The Optical Tube
The Orion SkyLine 6 is a 6” (152mm) f/8 Newtonian reflector with a resulting focal length of 1200mm. This size and focal length combination is pretty common for beginner telescopes and has been a mainstay of amateur astronomy since the 1960s. An f/8 telescope won’t show any coma or edge-of-field astigmatism with cheap eyepieces; it is easy to focus, and collimation tolerances are fairly lax. Manufacturing the optics to a high standard of quality is also easy. The primary mirror of the SkyLine 6 can be adjusted for collimation without using any tools; the secondary mirror requires a hex key to adjust. No collimation tools are supplied, but making one yourself is easy, and collimation itself takes only a few minutes. Read our collimation guide for more info.
In contrast to the cheap plastic rack-and-pinion or helical focusers that are usually included with telescopes of this size for beginners, the SkyLine 6’s focuser is a single-speed Crayford made entirely of machined aluminum. The Crayford focuser on the SkyLine 6 has adjustments for tension and uses a brass compression ring to grip your eyepieces. However, it only accepts 1.25” eyepieces, which limits the usable field of view with the SkyLine 6 to about 1.3 degrees in angle across the night sky.
The SkyLine 6 comes with two GSO-made 1.25” Plossl eyepieces: a 25mm providing 48x magnification and a 9mm for 133x magnification. Both of these eyepieces are well-made and deliver sharp views, with blackened lens edges and no plastic internal parts. The apparent field of each is about 52 degrees. The 9mm eyepiece, being a Plossl design, is a little short on eye relief and requires you to jam your eye into it to take in the entire field at once, which can be a little uncomfortable. However, the views through it are tack-sharp and more than worth the trade-off.
For a finder, Orion provides a standard 6×30 finder scope, which attaches to the SkyLine 6 using a standard Synta-style bracket to allow for easy interchangeability with other finders. The 6×30 finder provides a true field about 7 degrees across, like that of a pair of wide-angle 7x binoculars. The view is upside down, with crosshairs in the eyepiece, and focus is adjusted by turning the objective lens on a threaded ring at the front of the finder. Views through it are brighter than what you can see with the naked eye; the 30mm aperture of the finder will give a gain of about 2 magnitudes over your eyes alone, which is enough to see the brightest deep-sky objects even from mildly light-polluted suburban skies. However, looking through it is somewhat uncomfortable.
The SkyLine 6 uses a Dobsonian alt-azimuth mount to allow it to be smoothly aimed and repositioned throughout the night sky. It’s made out of melamine-covered ¾” particle board, similar to cheap big-box furniture. The mount arrives flat-packed, and tools are provided for you to assemble it on your own, which takes a few minutes. The particle board cannot withstand being disassembled, as the threads in it will be stripped from repeatedly installing and removing the screws, so assembly is effectively permanent.
The altitude axis consists of a pair of small circular bearings gliding on Teflon pads. As with most commercial Dobsonians, they are undersized, and unusually so with the SkyLine 6, being significantly smaller than the bearings on the XT6. Like the SkyQuest XT Classic Dobsonians, the SkyLine 6 uses spring-tensioning to keep the bearings from moving too smoothly and to compensate for the balance issues that can occur when using heavy eyepieces that bring the center of gravity of the telescope outside the diameter of the tiny altitude bearings. Motions are smooth, and most 1.25” eyepieces won’t cause balance problems. However, using a 2” eyepiece certainly would—and that’s probably why the SkyLine 6 is limited to a 1.25” focuser. A 9×50 finder will also upset the balance when used in conjunction with a heavy eyepiece that is too much for the springs to compensate for; a counterweight is needed under those circumstances. Why GSO/Orion won’t increase the size of these bearings is unknown.
The SkyLine 6 glides in azimuth using its melamine-coated surface on the base with low-friction Teflon pads, unlike the roller bearings of the larger Skyline Dobsonians.
The base of the SkyLine 6 contains very little in the way of weight optimization. The rocker box sides are wider than they need to be, and the ground board is circular instead of triangular. Due to the already-heavy nature of ¾” particle board, the base is 23.5 lbs (10.7 kg)—4 lbs heavier than the base provided with the SkyQuest XT6 Classic, which Orion also sells. This may not seem like much, but it makes the difference between being able to carry the telescope on one trip or not for many people.
Should I buy a Used Orion SkyLine 6?
A used SkyLine 6 is a good deal, provided the price is reasonable and the Dobsonian base is in good shape. Be sure to check that the mirrors are free of corrosion to their reflective coatings; some dust or dirt is fine; cleaning isn’t too difficult. And be prepared to pay less if the base is damaged or missing, or if the accessories are not included. A damaged or missing Dobsonian base can be replaced, but the plywood needed to do so may not be worth the cost savings compared to just buying a new scope (though a plywood base can be made a lot lighter).
The Orion SkyLine 6 isn’t our first pick in its price range due to the limited field of view with a 1200mm focal length and 1.25”-only focuser combined with its rather high price. Here are some alternatives we recommend:
- The Sky-Watcher Heritage 150P has equal aperture and performance to the SkyLine 6, but in a much more compact and portable package with a wider possible field of view thanks to its 750mm focal length.
- The Sky-Watcher Heritage 130P is essentially a scaled-down 150P at a lower price, with the same ultra-compact form factor, wide field, and high-quality provided accessories.
- The Sky-Watcher Virtuoso GTi 150P has the same features as the Heritage 150P but adds fully motorized GoTo and tracking capabilities to the mix, all controlled by your smartphone or tablet. It can still be aimed manually, too. A 130mm version, the Virtuoso GTi 130P, is also available.
- The Orion SkyQuest XT6 has similar features to the SkyLine 6 but comes with a true 2” Crayford focuser offering a wider achievable field of view and a lighter base. You don’t get two eyepieces and the finder is a red dot rather than 6×30 unit, but a red dot is arguably easier to use anyway and a 9mm Plossl eyepiece isn’t worth much.
- The Sky-Watcher 6” Classic Dobsonian has an inferior altitude bearing design to the SkyLine 6, but comes with a superior pair of eyepieces, the same finder, and a workable 2” rack-and-pinion focuser, offering the same views at a lower price tag.
- The Apertura AD8/Zhumell Z8/Orion SkyLine 8 offers substantially more performance than the SkyLine 6 with nearly double the light gathering power thanks to its larger aperture, but is equally portable and adds a 2” dual-speed Crayford focuser, 9×50 finder, 30mm SuperView 2” eyepiece, and laser collimator too.
- The Explore Scientific 10” Hybrid Dobsonian features a huge 10” primary mirror that blows away the views through a 6” telescope like the SkyLine 6 and offers yet another performance boost over an 8”, but collapses to fit in a small storage space in minutes. However, the included accessories are not the best.
Aftermarket Accessory Recommendations
The provided eyepieces with the SkyLine 6 are just fine and provide the magnifications you’ll probably end up using most of the time. However, a 32mm Plossl eyepiece provides a lower 38x magnification along with a slightly wider true field than the stock 25mm supplied with the SkyLine 6. A 15mm SWA or redline eyepiece will give you 80x, a good medium power for viewing the Moon and many deep-sky objects, while a 6mm goldline or redline eyepiece produces 200x, approaching the limit of what a 6” telescope or typical atmospheric conditions will allow but ideal for planetary viewing and splitting close double stars.
While a 9×50 finder scope would be a nice upgrade over the SkyLine 6’s provided 6×30 unit, it would upset the balance too much to work. A red dot finder will slide into the existing bracket’s place just fine, however, if you prefer one over a magnifying finder scope.
Finally, a UHC (ultra high contrast) nebula filter such as the Orion 1.25” UltraBlock filter will enhance your views of many emission and planetary nebulae by darkening the background sky and increasing contrast as a result, though it will not work on other objects like stars and galaxies and is still not a substitute for dark skies.
What can you see?
The SkyLine 6’s ability to deliver views of deep-sky objects is, as with any telescope, limited by your light pollution conditions. Open star clusters like the Double Cluster or the Pleiades (M45) shine brightly and aren’t diffuse, and they will look great through the SkyLine 6 under almost any conditions; darker skies will let you see more stars and more color in the brightest ones. Globular star clusters, such as M13 or M15, can be seen through the SkyLine’s 6×30 finderscope and are resolved into individual stars at high magnification under suburban or darker skies. Most planetary nebulae are too small and faint to see very well with a 6” telescope, but a few such as the Dumbbell (M27) and the Ring (M57) stand out.
Emission nebulae are strongly affected by light pollution, but the Orion Nebula (M42) and Lagoon (M8) dazzle with their billowing clouds of gas, dark dust lanes, and embedded star clusters with the SkyLine 6; darker skies reveal fainter portions of the nebula and a UHC filter also helps enhance contrast. The Veil supernova remnant in Cygnus spans several fields of view across with the SkyLine 6 and a UHC filter under dark skies.
Galaxies require dark skies to see, but the SkyLine 6 can show you the dust lanes and orbiting smaller galaxies of M31, the Andromeda Galaxy, the hydrogen filaments of M82, and dozens of galaxies littering the Virgo Cluster, along with many more galaxies that may show slight detail or come in groups.
The SkyLine 6 is great for viewing planets, too. Expect to see the phases of Mercury and Venus, and the polar ice caps on Mars. Mars also shows dust storms from time to time, and a few dark markings on its surface can be resolved with the SkyLine 6 when Mars is at its closest to Earth. The Moon shows countless details – craters, ridges, mountains, and more – regardless of phase. The moons of Jupiter appear in the SkyLine 6’s 6×30 finder scope and their disks can be seen – along with shadows to match – when they transit across Jupiter; the planet itself has many colorful and ever-changing cloud belts and storms, along with the Great Red Spot, which can be resolved on a clear and steady night despite its continually shrinking size.
The SkyLine 6 will of course show you the rings of Saturn, and a steady night will allow you to resolve the razor-thin Cassini Division splitting the rings in two, along with Saturn’s cloud belts and the shadow of the planet itself on its rings. Several moons accompany Saturn as seen with the SkyLine 6, with Titan and Rhea being the brightest and easiest to spot. Uranus’ turquoise disk can just about be resolved, but a 6” telescope is insufficient to reveal its dim moons or resolve cloud belts in the ice giant’s atmosphere. Neptune is hard to distinguish from a star at all with the SkyLine 6, even on the best of nights, but its moon Triton should be just barely visible next to it. Pluto is simply too dim to see without more than 6” of aperture, even under dark skies.