The Optical Tube
The Bresser Messier 6″ Tabletop Dobsonian is a Newtonian reflector with an aperture of 153mm (6”) and a focal length of 750mm. This is similar to a few other tabletop telescopes and numerous tripod-mounted reflectors of this aperture. Unlike standard 6” Dobsonians, which typically have a focal ratio of f/8 and a focal length of around 1200mm, the Messier 6” Tabletop Dobsonian is a compact f/5 thanks to its focal length of 750mm. As a result, the Messier 6” Tabletop Dobsonian yields about 60% lower magnification and a broader field of view with a given eyepiece compared to the XT6, and the tube is much shorter. However, at f/5, you’re starting to encounter coma, and inexpensive eyepieces may struggle to produce sharp images across the entire field of view. Collimation is also somewhat more challenging compared to with an f/8 telescope, as a faster telescope demands greater accuracy and it is harder to collimate without a tool such as a collimation cap/Cheshire sight. The primary mirror’s collimation can be adjusted with the hand knobs at the back of the scope, while the secondary mirror is adjusted with a hex key. You shouldn’t have to adjust the secondary mirror more than a few times ever, while the primary should at least be checked and tweaked for accurate collimation every time you set up the scope.
The Messier 6” Tabletop Dobsonian is provided with a 2”, all-metal single-speed rack-and-pinion focuser with a 1.25” adapter to enable the use of either size eyepiece. This focuser isn’t as smooth as a Crayford design but functions adequately, and the removable extension tube allows for enough focus travel that a coma corrector will work in this telescope if desired. The use of 2” wide-angle eyepieces with the Messier 6” Tabletop Dobsonian enables an enormous field of view, though such eyepieces can add up to a significant proportion of the cost of the Messier 6” Tabletop Dobsonian itself, as well as appearing a little out of place on such a small scope. Both the focuser and 1.25” adapter feature brass compression rings for a secure and non-damaging grip on even the beefiest eyepieces and accessories.
The Messier 6” Tabletop Dobsonian attaches to its mount with a Vixen-style dovetail, allowing it to be easily swapped onto another astronomical mount if you wish. The dovetail is in turn bolted to a pair of tube rings, allowing you to slide the Messier 6” f/5 optical tube along the altitude axis for balancing with different eyepieces/accessories as well as rotating the focuser and eyepiece to a comfortable position.
The Bresser Messier 6” Tabletop Dobsonian comes with two 1.25” Kellner eyepieces: a 25mm providing 30x and a 9mm for 83x. These eyepiece are acceptable quality at best, but they suffer from some edge-of-field aberrations at this scope’s fast f/5 focal ratio. The 9mm Kellner also has so little eye relief that you have to jam your eye into the lens to take in the whole field, which is rather uncomfortable. The apparent field of both eyepieces is about 50 degrees, translating to true fields of 1.7° and 0.6° with the 25mm and 9mm eyepieces, respectively.
For a finder, the Messier 6” Tabletop Dobsonian comes with a cheap red dot sight, which is fairly low quality and hard to align with the telescope. Furthermore, replacing it also would require adding a whole new bracket to the tube, requiring you to remove the optics and drill some holes. However, it suffices for pointing this wide-field instrument.
All of the Bresser Messier Dobsonian telescopes are supplied with a white light film solar filter, which affixes to the front of the telescope inside the tube end ring. This filter, with its all-plastic body, is prone to detaching from the telescope if it is knocked or caught by a gust of wind, which is incredibly hazardous. The only things securing it are a few tiny plastic tabs. As a result, it is crucial to come up with an alternative method for fastening it to the telescope if you intend to use the filter. however, the filter itself is perfectly safe and enables close-up views of the solar photosphere and sunspots with this scope.
Lastly, a cheap “moon filter” is included with the Messier 6” Tabletop Dobsonian. This is nothing more than a tinted piece of glass that screws onto your eyepieces. The Moon is perfectly safe to look at without any kind of filter, and the provided one is going to blur the image, obscuring fine detail and lowering contrast – not exactly a worthwhile trade-off.
The Bresser Messier 6” Tabletop Dobsonian utilises the same tabletop “Dobsonian” mount design as its smaller counterparts. Those who are particularly attentive to detail will observe that it is, in fact, a single-arm fork design, whereby the telescope pivots up and down on a solitary bolt and a nylon/felt bushing, while simultaneously moving in azimuth (left to right) on Teflon pads, as per the Dobsonian design. The Messier 6” Tabletop includes a tension adjustment knob, enabling users to establish the appropriate friction to prevent the optical tube from shifting by itself. Should you invest in supplementary eyepieces, a Barlow lens, or additional accessories which have to be inserted in the focuser, it is likely that you will need to make adjustments to this knob throughout the night in order to account for alterations in weight and balance. You may also simply slide the tube within the pair of tube rings to modify balance and rotate the eyepiece to a more comfortable position, though often isn’t worthwhile for small balance adjustments.
Setting the Bresser Messier 6” Tabletop Dobsonian atop a suitable surface may require some creativity. A milk crate or bin for seated observing works well; alternatively a picnic bench, bar stool, barrel or bucket will do. Few tables are actually steady enough. You can also build a custom stand for the scope if you wish.
Should I buy a Used Bresser Messier 6” Tabletop Dobsonian?
You may wish to contemplate the purchase of a pre-owned Bresser Messier 6″ Tabletop Dobsonian as a means of saving money on accessories or for other reasons. However, it is essential to examine any second-hand Dobsonian for potential damage to the mirror coatings or base prior to making a purchase. Replicating the Messier 6” base accurately is rarely worth the time or effort, and issues related to damaged mirror coatings can be even more problematic. If the mirror appears dull, it might simply require cleaning. However, if there is evidence of moss, chemical corrosion, pinholes, or a transparent appearance to the coating, the mirror may necessitate recoating, which can be quite costly. Consequently, it is important to weigh the expense of recoating the mirrors against the cost of acquiring a new telescope before making a decision in this instance.
Dents on the tube of a pre-owned Dobsonian are generally not a cause for concern, as they are often inevitable and usually do not interfere with the light path. In cases where dents do affect the optics, they can frequently be removed using tools akin to those employed for repairing dents on a car, or alternatively with a plunger or hammer.
The Bresser Messier 6” Tabletop Dobsonian is certainly one of the better options in its price range, but the Sky-Watcher Heritage 150P offers better accessories and a collapsible tube – as well as a lower price – with the same performance, while 8” and 10” Dobsonians offer more light-gathering and resolving capability.
- The Sky-Watcher Heritage 150P shares the optics and basic design of the Messier 6″ Tabletop Dobsonian, but features a collapsible tube for enhanced portability and a 1.25”-only helical focuser. It’s also considerably cheaper and includes better eyepieces and a more well-designed red dot finder compared to the Bresser tabletop scopes. The smaller Heritage 130P has the same excellent design, accessories, and excellent value for the money.
- The Ursa Major 6″ f/8 Planetary Dobsonian features an f/8 primary mirror and does not need a table or stand to be used, and of course at f/8 collimation and focusing are easier. It also includes a pair of high-quality Plossl eyepieces to get you started. However, the 1200mm focal length and 1.25”-only focuser considerably limit your maximum field of view.
- The Sky-Watcher Skyliner 150P Classic Dobsonian features a 2” rack-and-pinion focuser like the Bresser Messier 6” Tabletop, as well as a pair of decent eyepieces and all of the pros/cons of an f/8 primary mirror and full-sized base. The only major downside is that the mount is prone to balance issues with heavier eyepieces due to its simple friction-tensioning system and undersized bearings.
- The Bresser Messier 5” Tabletop Dobsonian has the same features, accessories, and basic design as the 6” model, but with a smaller aperture, and with the 2” focuser replaced by a cheap 1.25” rack-and-pinion focuser, which is all plastic and prone to sagging, while the 1.25”-only format constrains the telescope’s maximum field of view despite its shorter 650mm focal length.
- The StellaLyra 8″ f/6 Dobsonian offers almost twice as much light gathering area and significantly more resolving power than the Messier 6″ along with numerous features and accessories such as a high-quality dual-speed Crayford focuser, a built-in fan, a right-angle finder scope, and two decent included eyepieces. It stands on the ground and is easy to aim owing to its smooth Dobsonian base.
- The Sky-Watcher Virtuoso GTi 150P offers fully motorised tracking and GoTo, with identical views to the Messier 6″ Tabletop Dobsonian and a collapsible tube shared with the Heritage 150P. It also comes with a pair of decent eyepieces to get you started and can be aimed manually, with the GoTo system being operated by your smartphone or tablet.
- The Ursa Major 8″ f/6 Dobsonian’s 8” of aperture gives it a significant performance boost over a smaller 6” Dobsonian, and it features a pair of Plossl eyepieces and a basic but acceptable 2” Crayford focuser along with a 9×50 finder scope. It isn’t the most well-equipped or well-designed, but provides excellent performance for its low price.
- The Bresser Messier 8″ Dobsonian features an extremely well-designed mount and 2.5” hexagonal focuser, along with great 8” optics, but the provided finder and Plossl eyepiece leave much to be desired as with the other Messier scopes.
- The Bresser Messier 6″ Planetary Dobsonian has the same focuser and provides similar brightness and resolving power to the Messier 6” Tabletop Dobsonian, but its longer f/ratio of f/8 means easier collimation and no coma – at the cost of a much narrower maximum field of view and a significantly bulkier tube assembly. However, this scope stands on the ground without any need for a table or tripod.
- The StellaLyra 10″ f/5 Dobsonian features even more light-gathering and resolving power than an 8” or 6” instrument and isn’t much heavier or harder to store/carry 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 features excellent performance, as is to be expected from any 8” Dobsonian, with a weight-optimised base and the Celestron StarSense Explorer technology allowing for easy navigation of the night sky with your smartphone. However, it lacks much in the way of other provided features and accessories. A 10” model is also available and proves to be an equally good choice.
- The Bresser Messier 10″ Dobsonian offers the excellent performance of any good 10” Dobsonian as well as a high-quality focuser and mount design which rival the fit and finish of a premium custom scope. However, the provided accessories are of course quite poor and you’ll need to spend extra to upgrade to a dual-speed focuser.
- The Sky-Watcher Skyliner 250P Classic Dobsonian is a budget pick for a 10”. While the base is not the most well-designed and the single-speed Crayford focuser is hardly the fanciest, it works well enough if you just want aperture on the cheap and comes with a serviceable set of accessories too.
Aftermarket Accessory Recommendations
The Bresser Messier 6” Tabletop Dobsonian’s provided eyepieces are okay, but we wouldn’t exactly call them high-quality and you’ll want additional eyepieces for varying magnifications and different field of view requirements. A Celestron 32mm E-Lux 2” eyepiece (23x) yields the lowest magnification the Messier 6” Tabletop Dobsonian can handle, while a 32mm SWA is more expensive and loses some sharpness towards the edges of the field but provides a much more immersive experience and a wider true field of view overall.
For medium-power viewing, a 17mm Plossl (44x), 16mm UWA (47x), or 15mm “redline”/”goldline” (50x) is a decent pick for the Messier 6” Tabletop Dobsonian; the UWA is the sharpest of the three options as well as the most immersive while the redline isn’t exactly perfect at f/5 but is a decent budget wide-field choice.
For higher magnifications suitable for viewing the Moon and planets with the Messier 6” Tabletop Dobsonian, we recommend a 9mm redline/goldline (83x) to replace the low-quality 9mm Kellner eyepiece. The redline/goldline has a much wider apparent field of view of about 70 degrees, much more eye relief than the 9mm Kellner, and is quite a bit sharper. For even higher power, we recommend either a 6mm goldline/redline (125x), and 2x Barlow lens (for 160x/250x with the 9mm and 6mm eyepieces respectively) or a dedicated 2.5mm planetary eyepiece for 300x, though the latter may not be the most useful if you live under frequently turbulent skies compared to more moderate powers like 160x and 250x. 300x is the absolute limit of what this telescope can handle magnification-wise. We would also highly recommend obtaining a good Cheshire collimation tool to ensure the telescope is able to put up sharp views at these high magnifications.
Lastly, a narrowband UHC/OIII nebula filter helps with enhancing your views of nebulae such as the Orion Nebula with almost any telescope, including the Messier 6” Tabletop Dobsonian. It will also bring out planetary nebulae by reducing the brightness of surrounding stars, helping you to locate them at low power, while also providing sufficient contrast improvement to allow you to see previously-invisible targets like the Crab Nebula and Veil Nebula supernova remnants with this scope under dark skies. The 2” version will screw onto your 1.25” adapter and work with either size eyepiece.
What can you see?
The Bresser Messier 6” Tabletop Dobsonian offers remarkable views of open star clusters like the Double Cluster, M11, M35, and the Pleiades (M45). Even under light-polluted skies, these stunning clusters remain visible due to the scope’s ample aperture. Globular clusters such as M3, M13, M15, and M22 are also easily resolved at high magnifications with the Bresser Messier 6” Tabletop Dobsonian, although a better eyepiece than provided 9mm Kellner unit, with a slightly shorter focal length for 100x or more, is optimal for resolving individual stars in these clusters. Bright emission nebulae like Orion (M42) and the Lagoon (M8) look fantastic even under light-polluted skies, although dark skies and/or a UHC nebula filter offer the best views. With a 2” wide-angle eyepiece and UHC filter under decent conditions, the Bresser Messier 6” Tabletop Dobsonian provides amazing views of the Veil Nebula supernova remnant and the vast North America Nebula in Cygnus. Galaxies require dark skies to appear as anything more than dim fuzzy smudges in the eyepiece, but under good conditions, the Bresser Messier 6” Tabletop Dobsonian can reveal hundreds of galaxies, including the Virgo Cluster, and many of the brighter galaxies like M31, M82, and M64 show details such as dust lanes to the discerning observer. Planetary nebulae like the Blue Snowball also begin to display fine detail and a wide range of colourful tones, and there are countless double stars that can be split under good conditions with the Bresser Messier 6” Tabletop Dobsonian.
As for Solar System objects, the Messier 6” Tabletop Dobsonian’s included solar filter will of course allow you to observe sunspots and the granular solar “surface”, the photosphere. At night, Messier 6” Tabletop Dobsonian can reveal the phases of Mercury during a favourable apparition of the planet, and easily shows those of Venus as well, though no other detail can be seen on either planet with a backyard telescope. The Moon displays thousands of craters as small as a few miles, along with cracks, ridges, fault lines, mountain ranges, and frozen lava flows. Mars’ polar ice cap is visible most of the time, and when Mars itself is close to Earth around opposition biannually, you’ll have no trouble seeing a few dark patches and any Martian summer dust storms, which usually tend to envelop the entire planet and obscure all other surface details.
The Messier 6” Tabletop Dobsonian will show a wealth of festoons, storms, and cloud bands on Jupiter ranging from blue, to red, to tan, to pink, to grey and brown. The Great Red Spot is also clearly distinguishable, even as it continues to shrink over the years. You’ll also be able to see the 4 Galilean moons (Io, Europa, Ganymede, and Callisto) as tiny discs, with equally tiny shadows when they transit across Jupiter and eclipse its cloudy surface.
Saturn’s rings and the Cassini Division within them are well-resolved with the Messier 6” Tabletop Dobsonian at high magnification, and several cloud bands on the planet itself can be seen, along with a grey-blue area near the poles. A few moons are also visible, including Titan, Rhea, Tethys, Dione, Enceladus, Mimas, and Iapetus, the latter of which is much harder to see depending on whether its dark or bright side is facing the Sun and Earth.
The Messier 6” Tabletop Dobsonian reveals Uranus as a tiny greenish-blue dot barely bigger than a star, much as Sir William Herschel’s similarly-sized telescope did when he discovered it. The four observable Uranian moons are barely within reach of a 6” telescope, though it is unlikely you will see even the brightest two, Titania and Oberon.
Neptune appears as little more than a fuzzy bluish “star” with the Messier 6” Tabletop Dobsonian, but you can see its moon Triton without too much trouble; it’s a full magnitude brighter than Uranus’ moons. Pluto will require an 8-10” or larger telescope to see, and only under dark skies, thus putting it entirely out of range of the humble Messier 6” Tabletop Dobsonian.