The Optical Tube
The FirstLight 8” Dobsonian is seemingly a relatively normal 8” f/6 Newtonian on a Dobsonian mount. However, upon closer inspection, it’s a little obvious that the scope uses tooling and parts from other telescopes in some form. The most glaring aspects of this are the oversized secondary mirror hub and the telescope’s focuser. The secondary mirror in the FirstLight 8” is only 2” across, but the holder for it is 2.5” wide. This extra, unnecessary obstruction reduces contrast in the telescope, leading to slightly inferior planetary images. As for why it’s there, the answer is simple – the secondary hub is lifted from Explore Scientific’s 8” f/4 and f/5 Newtonians which have larger secondary mirrors. While the unnecessary extra obstruction is a bit annoying, it doesn’t seriously impact usage, and unlike most other mass-market Dobsonian telescopes these days you can collimate the secondary with a Phillips head screwdriver rather than an Allen key, a nice touch.
As for the primary mirror – the primary of the FirstLight 8” is easily collimated, with thumbscrews rather than the Philips heads of some other manufacturers. The mirror itself is of high quality and delivers splendid, sharp images at both low and high magnifications.
The other major oddity of the FirstLight 8” Dobsonian is its 2.5” (really 2”) hexagonal rack-and-pinion focuser. This high-quality focuser is lifted, again, from faster Newtonian reflectors intended for imaging – but more importantly, for whatever reason, it requires that an included extension tube be installed to reach focus with almost any eyepiece, resulting in the eyepiece being about 8 inches away from the tube wall (the focuser itself without the extension is already unusually tall). Most Dobsonians have a focal plane only a few inches from the tube wall. Having the focus further out means that the secondary mirror must be bigger than usual or else wide-angle eyepieces might vignette, and it means the focuser body itself is more likely to sag and the scope is usually more tricky to balance. While sagging isn’t a problem thanks to the 2.5” hex focuser’s high build quality, I can’t help but find this design choice a little strange. Thankfully it works quite well despite the unusuality of the arrangement.
The FirstLight 8” Dobsonian also has two finder brackets, on either side of the focuser. Unfortunately, they only accept Explore Scientific and some Meade finderscopes, so you’ll need an adapter or have to swap them with standard Synta/Vixen-style finderscope brackets.
Lastly, the FirstLight 8” Dobsonian uses rotatable tube rings with the scope’s altitude bearings screwed onto them, rather than having bearings bolted to the tube walls. This not only allows you to slide the tube back and forth for balance (which we’ll go into later) and rotate it to put the eyepiece at a convenient location, but it also means you could take the tube off the Dobsonian mount, attach a dovetail, and put it on an equatorial mount for astrophotography – and thanks to its ridiculous amounts of extra focuser travel, the FirstLight 8” will have no trouble focusing with a DSLR camera and adapter.
The FirstLight 8” Dobsonian’s greatest weakness is its accessories – or rather, its lack of usable ones. The scope comes with a red dot finder and a 25mm “Super Plossl” – the same as many beginner scopes. Unfortunately, both are of extremely low quality.
The included 25mm Plossl is, to me, somewhat horrific. Not only is the eye lens recessed quite a bit into the eyepiece body, which means you basically have to jam your eyeball up against the eyeguard to take in the full view, but the thing seems to be constructed mostly of plastic, and the lenses could be plastic as well. It works, but leaves much to be desired compared to the quality 25mm Plossls delivered with Orion and Sky-Watcher Dobsonians, which are sharper, more comfortable to use, and generally higher in build quality.
The red dot finder has a tinted plastic window which makes stars appear quite a bit dimmer when viewed through it, and it is a bit wobbly and doesn’t hold alignment well, making aiming the telescope a bit of a frustrating experience.
Overall, I would say that you will probably be unhappy with the included accessories out of the box and might find the telescope hard to use at all, so it’s definitely worth shopping for additional accessories or considering another telescope altogether.
The FirstLight 8” has a number of design improvements to its mount compared to the other non-premium 8” Dobsonians on the market that makes it far superior to its competitors.
For starters – the altitude bearings. Most cheap Dobsonians use either plastic circles less than ten inches across pivoting on nylon pads, which produces mostly-smooth motions – however, add a heavy eyepiece to the top of the scope and you’ll suddenly find it drooping over, unless you either have springs (in the case of the Orion XT and Apertura DT Dobsonians) or magnetic counterweights (which will produce the opposite problem when you remove the heavy eyepiece). The only other solution is to lock up the altitude axis, which results in sticky, jerky, and stiff motions with the telescope. The Zhumell Dobsonians attempt to work around this problem with ball bearings that slide up and down the telescope tube to adjust for different eyepieces, but they have limited travel and you’re left with the same drooping/swinging problem unless you either lock up the altitude motions or constantly shift the bearings back and forth when you swap eyepieces.
Rather than adopting either of the aforementioned two (flawed) approaches, the FirstLight 8” has large, semi-circular bearings, attached to tube rings. As was mentioned previously, the rings allow you to rotate the tube to put the eyepiece at whatever angle you want, have much more travel in either direction to compensate for the bottom- or top-heaviness, and the large diameter of the bearings means that the center of gravity of the scope simply doesn’t shift as much relative to the bearings with heavy eyepieces and accessories, which means that you likely won’t have to adjust them at all between eyepieces. The large altitude bearings also have the added advantage of smoother motions than their smaller counterparts on other telescopes, and they look prettier too.
For azimuth, the scope uses a fairly typical melamine-on-Teflon arrangement that works well, though it can be a little jerky when pointing the telescope near the zenith (straight up).
The FirstLight Dobsonian mount also has large cutouts in the base that function as handles.
As for downsides? With a really heavy eyepiece or a heavy eyepiece and heavy finder, you’ll have clearance issues with the tube hitting the base of the scope if you try to balance it correctly. However, the extra imbalance that can’t be completely compensated for by moving the tube could be solved with a relatively small counterweight (or even just by mounting a cooling fan on the back of the scope), so I don’t consider this an issue. The instructions for assembling the base are also a little confusing, with drawings/renders that do not match the actual mount and a convoluted labeling system, but thankfully there aren’t too many things to mess up during assembly so I wouldn’t recommend worrying much.
Should I buy a Used FirstLight 8” Dobsonian?
If the price reduction compared to buying new is fair, then go for it.
For the price of the FirstLight 8” Dobsonian, there are definitely a few alternatives you should consider:
- Apertura DT10 – More aperture, better accessories, better finderscope, similar price
- Zhumell Z8/Apertura AD8 – Cheaper, better accessories, slightly better focuser, better finderscope
- Apertura DT8 – Cheaper, better accessories, better finderscope
- Orion XT8 – Cheaper, slightly better accessories, better finderscope
- Sky-Watcher 8” Collapsible – Cheaper, collapsible tube, better accessories (but with a vastly inferior mount), significantly better finderscope
- Sky-Watcher 8” Traditional – Cheaper, better accessories, better finderscope
Aftermarket Accessory Recommendations
The first thing for the FirstLight 8” that I’d recommend is replacing the godawful included red-dot finder with a Telrad or Rigel Quikfinder, either of which will stick directly to the tube without needing to fit the proprietary finder brackets or you could bite the bullet and buy an Explore Scientific or Meade 9×50 finderscope.
As for eyepiece upgrades, there are a variety of options. If I had to pick three, I’d get 6mm, 9mm, and 15mm “goldlines” for high to medium power, and a low-power wide-field eyepiece like the Meade 20mm UWA or GSO 30mm/40mm SuperView for low power.
You might also want to pick up a collimation tool of some sort, such as the Farpoint Astro laser collimator or a Cheshire.
What can you see?
The FirstLight’s 8 inches of aperture gives you a heck of a lot of resolving power. Jupiter will show a wealth of detail in its cloud bands along with of course the Great Red Spot, and its moons appear as tiny dots – not starlike pinpoints of light – and cast shadows as they transit the planet. Saturn will show about half a dozen moons, the Cassini division within its rings, and some low-contrast cloud bands. Uranus and Neptune are merely turquoise and azure dots of course, but Neptune’s moon Triton is fairly feasible to spot and Uranus’ moons are on the cusp of visibility provided you have dark skies and good seeing. Mars will show some dark patches and its ice caps, and Venus and Mercury will always display nothing but their phases. And as with any telescope, the Moon shows a wealth of detail with features only a few miles/km across visible.
8 inches of aperture also allows you to seriously dive into the realm of deep-sky objects. Thousands of galaxies are visible with this scope under dark skies, and a few dozen such as M51, M82, M33, M101, M63, the Leo Triplet, and others will show some amount of detail such as dust lanes or spiral arms. The brighter Messier globular clusters such as M3, M15, M13, M92, and M5 can be resolved, while dimmer ones from the Palomar and NGC catalogs can be spotted as faint smudges. There are also, of course, a half dozen bright emission nebulae such as Orion, the Lagoon, and the Swan, dozens of planetary nebulae, thousands of double stars and of course open star clusters scattered throughout the sky which will look stunning in an 8” telescope.