Aperture: 203mm (8 inches)
Focal Length: 1,200mm, f5.9
Weight: 19k (tube 9kg, mount 10kg)
Supplier: The Widescreen Centre
Telephone: 020 7935 2580
When it comes to getting a good amount of aperture for your money, you would be hard-pressed to do better than a Dobsonian: a simple Newtonian optical design on a push-pull mount.
By keeping it simple, you can get a large aperture very cheaply.
However, many Dobsonians are packaged with the bare minimum of accessories and sometimes corners are cut in their manufacture, too.
Orion has addressed this issue with improved design features and the extra accessories included in its XT8 PLUS package.
In addition to the 8-inch, f5.9 Dobsonian, it includes a 28mm DeepView 2-inch eyepiece, 10mm Plössl 1.25-inch eyepiece, 1.25-inch 2x Barlow lens, full-aperture solar filter, red-dot finder, collimation cap and the planetarium program Starry Night.
The scope arrived in two boxes with all the tools you need to put it together provided.
Doing this is a one-person job – within an hour we had the scope assembled, collimated and ready to go.
The mount and scope are both lightweight and easy to carry in separate trips.
The overall build quality was good and the mount provided a solid base for the tube with very little flexing, but we felt it was let down a little by the use of chipboard.
Although laminated and sealed with a rubber rim, chipboard can be prone to water damage if left damp after observing in dewy conditions.
Orion SkyQuest XT8 PLUS Dobsonian telescope
Testing the extras
The mount’s axes were adequately smooth to slew the scope and track objects at high magnifications.
The scope is well-balanced and even when we inserted our own heavy eyepieces only a little tension adjustment was needed to stop the front end from tipping.
However, there is no handle on the tube for guiding the scope, which would have been a welcome addition.
Turning skywards, we slewed to Vega using the red-dot finder supplied, the Orion EZ Finder II reflex sight.
It is a little plasticky, with a small screen and slightly elongated red dot, but it still allowed us to locate our target.
The 28mm DeepView eyepiece was reasonably sharp, but showed astigmatism towards the edge of the field.
Switching to the 10mm Plössl eyepiece at 120x magnification, the diffraction rings were concentric but elongated, suggesting that some astigmatism was present in the optical train.
We discovered that this was due to the primary mirror clips being over-tight and deforming the mirror slightly.
This is a common problem and easy to fix, though it’s not mentioned in the instructions.
The very diffuse Triangulum Galaxy is a challenge under light-polluted skies, but the XT8’s 8-inch aperture succeeded in showing its faint glow in the 28mm DeepView eyepiece.
We got an excellent view of the Ring Nebula in Lyra – small, bright and glowing faintly in the middle.
Zooming in with the 10mm Plössl, the view was still sharp and well-defined, so we tried out the supplied 2x Barlow lens.
At 240x magnification, the view remained sharp in moments of good seeing.
Unfortunately, the 1.25-inch Barlow lens cannot be used with the 2-inch DeepView eyepiece.
The glaring issue
Observing deep-sky objects is a strength of Dobsonians and this one was no exception, but the next test was the Moon.
When slewing towards a bright gibbous Moon we noticed some glare in the eyepiece: this was due to light reflecting off the internal surface of the telescope, meaning it was not adequately blackened.
When observing objects near the Moon or a streetlight, these internal reflections severely reduced the contrast.
Looking at the lunar surface itself, the scope delivered, offering sharp, high-contrast views of crater Gassendi and the rilles on the floor of the Mare Humorum.
Although a few minor shortcomings mean it falls slightly short of getting top marks, the XT8 PLUS is a well thought-out package that offers a good option for a first scope.
All the accessories essential to getting started are included, while the detailed instructions will make the learning curve much easier for a first-timer.
The dread of collimating mirrors can be a turn-off, especially for a beginner, but the XT8 addresses this task admirably.
First, the instructions walk you through the process clearly with good illustrations.
Second, a collimation cap is included.
This is a basic tool, but it did the job and we did not feel the need to use a Cheshire or laser collimator.
But most importantly, both mirrors are fitted with thumbscrew adjustment knobs, so there’s no risk of dropping an Allen key onto the primary mirror.
As it happened, the factory-set collimation was not far off and we didn’t need to adjust the focuser’s collimation at all.
Five minutes with the collimation cap and a small tweak with a star test before each observing session resulted in perfect collimation.
The 8-inch, f/5.9 primary mirror is the heart of the XT8. The secondary mirror is only 23 per cent of the primary mirror’s diameter, and a small obstruction means high contrast.
Both mirrors are coated with enhanced aluminium and silicon oxide coatings, offering 94 per cent reflectivity.
The Teflon bearings on both axes allow the scope to slew and track smoothly. The altitude axis is well balanced, and by tightening the tension knob the scope doesn’t tip with heavier eyepieces. The manufacturer has added some nice touches too: an eyepiece rack, carry handle, weight-reducing cut-outs and a white edge around the base for visibility.
The coarse and fine focusing action of the dual-speed, 2-inch Crayford focuser was smooth and did not slip under the weight of heavy eyepieces. It worked well straight out of the box without needing adjustment and all our eyepieces came to focus. An extension tube and 1.25-inch adaptor are included.
The package includes a 28mm wide-field eyepiece (2-inch fit), a 10mm Plössl eyepiece (1.25-inch fit) and a 2x Barlow lens (1.25-inch fit). These offer magnifications from 43x to 240x: a good selection to get you started, but you’d do well to buy something in the 13-18mm range eventually.
The supplied Safety Film Solar Filter fits securely and covers the scope’s full aperture: a very safe way to view the Sun’s surface. The film delivered a detailed, high-contrast and neutral white image, revealing an incredible network of sunspots and even granulation, despite the poor seeing at the time we tested it.
This review originally appeared in the January 2014 issue of Sky at Night Magazine.