The Optical Tube
Optically, the Apertura DT8 is an 8” (203mm) f/6 (1200mm focal length) Newtonian reflector. At f/6, there basically isn’t any coma, most cheap eyepieces work well, and collimation tolerances aren’t insane.
The DT8’s optical tube is pretty typical for an 8” Dobsonian; it’s a thin-walled steel tube held together with thick metal castings on each end, about 4 feet (1.2m) long, just barely short enough to fit across the back of most vehicles. This is also the same length as a typical 6” or 10” Dobsonian, which are also sold under the Apertura DT line by High Point Scientific, so if you can’t afford the 8” or want to go bigger, the 6” or 10” models will be equally transportable and similar in overall handling characteristics (all have focal lengths of 1200 mm as well).
The focuser on the DT8 is GSO’s single-speed 2” Crayford design. This uses a metal drawtube against rollers to smoothly move the eyepiece/accessories back and forth with no gears or any kind of increments for ultra-fine focusing precision. You can actually upgrade it to a dual speed by either replacing the entire unit or buying an upgrade kit, but this is not wholly necessary and will bring you to the cost of just buying an AD8/Z8, which comes with a dual speed focuser by default. The focuser uses a compression ring to grab your eyepieces rather than a screw, so your eyepiece barrels won’t get annoying dents and scratches over time.
The DT8’s primary mirror is easy to collimate without tools, though the included lock bolts are a bit confusing and can actually be removed. The secondary mirror requires a hex key (included) to adjust, but this is infrequently necessary, if ever, and installing thumbscrews will lead to less accurate alignment and more collimation shift over time.
Accessories
The Apertura DT8 is pretty lacking when it comes to accessories. On the ocular side, all you get is a single 25mm, 1.25” barrel Plossl that provides 48x. This is fine for low power viewing of deep-sky objects. But for lunar and planetary views, smaller planetary nebulae, globular clusters, and double stars, 48x is plain insufficient, and you will want more eyepieces—the 2” focuser on the DT8 means it can take eyepieces with longer focal lengths and wider fields of view than the 25mm Plossl, too.
The only other accessory provided is a straight-through 9×50 finder scope. The image through this finder is upside down and, of course, magnified by 9x compared to what you see with the naked eye, but it also shows stars fainter than what you can see without it-along with some of the brighter deep-sky objects too. This is particularly helpful if you live in a light-polluted area and can’t see many stars with the unaided eye. The main drawback of the finder, however, is that it can be a bit uncomfortable to look through, and its crosshairs are also somewhat difficult to see at night.
The Apertura DT8 does not include any collimation tools. Our collimation guide details how to collimate the scope even without tools, as well as what to expect with each type. You really only need a simple collimation cap, sight tube, or Cheshire, and it’s not an intimidating process.
Mount
The DT8’s mount is basically the same as most commercial Dobsonians. A knock-down particle board base, mostly ¾” thick, is assembled with a few included hex wrenches and covered in melaine, which acts as a bearing surface to spin the scope left-right in azimuth on three small Teflon plastic pads. The scope pivots up and down on four more pads and a pair of plastic circular altitude bearings. The motions are quite smooth, and the mount doesn’t need any aftermarket fixes like the AD/Z series Dobsonians or the Sky-Watcher Dobs. Rubbing some bar soap on the pads may provide a slightly smoother motion, if you need it.
The DT series Dobsonians use springs to keep the bearings in tension and compensate for balance issues from heavy accessories; this is not perfect but works fairly well. Attaching the springs can be somewhat tedious and easy to forget, however, especially if you break or lose the fabric loops used to pull them into place.
Should I buy a Used Apertura DT8?
There’s absolutely nothing wrong with buying a used scope, and the DT8 is fantastic; since these scopes are fairly new entrants to the marketplace, it’s unlikely you’ll even find one in less-than-stellar condition. However, the same recommendations and precautions apply to any used scope; visibly corroded, damaged, or absent primary mirror coatings at this size are not really worth repairing unless you get the scope for a very low price; be sure to check that the mirrors are in reasonably good shape. The secondary can be replaced more cheaply, but is still an expense; small scratches and dust are fine, and anything on the primary directly obstructed by the secondary also does not matter.
A damaged Dobsonian base can be replaced with a new one either direct from Apertura or made out of plywood by you or a third party, but again, this adds to the price of the scope and is unlikely to save you money when you’re done.
Alternative Recommendations
The Apertura DT8 is a nice scope, but there are, of course, other options available at similar prices with differing capabilities.
- The Apertura AD8/Zhumell Z8/Orion SkyLine 8 (all made by GSO) are the same optically as the DT8, but include dual-speed focuser knobs (by itself worth the upgrade cost), a pair of high-quality eyepieces, a cooling fan, and a 9×50 right-angle finder instead of the DT8’s straight-through unit. The mount design is a bit different, however.
- The Sky-Watcher 8” FlexTube/Collapsible has similar optics and accessories to the DT8, albeit with an additional 10mm eyepiece included. However, its collapsible tube really needs a shroud, the altitude bearings aren’t the best, and collimation is a bit annoying since it requires tools.
- The Orion XT8 is basically the same as the DT8, but the focuser cannot be easily upgraded, and the finder included is simply a red-dot unit.
- The Explore Scientific FirstLight 8” has a superior mount to the DT8, as well as a pretty nice focuser, but the included accessories are very poorly made.
Aftermarket Accessory Recommendations
The Apertura DT8 only includes a single eyepiece. At the bare minimum, you need one or two others. There are a lot of different options you could go with, but we have a few favorites in mind that are all relatively low-cost.
A 9mm “gold-line” will give you 133x with the DT8 and is probably the first thing we’d recommend going out and getting. 133x is a good magnification for lunar and planetary viewing, as well as for smaller deep-sky objects, even under mediocre conditions.
Next, we’d probably recommend a 2x 1.25” Barlow lens. You can use this with the 9mm to get 266x and with the included 25mm eyepiece for 96x. This might be all you really need, but you might also want to consider some more eyepieces.
A 6mm goldline will provide 200x magnification with the DT8, and could be used with a Barlow lens to get 400x, which is about the most the telescope can ever handle. And a 15mm SVBONY wide-angle eyepiece (80x) will bridge the gap between the 25mm and a higher-power eyepiece, and could be used with a 2x Barlow to effectively replace a 6mm goldline.
Lastly, a 2” wide-angle eyepiece is a good idea for the maximum possible field of view. A 38mm Apertura SWA will give you 32x with the DT8 and provide a true field about 2.2 degrees across (or 4.5 times the angular diameter of the full Moon), making finding targets or fitting the largest deep-sky objects such as the Pleiades or Andromeda Galaxy a breeze.
While more expensive eyepieces do exist, the aforementioned oculars are all you really need to start and can always be replaced by premium stuff later.
A nebula filter—preferably an ultra-high-contrast (UHC) narrowband filter—will improve views of nebulae, especially under light-polluted skies. While not a substitute for dark skies and not useful for other deep-sky targets, it is still a great tool to have in your collection. A 2” Orion UltraBlock is the budget pick in this category. For use with 1.25” eyepieces, it can simply screw on to the DT8’s included adapter, which is threaded for filters.
Lastly, you could also swap out the 9×50 finder on the DT8 for something different. A right-angle 9×50 finder scope might be more comfortable-or more confusing-while a Telrad or Rigel Quikfinder provides a zero-power view with a simple red reticle that is a bit easier to understand than a magnifying finder, but at the expense of not showing stars fainter than what you can see with the naked eye.
What can you see with Apertura DT8?
An 8” Dob is one of the best choices for a beginner astronomer’s scope. It is still quite portable and easy to set up, but it can show you a lot and doesn’t cost too much. The DT8 has enough aperture to resolve globular clusters into individual stars even under less-than-ideal conditions. You can also see the different shapes and structures of globulars—some are more dense, such as M15, while some are loose, like M4. M13 has dust lanes, and M92 is elliptical in shape. Open clusters look great too, regardless of light pollution levels. Many will have hundreds or thousands of stars, often with colors too.
Emission nebulae such as the Lagoon, Swan, and, of course, the Orion Nebula look fantastic; for best results, you will want dark skies and/or a UHC filter. You can also see the Veil Nebula supernova remnant with decent skies and a UHC, while the Crab Nebula (M1) is rather tiny but easily seen as well. Planetary nebulae like the Ring and Dumbbell are easy to spot; smaller ones may show green, turquoise, or bluish colors at high magnification along with lots of small details and/or central white dwarf stars.
With suitably dark skies (the Milky Way should at least be visible overhead), you can see a lot of detail in galaxies with the DT8. The spiral arms of M51 can barely be seen, as can those in M81, while M101 is a bit more difficult and M33 equally so, albeit with H-II regions that are easily spotted. M82’s dust lanes are visible, as are those in the Andromeda Galaxy (M31), M64, and Centaurus A. The companions to galaxies like M31 and M81 are also easily seen; the Virgo Cluster shows dozens of individual galaxies, but few have details owing to their elliptical shapes.
Within the solar system, the DT8 can also show you a lot, assuming you are fortunate enough to have a night of good seeing and equip it with one of the high-power eyepieces we recommend (48x just isn’t enough to show much). You can see the phases of Venus and Mercury, but both planets are simply opaque disks with no details owing to Mercury’s small size and less-than-ideal location in the sky, and of course, Venus’ cloud cover. The Moon shows craters, valleys, and mountains mere miles wide, and Mars’ ice caps can be seen too. When Mars is close to Earth biannually in the months around opposition, you can see a few dark markings, or as many as a few dozen under ideal conditions.
Jupiter’s moons Io, Europa, Ganymede, and Callisto look like tiny disks with the DT8, and Ganymede is visibly non-uniform in color. Their shadows are also visible when they transit the planet. Jupiter itself shows a number of brightly colored cloud bands ranging from brown, to tan, to white, to pink and red, to blue in color. The Great Red Spot is also fairly easy to see.
Saturn and its rings are splendid to see with the DT8, and the Cassini Division, a small gap in the rings, is easily visible. You can also see some brown and gray linear cloud bands on the planet itself. Around half a dozen moons are visible, ranging from the obvious and bright Titan (magnitude 7), easily visible as a gold dot, to Hyperion (magnitude 14), which may take some time to locate, the small icy moon Enceladus, close to the planet and hard to pick out from its glare, and Iapetus, which varies drastically in brightness depending on whether its highly reflective ice-covered hemisphere or ruddy brown side is facing us.
Uranus and Neptune are easy to see with the DT8 and are clearly not stars, but you’ll be hard-pressed to see anything at all on the planets themselves due to their tiny angular sizes. Uranus’ moons Titania and Oberon are just barely visible; Ariel and Umbriel are theoretically possible but will be very hard to see due to Uranus’ glares. Neptune’s only large moon, Triton, is a bit easier to spot. Pluto is also visible in the DT8 but will appear as just one of many 14th-magnitude stars, as it is at present surrounded by them in the constellation Sagittarius. It may take several nights of careful observation to confirm that you have spotted the former ninth planet.
