The Optical Tube
The Bresser Messier 10″ Dobsonian is a Newtonian reflector with an aperture of 254mm (10”) and a focal length of 1270mm. It thus has an f/5 focal ratio, which as with any Newtonian reflector is fast enough to cause minor coma at the edges of the field of view, especially with wide-angle eyepieces. However, this is not very noticeable with well-corrected wide-angle eyepieces, unlike cheaper ones such as SWA/Erfles, which unfortunately tend to show other aberrations like astigmatism that hide the coma. Collimation is critical with this telescope, and it can be adjusted using three screws on the back for the primary mirror and smaller screws to tilt and rotate the secondary mirror. The secondary mirror holder on the 10” Messier Dobsonian is equipped with thumb screws to make adjustment easy, while the primary mirror of course requires no tools to adjust for collimation thanks to its simple spring-loaded mirror cell.
The Bresser Messier 10″ Dobsonian has a deluxe 2.5” hexagonal hybrid Crayford/rack-and-pinion hybrid focuser, borrowed from imaging telescopes. To achieve focus with the majority of eyepieces, it is necessary to install the scope’s provided extension tube, positioning the eyepiece rather far away from the tube wall. Although this design decision might appear peculiar, it functions efficiently in spite of the unconventional arrangement. This design choice means the Messier 10″ Dobsonian offers an ample amount of focuser travel for reaching focus with a DSLR camera for imaging purposes as well as almost any binoviewer or coma corrector.
The 2.5” Hex focuser holds heavy eyepieces and accessories with ease and has enough inward travel, or “back focus”, to reach focus with a DSLR or cooled astronomy camera without requiring an extension tube. However, it is a single-speed focuser, which can make focusing at high magnification a bit tricky. Fortunately, unlike Americans who are out of luck with the Messier’s Explore Scientific counterpart, a 1:8 dual-speed reduction knob is offered as an aftermarket accessory to make focusing easier at high power.
Furthermore, the Bresser Messier 10″ Dobsonian employs rotatable tube rings, with the altitude bearings attached to them rather than being bolted directly to the tube walls. This facilitates tube balance adjustments and enables the easy rotation of the eyepiece location. The design also permits the tube to be detached from the Dobsonian mount and connected to a dovetail bar, theoretically then allowing you to put the scope on equatorial mount for astrophotography purposes. However, a mount capable of holding a 10” reflector for deep-sky imaging can be quite expensive as well as bulky, and you probably would want to use a smaller and faster f/ratio instrument for the job anyway.
Regrettably, the Messier 10″ Dobsonian is accompanied by a rather disappointing set of accessories. Included is a solitary 25mm, 1.25″ Plossl eyepiece, providing 51x magnification. While Plossl eyepieces are usually quite respectable, this particular one is of an exceedingly low quality. The eye lens is unnecessarily recessed within the eyepiece body, requiring you to press your eye against it to view the entire field. The plastic body is poorly painted on the inside, which can cause issues with glare and scatter that are not present in higher-quality Plossl eyepieces. It works well enough, but in any case, for higher magnification you will need to purchase short focal length eyepieces, and you might want to invest in others including a low-power, 2” wide-angle eyepiece.
All of the Messier Dobsonian telescopes come with a white light film solar filter, which attaches to the front of the telescope (the 6×30 finder must be covered or removed for safety, as a filter for it is not provided). This filter, with its all-plastic body, is prone to detaching from the telescope if it is bumped or caught by a gust of wind, which is incredibly dangerous. The only things holding it on are a few tiny plastic tabs. Consequently, it is essential to devise an alternative method to secure it to the telescope if you plan on actually using the filter. Once this is done, however, the filter itself is perfectly safe and facilitates close-up views of the solar photosphere and sunspots with this scope. The only downside is that a 10” telescope is already usually bound by atmospheric conditions at night, and during the day you are looking through so much turbulent air (and dealing with thermal issues inside the tube and from the primary mirror) that a 6” or smaller telescope might actually beat the Messier 10” in resolving fine detail on the Sun’s surface.
As for a finder, the Messier 10″ Dobsonian includes a 6×30 unit, featuring crosshairs and an upside-down field of view approximately 7 degrees wide. This finder reveals stars fainter than what can be observed with the naked eye alone, and is technically more accurate than a reflex sight or red dot finder due to the magnification. However, it is uncomfortable to use, and the image it produces is not as bright as that of a 9×50 finder.
As with the 8” f/6 and 6” f/8 Messier Dobsonians, the Bresser Messier 10″ Dobsonian boasts several design improvements to its mount that almost no other mass-manufactured Dobsonians have, making it far superior to its competitors. The altitude bearings on many inexpensive Dobsonians use plastic circles less than a foot across, which pivot on nylon pads and produce mostly smooth motions. However, this means that heavy eyepieces can cause the scope to topple over unless springs, clutches, or magnetic counterweights are used, since the centre of gravity often shifts entirely outside these tiny bearings. Sliding bearings or counterweights can compensate, of course, but you’re left with the same drooping/swinging problem unless you either lock up the altitude motions or constantly shift the bearings back and forth when you swap eyepieces.
In contrast, the Bresser Messier 10″ Dobsonian has large, semi-circular bearings attached to tube rings that allow you to rotate the tube to position the eyepiece at the desired angle as well as set the middle of the bearings to approximately the average balance point between all of your frequently-used accessories. The large diameter of the bearings means that the centre of gravity of the scope simply doesn’t shift as much relative to the bearings with heavy eyepieces and accessories, which means that you likely won’t have to adjust them at all between eyepieces. The large altitude bearings also have the added advantage of smoother motions than their smaller counterparts on other telescopes, aided further by the pebbly material coating them, which glides smoothly against four Teflon pads on the rocker box, the same stuff used for azimuth (side to side) motion which is similarly buttery smooth. The whole Messier 10” rocker box assembles with simple peg anchors allowing you to pack it flat for transport and then re-assemble it in the field – most other mass-manufactured Dobsonians are screwed together with a hex key and sharp wood screws, and will not survive disassembly and re-assembly as the screws will shred the particle board and no longer fit together securely after doing this more than a couple of times.
Should I buy a Used Bresser Messier 10” Dobsonian?
You might want to consider purchasing a second-hand Bresser Messier 10″ Dobsonian to save money on accessories or otherwise. However, before purchasing any used Dobsonian, it is crucial to inspect it for damage to the mirror coatings or base. Replacing a damaged base is usually simple and cost-effective, but only if you still have the tube rings and altitude bearings. On the other hand, damaged mirror coatings can be a bigger issue. If the mirror appears dull, it may only need cleaning, but if there is evidence of fungus or chemical corrosion, pinholes, or a transparent appearance to the coating, the mirror may require recoating, which can be expensive. Therefore, you should always consider the cost of recoating the mirrors compared to purchasing a new telescope before making a decision in this case.
Dents on the tube of a used Dobsonian are typically not a concern since they are often unavoidable and usually do not affect the light path. If any dents do impact the optics, they can often be removed using tools similar to those used for removing dents on a car or even with a plunger or hammer.
The Bresser Messier 10” Dobsonian is one of the best picks in its price range, but you may wish to consider 10” Dobsonians of a different design or, alternatively, an 8” or 12” instrument.
- The StellaLyra 10″ f/5 Dobsonian is slightly heavier and less smooth to aim than the Messier 10” Dobsonian, but it comes with a much better set of accessories than the Messier, and a 2” Crayford focuser equipped with a 1:10 dual-speed fine adjustment knob by default. The smaller 8” f/6 StellaLyra has the same features/accessories but is of course smaller in aperture.
- The Explore Scientific 10″ Ultra Light Dobsonian shares the Bresser Messier 10” Dobsonian’s high-quality bearings and optics but has a nicer 2” dual-speed Crayford focuser and an all-metal truss tube design with built-in cooling fans – along with of course an extremely compact form factor when broken down for storage/transport. However, like the Messier 10”, you don’t get much in the way of accessories, while the truss tube is more complicated to assemble and will need a shroud to shield the optics from glare and dust.
- The Celestron StarSense Explorer 8” Dobsonian is a lightweight and convenient 8” Dobsonian which uses Celestron’s StarSense Explorer technology to aid in navigating the night sky. Being an 8” scope it of course can’t show you as much as a 10”, however, while the design of the mirror cell makes collimation more difficult than it should be and the included accessories are quite sparse.
- The Sky-Watcher Virtuoso GTi 150P is a compact and budget-friendly telescope option, complete with a fully motorised, tracking GoTo mount that can be managed by your smartphone or alternatively, aimed manually due to its innovative FreedomFind encoders, which enable the telescope to retain information about its current aim. Although it is not nearly as good at collecting light for viewing “faint fuzzy” deep-sky objects as larger telescopes, it certainly offers outstanding value for the money. Another option to consider is the manual Heritage 150P, which boasts the same design, optics and accessories, but without the inclusion of any electronic components.
- The StellaLyra 12″ f/5 Dobsonian comes with a vast array of accessories and offers even more impressive views in comparison to its 10” or 8” counterparts thanks to its large aperture. However, its solid tube design can make transportation rather challenging without the assistance of a dolly and/or a very spacious vehicle. Should you have a larger budget and are concerned about the size, you might want to contemplate a more costly collapsible or truss 12” alternative.
- The Explore Scientific 12″ Ultra Light Dobsonian features an expertly designed dual-speed Crayford focuser and a compact all-metal structure that can be easily disassembled for transportation purposes. Its movements are remarkably smooth as well, as it uses the same high-quality glassboard and Teflon bearing surface and oversized D-shaped altitude bearings like the Bressier Messier Dobsonians. Nonetheless, like the Messier 10” Dobsonian this scope lacks any useful eyepieces or a finder, and will necessitate an aftermarket purchase of these, along with supplementary accessories such as a shroud, for optimal usage.
- The Sky-Watcher Skyliner 300P FlexTube proves to be easier to transport than a solid-tubed scope like the StellaLyra 12”, and less complicated to assemble than a truss. Furthermore, it is not significantly more cumbersome or inconvenient to carry around than the Bresser Messier 10″ Dobsonian, while still providing considerably brighter views of deep-sky objects, though its mount is poorly designed thanks to the undersized and non-adjustable altitude bearings which can have issues when you start using heavy wide-angle eyepieces or a coma corrector.
- The Celestron StarSense Explorer 10” Dobsonian is a lightweight and easily transportable option among 10″ Dobsonians, utilising Celestron’s StarSense Explorer technology in conjunction with your smartphone to facilitate targeting deep-sky objects. However, it does not include as many features and accessories as the StellaLyra Dobsonians, and its mount and focuser are not as well-crafted as those of the Messier 10″.
- The StellaLyra 16″ f/4.5 Dobsonian offers incredible deep-sky views, featuring a colossal 16” primary mirror for nearly unrivaled light-gathering and resolving power at its price range. Its truss tube design means that it can be quickly and easily disassembled into relatively lightweight and compact pieces, although setting up and transporting it still requires a substantial effort. Nevertheless, the views through the eyepiece are undeniably rewarding.
- The Sky-Watcher Skyliner 350P FlexTube Dobsonian delivers a notably enhanced performance compared to the Bresser Messier 10″ Dobsonian, owing to its significantly larger aperture. The simplistic FlexTube design is more straightforward to set up than a truss tube but makes it somewhat more bulky and inconvenient to handle compared to a truss tube design at this aperture.
- The Sky-Watcher Skyliner 300P FlexTube GoTo Dobsonian provides fully motorised GoTo/tracking capabilities, as well as Sky-Watcher’s FlexTube system to reduce its size when not in use, alongside FreedomFind encoders that allow manual aiming, as with other Sky-Watcher GoTo Dobsonians. It considerably outperforms 8” or 10” scopes while remaining fairly easy to set up and transport independently, though weight is still of courses a concern.
- The Sky-Watcher Skyliner 250P FlexTube GoTo Dobsonian’s FlexTube design renders it more slightly compact than the Bresser Messier 10″ Dobsonian, although it is significantly heavier due to the weight of its motor drive systems. The fully motorised mount automatically manoeuvres to and tracks your targets, while still maintaining the capability for manual aiming, thanks to its innovative FreedomFind encoder design.
Aftermarket Accessory Recommendations
Since the Messier 10” Dobsonian includes only a single low-power eyepiece and 6×30 finder scope, and rather low quality ones at that, shopping for additional accessories isn’t a recommendation but rather an outright requirement for good views. To start out, you’ll need a medium to high power eyepiece. A 9mm goldline/redline (141x) or, alternatively, the more expensive 10mm UWA (127x) is an excellent choice, providing optimal magnification for viewing the Moon, planets, double stars, and smaller deep-sky objects like globular clusters, even on mediocre nights with the Messier 10” Dobsonian. You might also want to upgrade the Messier’s single-speed focuser to a dual-speed unit with the Bresser 1:10 dual-speed upgrade kit and obtain a decent collimation tool while you’re at it.
For low-power viewing with the Messier 10” Dobsonian, a 28mm UWA (45x) or 32mm SWA or PanaView (40x) eyepiece will offer approximately the lowest useful magnification and the broadest feasible field of view for this relatively fast telescope. Additionally, a coma corrector such as the Explore Scientific HRCC or Baader MPCC can help eliminate coma present at the edges of your low-power field of view with this scope, as it is otherwise fairly noticeable at f/5. For intermediate magnification, we suggest a 16mm Ultra Wide Angle (UWA) eyepiece (79x magnification) or, as a more budget-friendly alternative, a 15mm redline/goldline ocular (85x).
A 2x Barlow lens combined with a 9mm/10mm eyepiece, or preferably a dedicated 4mm eyepiece such as a UWA or 4mm planetary eyepiece (319x), will yield the highest magnifications likely to be significantly useful with the Messier 10″ Dobsonian, assuming the atmospheric conditions permit such observations.
The 6×30 finder scope included with the Messier 10” Dobsonian is fairly low quality. We would recommend replacing or complementing it with a Telrad or Explore Scientific ReflexSight, either of which is easily attached to the telescope and provides a simple zero-power illuminated reticle which you use to navigate the night sky.
Finally, a narrowband Ultra High Contrast (UHC)/OIII nebula filter can appreciably amplify your views of nebulae, such as the Orion Nebula, when used with virtually any telescope, including the Messier 10” Dobsonian. This filter also betters the visibility of planetary nebulae by lessening the brightness of adjacent stars, making it more straightforward for you to locate them at low power. Moreover, it affords ample contrast improvement to display previously unobservable nebulae, like the Crab Nebula, Crescent Nebula, Veil Nebula, or Flame Nebula, for experienced observers employing the Messier 10” Dobsonian under dark skies.
What can you see?
The Bresser Messier 10″ Dobsonian is an exceptional instrument, largely due to its sizeable aperture and high-quality optics. A common misunderstanding is that the “light bucket” status of large Dobsonians is solely beneficial for viewing deep-sky objects, won’t help in light-polluted conditions, or somehow linked to subpar optical performance. In reality, not only are the majority of modern Dobsonians equipped with high-quality optics, but their large aperture also facilitates increased resolution for smaller targets, such as planetary nebulae, double stars, and intricate details on planets and the Moon. However, it is worth noting that telescopes with an aperture much larger than 10” are seldom able to fully utilise their resolution capabilities, predominantly due to atmospheric conditions.
The visibility of celestial objects situated outside the Solar System, referred to as deep-sky objects, is heavily influenced by the prevailing light pollution conditions, with galaxies being particularly impacted. Under a dark sky, the Bresser Messier 10″ Dobsonian can unveil intricate details within thousands of galaxies, such as the stunning spiral arms of M51 or the dust lanes of M82 and M31. Conversely, under urban skies, only the most luminous galaxies are discernible as faint, dim smudges, with little to no detail visible, barring the occasional dust lane or elongated ovoid shape, regardless of the size and power of your telescope.
Emission nebulae like Orion (M42) appear truly spectacular when viewed through the Bresser Messier 10″ Dobsonian, particularly under dark skies and/or when using a suitable UHC nebula filter. The telescope also permits the observation of dozens of vibrant blue and green planetary nebulae, such as the striking emerald-hued Cat’s Eye Nebula, in addition to larger ones like M27 (the Dumbbell) and M57 (the Ring). Furthermore, the Bresser Messier 10″ Dobsonian is capable of resolving several dozen globular clusters, encompassing the majority of those found in the Messier catalogue. Thousands of stunning open star clusters can be observed as well, ranging from the vast Pleiades (M45), whose faint shimmer of reflective dust becomes visible under dark and clear skies, to smaller and more obscure open clusters from the NGC or IC catalogues that may be nestled within larger targets. Additionally, tens of thousands of double stars can be viewed with a 10” scope even from the city; many of these pairings also exhibit captivating colours.
The Bresser Messier 10” Dobsonian’s supplied film white-light solar filter enables you to safely observe the Sun, although it is essential to ensure that the filter is securely fastened and cannot be inadvertently blown or knocked off the scope before use. It is paramount for the safety of both your eyes and everything around you never to look through the telescope or its 6×30 finder at the Sun without employing a filter; the finder should be removed or covered as it can melt its internal crosshairs or start a fire even if you aren’t looking through it. A white-light solar filter allows you to view sunspots, the granular texture of the Sun’s photosphere, and is great for solar eclipses; however, observing flares or prominences necessitates a specialised hydrogen-alpha scope. To be frank, a 10” telescope is excessive for solar observations, as atmospheric turbulence, mainly induced by the Sun itself, typically restricts your maximum resolution to that of a 4-6” aperture instrument at best, and the Messier 10” might actually perform worse than a smaller telescope for solar viewing as a result.
As for Solar System targets, the Bresser Messier 10″ Dobsonian will enable you to observe the phases of Mercury and Venus, although little else on either planet. The Moon reveals intricate details merely kilometres wide, such as craters, mountain ranges, and smaller cracks and ridges. On Mars, you can observe the planet’s polar ice caps and any global dust storms, should they occur. Under optimal conditions, when Mars is closest to Earth, a skilled observer can spot dozens of dark markings or even Olympus Mons with steady air; however, most of the time, only a few surface features are visible even during a favourable apparition of the Red Planet.
Jupiter’s cloud belts can be easily observed with the Bresser Messier 10″ Dobsonian, and its moons appear as tiny disks. Regularly occurring shadow transits of the moons are a delight, as the disks of the moons and their inky black shadows slowly move across Jupiter’s face. Various other atmospheric details on Jupiter including the Great Red Spot are also visible with the Messier 10” Dobsonian on a steady night. Saturn’s rings are easy to spot with the Messier 10” Dobsonian or anygood telescope, as is the Cassini Division within them and some dull, linear cloud bands in the ringed planet’s atmosphere. A 10” instrument you to see half a dozen of Saturn’s moons, with the biggest and brightest, Titan, exhibiting a discernibly golden disk. On an exceptionally steady night, the extremely narrow Encke gap in Saturn’s rings can also be seen. The Bresser Messier 10″ Dobsonian is also capable of resolving Uranus as a teal dot, and under dark skies on a steady night, up to four of its moons can be observed. Neptune appears as a bluish orb with Triton quite visible even under mediocre conditions, while Pluto can be seen as a star-like point under dark skies if you can distinguish it from the thousands of faint stars near it that appear identical.