SkyWatcher FlexTube 300 Review
Achieving a middle ground between portability and price, the Sky-Watcher 12” FlexTube Dobsonian is a good choice for those interested in a large and capable telescope without a premium price tag.
The Sky-Watcher 12” FlexTube Dobsonian is an ideal choice for those in search of a 12″ Dobsonian telescope. Compared to traditional solid-tubed instruments, it is more portable and practical to transport due to its more compact design, with a tube that’s easier to carry around or fit in a car. The 12” FlexTube offers some of the advantages of a truss tube Dobsonian without requiring complex assembly or incurring high additional costs. When compared with smaller FlexTube scopes, the 12” FlexTube certainly stands out as a far better choice compared to alternatives, as it isn’t a lot more expensive compared to its solid-tubed counterparts and the 12” model’s collapsing tube makes a huge difference in some transport/storage situations where the 8” and 10” FlexTube models may not be of much benefit compared to a regular solid-tubed scope.
Image by Ed Ting
the optical tube
300mm (12”) Aperture
1500mm Focal Length
The 12” FlexTube Dobsonian is a 12” (300mm) Newtonian reflector with an f/5 focal ratio, giving it a focal length of 1500mm. Compared to a 10” reflector, the 12” FlexTube Dobsonian has 44% more light gathering power and 20% more resolution – though the latter is of course limited by your local atmospheric conditions. The 12” FlexTube’s optics are of good quality and theoretically capable of magnifications up to 600x under the best seeing conditions; however, under most circumstances, it will likely have trouble surpassing the resolving power of a typical 8” or 10” telescope, and we’d advise using no more than 300x on most nights, and even then only for bright targets like planets and double stars.
Coma is present in an f/5 reflector like the 12” FlexTube with wide angle 2” eyepieces, but other aberrations such as astigmatism are a bigger issue when using cheaper eyepiece designs such as Erfles and Kellners. It is essential to frequently adjust and ensure accurate collimation due to the scope’s fast focal ratio, and luckily this can be done without any tools on the primary mirror while the secondary requires a hex key to adjust, though this is seldom required. The primary mirror cell also sits on 9-point flotation support to help maintain image quality by preventing deformities caused by its own weight.
The 12” FlexTube optical tube of course stands out for its collapsible tube that can retract from 55” to 36”, saving 19” compared to the 8” and 10” models which only save 11”. This significant difference allows the telescope to fit in a closet or across a car’s back seat when collapsed – a normal 8” or 10” is 48” long and will fit without the need for a collapsible tube, but the length of a typical 12” f/5 Dobsonian is such that the FlexTube may make or break the case for your ability to transport and store one. It takes just seconds to extend the FlexTube’s struts, as you need merely unlatch a few knobs and let the poles reach their stops before tightening them again, and even after many uses, the scope holds collimation surprisingly well.
Weighing 46 lbs (20.9 kg), 2 lbs lighter than its solid-tubed counterparts, the FlexTube is also easier to move around when compacted on account of its shorter length; multiple carry handles are built into its design for your convenience. A standard 2” single-speed Crayford focuser is included, along with extension tubes which are required to reach focus with most eyepieces. Upgrading to a dual-speed focuser by swapping the provided unit out would be a good idea, albeit costly.
The open tube of the FlexTube design means that light from the Moon, streetlights, etc. can get in and spoil the image, as can dew, dust, or someone’s hands. As such, a stretchy fabric shroud can be made or purchased to go over the exposed strut section of the tube and protect the optics and your views. We would highly recommend one; without it the scope’s performance is severely compromised if any light pollution or other sources of glare or sky glow are present.
Single Speed 2” Crayford Focuser
The Sky-Watcher 12” FlexTube utilizes a Dobsonian mount with the same design as their other manual Dobsonians. It comes as a flat-packed box of ¾” melamine-covered particle board bits with screws and a hex key which you use to assemble the mount yourself. Unfortunately, the particle board construction and the time-consuming nature of threading the screws means that it is impractical to take the base apart again after assembly. There is little weight optimization, and at 38 lbs, the 12” FlexTube’s base is rather heavy and awkward to move around; you may have more issues fitting the base in a vehicle than the tube, and it is unnecessarily wide when stored.
The azimuth (side to side) motion of the 12” FlexTube Dobsonian is smooth, gliding on 3 plastic pads against its laminate-covered base. However, it uses the same altitude bearing design as the other Sky-Watcher Dobsonians—undersized cylindrical bearings that ride on plastic cylinders and are adjusted by bicycle handles. Due to the size and weight of the 12” FlexTube, any accessories you use with it constitute a smaller proportion compared to its mass than smaller instruments, so balance issues may not pop up at all. Even so, if top-heaviness does arises in extreme circumstances, one must lock the bearings or add counterweights to the tube, which is not ideal. Making or buying a new plywood base for the 12” FlexTube with a lighter and sleeker construction (as well as smoother bearing motions) would be a good idea if you are able to do so.
The Sky-Watcher 12” FlexTube Dobsonian comes with two “Super” Plossl 1.25” eyepieces–a 25mm giving 60x magnification and a 10mm giving 150x–which are good, but wide-angle eyepieces designed for fast telescopes would be better suited for such a large and expensive instrument. The finder scope included is a right-angle, correct-image 9×50 unit, which displays an upright image corrected left-right, consistent with star charts/astronomy apps. It can also allow you to make out stars beyond what the naked eye can see, as well as some bright deep-sky objects. The field of view is similar to that of binoculars at 6 degrees, a pretty broad patch of sky, but looking down the perpendicular eyepiece may make it difficult to aim the telescope coarsely. Many people opt for a zero-power red dot or reflex sight for initial aiming and use the 9×50 just for fine adjustment, or even ditch the 9×50 finder scope altogether.
What can you see if you look through it?
The 12” FlexTube Dobsonian is an excellent telescope for viewing deep-sky objects such as galaxies, open star clusters, nebulae, and globular star clusters. Under dark skies, you will be able to clearly observe details like spiral arms and dust lanes in galaxies like M51 and M82. Additionally, you can resolve the individual stars in the Andromeda Galaxy and even extragalactic globular clusters. Open star clusters like the Double Cluster show spectacular colors regardless of viewing conditions while globular star clusters can be resolved into individual stars too.
Regardless of your viewing conditions, bright nebulae like Orion look spectacular with the 12” FlexTube Dobsonian. Nebulae look best under dark skies but a UHC filter can bring detail out in many of them even under brightly lit conditions, and under dark skies sometimes revealing previously-invisible objects too, such as the Veil Nebula. Planetary nebulae in the 12” FlexTube show greenish, turquoise and bluish colors along with fine detail, sometimes including central stars within them.
The 12” FlexTube is great for observing the Moon and planets too: expect to see phases of Mercury or Venus, ice caps and various surface marking on Mars, thousands of details on the moon’s surface and spectacular atmospheric features on Jupiter, such as its Great Red Spot, along with its four Galilean moons and their transits. You can also see Saturn’s rings, the Cassini Division and possibly the Encke gap as well in the rings, a few stripes on the planet and a handful of moons. Uranus’ four largest moons can be faintly seen as can Neptune’s moon Triton, though little detail is visible in the atmospheres of these ice giants owing to their distance and tiny angular size. Pluto can also be glimpsed with a 12” telescope as a star-like point under dark skies if you know where to look.
As previously mentioned, the bulky and poorly optimized base of the 12” FlexTube can be a nuisance, though making or buying a new one isn’t too difficult or expensive and greatly improves your viewing experience. The need for a shroud can bother some, but most larger Dobsonians require one anyhow. The biggest downsides of the 12” FlexTube are that you don’t get as many accessories as one might be able to do with a cheaper solid-tubed Dobsonian from Apertura, Zhumell or Orion nor is the price as low, while a true truss tube telescope is only moderately more expensive but much more compact.
While it’s not perfect, the Sky-Watcher 12” FlexTube Dobsonian is excellent for those uninterested in the complexity of a truss who just need a little more portability than a standard solid-tubed 12” design provides. It’s even better with a few aftermarket/DIY improvements.