The Optical Tube
The Popular Science Celestron StarSense Explorer DX 100AZ is a 100mm (4”) f/6.6 achromatic doublet refractor with a focal length of 660mm. This is identical to the Inspire 100AZ. The 100AZ optics are identical to the optics used in 102mm f/6.5 refractors, such as the StarSense Explorer DX 102AZ or NexStar 102SLT, but the design of the objective lens cell stops the telescope aperture down by 2mm, a negligible amount (if anything, increasing performance, as optical quality issues can occur at the very edges of mass-manufactured lenses and mirrors). A typical achromatic doublet at this size and focal ratio will show chromatic aberration around bright objects, manifesting itself as a purple, defocused halo, which is particularly annoying when trying to observe the Moon and planets at high magnifications. However, views are still fairly sharp.
The StarSense Explorer DX 100AZ features a 1.25” rack-and-pinion focuser attached to the back of the tube. This focuser is fairly stiff and sturdy, but is noticeably inferior to a metal focuser, wobbles somewhat, and is more prone to slipping with heavy accessories; little tension adjustment is possible to prevent this.
The StarSense Explorer DX 100AZ includes a prism star diagonal, a red dot finder, and two 1.25” Konig eyepieces: a 25mm for 26x magnification, and a 10mm yielding 66x. These eyepieces are fairly good quality, offering a roughly 50-degree apparent field of view and sharp images, though they do have some chromatic aberration and issues with internal reflections on account of their simple 3-element design, cheap coatings, and plastic innards. However, the 10mm is significantly more comfortable to look through than a normal 10mm Plossl or Kellner eyepiece on account of its greater eye relief.
The 1.25” diagonal supplied with the StarSense Explorer DX 100AZ and many other offerings from Celestron is a plastic-bodied Amici erecting prism, which produces upright images that are corrected left-right instead of the normal mirror-reversed image from a standard star diagonal. This design makes a bright “spike” on bright targets like planets and bright stars, just like the spider vanes in Newtonian reflectors make diffraction spikes. Because the Amici diagonal is made cheaply, its prism is too small. This causes vignetting with eyepieces that have a wider field stop than the stock 25mm, and it can cause glare and ghost images.
For a finder, Celestron provides its standard “StarPointer” red-dot finder, a generic device that’s more than adequate for aiming a small, fairly wide-field instrument like the StarSense Explorer DX 100AZ.
The Popular Science StarSense Explorer DX 100AZ uses the same mount as the other StarSense Explorer DX telescopes: an “AZ3” alt-azimuth single-arm fork mount that uses a standard Vixen-style dovetail to clamp to your telescope tube, an extruded aluminum extendable tripod, and of course an attachment for the StarSense Explorer phone bracket. You aim the telescope coarsely by just pushing it around the sky, while fine adjustments are made by turning the two slow-motion adjustment cables, which move the mount in small increments using gears. The backlash in the cables/gears is a bit annoying, however, and it’s nowhere near as simple as a good Dobsonian mount. An accessory tray is provided to affix between the tripod legs, instead of an eyepiece rack, which isn’t generally that useful.
The StarSense Explorer Technology & App
The Celestron StarSense Explorer technology uses your phone’s existing camera and gyroscopes to provide real-time data on the position of your telescope and find objects. The provided bracket serves solely to line your phone’s camera up with the direction of the telescope, while the app and software technology use a technique known as “plate solving” to take snapshots of the sky with the camera during setup and occasionally thereafter, which calibrates a reference position for the gyroscopes and accelerometers in your smartphone to guess where the telescope is aimed in use. Constant plate-solving would produce too much lag and use up battery power and cellular data quickly. The app has a huge catalog, has an interface and the ability to turn your screen red like SkySafari or other astronomy apps, and shows a real-time indication of where in the sky the telescope is pointed.
Your smartphone’s camera and gyroscope quality dictate the accuracy of the StarSense Explorer technology, though even a low-quality phone will at least get your target in the field of view, while newer phones will have an accuracy of about ¼ of a degree (half the width of the full Moon) or better. This is not as precise as a good GoTo telescope, but it is plenty for finding and viewing almost any deep-sky objects.
The StarSense Explorer telescopes come with a code that can be used five times to activate the app on multiple devices. If you get a telescope with an invalid or used-up code, Celestron can give you a new one if you have proof of purchase.
Should I buy a Used StarSense Explorer DX 100AZ?
There’s a decent chance that a used StarSense Explorer telescope will be missing the phone bracket and/or app codes, as many people have bought these telescopes solely to remove the brackets to re-use somewhere else. If the telescope is complete and comes with valid app codes, however, it’s a good deal if you can get one for a decent discount off the retail price.
The StarSense Explorer technology is nice, but the limited aperture and optics of the StarSense Explorer DX 100AZ mean there are a few other options in its price range that can show you more stuff in the night sky.
- The Sky-Watcher Heritage 150P has over double the light gathering ability of the StarSense Explorer DX 100AZ and about 50% more resolving power, without a pesky tripod or annoying chromatic aberration to get in your way. Its collapsible tabletop Dobsonian design sets up in minutes and is easy to use.
- The Sky-Watcher Heritage 130P offers the same features of the Heritage 150P but has slightly less aperture – though still significantly more than the StarSense Explorer DX 100AZ, giving it greater light gathering and resolving power.
- The Sky-Watcher Virtuoso GTi 150P is identical to the Heritage 150P but has fully motorized GoTo and tracking, controlled via your smartphone or tablet. This is a huge step up from the manual-but-assisted StarSense Explorer technology. The Virtuoso GTi 130P uses the Heritage 130P optical tube on the same mount.
- The Orion SkyQuest XT6 offers double the light gathering ability and 50% more resolving power than the StarSense Explorer DX 100AZ, with a full-sized sturdy Dobsonian base, 2” Crayford focuser, and of course no chromatic aberration too.
- The Sky-Watcher 6” Classic Dobsonian offers similar features to the Orion SkyQuest XT6 though it includes a magnifying instead of a red dot finder and two eyepieces instead of one, albeit with an inferior and heavier Dobsonian base design.
Aftermarket Accessory Recommendations
Given the low quality of the provided Amici prism diagonal with the StarSense Explorer DX 100AZ, we’d recommend replacing that first. Celestron’s standard prism diagonal works well, and a dielectric mirror diagonal like the Apertura unit offers slightly better transmission as well as a compression ring instead of thumb screws to grip your eyepieces.
While the provided eyepieces are perfectly adequate, the 65x magnification provided by the included 10mm eyepiece is not nearly enough magnification for planetary viewing with the StarSense Explorer DX 100AZ. A 6mm goldline or redline eyepiece provides 110x magnification, which is about as high as you can go before the scope’s optics and chromatic aberration get in the way. At the low-power end, a 32mm Plossl eyepiece provides 21x and a wider field than the stock 25mm ocular (though you’ll need a new diagonal as it vignettes with the stock Amici prism), and a 15mm SWA or redline eyepiece provides 44x, midway between the 25mm and 10mm eyepieces and good for viewing many medium-sized deep-sky objects.
A UHC (ultra high contrast) nebula filter such as the Orion 1.25” UltraBlock filter improves contrast on nebulae as well as revealing previously-invisible nebulae and details in them, working well regardless of your sky conditions by limiting light throughput to certain spectral emission lines from these objects.
What can you see with Popular Science StarSense Explorer DX 100AZ?
The Popular Science Celestron StarSense Explorer DX 100AZ is best for large, bright deep-sky objects like open star clusters, which can be seen in cities and number in the hundreds under a dark sky, such as the Double Cluster in Perseus. You can’t quite resolve globular star clusters or most planetary nebulae at high magnification due to the telescope’s small aperture, however. The exceptions to the latter are the bright and fairly large Ring (M57) and Dumbbell (M27) which are fairly conspicuous with even a small telescope. A few galaxies, like Andromeda, show dust lanes and companion galaxies, and you can see a few dozen in the Virgo Cluster, but most are too dim for a 100mm telescope to show much detail and remain smudges even under sufficiently dark skies without too much light pollution to hide them entirely.
The StarSense Explorer DX 100AZ does quite well on bright nebulae like Orion (M42) or the Lagoon (M8). With a UHC nebula filter and dark skies, these nebulae are further enhanced, and you can go after very large targets like the North America Nebula or the Veil Nebula supernova remnant, too.
While limited by its chromatic aberration and small aperture, the StarSense Explorer DX 100AZ still works fairly well on planets and other Solar System objects and is capable of providing sharp images. Expect to see the phases of Mercury and Venus, thousands of details like mountains and craters on the Moon, and the polar ice caps on Mars. With some effort and when Mars is close to Earth, you might be able to see a dark marking or two on its surface at high magnification with the DX 100AZ. You can also see Jupiter’s moons, and their disks and shadows just barely show up during transits on a clear and steady night, while Jupiter itself shows its cloud belts and possibly the Great Red Spot. Saturn’s rings, the Cassini Division within them, and some cloud banding can be seen alongside a few moons. Uranus and Neptune can be seen, though both are hard to distinguish from nearby bright stars, particularly Neptune due to its distance, and their moons are too dim to see with only 100mm of aperture, as is the case with faint Pluto.