SkyWatcher Flextube 250 Review
- •Great Optics
- •Lots Of Aperture
- •Fairly Portable
- •Decent Included Accessory Set
- •Collapsible Tube Saves On Storage Space And Is Easier To Carry
- •Not Actually Any Lighter Than A Solid-Tubed Instrument
- •Needs A Shroud And Other Upgrades/DIY Modifications To Perform Well
- •Finderscope Can Be Confusing To Use
- •Annoying Adapter System For Eyepieces
- •Bearings Poorly Designed
10” Collapsible is a great scope with a slightly more compact form factor.
The Sky-Watcher Flextube 250P, otherwise known as the 10” Collapsible, is a great scope with a slightly more compact form factor than traditional, solid-tubed Dobsonians of its size. Almost any 10” Dobsonian is great for beginners or experienced users, providing significantly brighter views than a smaller 6” or 8” scope with a minimal increase in bulk or weight. However, there are a few design compromises made with the FlexTube design, as well as all of Sky-Watcher’s Dobsonians, which make the Flextube 250P less-than-ideal for all use cases.
250mm (10”) Aperture
1200mm Focal Length
The Flextube 250P is a 10” (254mm) Newtonian reflector with a focal length of 1200mm and a resulting focal ratio of f/4.7. Newtonian reflectors of f/5 and below tend to have some coma intruding into the field of view at low magnifications, and cheaper eyepieces tend to show additional aberrations towards the edges of the field of view at low power. However, you can probably forego a coma corrector unless you are very picky about pinpoint stars with wide-angle eyepieces.
The Flextube 250P of course needs frequent collimation; the collapsible tube makes this even more of a necessity. The primary mirror is easily adjusted without tools, though you’ll need a hex key for the secondary mirror.
The tube of the Flextube 250P is of course collapsible, a main selling point of the scope. It reduces the telescope from roughly 44” (1.2 m) to 32” in length. This allows the tube to fit in smaller spaces or even upright in a car seat with a seatbelt if need be, though it doesn’t cut back on weight at all compared to a solid tube and you are left with an open tube prone to letting in unwanted hands, bugs, dew, and stray light. A fabric shroud is a necessity under almost all circumstances with the Flextube 250P and needs to be made out of stiff but stretchy fabric to avoid it drooping into the light path; this is annoying to make yourself and expensive to purchase.
The focuser on the Flextube 250P is a basic 2” Crayford focuser. The scope requires an extension tube to reach focus; 1.25” and 2” extension tubes are provided. Swapping the 1.25” and 2” extension tubes is annoying and the separate hardware prevents one from using 2” filters on 1.25” eyepieces – you’ll need to get a 2” to 1.25” threaded adapter to fix that and allow you to keep the 2” extension tube installed at all times. Neither the focuser nor the provided extension tubes use brass compression rings, making them prone to marking up your eyepieces/accessories with screw marks over time.
The Flextube 250P’s mount is much like any Dobsonian telescope; it pivots up and down on a set of plastic pads and swivels with laminate gliding against plastic pads. The Sky-Watcher manual Dobsonians all have small altitude bearings for up/down motion which leads to the scope struggling to stay put if it is even slightly top-heavy, and Sky-Watcher “solves” this problem with a brake system consisting of a pair of bicycle handles to pull the bearings tightly against the sides of the base. This adds enough friction to keep the scope stationary but inhibits smooth motion around the sky; aiming the 250P with any kind of heavy accessories or a shroud on the front end requires constantly unlocking and locking the brake handle which can get annoying rather quickly. A simple counterweight of some kind works but causes the opposite problem if you switch to a significantly lighter eyepiece. Solving the scope’s balance issues entirely requires building or buying a new base with larger altitude bearings.
The Flextube 250P includes:
Two 1.25” “Super” (actually Konig) eyepieces – a 25mm providing 48x and a 10mm providing 120x
A 9×50 right-angle correct image finderscope
The aforementioned 1.25” and 2” extension tubes
The two 1.25” “Super” eyepieces included with the Flextube 250P are of the rarely-seen Konig optical design (this took a lot of research to figure out) – these eyepieces are more comfortable to use than a standard Kellner or Plossl thanks to their larger eye lenses and greater eye relief, and they are a bit sharper towards the edges of the field of view in a fast scope – particularly helpful in the 250P’s case. The barrels are largely plastic but the lenses are all multi-coated glass. These are a good pair to start off with, but almost any astronomer will use 3-4 eyepieces if not more in their toolkit for varying levels of magnification. A shorter focal length planetary eyepiece in the 4-6mm range such as a 6mm “redline” to get more magnification, and a sharp, wide-angle 2” eyepiece in the 20-35mm range for a wider field such as a 34mm SWA would be good additions to your starter eyepiece set.
The finder included with the Flextube 250P is a 9×50 right-angle, correct image unit. It displays images that are neither flipped nor upside down relative to a star chart and doesn’t require awkwardly crouching over to look through like a straight-through finder. Its 50mm aperture shows stars a couple of magnitudes fainter than what you can see with your eyes alone, and the 5-degree true field is a bit narrower than a pair of standard 7×50 binoculars. However, you end up having to sight along the tube to get roughly where you want to be anyway, which can be inaccurate and confusing. Augmenting it with a reflex sight like the Rigel Quikfinder or replacing it entirely is a good idea, though this can add top-heaviness of course.
What Can You See?
As with any good scope in its size range, the Flextube 250P has no trouble showing planetary details under almost any conditions. Mercury and Venus reveal their phases, Mars its ice caps and dark markings, Jupiter’s Great Red Spot is easy to see amidst its colorful cloud belts, and Jupiter’s moons appear as tiny, colorful disks with inky black shadows when they transit across Jupiter. The two-toned coloration of Ganymede is even detectable with good seeing. Saturn’s rings and cloud belts are easy to spot; the Cassini Division is visible under steady skies and perfect skies may reveal the much thinner Encke gap in the rings too.
Half a dozen of Saturn’s moons can be seen with the 250P, and when Saturn reaches equinox in 2025 its moon Titan and its shadow will be visible as tiny disks – along with much smaller Rhea under steady skies too. At least one or two of Uranus’ 4 main moons are visible, and under dark and steady skies all of them should appear to you next to Uranus’ bright blue-green disk. Neptune is clearly resolvable as a blue dot with Triton quite obviously visible beside it. Pluto can also be seen as a dim star-like point under dark skies.
Light pollution mires the view of any deep-sky objects, but the Flextube 250P will resolve globular clusters into their individual stars even under suburban or city skies, as well as show you dozens of beautiful open star clusters and split countless close double stars. Bright nebulae like the Orion Nebula or the Lagoon can be seen, and benefit from a UHC filter, though darker skies almost always give the best view. Galaxies like M82 and M64 show obvious dust lanes, while the spiral arms of M51, M33, M101, and M81 can be seen under good conditions, though faintly. You can also resolve details within tiny planetary nebulae at high magnifications with good seeing, and the blue-green coloration of many of them is obvious.
Not Lighter Despite Smaller Size
Base Is Difficult to Transport
The Flextube 250P’s optical tube is not any lighter than a regular solid-tubed 10”, and for many users, the benefit of the collapsible tube is minimal and is outweighed by the need for a shroud and complexity of assembly.
In addition to the brake handle problem, it should also be noted that the Flextube 250P’s base is arguably more difficult to transport than the optical tube itself due to its awkwardness and comparable volume; it can technically be dismantled the same way it is assembled with a hex key but frequently doing this will probably wear out the particle board that makes up the base. As with the bearing problem, the only way to remedy this issue is a new base – bigger altitude bearings on the side of the scope would lower the profile of the base itself, plywood is lighter and could have cutouts, and if you really wanted a base with hinges or no-tool assembly would be possible to build – albeit at quite an amount of effort/expense on the part of the user.
The Sky-Watcher FlexTube 250P is a great scope, but only provided you’re willing to deal with its shortcomings, and make a few upgrades and modifications to allow it to perform at its best. If this is your first scope and portability is not of the utmost concern, a regular 10” Dob like the Aperture AD10 and identical models sold by Zhumell and Orion is a better pick, while those looking for the most compact scope possible might want to consider the 10” or 12” truss tubes from Explore Scientific or a premium manufacturer.