The Refractor OTA and the Focuser
The DX 102’s optical tube is a 102mm f/6.5 refractor with a focal length of 650mm, the same as used on many other Celestron telescope/mount packages like the Omni 102 AZ and NexStar 102SLT. At this aperture and focal ratio, there is a fair amount of chromatic aberration, but sharp views of the Moon and planets are still possible.
The DX 102 has a 2” rack-and-pinion focuser, but it cannot actually balance on its mount with a 2” diagonal and eyepiece, so in practice, the scope is limited to 1.25” eyepieces and accessories only. Thankfully, even with 1.25” eyepieces, you can squeeze out a field of view of about 2.5 degrees with a 32mm Plossl or similar, so this should not be of huge concern to a beginner.
A Fair Alt-Azimuth Mount
The StarSense Explorer DX mount is nothing more than a repainted Omni XLT AZ mount with a bracket for the StarSense Explorer device. This mount is a little on the small side for either optical tube, but it works just fine. It’s a simple, aluminum-legged alt-azimuth mount with slow-motion controls on both axes. The accessory tray is a nice, sturdy affair and an actual tray rather than the silly eyepiece rack supplied with many scopes. There are no slow-motion controls; you just push the whole mount/tube around the sky.
The StarSense Explorer Technology & App
At its core, the StarSense Explorer actually uses a relatively old technology known as plate-solving. In essence, what it does is take a snapshot of the sky and use computer algorithms and star maps to figure out where it is pointing. Normally, this is done for astrophotography to avoid performing a time-consuming GoTo alignment and is only used to find one target.
In principle, the StarSense Explorer tech is basically a bracket to point your phone at a small mirror that has been aligned to the telescope mount, and then uses the phone’s onboard camera and processing power to plate-solve.
Thanks to your phone’s limited battery life and computing power, the StarSense Explorer technology obviously can’t take a new picture of the sky every time you move the telescope. It would kill your phone quite fast. Instead, it occasionally uses plate-solving technology when you first set up the telescope or move it across a significant portion of the sky, then tries its best to extrapolate finer movements using your phone’s relatively inaccurate gyroscope and accelerometer. In practice, this system is limited to an accuracy of about 0.25 degrees, or half the width of a full moon. This is much less precise than a real GoTo system with tracking but much simpler, easier, and more reliable than a motorized telescope.
RECOMMENDED BUY FOR THE STARSENSE TECHNOLOGY
The StarSense Explorer app is ridiculously easy to set up. All you need to do is install the app, enter the unlock code that came with your telescope, and dock the phone to your telescope. The bracket fits most phones and will work just fine even if you have a relatively thick case (or even a PopSocket). Once you undergo a super-simple alignment procedure, the StarSense Explorer app has a couple hundred objects it can find for you–the Moon, planets, most of the Messier catalog, and some of the brighter NGC/Caldwell objects.
Many people have asked on astronomy forums and contacted Celestron themselves, asking why the bracket and code cannot be sold as a stand-alone item. Celestron’s main explanation is that many beginners would buy the bracket and attempt to fit it onto substandard telescopes (or simply do it improperly) and become frustrated. In any case, the StarSense Explorer technology would simply be of little use on a large Dobsonian or high-end altazimuth mount. It is not accurate enough to be useful for a really large scope, and the catalog is too sparse anyway.
The Subpar Eyepieces of the StarSense Explorer DX Series
The StarSense Explorer DX 102 includes two 1.25” eyepieces: a 25mm Kellner providing 26x and a 10mm Kellner providing 65x. They are by far the weakest links in the scope. The coatings seem to be of very low quality, the whole build is plastic, and the eyepieces have lots of internal reflections and ghosting that are very evident on the Moon, planets, and bright stars. They would be fine for a sub-$200 telescope, but for the price Celestron is asking for the DX scopes, real Plossls would have been perfect.
Should I buy a used StarSense Explorer DX 102AZ?
A used StarSense Explorer scope will likely be missing the code for the app and many of the scopes floating around have had their phone brackets yanked off as well for use on other instruments. So unless you can be sure it has those or the price is absurdly low, we’d recommend you pass.
There are some other manuals as well as computerized scopes in the DX 102 AZ’s price range that you might want to take a look at:
- The Apertura AD8/Zhumell Z8/Orion SkyLine 8 has nearly double the aperture, significantly better accessories, and a simpler mount than the StarSense Explorer DX 102 AZ. You can actually buy digital setting circles/encoders such as the Romer Optics EZ Push To that basically emulates the StarSense Explorer setup with your phone.
- The Orion StarBlast 6i won’t show you on your phone or tablet where you’re pointed, but its IntelliScope digital object locator is pretty straightforward to use, and its 6” aperture will show you a lot more than the DX 102 AZ-and all in a more compact package.
- The Celestron Astro-Fi 130 has a bit more aperture than the DX 102 AZ and will automatically point itself via commands from your smartphone.
What can you see with Explorer DX 102AZ?
The StarSense Explorer DX-102 is limited to brighter objects by the nature of its small aperture. The Moon looks pretty good, while Mercury and Venus show nothing besides their phases. Mars’ dark spots can be seen, although barely, when the planet is close to Earth, while its polar ice caps are a little more obvious. Jupiter’s cloud belts and the Great Red Spot are relatively easy to see, and you can just make out the disks of its four moons when they transit the planet. Saturn’s rings and the Cassini Division within them look fabulous, while its dimmer moons and cloud belts are a bit harder to spot. Uranus and Neptune are barely more than star-like dots, with blue disks barely bigger than the resolving limit of the telescope itself.
Deep-sky objects are a little less exciting. Open star clusters look great and benefit from the 102AZ’s wide field of view, but globular star clusters are little more than fuzzy balls. Particularly under dark skies, bright nebulae like Orion and the Lagoon look great, but planetary nebulae such as the Cat’s Eye are really too small and dim to be interesting in the 102. Galaxies are almost certain to disappoint, as few will show detail under dark skies, and a beginner will struggle to see them all in light-polluted conditions.
Pricing and Availability
This StarSense Explorer DX 102 review was written in January 2020, when the scope was first released for $399. We recommend High Point Scientific (#1 US retailer) and AgenaAstro (#2 choice) for finding the current retail price and purchasing/backordering. Though most other popular telescopes are on months-long backorders, the DX 102 and its cousin, DX 130AZ, appear to be in stock most of the time, and even when they are on backorder, there have been reports that deliveries are quicker than usual. The scope is also available on Amazon, which is unquestionably the most popular e-retailer in the United States, even when telescopes alone are taken into account. However, we have some reservations on telescope vendors and recommend that you go with HPS or Agena.