The Optical Tube
The Sky-Watcher 10” Classic Dobsonian is optically a 10” (250mm) f/4.7 Newtonian with a focal length of 1200 mm. This is basically the same focal length as the vast majority of 6” and 8” Dobsonians on the market, including those offered by Sky-Watcher themselves, so the end result is a fat tube not much different in length from those instruments. Thus, as with smaller models, you should be able to easily fit the optical tube of the Sky-Watcher 10” Classic across the back of most vehicles (or fold down a seat if you can’t) and thus easily transport it to dark skies. You don’t need a case or carry bag; these are a bit of an annoyance, and wrapping the scope in a towel, coat, or blanket should suffice to prevent it from sliding or rolling around.
The 10” Classic has a rather simple primary mirror cell which directly exposes the back of the mirror for maximum ventilation and, thankfully, doesn’t require tools to adjust for collimation, as opposed to the 6” and 8” models, which are rather infuriating devices that require screwdrivers. The secondary mirror does require a hex key to adjust, but secondary mirror alignment is an infrequent process and may never be needed over the entire lifetime of the telescope unless you drop or disassemble it.
The focuser on the 10” Classic is a 2” single-speed Crayford. This works pretty well; a dual-speed fine focus knob would be nice but isn’t absolutely necessary. However, there’s an annoying system of extension tubes for the telescope; the 2” extension must be used for 2” eyepieces and the 1.25” extension for 1.25”. You could also buy a regular 2” to 1.25” adapter, keep the 2” extender in all the time, and use the 1.25” adapter for 1.25” eyepieces, but apparently this was just too much trouble for Sky-Watcher, so they supplied a convoluted system instead.
The whole optical tube for the 10” Classic weighs about 28 pounds (14 kg), so it isn’t too hard to carry around or set onto its base. And it’ll move smoothly and easily once installed on the Dobsonian mount; the end of the tube has a small guide knob that you can use to pivot it around the sky. If you are concerned about the weight during transport, a dolly or hand truck will easily carry the whole scope around and it doesn’t have to take up much space. Lifting straps for the optical tube are also an option, but may or may not be necessary.
Accessories with Classic 250P
The 10” Classic comes with two 1.25” “Super” eyepieces, a 25mm providing 48x and a 10mm providing 120x. While superficially similar to the metal-bodied Plossls supplied with many other Dobsonians, the Super eyepieces are made largely out of plastic and seem to be some sort of modified Kellner design (the lenses are, thankfully, still glass). They have longer eye relief than a Plossl and thus are more comfortable to look through—particularly the 10mm, which in Plossl form would require jamming into your eye socket to actually see through. The magnifications provided by each eyepiece are enough to get you started, but you’ll probably acquire additional eyepieces for higher-power and wider-angle views over time.
The 10” Classic also includes a 9×50 finder scope, which you view straight through. The image is upside down, just like through the telescope itself. This can be a little confusing when trying to use star charts, but it is easier to see where you actually are in the sky compared to a right-angle finder (if a bit less comfortable for your neck). The 50mm aperture of the finder allows you to see stars about 3 magnitudes fainter than with your naked eye, so between magnitudes 7 and 10 depending on your light pollution conditions. It’ll also show the brightest deep-sky objects all by themselves, even under mediocre or poor conditions (under dark skies, half of the stuff in the Messier catalogue can be found with the naked eye anyway).
The main weakness of the 9×50, besides the lack of comfort when using it, is that the crosshairs are a bit difficult to see. Theoretically, a DIY illuminator is possible, but in practice, it just takes getting used to. You could replace or supplement it with a red dot finder or reflex sight, but this would cause too many balance problems with the 10” Classic for us to really recommend it.
No collimation tools are included with the Sky-Watcher 10” Classic. Our collimation guide details how to collimate the scope even without tools, as well as what to expect with each type.
The Dobsonian Mount
The Sky-Watcher 10” Classic uses a pretty bog-standard Dobsonian mount made out of particle board. The telescope swings side-to-side (in the direction known as azimuth) on a trio of small plastic pads riding against the body’s melamine coating, and pivots up and down on plastic bearings gliding on Teflon pads, though to simplify construction, instead of pads, the altitude bearings are just plastic bushings secured to the rocker sides with screws. The whole base is assembled with the included tools, much like a piece of flat-pack furniture; the whole process takes a few minutes.
The altitude bearings on the 10” Classic are pretty small, and as a result, the centre of gravity of the scope can move outside of them quite easily if you use heavy accessories, or even just swap out a heavy eyepiece for a light one. Most other commercial scopes fix this by simply enlarging the bearings, adding springs for tensioning, or allowing you to slide the bearings up and down the tube for optimum balance. Sky-Watcher’s approach is to simply add a pair of bicycle handles to lock the bearings in place when swapping accessories, or tighten them when using something heavy. This technically works, but doesn’t provide a comfortable viewing experience. Sky-Watcher has actually patented their tension knob “technology” for whatever reason, and it’s advertised as a selling point; it’s in fact one of the biggest flaws in the whole telescope. The handles/knobs also tend to get bumped into or catch on loose clothing, which is also frustrating. The only real benefit to them is that you can use them as secure handles to carry the whole telescope in one piece, which is probably not the best idea with the 10” model due to its weight and large size.
There’s also an eyepiece rack attached to the front of the base, which we wouldn’t recommend using, as it’s a great way for your eyepieces to dew up or get damaged by accident.
You could make a new base out of plywood and engineer your own enlarged-bearing or spring-tensioning solution to alleviate the motion problems of the Sky-Watcher 10” Classic, or buy one from a manufacturer of custom bases-with the added advantage that plywood lasts longer and weighs less, but the added expense may be hard to justify.
Should I buy a used Sky-Watcher 10” Classic?
A used Sky-Watcher 10” Classic will be a nice scope. However, make sure the mirror coatings are still in good shape. If they are dull or dusty, cleaning should be a quick remedy, but any splotches, holes in the coating, or transparency mean the coating is chemically compromised and thus the mirror needs a recoat. This can cost a significant proportion of the price of the telescope, so it is probably a deal breaker if buying used.
Dents in the telescope’s tube can be safely ignored if they don’t intrude on the optical path, and if they do, a hammer or dent removal tool will take care of them in just a few minutes.
Missing accessories can be replaced, though be sure to account for them in your budget. Among the most common items to go missing are the 1.25” and 2” adapters. A missing 1.25” adapter is of little concern, since a regular 2” to 1.25” adapter is just better anyway. A missing 2” adapter is a little more worrying; you’ll want a good 2” extension tube to replace it, and these aren’t always the cheapest.
And lastly, a damaged or missing base is really just an excuse to make one better than the original-but again, be sure to account for this in your budget! When all is said and done, there’s no sense in paying nearly as much for a used scope as a new one.
Aftermarket Accessory Recommendations
The eyepieces included with the Sky-Watcher 10” Classic are adequate to start out with, but for the best views of the Moon, planets, double stars, and globular clusters, a higher magnification eyepiece is a good idea. You don’t need anything fancy; a 6mm “gold-line” or “red-line” is quite cheap and will give you 200x. For more power, a 4mm Astromania Planetary will give you 300x, which is the most that typical atmospheric conditions will allow, and tracking at higher magnifications without frustration takes a fair amount of practice. While premium wide-angle eyepieces will give you a sharper and more immersive field of view, these low-cost oculars will do just fine and can always be replaced later by higher-quality gear.
A medium-power eyepiece to bridge the gap between the included 25mm and 10mm units might also be a good idea. A 15mm “gold-line” exists but won’t work well with a fast instrument like the 10” Classic; our recommendation would be a 15mm Agena Starguider or a 15mm SVBONY unit. Either will give a fairly wide field of view and is comfortable to look through.
We’d normally recommend a low-power 2” eyepiece as well, but seeing as this will upset the balance of the 10” Classic and interfere with its aiming, you unfortunately should probably forgo such an accessory.
A nebula filter, specifically a UHC or ultra-high-contrast filter, will improve the views of nebulae with the 10” Classic. Do note that the UHC filter doesn’t “remove” light pollution or “filter it out”; it instead increases contrast on nebulae that emit oxygen-III or hydrogen-alpha emission lines, which can make them show more detail and blacken the sky background. The 1.25” Orion UltraBlock is our pick in this category.
Lastly, you could swap out the 9×50 finder on the 10” Classic (adding a second finder will, again, weigh down the front too much and cause balance issues). A right-angle 9×50 finder scope may or may not be an improvement based on your preferences, while a Telrad or Rigel Quikfinder provides a zero-power view with a simple red reticle that may be easier to get the hang of than a magnifying finder.
What can you see with Skywatcher Classic 250P?
The Sky-Watcher 10” Classic, being a rather large aperture instrument, can show you a lot. Smaller targets are primarily limited by your atmospheric conditions rather than the telescope itself; large extended deep-sky objects are similar, often more limited by the darkness of your night sky than what the aperture can grab hold of.
Within the solar system, you can easily see the phases of Venus and Mercury almost any night they’re up. Mercury’s small disk and proximity to the Sun mean you’re unlikely to spot any detail, while Venus, of course, is covered in clouds. When it’s far from Earth, Mars will look nearly featureless apart from an ice cap, but when it’s close to us for the few months biannually around opposition, you will see quite a few dark markings on its surface. Conveniently, opposition also happens to be when Mars tends to be closest to the Sun and thus most likely to have planet-wide dust storms, which will obscure all surface details, even the ice caps at times. These storms can last for months. You can also see Mars’ outer moon Deimos under favourable conditions if you can block out the glare from the planet, but this is difficult—Phobos is almost impossible to see as it’s much closer to Mars and moves faster.
Jupiter’s cloud belts can be easily seen at low magnification with the 10” Classic—pop in a high power eyepiece and the Great Red Spot is there too. You can also distinguish the 4 largest moons of Jupiter, the Galilean moons Io, Europa, Ganymede, and Callisto, as not-quite-uniform disks and their individual colours especially pop out when they transit in front of Jupiter-as do their jet-black shadows following them. Saturn’s rings and the Cassini Division within them are clearly visible too, along with some cloud bands on Saturn and half a dozen or so of its moons, all of which appear as points of light due to their smaller angular size.
Uranus and Neptune are very small, even at high magnification with the AD10; at low power, they’re hard to distinguish from stars, and neither will show any kind of detail. However, you can see their moons. Oberon and Titania around Uranus are fairly easy, while Ariel is harder and Umbriel is very difficult to spot. Triton, the only large moon of Neptune, is a bit brighter and thus easier to see than Titania or Oberon, and Neptune’s lower brightness means it’s easier to see in the planet’s glare too. You can also see Pluto, though it’s nothing more than a star-like point in a sea of other star-like points (well, actual stars) in the constellation of Sagittarius for the foreseeable future.
Outside the Solar System, the capabilities of the 10” Classic for viewing “faint fuzzies” (usually known as deep-sky objects) are again largely dependent on the darkness of your skies above all else. Under light-polluted skies, you’re mostly limited to bright open and globular star clusters, and most galaxies are washed out, with little more than their bright cores visible. But under dark skies, you can see the spiral arms of brighter galaxies like M51 and M33, observe dust lanes in galaxies like M82 and M31, and even see the H-II regions in M33, M101, and a few other galaxies. You’ll be able to see several thousand more as faint smudges. Globular clusters can be resolved into hundreds or thousands of individual stars, and emission nebulae like Orion or the Lagoon look fantastic. Planetary nebulae tend to be colourful with blue, green, or aquamarine hues and have all sorts of small details that can be resolved on a night of good seeing.