The Optical Tube
The StarSense Explorer 10” Dobsonian is optically a 10” (254mm) f/4.7 Newtonian reflector with a focal length of 1200mm. At f/4.7 focal ratio, “SuperView” or “SWA” eyepieces derived from the Erfle design have edge-of-field astigmatism and field curvature (making it look like you’re viewing at warp speed or from inside a fishbowl), and any low-power eyepiece with a true field much wider than the included 25mm Plossl eyepiece has obvious coma around the edges of the field of view.
Coma is easily ignored and often masked by other eyepiece aberrations; edge-of-field astigmatism and field curvature are less so. This is important to keep in mind when shopping for eyepieces; the cheap, poorly corrected wide-angle eyepieces practically thrown in for free with similarly fast scopes are better than nothing, but paying large sums for them to use with the StarSense Explorer 10” Dobsonian isn’t as logical, especially for a scope that already costs several hundred dollars more than the more well-equipped competition.
Collimating a faster telescope like an f/4.7 is slightly more difficult than a slower instrument. Unlike the 8” model, the StarSense Explorer 10” doesn’t require a screwdriver to adjust the primary mirror. However, since no collimation tools are provided, you’ll need to make or purchase one separately. You should expect to have to collimate pretty frequently, though maybe not every time you set up the scope, but it’s not a particularly difficult process.
As with the 8” model, the focuser on the StarSense Explorer 10” Dob is a basic 2” single-speed Crayford, which uses thumb screws to grip an extension tube (required for most eyepieces to reach focus) that also uses thumb screws. Most well-made focusers and extension tubes use compression rings to grip your eyepieces, and the 1.25” adapter provided uses one and also has threads to install 2” filters on your 1.25” eyepieces—a nice touch.
You can replace the provided extension tube with one that uses a compression ring to provide a more secure, non-marring connection for 2” eyepieces, but for a £1000+ telescope, this is really inexcusable to have to do. The focuser can be upgraded to a dual-speed unit, but most upgrade kits (sold usually for Sky-Watcher focusers) are not necessarily labeled as compatible and are often not available in the United States. A single-speed focuser is fine for general use, but with a fast scope at high magnifications, a 1:10 dual speed reduction is helpful in easily dialing in focus (especially if you lack a very steady hand) and should really be included at such a high price.
The Supplied Accessories
The StarSense Explorer 10” Dobsonian includes a 25mm Plossl (48x) with a 55-degree apparent field of view. It works well enough at f/4.7, but you’ll probably want to pick up some additional eyepieces to enhance your observing experience (100x or above is needed for good views of planets and globular star clusters, for example). For a finder, a simple red dot sight is provided, which is more than adequate, especially since you’ll probably be using the StarSense Explorer app to aim the scope most of the time anyway.
The StarSense Explorer 10” Dobsonian is, of course, a Dobsonian telescope, an alt-azimuth that pivots up and down on plastic bearing pads and swivels left-right like a “lazy Susan” on a set of three plastic pads arranged in a triangle above the feet on the base. There are no gears, locks, or cables. The base is made out of melamine-covered particle board and thus is heavier than it initially looks. Thankfully, Celestron has added cutouts to the base to act as handles and keep the weight to a minimum. You assemble it yourself with a hex key when it arrives, just like knock-down furniture. There’s an eyepiece rack on the front.
The altitude axis on the StarSense Explorer Dobsonians does have a clutch/brake on it similar to the one on the Sky-Watcher Dobsonians; you can in principle tighten the knobs on the sides of the bearings to increase friction. The main actual purpose of this is to lock the telescope in place if you use a heavy 2” eyepiece, which will upset the balance of the scope by moving the center of gravity outside the bearings, leading to it tipping over when aimed low in the sky. However, locking the bearings, of course, inhibits smooth motion, so the real solution is either a counterweight or a better mount design, such as Dobsonians that use spring tensioning or simply larger bearings. It’s possible to retrofit larger bearings onto the scope and build a new plywood base to match, but this is expensive to have custom-made and time-consuming to construct yourself.
Should I buy a Used Celestron StarSense Explorer 10”?
The Celestron StarSense Explorer Dobsonians are very new to the marketplace, so it’s unlikely you’ll find a used one at all, especially not one with any kind of issues due to long-term neglect. However, as always, you should check the quality of the mirror coatings and make sure there is no obvious severe damage.
- The StellaLyra 10″ f/5 Dobsonian is slightly heavier and bulkier than the StarSense Explorer 10”, but it comes with a nice set of high-quality accessories, a better 2” Crayford focuser equipped with a 1:10 dual-speed fine adjustment knob, and a simple and sturdy Dobsonian mount.
- The Explore Scientific 10″ Ultra Light Dobsonian is extremely high-quality in design and construction, with a truss tube that compacts into a very small package, smooth bearings, a nice dual-speed Crayford focuser, and an all-metal constructions but lacks quality accessories, which may make getting it set up and usable daunting for beginners who will have to shop for a shroud and several eyepieces at the minimum.
- The Celestron StarSense Explorer 8” Dobsonian offers the same features and portability as the 10” model, with the added benefit of being more affordable. However, collimating the primary mirror can be a bit of a hassle and the smaller aperture of course means you’re not going to get quite as much performance.
- The Sky-Watcher Virtuoso GTi 150P is a compact and affordable telescope with a fully motorized, tracking GoTo mount, which is controlled by your smartphone, or simply aimed manually thanks to its FreedomFind encoders which allow the telescope to retain information on where it is aimed. It may not be as capable as larger scopes, but it offers great value for the money. Alternatively, the manual Heritage 150P is also a good choice, featuring the same design, optics, and accessories but without any electronics.
- The StellaLyra 12″ f/5 Dobsonian includes a huge variety of accessories and offers even more spectacular views than the 10” or 8” models, but the solid tube makes it difficult to move without a dolly or large vehicle. You may wish to consider a more expensive collapsible or truss 12” instead if you have the budget and are worried about size.
- The Explore Scientific 12″ Ultra Light Dobsonian has a well-designed dual-speed Crayford focuser and a compact all-metal structure that is easy to disassemble for transport. Its movements are also very smooth. However, it does not include any useful eyepieces or a finder and will require these as well as additional accessories like a shroud for optimal use.
- The Sky-Watcher Skyliner 300P FlexTube is easier to transport than a solid-tubed scope like the StellaLyra and less complex to assemble than a truss, and isn’t too much more bulky or inconvenient than the StarSense Explorer 10” Dobsonian while putting up significantly brighter views of deep-sky objects.
- The Celestron NexStar 6SE is compact and offers motorized GoTo and tracking, but it is limited by its small aperture and narrow field of view which are hardly comparable to the wide-field vistas and powerful light-collecting abilities of the StarSense Explorer 10” Dobsonian, and the GoTo mount/tripod is expensive and time-consuming to set up.
- The StellaLyra 16″ f/4.5 Dobsonian features an enormous 16” primary mirror for incredible deep-sky views. Its full truss tube design can be disassembled into fairly lightweight and compact pieces, though it is still quite an effort to set up and transport. However, the views through the eyepiece are certainly rewarding.
- The Sky-Watcher Skyliner 350P FlexTube Dobsonian delivers significantly improved performance compared to the StarSense Explorer 10” Dobsonian, owing to its much larger aperture. The simple FlexTube design is easier to set up than a truss tube, but makes it quite a bit more bulky and inconvenient to deal with compared to a truss.
- The Sky-Watcher Skyliner 300P FlexTube GoTo Dobsonian offers fully motorized GoTo/tracking as well as Sky-Watcher’s FlexTube system to decrease its size when not in use along with FreedomFind encoders allowing manual aiming as with other Sky-Watcher GoTo Dobsonians. It significantly outperforms an 8” or 10” scope but is still fairly easy to set up and transport on your own.
- The Sky-Watcher Skyliner 250P FlexTube GoTo Dobsonian’s FlexTube design makes it more compact than the StarSense Explorer 10” Dobsonian, though it is quite a bit heavier thanks to the weight of its motor drive systems. The fully motorized mount automatically swings to and tracks your targets, while still being capable of manual aiming thanks to its FreedomFind encoder system.
What can you see with StarSense 10″ Dobsonian?
A 10” Dobsonian is a great choice for beginners and can show you significantly more than a smaller 8” or 10” without a huge increase in bulk or a claustrophobically long focal length. You can probably move the scope fully assembled if you’re in good shape, take two trips to set it up in your backyard, or stick it on a hand truck or dolly. The StarSense Explorer 10” Dobsonian should be able to resolve most of the globular star clusters in the Messier catalog and many of the brighter NGC globular clusters. M13’s “propeller” dust lanes show up at high magnification, M15’s bright nucleus is dazzling, and you can spot G1, a globular cluster millions of light-years away orbiting the Andromeda Galaxy, as a tiny, fuzzy dot if you can identify it amongst the stars.
Open star clusters are colorful, and often show wisps of nebulae or dust lanes under dark skies. The wispy nebula surrounding the Pleiades (M45) can be seen under reasonably good conditions, though it’s easy to confuse with glare or smudges on your eyepiece. Emission nebulae like the Swan (M17), Lagoon (M8), and Orion Nebula (M42) are bright and look especially good under dark skies and/or with a UHC filter. The Horsehead Nebula can be seen under dark skies with a good UHC filter too, though the nearby Flame Nebula is much more obvious due to its brightness and size. The Veil Nebula dazzles under dark skies with a UHC filter, spanning several degrees across and requiring you to sweep the telescope around to see the whole thing. Small planetary nebulae are great too; some like the Cat’s Eye are green or blue in color and show tiny details during moments of good seeing if you’re using a good high-magnification eyepiece.
Galaxies are the most numerous deep-sky objects available, and 10” of aperture allows you to see a lot of them—theoretically some number in the tens of thousands, though most will be dim, devoid of detail, and often easy to miss at first glance. However, the entire Herschel 400 list and Messier catalog are easy to see; the Virgo Cluster is populated with hundreds of easily-visible targets; and dimmer clusters like those in Fornax, Coma Berenices, and Pegasus are possible to observe too. Bright galaxies like M65, M31, M82, M64, M104, and NGC 7331 show obvious dust lanes even with moderate light pollution. The spiral arms of a few galaxies such as M51, M81, M101, and M33 can be seen if you have dark skies and a careful eye, though don’t expect anything super obvious or easily visible with direct vision.
A 10” scope is about the biggest where you can regularly expect to see tangible gains in lunar and planetary views from more aperture; larger scopes only truly live up to their capabilities under exceptional seeing conditions (though their other advantages do stack up well). The Cassini Division in Saturn’s rings is easy to see, along with cloud belts, a smattering of moons including orange-gold Titan, and, under very good conditions, the Encke gap in the planet’s rings can also be seen.
Jupiter’s cloud belts are bold and brilliant, with the Great Red Spot immediately visible at high magnification and detailed within. Jupiter’s four large Galilean moons are all usually resolvable into disks, and their jet-black shadows make for a striking contrast when they transit in front of the planet. A brown spot on Ganymede, Galileo Regio, can also be seen under exceptional conditions. Uranus and Neptune are obviously disks; a few of Uranus’ moons can be faintly seen, and Neptune’s moon Triton is fairly easy to spot. Pluto is, of course, a star-like point, but you can definitely see it with a 10” scope even as it dims as it retreats further from the Sun.
Venus and Mercury are devoid of detail visually in any amateur telescope, but you’ll probably have an easier time finding and resolving Mercury with a bigger scope like the StarSense Explorer 10” Dob. You’ll be able to see the polar ice caps and a few dark markings on Mars; skilled observers can also find Deimos and maybe even resolve geological features like Olympus Mons and Valles Marineris given very good conditions when Mars is at its closest to Earth. And the Moon is, of course, jaw-dropping under any conditions and at any magnification level with a high-quality big Dobsonian.