The Optical Tube
The optical tube of the StarSense Explorer DX 6″ SCT is just an adaptation of the Celestron C6 XLT, which is a 6” (150mm) f/10 Schmidt-Cassegrain telescope with a resulting 1500mm focal length. Boasting considerably greater light-gathering capacity and resolution than the smaller C5, which it has largely supplanted, the C6 is a favoured choice among seasoned astronomers seeking a “grab n’ go” telescope and the StarSense Explorer DX 6” SCT is a decent setup in this regard.
Similar to numerous other catadioptric telescopes, the C6 XLT features a knob at the rear of the telescope to focus the primary mirror by moving it back and forth within the tube. This can occasionally result in “image shift” during focusing, which is particularly troublesome at high magnifications or when undertaking any form of astronomical imaging. Nevertheless, the C6 XLT experiences minimal issues in this regard, partially attributable to the modest size and weight of the primary mirror.
A Schmidt-Cassegrain telescope such as the C6 XLT necessitates regular collimation by adjusting the secondary mirror. However, the collimation process for the C6 XLT is relatively swift and straightforward, meaning it won’t be required each time you assemble the telescope. The C6 XLT is equipped with a standard threaded port at the back, permitting the use of Schmidt-Cassegrain accessories and adaptors, including an f/6.3 reducer. The compact size of the interior baffling of the C6 XLT implies that vignetting issues may arise when using an f/6.3 reducer with a large camera sensor or for visual purposes; the same applies if you attempt to use a 2-inch diagonal. Consequently, the genuine field of view of the C6 XLT is confined to slightly more than 1 degree in the sky, which is relatively narrow for a 6-inch telescope.
As a Schmidt-Cassegrain telescope, the C6 occasionally requires collimation. Contrary to what some people may suggest, this is not a particularly daunting or complicated procedure and does not warrant sending the telescope back to Celestron. Instead, you simply adjust three small screws on the secondary mirror housing whilst pointing the telescope at a bright star – a process arguably easier than collimating a Newtonian telescope. For more information, consult our collimation guide. However, it is advisable not to purchase the frequently advertised thumbscrew collimation knobs for the C6 XLT, as they are overpriced and, counterintuitively, cause the telescope to fall out of collimation more frequently due to the inadequate torque they provide to securely fasten the secondary mirror.
The StarSense Explorer DX 6″ SCT comes with a fairly standard accessory kit. Firstly, it includes a 1.25″ visual back, which connects to the rear of the tube and houses a 1.25″ prism star diagonal. The provided prism diagonal is of outstanding quality, featuring multi-coated optics and displaying no noticeable vignetting or significant glare issues, unlike cheaper Amici erecting prism units.
For low power, the StarSense Explorer DX 6″ SCT includes a 1.25”, 40mm E-Lux Plossl eyepiece for 38x magnification. This eyepiece provides the widest possible field of view with this scope – about 1 degree of sky, or twice the apparent diameter of the full Moon. The 38-degree apparent field of view of this eyepiece is admittedly rather narrow, and the true field is not actually any wider than that of a typical 32mm Plossl, but it does the job.
A 10mm Kellner is included with the StarSense Explorer DX 6″ SCT, yielding 150x magnification. This eyepiece is rather short on eye relief, as is always the case with Kellner or Plossl designs, and boasts a 50-degree apparent field of view – acceptable, but leading to objects drifting across the field of view rather fast at this magnification and given the StarSense Explorer DX 6″ SCT’s lack of motorised tracking. It also lacks a rubber eye guard. While functional, we would recommend replacing it with a higher-quality wide-angle eyepiece for a more enjoyable user experience as soon as possible.
The StarSense Explorer mount/tripod assembly is essentially a repainted Omni XLT AZ or “AZ3” mount with an additional bracket for the StarSense Explorer device. While this mount may seem slightly undersized for the C6 XLT optical tube, it functions just fine. It consists of a straightforward, aluminium-legged alt-azimuth mount with slow-motion controls on both axes. The accessory tray is a robust and practical addition, serving as an actual tray as opposed to the impractical eyepiece racks supplied with numerous other scopes. A set of flexible slow-motion cables are provided for making precise adjustments, such as tracking objects at high magnification; however, the backlash from them can be irritating when using high magnifications, and it is not as intuitive as a straightforward Dobsonian mount, for example. The C6 XLT attaches to the mount with a standard Vixen-style dovetail saddle.
In contrast to Celestron’s other computer-assisted telescope models, the StarSense Explorer telescopes lack motors. Instead, the mount utilises an adapter and your smartphone’s computing power to help you navigate the sky. The StarSense Explorer technology is essentially a streamlined version of the widely used astrophotography technique known as plate solving. This technique involves taking a short exposure of a star field and using an image-matching tool and database of astronomical images to determine where in the sky the telescope is aimed. Instead of utilising a dedicated camera and computer or hardware encoders that are calibrated by pointing the scope at stars, the StarSense Explorer simplifies and reduces costs by leveraging the precision instruments already available in your smartphone.
As you frequently move the telescope to different targets, constantly taking short exposures and referencing them to a cloud database would rapidly deplete your battery. The StarSense Explorer technology uses just a few snapshots of the sky (captured via your phone camera with a mirror/bracket attached to the mount) and estimates your position using your phone’s internal gyroscopes. Even a poorly set up StarSense Explorer can achieve an accuracy of a degree (equivalent to two full Moons) or less, which will bring your target into the field of view at low power. With a good alignment, an accuracy of around ¼ of a degree is achievable. The app features a catalogue of thousands of deep-sky and solar system objects, offering straightforward instructions for alignment and guidance on where to move the telescope to locate your target.
Should I buy a Used Celestron StarSense Explorer DX 6″ SCT?
Beware that a second-hand StarSense Explorer telescope may be missing the app code, and many such scopes have had their phone brackets removed for use on other devices. Unless you can be certain that both a valid app code and the smartphone bracket are included, or the price is exceptionally low, we would recommend against purchasing a used StarSense Explorer telescope for this reason.
Additionally, you’ll want to be sure that the C6 XLT optical tube is in good shape. is crucial to be cautious of a broken front corrector plate, which cannot be repaired or replaced without also replacing the primary and secondary mirrors “matched” to it; this would cost more than simply acquiring a new or used C6 XLT in working order. Additionally, it is vital to ensure that both mirrors in the C6 XLT are free from significant corrosion, as recoating them would also be too expensive to be worthwhile. Lastly, make sure the front corrector plate of the telescope is devoid of fungus, which can permanently damage the glass through chemical etching.
The Celestron StarSense Explorer DX 6″ SCT is decent, but the fully motorized, GoTo Astro Fi 6” SCT is available for about the same price and may be preferable if you want tracking for high-magnification viewing, while a 6” or larger Dobsonian offers better performance and value for the money.
- The StellaLyra 10″ f/5 Dobsonian boasts over 50% greater resolution and approximately triple the light-gathering capacity compared to the Celestron Astro Fi 6″ SCT, attributed to its remarkable 10″ primary mirror. Accompanying the telescope are a myriad of accessories, including a 2″ low-power, 30mm focal length wide-angle eyepiece, a 9×50 finder scope, and a 9mm high-power Plossl eyepiece. The Dobsonian mount is more straightforward to aim, rapid to set up, and far more stable than the StarSense Explorer mount. The 8″ StellaLyra is an equally great choice if you are on a tighter budget or worried about weight.
- The Celestron StarSense Explorer 8″ Dobsonian utilises Celestron’s StarSense Explorer technology just like the DX 6” SCT but features superior light-gathering and resolving power, owing to its larger 8″ aperture. The telescope is user-friendly, easy to set up, transport, and operate, although the number of accessories included is more limited compared to other alternatives.
- The Sky-Watcher Virtuoso GTi 150P offers a much wider maximum field of view than the StarSense Explorer DX 6″ SCT due to having half the focal length. Equipped with fully motorised tracking and GoTo technology, it also incorporates the FreedomFind encoder system, allowing for manual aiming by hand, irrespective of whether the mount is powered on or aligned. The telescope is controlled via your smartphone or tablet, as with the Astro Fi, and its collapsible tube ensures effortless transportation. The Heritage 150P, a more budget-friendly option, is optically identical to the Virtuoso GTi 150P and includes the same accessories but lacks electronics.
- The Celestron Astro Fi 6” SCT is priced the same and uses the same C6 XLT optical tube as the StarSense Explorer DX 6″ SCT, but features full motorised tracking and GoTo in lieu of a manually-aimed mount.
- The Sky-Watcher Skymax 127 AZ-GTi offers motorised tracking GoTo functionality, and can be operated through your smartphone or simply pushed around the sky by hand, thanks to its FreedomFind encoders. The Skymax 127 Virtuoso GTi boasts the same features but is mounted on the Virtuoso GTi tabletop Dobsonian mount, with the option to connect it to a third-party tripod. The Skymax 127 compares to the StarSense Explorer DX 6″ SCT in planetary views but falls short of it for deep-sky observation due to its smaller aperture.
- The Celestron StarSense Explorer 10″ Dobsonian delivers roughly triple the light-gathering power and 50% more resolution than the Astro Fi 6” SCT, with Celestron’s StarSense Explorer technology offering assistance in manually aiming this telescope around the night sky. The base is relatively lightweight for a 10″ Dobsonian, and transportation is made more manageable with cutouts in the base and handles on the tube. Although this telescope comes with minimal accessories besides the StarSense Explorer technology, it offers outstanding value in terms of aperture and portability for its price.
- The Celestron NexStar 6SE utilises the same C6 XLT telescope optical tube as the StarSense Explorer and Astro Fi 6” SCTs and features motorised tracking and GoTo, but lacks WiFi functionality – though the mount is rock-solid and high-quality, certainly a lot more well-made than the Astro Fi or StarSense Explorer DX mounts and tripods.
- The Sky-Watcher Skyliner 250P FlexTube GoTo Dobsonian The Celestron NexStar Evolution 6 is similar to the NexStar 6SE, sharing the C6 XLT optical tube, but offers various mechanical enhancements compared to the more affordable NexStar 6SE. It also includes a built-in Wi-Fi adapter and lithium battery, making setup and use more straightforward.
Aftermarket Accessory Recommendations
The diagonal and pair of eyepieces included with the StarSense Explorer DX 6″ SCT are of reasonable quality, but acquiring a few additional accessories and at least a couple more eyepieces will enhance your overall stargazing experience. A dew shield is essential for the StarSense Explorer DX 6″ SCT, as it helps reduce glare from nearby light sources entering the telescope while also delaying frost or dew formation on the front corrector plate of the StarSense Explorer DX 6″ SCT and preventing the accumulation of pollen, dirt, and dust.
The 40mm E-Lux Plossl provided with the StarSense Explorer DX 6″ SCT already provides the maximum possible field of view with this telescope, and as such, does not need to be replaced or complemented by our usual recommendation of a low-power, wide-field eyepiece. The provided 10mm Kellner, however, might be worth replacing with a 10mm UWA (150x) or a 9mm redline/goldline (167x) eyepiece, either of which is sharper, more comfortable, and provides a wider field of view than the Kellner design. We would also recommend a 16mm UWA (94x) or 15mm redline/goldline (100x) eyepiece for medium power.
A 7mm focal length eyepiece, such as a 7mm UWA or 7mm planetary (214x), delivers magnification close to the limit of what is typically useful with the StarSense Explorer DX 6″ SCT for observing the Moon, planets, and double stars.
Finally, although slightly expensive and of limited utility, a UHC nebula filter can be attached to any of your eyepieces, enhancing views of nebulae with the StarSense Explorer DX 6″ SCT, particularly if you mainly observe from light-polluted skies. While the scope’s restricted field of view is not ideal for viewing vast objects like the Veil Nebula, the filter aids in observing smaller objects such as, most notably, the Orion Nebula, by increasing their contrast and dimming the surrounding sky background.
What can you see?
The StarSense Explorer DX 6″ SCT lacks the performance for deep-sky viewing that a larger aperture or wide-field instrument will bring, but still does a reasonably good job at it despite its limitations. Keep in mind that the quality of a telescope’s views of most deep-sky objects is heavily dependent on the level of light pollution in your area. Suburban light pollution can effectively obliterate galaxies and significantly impair nebulae, whereas highly light-polluted skies will make observing anything other than star clusters a frustrating experience. To achieve optimal viewing of galaxies and nebulae with any telescope, moderately dark skies are essential. Nevertheless, with the StarSense Explorer DX 6″ SCT, even under less-than-optimal conditions, you can still appreciate views of medium-sized clusters such as M35 and M38, and begin to discern the brightest globular star clusters, like M13 and M3, as composed of individual stars at high magnifications.
Planetary nebulae like the Cat’s Eye and Blinking Planetary nebulae display delicate details and greenish-blue hues, together with the larger and more well-known Ring Nebula (M57). Larger nebulae such as Orion (M42) are best viewed with a filter and/or dark skies but can also be observed unfiltered even in moderately light-polluted locations with the DX 6” SCT. The StarSense Explorer DX 6″ SCT razor-sharp optics enable the separation of thousands of double stars, which are easily found in the StarSense Explorer app database.
Dark skies are essential for observing galaxies, and the StarSense Explorer DX 6″ SCT can exhibit high-contrast dust lanes in galaxies like M64, M82, and M104 while starting to unveil hints of not-quite-resolved spiral arms in galaxies like M51 at low magnification. Numerous galaxy groups and clusters can also be viewed, with the Virgo Cluster of galaxies being a prime example, featuring dozens of members.
The high-quality optics and long focal length of the StarSense Explorer DX 6″ SCT render it ideal for planetary observation, although its large central obstruction and modest aperture still impose constraints. Proper collimation, allowing the telescope to acclimate to ambient nighttime temperatures for at least 15-30 minutes, and stable atmospheric conditions are also vital for obtaining crisp views of planets, lunar details, and other small targets like close double stars. The StarSense Explorer DX 6″ SCT makes it simple to distinguish the phases of Mercury and Venus, polar ice caps and dark surface features on Mars when it’s closest to Earth, and an abundance of fine details such as craterlets, mountains, and ridges on the Moon.
The StarSense Explorer DX 6″ SCT also enables you to observe the cloud belts, the Great Red Spot, and other atmospheric features of Jupiter, as well as the discs and shadows of its four large moons, the Galilean moons, whenever they transit in front of the immense planet. The rings of Saturn, the Cassini Division within them, Saturn’s own faint cloud belts, and a few moons can be seen too. The StarSense Explorer DX 6″ SCT lacks the light-gathering capacity to display the moons of Uranus and Neptune and will have difficulty resolving the discs of either ice giant, while Pluto remains unattainable for a 6-inch telescope due to its faintness.