.
Focusing, Accessory Attachment, and Mount Compatibility
The EdgeHD’s focus is achieved by adjusting a knob at the back of the telescope, which moves the primary mirror inside the tube.
We 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.
Set of Included 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.
I spotted that the visual back is a little longer than the ones I’ve seen in normal SCTs, and that is to provide optimal spacing.
The provided diagonal is the same unit that I received 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. I can achieve a wider true field of view with a 2” diagonal and 2″ 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 my eyes alone. For aligning the Advanced VX mount, it felt like somewhat of an overkill, but the magnification and crosshairs make it easier to be sure I’ve got my target stars centered in the telescope’s field of view. For deep-sky imaging, I remove the finderscope due to its weight, which exacerbates that of the already-heavy EdgeHD 8 optical tube. I don’t need it for plate solving anyway.
The Advanced VX Equatorial Mount
The Advanced VX is 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. The saddle makes use of cheap thumb screws instead of a clamping saddle that won’t mar our dovetail’s anodized finish.
Difficulties for Long Exposure Deep Sky Imaging
On the surface, the VX’s 30 lb weight capacity and various features seem like a bargain. First of all, I’m in full agreement that it’s rock solid for holding the 8” EdgeHD optical tube for short exposure/planetary imaging as well as visual observation use. However, for deep-sky imagers, the Advanced VX mount presents various concessions due to its cost-cutting measures in the design.
The Advanced VX’s rated payload capacity of 30 lbs is actually for visual use. For deep-sky astrophotography, even with a good mount, it’s generally not advised to exceed half that amount. The EdgeHD 8 weighs 14 lbs before I add any accessories to it, so it is bound to exceed the Advanced VX’s limitations.
The Advanced VX’s cheap servo motors and flaws in the design of the mount’s declination axis make tracking errors common when I use it. An autoguider can only compensate for so much thanks to the inherent inferior design of servo motors compared to good stepper-driven mounts. I’m certain that 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.
The Advanced VX has ASCOM drivers for control via a computer, but the mount requires me to connect my PC through the hand controller to it to control the mount directly for imaging with NINA or SGP. As a byproduct of this decision, I 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. I also cannot use the popular EQMOD program to control tracking or guiding.
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 focal 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.
All being said, even in the best-case scenario, it would be inadequate for deep-sky astrophotography with the EdgeHD 8” optical tube. The EdgeHD 8’s 1425mm focal length, even when I use it with an f/7 focal reducer, is extremely demanding on any mount that I use.
Setting up and Using the Mount
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-pound counterweight is provided to balance the EdgeHD 8 optical tube for visual use. For imaging, I needed a second counterweight.
Planetary Imaging Capabilities
The Advanced VX 8” EdgeHD is ideal for planetary imaging, coupled with a 2x, 2.5x, or 3x Barlow lens to boost it to a focal ratio of 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-sighting conditions, and I 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.
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 I’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.
- 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 Accessories 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 our 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. I can use the reducer for visual astronomy as well, though a 2” star diagonal and 2” eyepieces are more effective for such a 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; my 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 telescope 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.
Observing With the EdgeHD 8
The EdgeHD 8 can achieve a maximum field of view of around 1.3 degrees with a 2” wide-angle eyepiece or with a 1.25” eyepiece and its f/7 reducer. This is rather small when I consider most 8-10” Dobsonians can reach a true field of around 2 degrees.
A narrower field limits our 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 I 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 are washed-out smudges under light-polluted skies. If I transport the telescope to a suitably dark location, I’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.
