Overview of NexStar 102SLT Optical Tube
The NexStar 102SLT is a 102mm (4”) f/6.47 achromatic refractor, thus with a focal length of 660mm. Being a standard Fraunhofer doublet achromatic refractor with crown and flint glass lenses, the 102SLT does show chromatic aberration or “false color”, which is worsened by the fast f/6.47 focal ratio. But otherwise, the optical quality of the scope overall is pretty good.
The 102SLT’s dew shield is quite short, at only 3” long from the front of the lens. As a result, stray light and dew are not very well-controlled – the objective lens will fog up pretty fast on damp nights, and glare can be quite problematic – especially if you observe near a streetlight or the moon is up. You can make your own dew shield extension out of foam or a yoga mat, or buy a more rigid aftermarket plastic unit. Either will significantly improve your observing experience.
The NexStar 102SLT’s focuser is a high-quality, all-metal 2” rack and pinion unit. Unfortunately, using a 2” diagonal and a wide-angle eyepiece will probably make the scope too rear-heavy to balance on the SLT mount, as the scope’s dovetail plate is short and you cannot slide it forward in the mount saddle very far. The balancing issue could be solved by putting on a longer dovetail bar and/or tube rings, but that would be problematic with the already-wobbly NexStar SLT mount.
The NexStar 102SLT comes with a StarPointer red dot finder, 1.25” prism star diagonal, and two eyepieces: A 25mm Kellner (26x) and 9mm Kellner (73x). Both Kellner eyepieces are mostly plastic but of decent enough quality to get you started.
A 1.25” prism diagonal is supplied with the 102SLT.
The StarPointer is the same red dot finder supplied on most inexpensive telescopes these days. While not satisfactory for star-hopping with a Dobsonian, it is just fine for its sole purpose on the SLT: Aligning the GoTo system.
The NexStar 102SLT comes with the same Star Locating Telescope mount that all of the other SLT telescopes use – the same chassis and motors are used for Celestron’s NexStar GT, SkyProdigy and AstroFi telescopes.
The SLT mount is lightweight, using thin steel legs for the tripod. It is not what we would call stable. This is particularly so with the 102mm refractor optical tube, which is longer than any of the other telescopes supplied on the SLT mount – thus requiring the tripod legs to be extended further, decreasing stability, and creating more of a moment arm with a longer (if not that heavy) tube. With the tripod legs extended, the tripod assembly easily twists and buckles and can be knocked over by a strong breeze or an impatient child. Consequently, focusing or aiming the 102SLT at high magnifications is difficult and keeping the computer alignment accurate for a whole night is unlikely. You could fill the legs with sand, spray foam, or pebbles and put a brick or rock on the accessory tray to try to increase stability, but filling the legs is inconvenient and time-consuming and ultimately may not be that effective. As a result, using the 102SLT is a frustrating experience if for no other reason that keeping it pointed at something without shaking is a difficult task.
The database on the SLT scopes is variably mentioned as having either 4,000 or 40,000 deep-sky objects in its catalog. Regardless of which it actually has, there are probably a few hundred deep-sky objects that are actually interesting to observe with the 102SLT.
The SLT mount is powered by 8 AA batteries which you put into a simple pack attached to a tripod leg, which plugs into a DC power jack into the side of the mount head.
As is typical with all of Celestron’s computerized telescopes, their SkyAlign auto-alignment feature never actually works – it requires perfect time/date/location settings, and perfect leveling of the tripod, a combination you are unlikely to ever achieve. Use Auto Two-Star Alignment – it’s almost as easy. Keep in mind that the time and date must be entered every time the scope is powered up, and changing location is a bit of a hassle.
Should I buy a Used NexStar 102SLT?
The 102SLT’s mediocre optics and low quality mount mean it’s probably not a good idea to buy one, new or used.
There are a few alternatives to the NexStar 102SLT you may want to consider, all with different advantages:
- The Celestron Astro-Fi 130 provides slightly more aperture, with a similar, but easier to use and steadier GoTo mount controlled by your phone or tablet instead of an old-fashioned hand controller.
- The Orion StarBlast 6i isn’t a GoTo like the NexStar or Astro-Fi, but its Intelliscope hand controller will aid you in pointing it at targets. Plus, its stable and easy-to-use tabletop Dobsonian mount and 6” aperture ensure you’ll get to see a lot for your money’s worth.
- The Apertura AD8/Zhumell Z8/Orion SkyLine 8 each offer double the aperture of the 102SLT on a rock-solid mount with great accessories, all at a great price and with a set-up time of just a few minutes.
What can you see with Nexstar 102SLT?
Being a 4” refractor, the 102SLT has enough aperture to show a fair amount of nebulae, star clusters, and galaxies. However, the wide field of view means that the GoTo system is kind of unnecessary to find many of them. Furthermore, you can’t move the scope manually, and half the fun of a wide-field refractor is panning around the Milky Way and star fields, which you can’t really do with this telescope. Globular clusters will lack resolution, while most galaxies are too dim to catch with the 102SLT’s small aperture – particularly under light-polluted skies. Open star clusters and large nebulae like the Veil, Swan, and Lagoon are the main treats with this telescope.
The Moon and planets look good with the 102SLT as well – provided you can get the scope to stop shaking. Jupiter’s cloud belts, Great Red Spot, and 4 brightest moons can be seen, and Saturn’s rings are visible along with a handful of moons. You might have trouble seeing much in the way of detail on Mars, even at opposition, due to the 102SLT’s chromatic aberration smearing out the planet’s red disk. Uranus and Neptune are little more than starlike dots, while Venus and Mercury’s phases are visible (albeit barely with the latter due to its small size).
The alt-azimuth nature and cheap gears of the SLT mount, combined with the inability to balance with heavy accessories and of course chromatic aberration means that serious astrophotography, be it deep-sky or lunar/planetary imaging is pretty much out of the question with the NexStar 102SLT. You can have some fun shooting the Moon with a phone adapter such as Celestron’s NexYZ (which they offer bundled with the telescope) but that is about the limit of the telescope’s capabilities.