Personal Experience
I’ve had one of these for a little over a year. Unfortunately, the weather has prevented me from getting as much use out of it as I’d like, but this image of M51 was taken with it (105x two-minute subs using an SBIG STF-8300C from my backyard just outside of Houston).
The OTA is a little on the heavy side. My total rig weighs in at around 25 lbs., which my mount handles ok, but sometimes I wish I’d gotten the 6” version (which also has a bit wider field of view).
Overall, however, I love this scope and expect to get a lot of use out of it over the next several years. I would not, however, recommend this to a beginner. This is good for someone with at least a little experience under their belt, but it might be a little challenging for someone just starting out. In the hands of someone who knows what they’re doing, this sucker does perform.
The Primary and Secondary Optics
The Orion 8 inch f/3.9 Imaging Newtonian is, as its name suggests, a Newtonian telescope that has been optimized for astrophotography with an 8-inch (200mm) aperture and f/4 focal ratio. The optical tube’s short focal length of only 800mm allows your camera to capture a lot of photons quickly.
The 8″ astrograph’s BK7 primary mirror cools down quicker than a plate glass primary mirror but is not as low in thermal expansion as a true borosilicate (Pyrex) primary mirror. But I guess most users won’t notice much of a difference. The back of the primary mirror cell features a 12V DC-powered 80mm fan to help cool the primary mirror down to ambient temperature faster.
Many other Newtonians that I’ve handled often had secondary obstructions with diameters around 20–25% of the aperture. When I use such scopes for imaging, I often find that they don’t fully and evenly illuminate my camera’s sensor, especially if I have to modify the scope and move the mirror forward to address focus issues with the scope. I end up getting significant vignetting in images, and flat frames don’t always get rid of all of it.
However, Orion has this base covered: the secondary mirror in the Orion 8” f/4 Astrograph is a full 70mm, or nearly 35% of the aperture, offering full illumination for common APS-C sensors in most consumer DSLRs, as well as many CCD or CMOS imaging cameras I’ve tested it with.
While a larger 70mm secondary may slightly decrease the total light-gathering area and decrease contrast, Orion’s addition of nine internal baffles inside the optical tube helps reduce stray and off-axis light, effectively increasing contrast. This makes up for most of the lost contrast, if not increasing it further.
Focuser, Collimation, and Other Mechanics
The Orion 8” f/4 Astrograph uses a GSO Linear Bearing 2” dual-speed focuser, as seen in the picture above. This Crayford focuser design includes a smooth metal rail to keep the focuser as stiff as possible, with as little play or wobble as possible. However, in practice, I encountered some issues with the focuser seizing up, which needed some tinkering with the screws to achieve a balance between smooth motion and overall stiffness.
The collimation of the Orion 8” f/4 Astrograph is adjusted with a set of 3 spring-loaded knobs at the back for the primary mirror (secured by three additional locking screws), while the collimation of the secondary mirror requires a hex key. Our collimation guide goes into more detail on the process. In my experience, the scope holds collimation pretty well, though I replaced the stock springs in the primary mirror cell to make it even stiffer.
To attach to a mount, the Orion 8” f/4 Astrograph comes with a pair of standard tube rings (visible in the above picture) and a Vixen-style dovetail bar. The bar can easily be replaced with a Losmandy-style bar if you wish. I’d also recommend you attach a second dovetail to the top of the rings for increased rigidity and to mount accessories such as a guide scope.
Included Accessories
The Orion 8” f/4 Astrograph includes a standard 35mm long 2” diameter extension tube to reach focus with eyepieces for visual use, a collimation cap, and a 1.25” compression ring adapter. You also get an 8×50 straight-through finder scope, which attaches to the standard Vixen/Synta-style shoe on the tube and is more than sufficient for most purposes.
Mount That I’d Recommend
For imaging use, you’ll need a solid mount. Something with a payload capacity of 40 lbs. or better is what I’d recommend.
Mine sits on top of my iOptron iEQ45. With my SBIG STF-8300C for imaging, along with an Orion ST-80 and Atik 16C for autoguiding, plus the necessary mounting hardware, cords, wires, cables, etc., my imaging payload weighs in at around 25 lbs.
While this is well within the weight range for the mount, any experienced astrophotographer will recommend you keep the payload at or less than half of the mount’s rated weight. Unless you have a mount with a higher limit, you will most likely be over the recommended imaging weight. Still, as long as your mount is dialed in correctly and has good autoguiding, I think you should find that this scope works nicely.
That being said, I wouldn’t recommend using it for imaging on a lesser mount like the Celestron Advanced VX or any other mount that isn’t capable of 40 lbs. of payload or more. Something like my iEQ45 or a SkyWatcher EQ-6R Pro should handle it just fine, and a Celestron CGEM II or Orion Atlas EQ-G should handle it as well.
A Note on Buying Used Orion 8” f/4 Astrograph
A used Orion 8” f/4 Astrograph may be an older version with a standard dual-speed 2” Crayford focuser rather than a linear bearing hybrid unit, but it is otherwise identical.
As usual, be sure that the scope’s mirrors are clean and free of corrosion; a little dust or dirt is fine and is fairly easy to clean.
Note that missing mounting rings are actually a fairly expensive item to replace (over $75 USD) and you’ll need to be sure to get the correct 230mm GSO-made mounting rings if so.
Aftermarket Accessory Recommendations
- A Coma Corrector
The last concern of a Newtonian for imaging is coma. All Newtonians experience it to some degree or another. One of the easiest remedies is to increase the focal ratio. Over f/6, coma becomes much less noticeable, and around f/8 or so, it’s nearly gone. But at f/3.9, it’s obvious.
Anyone who gets Orion 8″ f/4 astrograph or one of its siblings will need a coma corrector for imaging use. I don’t really see it as an option. For visual observation, if you are using any kind of 2” wide-angle ocular, you will probably get annoyed by the coma, as I did, and will also want a corrector.
Prices vary on these. At the lower end of the price spectrum is the GSO Coma Corrector, sold under several brand names. Reviews of its performance are mixed, however, and it was designed more with visual observation in mind.
At the top of the line, I know of no better option than the TeleVue Paracorr. But while these tend to be the best, they also tend to be the most expensive—often as much as or more than the telescope itself. The Explore Scientific HRCC and SharpStar coma corrector also work well.
- Better Collimation Tool
A serious user will want something better than the stock collimation cap—at least a Cheshire and probably a high-quality laser collimator. If it was upto me, Orion should consider changing out the collimation screws in the secondary with knurled-knob screws like those available from Bob’s Knobs. That all being said, the scope holds collimation well when not moved around constantly.
- Eyepieces and Filters
For visual use, this scope does best with UWA-type and similar well-corrected eyepieces like the Explore Scientific 82-degree series, Tele-Vue Naglers, and similar eyepieces from APM and Astro-Tech. You’ll want a number of different focal lengths for varying magnifications. For visual use, the widest possible field is around 3 degrees, or 6 times the angular diameter of the Moon.
You might also want a good UHC nebula filter such as the Orion UltraBlock 2” if you plan on doing deep-sky observation with the Orion 8” f/4 Astrograph.
Deep Sky and Planetary Astrophotography Capability
The Orion 8” f/4 Astrograph is a solid imaging scope with a lot of light grasp. If you have the mount for it, this scope performs very well, particularly on fainter targets. On brighter targets, like Messier objects, you might even need to reduce the exposure time for individual subs to avoid overexposure.
The field of view you’ll get will depend largely on your image sensor, but DSLR imaging should yield a field of view close to 1.5° wide by 1° high, just about perfect to frame M42 or M8 nicely, big enough to fit the Flame and Horsehead nebulae in the field, as well as M81 and M82, or the Leo Triplet.
A 5x Barlow lens or multiple stacked weaker Barlows/focal extenders will allow you to do planetary imaging with this scope, though it’s harder to achieve sharp focus and good enough collimation at f/4. You can still get good images of the Moon, Mars, Jupiter, and Saturn with a suitable high-speed CMOS camera. Given that many of these cameras double as guide cameras, which you will need for deep-sky astrophotography anyhow, it’s worth giving planetary imaging a shot with the 8” f/4 Astrograph given the only additional cost is that of the Barlow lens.
What can you see?
As a visual scope, this instrument performs admirably but is definitely not ideal. If mounted to a German Equatorial Mount (GEM), I find the eyepiece ending up in all sorts of awkward and uncomfortable viewing positions. This is best dealt with through some sort of tube rotation device. I, being a DIY-minded user, opted Wilcox Rotating Rings, a homebrewed solution.
Once you’ve got a comfortable mounting situation figured out, the Orion 8” f/4 Astrograph is a great scope for viewing deep-sky objects, though as always, light pollution is a big factor.
- Open star clusters – even the biggest ones, such as the Beehive (M44) and Sagittarius Star Cloud, are jaw-dropping under most conditions with this scope and a 2” wide-angle eyepiece.
- The brighter globular star clusters such as M13 and M15 can be resolved into their individual members with magnifications of 100x or more even from suburban skies.
- Nebulae such as Orion (M42) and the Lagoon (M8) are nice even from light-polluted locations but truly shine under dark skies, especially with a UHC nebula filter, which also allow for superb views of huge nebulae like the Veil supernova remnant and North America Nebula in Cygnus.
- Galaxies show details such as dust lanes and hints of H-II regions under optimal conditions, and I can of course make out various groups including the Virgo Cluster of galaxies.
- Smaller planetary nebulae are quite colorful and look great at high magnifications under good seeing conditions with this scope as well.
The Orion 8” f/4 Astrograph isn’t quite as good as a slower f/ratio Newtonian reflector such as a standard 8” f/6 Dobsonian for lunar and planetary viewing. It’s mainly because focusing is harder at f/4 and the huge 35% central obstruction creates additional diffraction, causing slightly fuzzier images much like an 8” Schmidt-Cassegrain. I can still get impressive views at the eyepiece nonetheless, though I’ll need very short focal length eyepieces or a good Barlow lens to get above 100x for optimal planetary views and splitting double stars.
- Mercury and Venus show their phases in the 8” f/4 Astrograph.
- Mars displays a polar ice cap and a few dark markings when it’s close to Earth.
- The Moon is, of course, a delight at any magnification.
- Jupiter’s cloud belts and Great Red Spot are vivid and detailed, while its four Galilean moons appear as tiny disks with jet-black shadows during occasional transits.
- Saturn’s glorious ring system and the Cassini Division in them can be seen along with the planet’s own dull stripes and a handful of moons.
- The teal disk of Uranus is accompanied by up to 4 faint moons under optimal conditions (though you may struggle to see any of them at all without a bigger scope).
- Neptune appears as a fuzzy blue dot with its icy moon Triton fairly apparent next to it, while Pluto is hypothetically visible as a star-like point with a telescope of this size but in practice needs more aperture even under dark skies owing to its faintness.
