The Optical Tube
The Bresser Messier 6″ Planetary Dobsonian is a 6-inch (153mm) f/8 Newtonian reflector with a 1200mm focal length – a fairly common design that can be manufactured with remarkable precision and is relatively straightforward to produce. The f/8 focal ratio of this scope means that this telescope functions optimally even with more low-end eyepieces, such as SWA/Erfle type wide-angle eyepieces, which are flawless at f/8 but may exhibit astigmatism and other issues in telescopes with faster focal ratios. Moreover, the 1200mm focal length positions the eyepiece at a comfortable height for children or adults when seated. The telescope’s 1.2-meter long tube can be laid across the back seat of most vehicles, although it might not fit in the boot of a smaller car.
The focuser on the Messier 6″ Planetary Dobsonian is a single-speed, 2-inch rack-and-pinion mechanism, predominantly constructed from metal. This distinguishes it from the 1.25-inch plastic rack-and-pinions that are commonly found on telescopes of a similar aperture. It uses a compression ring to grip your eyepieces, as does the provided 1.25” adapter, a nice extra touch for those who use high-end oculars and don’t want to risk scratches to the barrel or the eyepiece falling out.
In addition, the Bresser Messier 6″ Planetary Dobsonian utilises rotatable tube rings, which have the altitude bearings attached to them instead of being directly bolted to the tube walls. This design feature facilitates adjustments to the tube balance and allows for effortless rotation of the eyepiece location. Furthermore, it enables the tube to be detached from the Dobsonian mount and connected to a universal Vixen or Losmandy-style dovetail bar, potentially allowing the telescope to be mounted on an equatorial mount for astrophotography purposes. However, a mount capable of supporting a 6-inch f/8 reflector for deep-sky imaging can be both expensive and unwieldy. Additionally, the scope’s focuser is not really up for the task of imaging, while an f/8 telescope requires longer exposures, and the 1200mm focal length limits your maximum field of view, so you may prefer to use a smaller, faster f/ratio instrument for this purpose.
Unfortunately, the Messier 6” Planetary Dobsonian is accompanied by a rather underwhelming assortment of accessories. Included is a single 25mm, 1.25” Plossl eyepiece, which offers 48x magnification with the Messier 6” Planetary Dobsonian. While Plossl eyepieces are typically quite commendable, this specific one is of surprisngly poor quality. The eye lens is unnecessarily recessed within the eyepiece body, restricting its eye relief and thus necessitating you to press your eye against it to view the entire field. The plastic body is inadequately painted on the inside, leading to issues with glare and scatter that are absent in higher-quality Plossl eyepieces. Although it functions reasonably well, you will need to acquire short focal length eyepieces for higher magnification and might want to consider investing in others, including a low-power, 2″ wide-angle eyepiece.
The Messier 6” Planetary Dobsonian includes a 6×30 straight-through finder scope featuring crosshairs and an upside-down field of view approximately 7 degrees wide, or 14 times the angular diameter of the Moon in the sky. This finder reveals stars fainter than those visible to the naked eye alone and is technically more accurate than a reflex sight or red dot finder due to the 6x magnification. Nonetheless, it is uncomfortable to use, and the image it produces is not as bright as that of a 9×50 finder.
All of the Bresser Messier Dobsonian telescopes come with a white light film solar filter, which attaches to the telescope’s front (the Messier 6” Planetary Dobsonian’s 6×30 finder must be covered or removed for safety, as no solar filter is provided for it). This filter, with its all-plastic body, is susceptible to detaching from the telescope if bumped or caught by a gust of wind, posing a significant hazard. The only elements holding it in place are a few minuscule plastic tabs. As a result, it is crucial to devise an alternative method for securing it to the telescope if you intend to utilise the filter. However, once this issue is addressed, the filter itself is perfectly safe and enables close-up views of the solar photosphere and sunspots with this scope.
Just like the 8” and 10” Messier Dobsonians, the Bresser Messier 6” Planetary Dobsonian boasts a number of design enhancements to its mount which are rarely found in other mass-manufactured Dobsonians, making it far superior to its competitors. The altitude bearings on many budget Dobsonians utilise plastic circles with a diameter of less than a foot, which pivot on nylon pads, resulting in mostly smooth motions. However, this design means that heavy eyepieces can cause the scope to topple over unless springs, clutches, or magnetic counterweights are employed since the centre of gravity often shifts entirely outside these small bearings. While sliding bearings or counterweights can compensate for balance shift with different accessories, you are still faced with the same drooping or swinging issue unless you either lock up the altitude motions or constantly adjust the bearings when swapping eyepieces.
In contrast, the Bresser Messier 6” Planetary Dobsonian features large, semi-circular bearings attached to tube rings, which allow you to rotate the tube to position the eyepiece at the desired angle, as well as set the midpoint of the bearings to the approximate balance point between all of your frequently-used accessories. The substantial diameter of the bearings means that the centre of gravity of the scope does not shift as much relative to the bearings when using heavy eyepieces and accessories, which means that you likely won’t need to adjust them at all between eyepieces. The large altitude bearings also offer the added advantage of smoother motions than their smaller counterparts on other telescopes, further enhanced by the pebbly glassboard material coating them, which glides effortlessly against four Teflon pads on the rocker box. The same glassboard material is used for azimuth (side-to-side) motion atop a set of three Teflon pads, resulting in a similarly smooth experience.
The entire rocker box of the Messier 6” Planetary Dobsonian assembles using simple peg anchors, allowing you to pack it flat for transport and then reassemble it in the field. In comparison, most other mass-manufactured Dobsonians’ bases are screwed together with a hex key and sharp wood screws, which are not designed to withstand disassembly and reassembly. After being taken apart and reassembled more than a couple of times, the screws will shred the particle board, preventing the parts from fitting together securely. This is not a problem with the Bresser Messier Dobsonians.
Should I buy a Used Bresser Messier 6” Planetary Dobsonian?
Prior to purchasing any second-hand Dobsonian, such as the Messier 6” Planetary Dobsonian, it is essential to examine it for damage to the mirror coatings or base. Replacing a damaged base with a homemade plywood one is typically straightforward and cost-effective, provided you have access to basic carpentry tools, and it’s easier if you still possess the tube rings and altitude bearings. Damaged mirror coatings can pose a more significant problem. If the mirror appears dull or very dusty, it might only require cleaning, but if there is evidence of fungus or chemical corrosion, pinholes, or a see-through appearance to the coating, the mirror may necessitate recoating, which can be costly. Consequently, you should always weigh the expense of recoating the mirrors against purchasing a new telescope before making a decision in such cases.
Dents on the tube of a used Dobsonian are generally not a cause for concern, as they are often unavoidable and typically do not influence the light path. If any dents do affect the optics, they can frequently be removed using tools akin to those employed for eliminating dents on a car or even with a plunger or hammer.
The Bresser Messier 6” Planetary Dobsonian is certainly a good scope, but you may wish to opt for a more compact tabletop telescope or a larger and more powerful 8” or 10” Dobsonian, which won’t take up much more space but provides significantly better performance than a 6” telescope.
- The Sky-Watcher Heritage 150P Dobsonian offers the same 6” of aperture as the Messier 6” Planetary Dobsonian but in a substantiantially more compact form factor and with a much better provided accessory set. However, it is of course going to need a table of some sort as well as a shroud or liner for the exposed secondary mirror, and the f/5 focal ratio is more demanding of high-quality eyepieces and accurate collimation. The smaller Heritage 130P has similar benefits and drawbacks with slightly smaller aperture.
- The Ursa Major 6″ f/8 Planetary Dobsonian is an excellent 6” f/8 Dobsonian like the Bresser Messier 6” Planetary, but features a better pair of eyepieces – albeit a 1.25”-only focuser.
- The Sky-Watcher Skyliner 150P Classic Dobsonian boasts a 2″ rack-and-pinion focuser, akin to the Bresser Messier 6″ Planetary Dobsonian, as well as a pair of commendable eyepieces and all of the advantages and disadvantages associated with an f/8 primary mirror and full-sized base. The primary drawback is the mount’s predisposition to balance issues with heavier eyepieces, owing to its simplistic friction-tensioning system and undersized bearings.
- The StellaLyra 8″ f/6 Dobsonian offers nearly twice the light-gathering area and significantly greater resolving power than the Messier 6″, along with a plethora of features and accessories, including a high-quality dual-speed Crayford focuser, an integrated fan, a right-angle finder scope, and two respectable included eyepieces. It stands on the ground and is easy to aim, thanks to its smooth Dobsonian base.
- The Sky-Watcher Virtuoso GTi 150P provides fully motorised tracking and GoTo capabilities, with performance identical to the Messier 6″ Planetary Dobsonian and a collapsible tube shared with the Heritage 150P. It also includes a pair of decent eyepieces to get started and can be aimed manually thanks to its FreedomFind encoders, with scope’s the GoTo system operated by your smartphone or tablet with the SynScan app.
- The Ursa Major 8″ f/6 Dobsonian’s 8″ aperture grants it a significant performance enhancement compared to a smaller 6″ Dobsonian. It features a pair of Plossl eyepieces and a basic but acceptable 2″ Crayford focuser, along with a 9×50 finder scope. While it may not be the most well-equipped or well-designed, it delivers outstanding performance for its modest price.
- The Bresser Messier 8″ Dobsonian showcases an exceptionally well-designed mount and 2.5″ hexagonal focuser, along with impressive 8″ optics. However, the supplied finder and Plossl eyepiece leave much to be desired, as is the case with other Messier scopes.
- The Bresser Messier 6″ Tabletop Dobsonian shares the Messier 6” Planetary Dobsonian’s 2” rack-and-pinion focuser and (regrettably mediocre) accessories, but is of course a fast f/5 scope with a short 750mm focal length, enabling wide-field views with 2” oculars simply not possible with the 6” Planetary Dobsonian. However, collimation is more critical, as is the selection of sharp well-corrected eyepieces, you’ll need a shorter focal length eyepiece or Barlow lens for suitable magnifications for planetary viewing, and of course the scope requires a table to be set up on.
- The StellaLyra 10″ f/5 Dobsonian offers even greater light-gathering and resolving power than its 8″ or 6″ counterparts. It is not considerably heavier or more challenging to store or transport than its 8″ counterpart and comes equipped with the same high-quality dual-speed Crayford focuser and accessory kit.
- The Celestron StarSense Explorer 8″ Dobsonian boasts exceptional performance, as one would expect from any 8″ Dobsonian, with a weight-optimised base and the Celestron StarSense Explorer technology, enabling easy navigation of the night sky using your smartphone. However, it is lacking in terms of other provided features and accessories. A 10″ model is also available and proves to be an equally sound choice.
- The Bresser Messier 10″ Dobsonian offers the superb performance expected of any good 10″ Dobsonian, as well as a high-quality focuser and mount design that rivals the fit and finish of a premium custom scope. However, the provided accessories are, of course, quite substandard, and you will need to spend extra to upgrade to a dual-speed focuser.
- The Sky-Watcher Skyliner 250P Classic Dobsonian is a budget-friendly option for a 10″ telescope. Although the base is not the most well-designed and the single-speed Crayford focuser is far from the fanciest, it works sufficiently well if you are seeking aperture at an affordable price and comes with a serviceable set of accessories as well.
Aftermarket Accessory Recommendations
The Bresser Messier 6” Planetary Dobsonian will only be able to unlock its potential with a few additional eyepieces. Not only does the single provided eyepiece not exactly provide the sharpest views, but you’ll want a wide range of magnifications for viewing different types of celestial objects. A Celestron 40mm E-Lux (30x) 2” eyepiece yields the lowest magnification and nearly the widest possible true field of view the Messier 6” Planetary can achieve; a 38mm OVL PanaView or similar SWA eyepiece (32x) provides a slightly sharper, wider and more immersive field. Either is excellent for low-power viewing of deep-sky objects with the Messier 6” Planetary Dobsonian.
For medium magnification, a 17mm Plossl (71x), 16mm UWA (75x), or 15mm SWA “redline” (80x) is a decent pick for the Messier 6” Planetary Dobsonian; a UWA or SWA eyepiece provides a wider and more immersive field of view than a Plossl and is more useful should you buy a faster f/ratio instrument in the future. For the highest useful magnifications possible with this telescope, we recommend a 9mm goldline/redline (133x) and either a 6mm goldline/redline (200x), 2x Barlow lens and/or 5mm planetary eyepiece (240x) to provide the maximum magnifications that the Messier 6” Planetary Dobsonian can handle under steady atmospheric conditions for viewing bright objects like the planets and double stars.
Additionally, you may wish to replace the stock 6×30 finder provided with the Messier 6” Planetary Dobsonian with a Telrad or Explore Scientific ReflexSight. Either is much easier to use than the 6×30 and provides a simple illuminated reticle against a window aimed at the sky, which makes it extremely intuitive to align and use. At f/8, collimation tolerances aren’t critical, but a cheap Cheshire collimation tool is a good idea and will make collimating the Messier 6” Planetary Dobsonian a lot easier.
Lastly, a narrowband UHC/OIII nebula filter is highly recommended for almost any telescope including the Messier 6” Planetary Dobsonian to enhance contrast on nebulae like Orion and bring out previously unseen detail and structure, which particularly helps if you are stuck under light-polluted skies. A 2” UHC filter will screw onto the Messier’s provided 1.25” adapter and work with either size eyepiece.
What can you see?
Many astronomers concur that a 6-inch aperture represents the smallest size suitable for serious observation of deep-sky objects, such as Messier objects and many of the better NGC objects like the Herschel 400, whilst remaining both affordable and easily transportable. It’s worth noting that the quality of your deep-sky observations with any telescope will be heavily influenced by the degree of light pollution present in the skies where you undertake your stargazing sessions. The Messier 6” Planetary Dobsonian can achieve a wide enough field of view with a 2” eyepiece that it can still excel in observing large open star clusters, regardless of your sky conditions. Objects such as the Double Cluster in Cassiopeia, the Wild Ducks Cluster (M11) in Scutum, or the renowned Pleiades cluster (M45) in Taurus make for fantastic targets. Additionally, with the Messier 6” Planetary Dobsonian, you can begin to resolve the brightest globular clusters, such as M13, M15, and M3, into individual stars under the majority of viewing conditions, although you will probably need to employ a magnification of 100x or greater with the Messier 6” Planetary Dobsonian to accomplish this with ease.
Under skies burdened with light pollution, the Messier 6” Planetary Dobsonian or pretty much any telescope, no matter how big and powerful, is unable to reveal much detail in galaxies beyond their bright cores and high-contrast dust lanes. However, with sufficiently dark skies, the Messier 6” Planetary Dobsonian is capable of providing a satisfactory experience with observing galaxies, though a larger aperture brings out more detail and makes easier sights more apparent, especially helpful for beginners or under mediocre conditions. You can discern dust lanes in large, brighter galaxies like M31, M64, and M82, and you can almost identify that galaxies such as M51 and M101 possess spiral arms, although the arms themselves remain just beyond reach. The Virgo Cluster displays dozens of members, and numerous galaxy groups can be observed as well with the Messier 6” Planetary Dobsonian.
Thje Orion Nebula and Lagoon Nebula both appear spectacular even under fairly light-polluted skies when observed with the Heritage 150P. Utilising a UHC filter can enhance the view, but the best results will be achieved under dark skies. A UHC filter also assists in revealing faint targets such as the Veil Nebula, which can be challenging to see without a filter, even under dark skies. Small planetary nebulae like the Ring, Cat’s Eye, and Blue Snowball can also be observed; with 6 inches of aperture, the blue and green colouration begins to stand out, along with tiny fine detail which can be resolved in some of these objects under steady conditions.
The Messier 6” Planetary Dobsonian, as its namesake implies, delivers outstanding performance when observing Solar System objects. The Sun shows sunspots and its granular surface with the provided solar filter, and of course there’s plenty more to be seen at night. The phases of Venus can be easily resolved with the Messier 6” Planetary Dobsonian, as can those of Mercury, though neither inner planet has any surface features that an amateur telescope can reveal.
Mars easily displays its polar ice cap and any ongoing dust storms through the Messier 6” Planetary Dobsonian, while a few dark markings can be seen on its surface when the planet is close to Earth and conditions are favourable. Jupiter’s four large Galilean moons can, of course, be seen effortlessly even in the 6×30 finder scope and, of course, with the Messier 6” Planetary Dobsonian itself at any magnification; high power reveals their disks and dark shadows as they transit across Jupiter, along with Jupiter’s colourful pastel cloud belts, festoons, and the Great Red Spot.
Saturn’s rings and the razor-thin Cassini Division within them appear razor-sharp through the Messier 6” Planetary Dobsonian; its linear, dull cloud belts are visible, and a half dozen or so of its moons appear around it as star-like pinpoints with the Messier 6” Planetary Dobsonian. Uranus and Neptune can be seen as fuzzy greenish and bluish splotches, and Uranus’ disk is fairly apparent, but the Messier 6” Planetary Dobsonian does not possess sufficient aperture to reveal any of Uranus’ moons, while Neptune’s moon Triton is visible, albeit often difficult to see without more aperture. Pluto remains just beyond the reach of a 6” telescope under dark skies, necessitating an aperture of 10 inches or more to be seen.