The Optical Tube
The Sky-Watcher Explorer 200PDS optical tube assembly comprises a 8-inch (200mm) f/5 Newtonian reflector with a 1000mm focal length. As is typical of imaging Newtonian telescopes, the optics in the Explorer 200PDS are of a high standard of quality. With an f/5 focal ratio, coma is barely noticeable at the edge of the visual field when using a 1.25-inch eyepiece. However, cheaper wide-angle eyepieces such as the supplied 28mm 2″ LET ocular tend to display other aberrations at lower magnifications, particularly away from the centre of the field – chief among them being edge-of-field astigmatism, and even very well-made wide-field 2” eyepieces will show plenty of coma too unless you purchase a coma corrector.
The 200PDS is furnished with a relatively uncomplicated 2-inch, dual-speed Crayford focuser. This component doesn’t incorporate a compression ring to secure 2” accessories, such as the provided 2” LET eyepiece or the included 1.25″ adapter. Therefore, under heavy loads such as a large camera and coma corrector, it might be prone to some slippage or sag. Nevertheless, for standard payloads like a DSLR or a colour camera, this is only a minor concern. Impressively, the focuser exhibits smooth movements and can accommodate an add-on motor focuser unit, like the ZWO EAF.
Collimation is critical with any f/5 telescope, particularly one primarily used for astrophotography. The collimation of the Explorer 200PDS is adjustable via a trio of spring-loaded knobs located at the rear of the primary mirror (further secured by an additional set of locking screws). The secondary mirror adjustment, on the other hand, requires a hex key. For a comprehensive understanding of the collimation process, you might find our collimation guide particularly useful. This telescope manages to maintain its collimation quite well. However, the replacement of the primary mirror cell’s standard springs with sturdier alternatives can further enhance the telescope’s stability over time and when moved across the sky. The rear of the primary mirror cell houses a 12V DC-powered 80mm fan which aids in quickly bringing the primary mirror down to ambient temperature.
The Explorer 200PDS comes with a pair of standard tube rings and a Vixen-style dovetail bar to facilitate the attachment to any astronomical mount, such as the supplied HEQ5 Pro. If preferred, the bar can be replaced with a Losmandy-style one, though you’d have to upgrade the HEQ5 Pro’s saddle to match. For enhanced rigidity and to enable the mounting of additional accessories like a guide scope, it’s recommended that you attach a second dovetail to the top of the rings as well.
Accompanying the Explorer 200PDS, you’ll find a single eyepiece – a 2″, 28mm focal length Sky-Watcher L.E.T. ocular. This three-element eyepiece is equipped with a convenient twist-up rubber eyecup for optimal comfort. With the 200PDS, this eyepiece provides a magnification of 36x. Its apparent field of view is approximately 60 degrees, which translates into a true field slightly in excess of 1.5 degrees, equivalent to about 3 times the angular diameter of the full moon, when employed with the 200PDS. This is enough for viewing even the largest deep-sky objects.
However, under heavily light-polluted skies, the 36x provided by the 28mm LET may constitute too low a power for the 200PDS and might result in a rather washed-out, grey-brown background sky. Consequently, for deep-sky viewing with the 200PDS, an eyepiece within the 16-22mm focal length range might be more suitable. Higher magnification eyepieces would also be advisable for observations of the moon, planets, and double stars.
Due to the simple 3-element optical design of the L.E.T eyepiece, it also falls short in its correction for edge-of-field astigmatism when combined with the fast f/5 focal ratio of the 200PDS. This combined with the scope’s inherent coma at f/5 means that half the field will be populated by blurry stars.
Sky-Watcher also includes their standard 9×50 finder scope with this model. It is conveniently attached with a Synta/Vixen-style shoe, facilitating easy interchangeability with other finders, such as a red dot unit. The 9×50 finder scope allows the observation of stars several magnitudes fainter than what the naked eye could perceive, as well as the brightest of deep-sky objects like star clusters. This is all visible within an upside-down field of view spanning roughly 5 degrees, delineated by non-illuminated crosshairs. The finder scope functions admirably for the task of aligning the HEQ5 Pro mount with the celestial sphere.
The HEQ5 Pro Mount
The SKy-Watcher HEQ5 Pro mount is an award-winning, popular GoTo equatorial mount designed with imagers in mind. It’s well-suited for smaller telescopes for both imaging and visual use.
Setting up the HEQ5 Pro for visual astronomy or planetary imaging is pretty simple. You first need to get the mount leveled, then put the telescope and counterweights on. Careful balancing is not as crucial as with astrophotography, but poor balancing will wear out the gears, so try to do your best. Once that’s done, you need to rotate the scope 90 degrees on the declination axis (so it’s pointing near the horizon) and look through the polar scope, with the aim of getting the outer circle in the reticle closely aligned with Polaris. Then you boot up the mount and star align it as with any computerized mount, using the provided SynScan hand controller. For deep-sky imaging, you can bypass the SynScan controller entirely and just polar align then plate solve your way to your target with your camera and computer.
The HEQ5 Pro of course has an autoguide port, so a guide camera can interface with it, and you can control most guide cameras with PHD2 on most laptops. Without guiding, the HEQ5’s tracking errors will result in blurred subframes with exposures longer than 30-45 seconds with the 200PDS.
The HEQ5 Pro’s 1.75” tripod legs and beefy head support a payload of around 11 kg for visual use or 7 kg for imaging – so it’s no surprise that this mount is not exactly ideal for the 8.8-kg 200PDS, which will quickly exceed 10kg with most imaging equipment. For visual use, the HEQ5 Pro is steady enough with the 200PDS; however an equatorial mount is unnecessary for this task and makes for a bulky setup, frequently places the eyepiece in an uncomfortable position, of course has a long setup time, and is quite expensive – you should probably get an 8-12” Dobsonian if you’re not interested in imaging, or a more ergonomically friendly Schmidt-Cassegrain if you must have an equatorial mount and tripod.
Should I buy a Used Sky-Watcher Explorer 200PDS HEQ5 Pro?
Opting to purchase a second-hand Explorer 200PDS/HEQ5 Pro could be a worthwhile decision, as the money saved by investing in a pre-owned model might be substantial enough to afford a guiding setup and coma corrector.
Prior to finalising the purchase, it is imperative to ensure that the HEQ5 Pro mount powers up, slews, and tracks as it should, and does not exhibit significant signs of corrosion. The optics within the Explorer 200PDS optical tube should be free from any signs of corrosion or damage to the mirror coatings; the expense of recoating could easily surpass the price of a new optical tube assembly. Missing accessories or counterweights can be replaced inexpensively and without much difficulty, as can a misplaced SynScan hand controller. Sky-Watcher provides parts like adjustment/saddle knobs or the counterweight shaft as spare parts for the HEQ5, and ADM offers upgraded versions.
For those individuals particularly drawn to deep-sky astrophotography, we would recommend pairing the Explorer 200PDS with the heavier duty NEQ6 equatorial mount from Sky-Watcher, if your budget allows. Alternatively, you might find our articles on the Best Equatorial Mounts and Best Optical Tubes to be worth exploring. These resources aim to guide you in selecting an optical tube and mount combination that aligns most suitably with your personal preferences, budget constraints, the specifics of your camera, and the celestial objects you’re most interested in imaging. Below, we’ve curated a selection of telescopes that are well-suited for visual observation and/or light astrophotography:
Under 1200 Range
- The StellaLyra 10″ f/5 Dobsonian sports a larger 10” diameter primary mirror, delivering superior resolution and light-gathering capabilities when compared to the 200PDS/HEQ5 Pro. Despite its impressive size, it maintains plenty of portability and comes with a plethora of accessories and features. The 8” f/6 StellaLyra model, although equally rich in quality features/accessories, is cheaper but roughly the same physical size in practice.
- The Celestron StarSense Explorer 10″ Dobsonian boasts not only a 10” aperture, but also a degree of computerised pointing functionality, albeit without motorised tracking, courtesy of its pioneering StarSense Explorer technology. The telescope’s practical design incorporates various knobs, handles, and cutouts, which greatly ease its transportation. The 8” model offers a similarly excellent experience.
- The Sky-Watcher Virtuoso GTi 150P features a 6” aperture with a collapsible tube for maximum portability. Its GoTo tabletop Dobsonian mount can be manually adjusted without compromising its tracking or pointing accuracy, and the mount’s automatic pointing is controlled via your smartphone or tablet. The manual Heritage 150P matches the Virtuoso GTi in terms of features and specs, barring its lack of electronic components.
Over 1200 Range
- The Celestron NexStar Evolution 8 utilises Celestron’s compact C8 XLT optical tube which, despite its petite nature, offers equal light-gathering and resolving power to the larger Explorer 200PDS. The NexStar Evolution mount sports fully automated GoTo and tracking capabilities, alongside an in-built lithium battery and WiFi adapter, offering the convenience of controlling the telescope from your smartphone or tablet. Some deep-sky astrophotography is possible with this scope, though you’ll get the best results by using the C8 XLT optical tube atop a different, equatorial mount like the HEQ5 Pro or NEQ6.
- The Sky-Watcher Explorer 200PDS NEQ6 Pro uses the same 200PDS optical tube as the HEQ5 Pro package reviewed here but atop the sturdier and more well-designed NEQ6 mount, which is more suitable for consistently good quality astrophotos with the 200PDS optical tube. However, it is of course heavier and more expensive.
- The Sky-Watcher Skyliner 250P FlexTube GoTo Dobsonian features a fully automated GoTo and tracking system. Its unique FreedomFind encoder system allows for manual telescope aiming, even when powered on, and thanks to the motorised tracking you can of course do planetary imaging with this telescope as well as enjoy excellent views at the eyepiece.
Aftermarket Accessory Recommendations
If you aspire to engage in visual observation with your Explorer 200PDS, upgrading your eyepiece collection is an essential step. Eyepieces providing higher power and thus with shorter focal lengths than the provided 28mm LET are vital for observing the Moon, planets, smaller deep-sky objects, and double stars. A 16mm UWA (63x) is ideal for medium power viewing of deep-sky objects and observing the whole Moon at once. For many nights of planetary viewing, even under mediocre seeing conditions, a 10mm UWA (100x), or 9mm “redline” or “goldline” (111x) provides an optimal magnification. It’s also perfect for observing globular clusters. The Explorer 200PDS can handle magnifications of up to around 375x, thus a 2x or 3x Barlow lens or an eyepiece with a very short focal length in the range of 3-5mm is perfect for achieving very high powers.
It would be beneficial to have a Cheshire collimation tool at your disposal when using the Explorer 200PDS as well. This tool will assist you in maintaining accurate collimation, guaranteeing sharp stars across the field when paired with a coma corrector, along with sharp views at the eyepiece.
For enhanced contrast on nebulae at the eyepiece through any telescope, a UHC nebula filter is an indispensable accessory. It brings out previously unseen details or entirely new objects from the void, even under light-polluted skies. However, dark skies still offer the best viewing experience, both with and without a filter.
Whether you are viewing or imaging, considering the fast f/5 focal ratio of the Explorer 200PDS, a coma corrector is a worthwhile investment. The Baader MPCC is a viable option for visual use at low powers as well as for imaging. It attaches directly to your eyepiece or camera. The Explore Scientific HRCC and Tele-Vue Paracorr II are excellent alternatives, albeit more expensive.
For imaging with the Explorer 200PDS, a motor focuser like the ZWO EAF is ideal. It allows for finer focus adjustments in combination with an appropriate Bahtinov mask. We recommend a 50-60mm guide scope and suitable guide camera for piggybacking atop the Explorer 200PDS. Additionally, a T-adapter for attaching the scope to a DSLR or mirrorless camera and a suitable T-ring are necessary. Moreover, you will need some form of DC power supply, such as the Celestron PowerTank Lithium, for the operation of the HEQ5 Pro mount, unless you are within reach of a wall outlet.
What can you see?
For the Explorer 200PDS, using the HEQ5 mount, or any other equatorial mount, for visual usage can present a unique set of challenges. You may frequently find yourself in awkward positions due to the eyepiece’s orientation, necessitating rotating the tube within its rings for comfortable viewing. However, this simple act can disrupt the balance and alignment of the HEQ5 Pro mount. A potential solution could involve using a pair of homemade Wilcox rotating rings, but even with this modification, it may not fully rectify the issue and achieve the straightforward ergonomics of a Dobsonian telescope. This characteristic is an inherent part of the user experience when working with equatorially mounted Newtonians, and this becomes more pronounced as the size of the telescope increases.
When employing a 2” wide-angle eyepiece, the Explorer 200PDS boasts a wide field of view that slightly exceeds that which can be expected of a typical 8” f/6 Dobsonian, and this makes it particularly effective in observing expansive open star clusters such as the Double Cluster, Wild Ducks Cluster (M11), and Pleiades (M45). These clusters can be viewed effectively under almost all conditions, and you may notice that many of the stars within them appear notably colourful. Furthermore, this telescope possesses the capability of discerning individual stars within a myriad of globular clusters, inclusive of nearly all the clusters in the Messier catalogue, amongst others. To clearly observe these globular clusters, it’s recommended to use magnifications of 80x or higher and to observe under dark skies.
Under conditions of moderate light pollution, the Explorer 200PDS is able to unveil the intricate details within bright nebulae, including M42 and M8. However, for an optimal viewing experience, it is strongly recommended that you observe these celestial objects under darker skies and/or through a high-quality UHC nebula filter. If you have access to suitably dark skies and a UHC filter, it becomes possible to view fainter nebulae like the Veil and North America Nebula, as well. The 8″ aperture of the Explorer 200PDS also enables you to discern fine details and striking azure, turquoise, and emerald hues in planetary nebulae like the Blue Snowball, the Ghost of Jupiter, and the Cat’s Eye.
Any 8” telescope, the Explorer 200PDS included, allows for the observation of details within galaxies under dark skies. However, light pollution often washes out many of these details. Galaxies like Andromeda (M31), M82, M64, M65, and M101 can exhibit dust lanes, while you might discern traces of spiral arms in galaxies like M51, M33, and M101. Moreover, it is also feasible to observe numerous galaxy groups and clusters, such as those found in Virgo, Leo, and Coma Berenices.
Comparatively speaking, the Explorer 200PDS might not quite measure up to a typical 8” f/6 Dobsonian when it comes to planetary viewing. This is primarily because the shallower depth of field at f/5, compared to f/6, makes focusing at high magnifications a bit more challenging. The importance of collimation is heightened, and to achieve equivalent magnification, eyepieces with shorter focal lengths are necessary. Nevertheless, satisfactory views of planets and the Moon are achievable. You can expect to see an abundance of detail on the Moon, and the phases of Mercury and Venus, as well as a few dark markings on Mars together with its polar ice caps.
On a good night with the Explorer 200PDS, Jupiter showcases a wide variety of colourful cloud belts and storms, including the prominent Great Red Spot. Additionally, Jupiter’s moons manifest as clear disks, accompanied by their respective shadows during transits. Saturn’s cloud bands are discernible, as is the Cassini Division within its rings, along with several of Saturn’s moons. Uranus presents as a somewhat resolved fuzzy teal disk, with a few of its moons faintly visible to the keen observer under dark skies. Neptune often poses a challenge to differentiate from a star, but its moon Triton usually stands out prominently. However, Pluto demands larger aperture – typically 10-12” or more – and dark skies to be spotted at all, and even then only as a star-like point.
Although the Explorer 200PDS is certainly undermounted atop the HEQ5 Pro, it is by no means impossible to capture good images, albeit with some limitations. These include a restriction to shorter individual exposures, typically of a minute or two at most. With this constraint in mind, be prepared to discard a considerable portion of frames that might exhibit trailing, even with competent autoguiding. Further, the acquisition of a motorised focuser and, in all likelihood, a coma corrector, would be necessary, as previously discussed.
Despite these limitations, the Explorer 200PDS’ 1000mm focal length makes it an ideal fit for imaging smaller celestial objects, such as galaxies, star clusters, and nebulae like the Orion Nebula. Additionally, the telescope’s f/5 speed allows for a respectable signal-to-noise ratio, even with the short exposure times imposed by the lightweight design of the HEQ5 mount.
The Explorer 200PDS also holds plenty of potential for planetary astrophotography. However, capturing an image scale large enough for detailed viewing would necessitate the use of a 4-5x Barlow lens. Finding a quality Barlow lens of this niche can prove somewhat challenging, in contrast to the more commonly available 2-3x Barlow lens typically sufficient for an f/10 Schmidt-Cassegrain telescope.
If you can secure a good Barlow and high-speed planetary camera to use with it, the 200PDS is capable of delivering excellent shots of lunar surface features, as well as sunspots when used in conjunction with a solar filter. It is also possible to capture images of the phases of Venus and Mercury, surface details and dust storms on Mars, atmospheric details on Jupiter and Saturn along with the disks of their larger moons too. You might even discern subtle hints of atmospheric detail on Uranus. Moreover, for those willing to experiment with longer exposures or higher gain settings, capturing images of the faint moons of Mars, Uranus, and Neptune is within the realm of possibility.