The Optical Tube
The 10” FirstLight Dobsonian is a 10” (254mm) f/5 Newtonian reflector with a focal length of 1270mm. An f/5 reflector does have some minor coma at the edges of the field of view, especially with a wide-angle eyepiece. However, cheaper wide-angle eyepieces like Erfles show other edge-of-field aberrations like astigmatism that easily hide the coma, while more well-corrected wide-angle eyepieces make the coma almost invisible. Collimation at f/5 is fairly critical and is done in the same manner as with most reflectors: a set of three screws can be adjusted on the back for the primary mirror while smaller screws adjust the tilt and rotation of the secondary mirror. Though, the FirstLight Dobsonians are provided with thumb screws to adjust the secondary mirror rather than annoying recessed hex screws, which require a key (and praying you don’t drop it onto the primary mirror) to adjust.
The focuser on the 10” FirstLight Dobsonian is a massive 2.5” single-speed hexagonal rack-and-pinion/Crayford hybrid focuser, borrowed from some of the imaging telescopes Explore Scientific sells. This focuser holds the heaviest of eyepieces and accessories with ease and also features enough inward travel to reach focus with a DSLR or cooled astronomy camera by default, a nice if unnecessary bonus. However, it’s only a single-speed design, so focusing at high magnification can be a little trickier than with a dual-speed Crayford unit. Since the focuser and optical tube are designed to have sufficient in-travel for a camera, using the provided extension tube is mandatory for most eyepieces, and with the focal plane so far from the center of the tube, the secondary mirror is a little bit bigger than it otherwise would need to be. But this is much less of an impact on performance than with the 8” FirstLight Dobsonian.
The 10” FirstLight optical tube sits in an adjustable tube cradle with the altitude bearings screwed on to the sides. This means that you could put a Vixen- or Losmandy-style dovetail bar on the rings and use the scope atop an equatorial mount for astrophotography. However, a mount capable enough to hold a 10” reflector for deep-sky imaging is going to cost several thousand dollars at a minimum and isn’t really portable, while planetary imaging can be done by tracking by hand or building/buying a Poncet-style equatorial platform to attach beneath the Dobsonian base.
Accessories
The 10” FirstLight Dobsonian doesn’t include much in the way of accessories. You get a 25mm, 1.25” Plossl eyepiece providing 51x magnification and a red dot finder. The 25mm Plossl is not the best; it’s rather short on eye relief, the body is plastic, and there are some issues with glare and scatter that are not present in better-quality Plossl eyepieces. You’re also going to want more eyepieces for higher magnification and probably a low-power, 2” wide-angle eyepiece anyway. The provided red dot finder has a tinted window, is annoying to adjust and turn on/off, and doesn’t maintain alignment well. It also attaches via a non-standard bracket, so it’s not a simple matter of swapping on another finder such as a red dot finder or 9×50 right angle unit without drilling additional holes and installing a new bracket (though a finder that attaches with tape like a Rigel Quikfinder or Telrad will be fine).
Mount
The 10″ FirstLight Dobsonian is pretty typical in that it has a particle board rocker box that you have to put together from its flat-packed box. However, Explore Scientific’s design doesn’t have the screws holding the mount together thread directly into the particle board but rather into embedded anchors. This means that it’s possible to take the rocker apart for transport repeatedly without causing damage or a loose fit over time. The rocker box features cutouts to reduce weight and provide built-in handles. For azimuth (side-to-side) motion, the bottom of the melamine-covered rocker box pivots smoothly on a set of three Teflon pads, rather than cheap roller bearings or nylon pads like in most other mass-manufactured Dobsonians.
For altitude motion, a pair of large, half-circle bearings are attached to the tube rings holding the 10” FirstLight optical tube. The bearings’ large size means that the telescope won’t go out of balance when you put a heavy eyepiece, finder, or other accessory on the front end, though for extreme scenarios, you can slide the tube in the cradle to adjust its center of balance. The bearings are covered in pebbled glassboard and glide smoothly against the Teflon pads on the rocker sides; there’s no need to adjust clutches or springs, and the motions don’t get “stuck” when trying to make small position adjustments at high magnification. You can also rotate the optical tube in its cradle to adjust the placement of the focuser/eyepiece if you prefer it at a different angle or on the other side of the tube.
Should I buy a Used Explore Scientific 10” FirstLight Dobsonian?
A used 10” FirstLight Dobsonian would be an excellent telescope. However, since the base is particle board and the tube is thin-walled steel, it’s possible you might find one in damaged condition. Removing large dents from the tube can be done; small ones that don’t get in the way of the optical path can and should just be left alone. A damaged Dobsonian base can be either repaired or replaced, but you should account for the cost of replacement lumber/paint/varnish as well as your time when purchasing a used sample. And as with any used reflector, always make sure that the mirror coatings are in good condition and free of corrosion or missing spots (though some dust/dirt is fine and can easily be rinsed off; see our mirror cleaning guide for more information).
Alternative Recommendations
The 10” FirstLight Dobsonian is a fairly good telescope. However, you may want to opt for something with either a little more portability or more accessories included for the money, and as such, we’ve picked out a few different alternative options for you to consider:
Under £600
- The Explore Scientific 10” Hybrid Dobsonian features the same optics and giant altitude bearings of the 10” FirstLight, but with a truss tube design for increased portability, all-metal construction, and a significantly lower price. The issues with the provided accessories, however, remain, and the focuser is a standard single-speed 2” Crayford unit.
- The Apertura AD8/Zhumell Z8/Orion SkyLine 8 is smaller than the 10” FirstLight and has a decidedly inferior mount design – though it’s still plenty functional. However, it includes a large assortment of high-quality accessories such as a 9×50 finder, 2” wide-angle eyepiece, and built-in 2” dual-speed Crayford focuser, which would easily cost a few hundred dollars to purchase separately as an upgrade.
- The Sky-Watcher Virtuoso GTi 150P features a collapsible tube and tabletop Dobsonian mount for maximum portability, and can even fit in a backpack. Its super wide field of view and full motorized GoTo and tracking capabilities – which are controlled by your smartphone or tablet – somewhat compensate for the much smaller aperture, and the scope can be aimed manually freely without compromising the accuracy of its GoTo or tracking capabilities when powered on. The manual Heritage 150P is identical apart from lacking electronics, and 130mm Virtuoso GTi and Heritage models are also available at an even lower price tag than their big brothers.
£600-£850
- The Apertura AD10/Zhumell Z10/Orion SkyLine 10 offers the same performance as the 10” FirstLight Dobsonian, but with the same improved accessories and features as the AD8/Z8. You don’t get quite as good of a Dobsonian base design due to the use of the roller/ball bearings, but the included dual-speed focuser, 9×50 finder, eyepieces, and built-in cooling fan make up for it somewhat, especially given the price.
- The Celestron StarSense Explorer 8” Dobsonian has less aperture than the 10” FirstLight but does feature a lightweight rocker box with cutouts, handles on the tube for portability, and Celestron’s StarSense Explorer technology to assist you in aiming it. However, as with the FirstLight Dobsonians, you only get one eyepiece, a red dot finder, and a single-speed Crayford focuser. A 10” model is also available, and we’d recommend it if you can afford both the scope and the mandatory accessory upgrades.
- The Sky-Watcher 8” FlexTube Dobsonian’s collapsible tube makes it a little more compact when disassembled than a standard 8” or 10” Dobsonian (though the easy-to-dismantle rocker of the FirstLight Dobsonians does provide some competition in that regard) and the included eyepieces, finder, and focuser are of acceptable quality. However, it needs a shroud, the altitude bearing design is not very good, and the scope is rather heavy.
Aftermarket Accessory Recommendations
The 10” FirstLight Dobsonian probably needs a new finder to replace the poor-quality, provided red dot one. The Rigel Quikfinder is lightweight, sticks on with included adhesive, and takes up fairly little real estate on the scope’s optical tube, but the Telrad or QuInsight are also great options; all provide a zero-power reticle that’s easy to view; the QuInsight and Rigel have built-in dew shields; and the Rigel Quikfinder features a blinking/pulse option as well. A 9×50 right-angle, correct-image finder will also work, but you’d have to drill holes in the scope’s tube to fit a bracket, and right-angle finders can be confusing to use on their own.
While the included 25mm Plossl eyepiece is functional, you do need additional eyepieces for the 10” FirstLight Dobsonian anyway. Your budget is going to largely dictate what eyepieces you get for this telescope, but our top picks for an affordable starter set would be the SVBONY 26mm wide-angle (49x), a 15mm wide-angle or redline eyepiece (85x), and a 9mm gold-line or red-line eyepiece (141x). A shorter focal length eyepiece, such as the Astromania 4.5mm (285x), is ideal for planetary and double star work but may not be necessary right away, especially if you have sub-optimal seeing conditions on a regular basis.
Once you have a full set of eyepieces and a good finder, you should buy a good UHC (ultra high contrast) 2″ nebula filter. Our top pick in this category is the 2” Orion UltraBlock filter. It’ll improve contrast on nebulae like Orion, the Swan, and the Lagoon and bring out previously-invisible objects like the Helix Nebula or the Veil Nebula under sufficiently dark skies. A 2” filter will screw onto the scope’s provided 1.25” eyepiece adapter for use with 1.25” oculars and future-proof you even if you don’t have any 2” eyepieces right away.
What can you see with Explore Scientific 10″ FirstLight Dobsonian?
Your views of deep-sky objects—that is, stuff outside the Solar System—with any telescope, including the 10” FirstLight Dobsonian, are going to be dictated by the severity of your light pollution conditions. Light pollution affects extended objects, or “faint fuzzies,” like galaxies and nebulae, the most, and point sources (i.e., stars and clusters of them) the least.
Even from a suburban or city sky, the 10″ FirstLight Dobsonian will be able to separate most large to mid-sized globular star clusters into individual stars. Many of these clusters have clearly different shapes and morphologies, like M13’s dust lanes, M15’s nearly stellar core, and M92’s flattened elliptical shape. Open star clusters number in the thousands, and the brighter and more interesting ones like M11, M35, or the Double Cluster show lots of beautiful star colors, which appear far richer than with a smaller telescope thanks to the 10” FirstLight Dobsonian’s superior light-collecting abilities. A 2” wide-angle eyepiece makes scanning the open clusters and dark nebulae along the Milky Way in Auriga, Cassiopeia, Cygnus, Scutum, and Sagittarius even more enjoyable, and you’ll be sure to stumble upon a few globular clusters in the summer Milky Way too.
As previously mentioned, extended objects like nebulae and galaxies are more affected by light pollution, though the 10” FirstLight Dobsonian will have no trouble showing you brighter objects like the Andromeda Galaxy (M31) or Orion Nebula (M42), if perhaps mere washed-out shells of their former glory compared to the view under better observing conditions. The 10” FirstLight Dobsonian will show you thousands of galaxies under dark skies, with dozens or hundreds showing some sort of detail such as shapes, dust lanes, or star-forming regions. The dust lanes and orbiting companion galaxies of M31, details in the Leo Triplet group of galaxies, the eponymous Sombrero Galaxy, and hints of spiral arms in galaxies like the Whirlpool (M51) and others like M33 are all possible to see under reasonably dark skies. You can also see hundreds of galaxies in the Virgo Cluster; sometimes dozens of easily visible ones will fit in a single low-power field of view.
While you don’t need a filter to see nebulae, a UHC filter like the one we mentioned earlier is a really great accessory to have for any telescope, especially the 10” FirstLight Dobsonian. The Orion Nebula (M42) shows a greenish color when unfiltered, and you can resolve the Trapezium star cluster at its center with high magnification. A UHC filter brings out the fainter sections of the nebula and increases the contrast of its darker areas. The Lagoon Nebula (M8) and its embedded star cluster are dazzling, and you can see the dark lanes in the Trifid (M20) and Eagle (M16). The Veil Nebula can be seen under dark skies with a UHC filter and spans several fields of view at low power with the 10” FirstLight Dobsonian.
