Reviewing the Optical Tube Of Orion XT6
The XT6 is a 6” (152mm) f/7.8 reflector with a focal length of 1178 mm, approximating a common standard of telescope for the past century. The reason the 6” f/8 has been so ubiquitous and is perhaps the perfect beginner’s telescope, is because it works. A 6” f/8 parabolic primary mirror is very easy to make, and the tube of a 6” f/8 is only 48” long, making it fairly portable and keeping the eyepiece at a comfortable height. Lastly, at f/8, there’s no need to worry about ultra-precise collimation or the aberrations caused by using inexpensive eyepieces. As with the XT8, the XT6 uses a plate glass primary mirror, not the BK7 or Pyrex primary mirror material found in many other full-sized Dobsonians. The difference in glass substrate has a negligible impact on cooldown time at this size.
The XT6 can be easily collimated, though adjusting the secondary mirror does require tools—namely, a small hex/Allen key. However, you’re unlikely to need to align the secondary mirror very often or at all.
The newest incarnation of the XT6 finally sports a 2” focuser, and an all-metal Crayford unit at that. It uses a brass compression ring to grip your eyepieces, as does the 1.25” adapter, which also has T threads for installing a DSLR camera. The 1.5” secondary mirror is also big enough to fully illuminate the field of a low-power, wide-angle 2” eyepiece, unlike the smaller secondary mirrors in most other 6” f/8 Dobsonians. However, if wide views are what you’re looking for, a 6” f/5 tabletop scope will provide a wider field of view even with only a 1.25” focuser and at a similar cost.
About the Accessories
The XT6 comes with a single eyepiece – a 25mm Plossl providing 47x magnification. While nice, you do need a high-power eyepiece or two to get the most out of the telescope, which is, of course, an additional investment you should factor into your budget.
The included red dot finder works adequately, but a 9×50 finderscope or Telrad is a vastly better choice if you plan on doing much deep-sky observing. However, either is going to cost you some money that could also go towards another eyepiece.
A smartphone adapter is included with the XT6. It’s great for taking photos of the Moon. With some practice, imaging some planetary detail with a high-magnification eyepiece is possible – though inferior to a dedicated camera. However, a smartphone is much better for taking pictures through the XT6 than a DSLR is – and easier to use, too.
Lastly, the XT6 includes a collimation cap, which is really all you need to collimate this telescope. Our collimation guide explains in detail how to use one.
How Good Is The Mount?
The XT6 uses a fairly standard Dobsonian mount with plastic altitude bearings supported by Orion’s spring tensioning system, which prevents the scope from swinging around the sky when you swap out eyepieces or use heavy accessories on the front of the scope that would otherwise cause its balance point to shift. Besides attaching the springs, there is no additional setup required for the mount – just plop the scope on, attach the springs to their holders on the base and you’re ready to go. Like almost all Dobsonians, there are no clutches or slow-motion controls – just grab the tube and swing it around the sky.
The XT6’s base is made from particleboard overlaid with melamine. Not only is it heavy, but if the melamine is damaged the whole thing will quickly warp and rot. Thankfully, you can easily make your own base out of ¾” plywood or buy one from a third party should this ever become an issue. However, provided you take care of it and don’t mind the weight the stock base is just fine and conveniently assembles out of the box in just a couple of minutes with the included Allen key and screws.
Should I buy a used Orion SkyQuest XT6?
There are XT6 units floating around that are close to 20 years old now – older ones have a 6×30 finder which is nearly useless, and a metal focuser that is arguably superior to the current one, but otherwise there have been no changes. Provided the mirror coatings are in good condition, there is little to go wrong with a used one. If the base is damaged or missing, it can easily be replaced with a homemade plywood one that requires just a few tools. Very old units have a sturdy metal 1.25” rack-and-pinion focuser; scopes made from around 2007–2021 have plastic 1.25” focusers which are easily damaged. However, all have good optics.
There are two arguably better alternatives to the Orion SkyQuest XT6 in its price range:
The Sky-Watcher Virtuoso GTi 150P comes with a fully motorized GoTo mount, a collapsible tube, and two eyepieces. Its focuser is 1.25” only, but at f/5 you can achieve a similarly wide field of view. The optics are outstanding and the scope fits in a suitcase. It is easily one of the best deals in astronomy equipment available today.
If you still want a manual 6” f/8, the Apertura DT6 is very similar to the XT6 apart from its 1.25”-only focuser, but it has a significantly lower price tag. If you can live without 2” capability, you should consider the DT6 instead.
What can you see?
Even from the suburbs, a 6” telescope can be an absolute powerhouse.
Neptune’s moon Triton can be spotted, Saturn’s bands, Cassini Division, and several moons are easy, and Jupiter’s moons become disks rather than pinpoints. The smallest craters on the Moon visible are around a mile in size. Mars at opposition shows several dark markings and its ice cap.
The Orion Nebula begins to show a slight greenish coloring with a 6”, and globular clusters are somewhat resolvable. Many planetary nebulae, some showing a slight greenish or bluish tint, can be spotted. Under dark skies, M51’s spiral arms can be seen, along with several hundred other galaxies—a few dozen of which display considerable structure. But keep in mind that for deep-sky objects, your skies will be the limiting factor of what you can see. If you can’t see the Milky Way with your naked eye, galaxies are likely to be quite disappointing in the XT6, as only their oval centers are bright enough to be seen through strong light pollution. Globular clusters and open star clusters are, thankfully, significantly less affected but still somewhat affected by light pollution.