Orion’s XT series is the quintessential, a most well-known line of Dobsonian telescopes. With scopes ranging from apertures of 4.5” to 12”, they are often recommended to beginners and experienced amateurs alike.
The XT10 is the largest of the non-computerized, black-tube XT scopes, with more or less just a scaled-up design of the smaller ones. Let’s dive right in.
The Optical Tube
The XT10 is a 10” f/4.7 Newtonian. This moderately fast focal ratio means that collimation is more challenging and the tolerances are lower, but, more importantly, it doesn’t perform as well with cheap eyepieces. A wide-field eyepiece which works moderately well in an f/6 or longer telescope can be disastrous in the XT10. To get the most out of this scope, plan on spending at least a few hundred bucks on eyepieces.
Ideally, one would get a coma corrector such as the Explore Scientific HR Coma Corrector or Tele-Vue Paracorr to use with this scope, but the former is significantly expensive and the latter costs almost as much as the whole telescope – I do not recommend the GSO coma corrector as it lacks a tunable top.
If you can find a good deal on a coma corrector and some well-made wide-field eyepieces, you’ll really get the most of what the XT10 has to offer and pinpoint stars from one edge of the field to the other.
The XT10 comes with a large – but very well-made – fully metal single-speed Crayford focuser. The only gripe I have with the focuser is that it doesn’t use a compression ring, which can result in offset eyepieces and slight image quality loss.
The XT10 comes with a lone 25mm Plossl eyepiece for low power. While it is functional, you’d be best served by getting a 2” wide-angle eyepiece in the 26mm to 32mm range for low power as well as eyepieces of around 14mm, 9mm, and 6mm focal length for progressively higher magnifications.
The XT10’s supplied red-dot finder works, but it’s not useful in finding faint deep-sky objects. A Telrad/Rigel Quickfinder and/or a 50mm finderscope will do wonders in improving your ability to locate faint fuzzies.
The XT10’s mount is made out of melamine-covered particle board. While cheap and functional, if damaged it’s hard if not impossible to repair, and furthermore if damaged it will quickly warp and rot due to moisture seeping in. Also, it’s heavy compared to a plywood or hardwood mount.
The XT10 uses Orion’s spring tensioning system to balance properly with heavy eyepieces even though its altitude bearings are small (we’ll get to this in a moment), which works reasonably well but doesn’t allow for adjusting the tension (ease of movement) in altitude.
The bearing pads are made of Nylon instead of genuine Teflon and the laminate is just melamine rather than Formica or Ebony Star laminate. While this isn’t a problem with the smaller XTs, it leads to less-than-ideal motion, particularly at high power and in altitude. The scope’s tiny altitude bearings don’t aid this, either, as the massive 30-lb weight of the telescope’s tube pivots down on just a few square inches of area.
You can order real Teflon and cut some pads out of it for less than $30 (use brads and a hammer to nail it in place) and nail a piece of scrap Formica to the bottom of the azimuth bearing for a pretty good price. These improvements will mostly fix the sticky, squeaky bearings, though the scope’s altitude motions will never be quite perfect.
In The Field
The XT10 is large. Some would even call it intimidating. The complete scope weighs 53.4 lbs, with 30 of those being the tube and 23 in the mount. The problems handling it don’t arise as much from the scope’s weight as its sheer width – the smooth metal tube has nowhere to grab onto except the bearings and each end, which makes carrying it awkward and difficult. Adding a handle or straps of some kind helps tremendously.
The XT10’s tube fits across the back seat of most cars, so portability is no worse than a 6” or 8” telescope.
One of the first telescopes I ever looked through was an XT10 (actually, two of them). These scopes are often decried as mere “light buckets”, only useful for deep-sky observation, but they perform quite favorably on the Moon, planets, and other high-resolution targets as well. A 10” is at just the right size for these things, in fact, as it is that largest aperture that only has to put up with one atmospheric “air cell” – that is, one column of turbulent air. A scope any larger than 10” is looking through multiple air cells and will suffer more from bad atmospheric “seeing” as a result.
The Moon is fantastic in a 10” telescope, with craters down to a couple kilometers in diameter visible.
Mars when it reaches opposition (the next time this happens will be in 2020) can show up to an astounding two dozen dark markings (areas of darker sand and rocks on the planet’s surface) as well as its ice caps. If timed correctly and if one places the Red Planet just outside the field of view, Mars’ outer moon Deimos is a pretty easy catch, while Phobos can be spotted on rare occasions (though I’ve yet to do so) if one can shield it from Mars’ bright glare.
The asteroid (4) Vesta can just barely be surmised as non-stellar on an excellent night when it is closest to Earth and is a brilliant gold color.
Jupiter’s moons are not only disks with a 10” scope, but they actually begin to show little bits of color. Io is a nice orange-yellow, Europa is a faded white, and Ganymede and Callisto are brownish-gray.
Saturn’s moon Titan is clearly more than a star-like point and is a distinct yellow-orange color (which results from methane smog in its upper atmosphere). Saturn itself will show numerous cloud bands and about a half-dozen other moons.
Uranus’ moons can be caught with a 10” telescope. In mine, I’ve only spotted the brightest two – Titania and Oberon.
Neptune and its moon Triton are an easy catch in a 10”, while Pluto can just be glimpsed from a dark site with minimal light pollution to the south – something I am not blessed with.
Outside the solar system, a 10” scope shows you a lot. Many bright globular clusters (the brightest few dozens) are resolvable into stars, while scores of them are at least visible.
The Blinking Planetary nebula in Cygnus is bright enough that it no longer “blinks” like in a smaller telescope. Many other planetary nebulae previously invisible or dim in a smaller aperture are colorful, ranging from azure to turquoise, and can have structure visible in them.
The Virgo Cluster is pretty crowded in the spring, while the dimmer galaxy clusters in Perseus and Coma have several members. NGC 206, the star cluster in the Andromeda Galaxy, is visible as a grainy fuzz – and Andromeda itself stretches out as an oblong glow for several degrees. The famous Whirlpool Galaxy starts to show hints of spiral arms from a reasonably dark site.
What's The Bottom Line?
The Orion XT10 is excellent value for the money, though it’s better to think of it as an upgradable kit than a completely functional instrument right out of the box – at the very least, you can use more eyepieces and a real finder. But in terms of value and all-around usefulness, I can think of nothing better. If I could have only one telescope, it’d be a 10” Dobsonian like the XT10.