The Optical Tube
The Bresser Messier 8” Dobsonian 8” f/6 Dobsonian’s primary mirror is a 203mm (8”) f/5.9 unit with a resulting 1200mm focal length. It is made of ordinary BK7 glass which cools down a bit faster than plate glass but not as fast as Pyrex. You may want to install a fan to speed up the cooldown process but it is generally pretty quick.
The Messier 8” Dobsonian’s primary mirror is collimated with thumbscrews, and it is of high quality, providing sharp images at both low and high magnifications. The secondary mirror can be collimated using a Phillips head screwdriver.
The Bresser Messier 8” Dobsonian also features an unusual 2.5″ hexagonal rack-and-pinion focuser, which is lifted from faster Newtonian reflectors designed for imaging. It is extremely high quality, and can be upgraded to a dual speed focuser with an aftermarket add-on fairly easily. However, to achieve focus with most eyepieces, an extension tube must be installed, placing the eyepiece about 8 inches away from the tube wall. While this design choice may seem strange, it functions well, despite the unusual arrangement.
Finally, the Bresser Messier 8” Dobsonian uses rotatable tube rings with the altitude bearings screwed onto them rather than having bearings bolted to the tube walls. This allows for tube balance adjustments and convenient eyepiece location rotation. Additionally, the design allows the tube to be removed from the Dobsonian mount and attached to an equatorial mount for astrophotography. The Bresser Messier 8” Dobsonian has a generous amount of focuser travel, making it easy to focus with a DSLR camera and adapter.
The Messier 8” Dobsonian comes with a rather pathetic set of accessories. A single 25mm, 1.25” Plossl, providing 48x, is included. Normally Plossl eyepieces are pretty decent but this one is extremely low quality. The eye lens is pointlessly recessed inside the body of the eyepiece requiring you to jam your eye into it to take in the whole field, it’s got some glare problems and the whole thing just feels cheap. You’ll need additional eyepieces anyway, and you should probably consider replacing this one too.
For a finder, the Messier 8” Dobsonian includes a 6×30 unit, which has crosshairs and an upside-down field of view about 7 degrees across. This finder shows stars fainter than what you can see with your naked eye alone, but it is uncomfortable to use and the image is not as bright as that of a 9×50.
Lastly, the Messier Dobsonians all include a while light film solar filter which you attach to the front of the telescope (the 6×30 finder must be covered or removed for safety since a filter for it is not provided). This filter has an all-plastic body and is prone to falling off the telescope, which is obviously extremely unsafe, so you’ll need to come up with some additional way to securely fasten it to the telescope – why Bresser/Jinghua is seemingly so unconcerned with such an important safety feature is a little worrying, but the filter is perfectly safe and allows form close-up views of the solar photosphere and sunspots with this scope.
Compared to other non-premium 8” Dobsonians on the market, the Bresser Messier 8” Dobsonian boasts several design improvements to its mount, making it far superior to its competitors. The altitude bearings on many cheap Dobsonians use plastic circles less than ten inches across, which pivot on nylon pads and produce mostly smooth motions. However, heavy eyepieces can cause the scope to fall over unless springs or magnetic counterweights are used, which can cause other problems. The StellaLyra Dobsonians, for example, attempt to work around this problem with ball bearings that slide up and down the telescope tube to adjust for different eyepieces. But they have limited travel, and 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. Springs are finite in the amount of tension they can provide before making the scope immobile, and clutches will of course produce bumpy and jerky motions if they are forced to remain tightened on an unbalanced base.
In contrast, the Bresser Messier 8” Dobsonian has large, semi-circular bearings attached to tube rings that allow you to rotate the tube to put the eyepiece at whatever angle you want. The rings also have much more travel in either direction to compensate for bottom/top-heaviness. The large diameter of the bearings means that the center 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. For transport, the bearings can be detached from the rings; as previously mentioned the rings can also be bolted to a Vixen-style dovetail to put the Messier 8” optical tube but we wouldn’t really recommend doing so due to its huge size and rather long focal length compared to dedicated 8” imaging Newtonians.
For azimuth, the Messier 8” uses a melamine-on-Teflon arrangement that works well, although it can be a little jerky when pointing the telescope near the zenith (straight up). The Bresser Messier 8” Dobsonian mount also has large cutouts in the base that function as handles, and the base assembles with 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 and will not survive disassembly and re-assembly as the screw threads will quickly disappear from the particle board fittings.
Should I buy a Used Bresser Messier 8” Dobsonian?
A second-hand Bresser Messier 8” Dobsonian could be a wise choice, as purchasing a used unit can save you money that can be used to buy additional accessories (sorely needed since the scope comes with next to nothing). However, it is crucial to inspect any used Dobsonian for damage to the mirror coatings or base. Replacing a damaged base is usually simple and cost-effective, though 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 moss or chemical corrosion, pinholes, or a transparent appearance to the coating, the mirror may require recoating, which can be expensive. Before making a decision, it is essential to consider the cost of recoating compared to purchasing a new telescope.
It is not typically necessary to worry about dents on the tube of a used Dobsonian since they are often unavoidable and usually do not impact the light path. In cases where dents do affect the optics, they can often be eliminated using tools similar to those used for removing dents on a car or even with a plunger or hammer.
- The StellaLyra 8” f/6 Dobsonian offers features the Messier 8” lacks such as a dual-speed focuser, a pair of high-quality eyepieces, a 9×50 right-angle finder, and a built-in cooling fan by default. This makes it much better for the monye compared to
- The Celestron StarSense Explorer 8” Dobsonian, like the Messier 8” Dobsonian, comes with few useful accessories or bonus features. However, it does have a lightweight base and features Celestron’s
- The Ursa Major 8” Dobsonian is basic, but has all of the same features an 8” Dobsonian should provide including a better finder scope than the Bresser Messier 8” and a pair of decent Plossl eyepieces. However, its undersized altitude bearings (in stark contrast to the Messier 8”) frequently lead to balance problems with heavier eyepieces and the base is kind of heavy.
- The Sky-Watcher Virtuoso GTi 150P is an exceptionally transportable telescope, complete with a fully motorised mount equipped with GoTo technology. This technology can be operated using a smartphone app or manually directed by hand. Although its aperture is more diminutive compared to the 8” Dobsonians in this price range, its compact design renders it an outstanding choice for individuals who prioritise easy transportation and user-friendliness. The manually operated Heritage 150P is also an excellent option if you can forgo the computerised functionality.
- The StellaLyra 10” f/5 Dobsonian possesses the remarkable features of its 8” equivalent, such as its superior quality focuser and additional accessories, but it also benefits from its more substantial aperture, which collects 36% more light than an 8” Dobsonian telescope. Despite the increase in aperture, the overall dimensions and weight of the telescope remain only marginally larger due to the comparable proportions of the base and tube.
- The Bresser Messier 10” Dobsonian has the same features, design, and accessories as the 8” model with a larger aperture and more or less the same pros/cons but better performance due to the larger primary mirror.
- The Explore Scientific 10” Ultra Light Dobsonian exhibits a more streamlined, all-metal design in stark contrast to the bulky tubes and particle board bases of most commercial solid-tubed Dobsonians. This makes it an ideal option for those seeking a more easily transportable telescope. Nonetheless, it demands more assembly and offers a smaller range of accessories. Conversely, the 10″ aperture provides superior performance and is guaranteed to deliver astonishing views of the night sky.
- The StellaLyra 12″ f/5 Dobsonian is a formidable telescope that boasts an extraordinary selection of accessories, offering excellent value for your investment, much like its smaller StellaLyra Dobsonian counterparts. However, manoeuvring its solid tube may prove difficult without a dolly, and a sizeable vehicle is essential for transporting it to dark sky locations. If your budget permits, a pricier collapsible or truss 12″ model could be a more suitable choice for simpler transportation and assembly.
- The Explore Scientific 12″ Ultra Light Dobsonian features a refined truss design, substantial altitude bearings, and all-metal components, ensuring a compact and lightweight storage solution with smooth movements devoid of springs, clutches, or other aids. Additionally, it is equipped with a dual-speed 2” Crayford focuser and delivers all the performance expected from a 12” telescope. Regrettably, it lacks supplementary accessories or electronic features, and collimation along with the assembly of the many fiddly parts of the truss tube can be a little more time-consuming if you’re not used to telescopes.
- The Sky-Watcher Skyliner 300P FlexTube isn’t significantly lighter than a solid-tubed scope of its aperture but is certainly more compact, and unlike a truss there are no removable parts to worry about.
- The Celestron StarSense Explorer 10” Dobsonian offers a lightweight base and the same StarSense Explorer technology as its 8” counterpart, though it of course comes up short with a single-speed focuser that’s not easy to upgrade to a dual-speed unit along with no other features or accessories.
Aftermarket Accessory Recommendations
The Bresser Messier 8” Dobsonian will only be able to unlock its full potential with a few additional eyepieces. Not only does the single provided eyepiece not exactly provide the sharpest views even by the low standards of a low-power kit eyepiece, but you’ll also want a wide range of magnifications for viewing different types of celestial objects anyways. A decent but fairly inexpensive 2” super wide angle (SWA) eyepiece, such as the 38mm PanaView (providing 32x magnification), delivers the lowest magnification and almost the widest possible true field of view that the Messier 8” Dobsonian can achieve, ideal for locating your target initially and perfect for breathtaking views of wide-spanning open star clusters.
For medium power, we would recommend either a 16mm UWA eyepiece (76x magnification), a cheaper but still decent quality 15mm redline/goldline ocular (81x magnification) for use with the Messier 8” Dobsonian, along with a 10mm (122x) UWA or 9mm redline/goldline (135x) for medium-high power and a 6mm redline/goldline (203x) for high power. Some users may even wish to spring for a 4mm planetary eyepiece or an immersive but costly 4mm UWA, either of which provides 304x with the Messier 8” Dobsonian – about the highest you can go before running into the trifecta of atmospheric turbulence, the telescope itself, and your ability to nudge the telescope along manually preventing the use of higher power. Bear in mind that magnifications above around 30x per inch of aperture are rarely of use outside the Moon, planets, and double stars due to the way they dim the image, and even then only during steady atmospheric conditions.
Additionally, you may wish to replace the stock 6×30 finder provided with the Messier 8” Dobsonian with a simple reflex sight, such as the Telrad or aptly-named Explore Scientific ReflexSight. Either option is much easier to use than the 6×30 finder scope, and provides a simple illuminated reticle against a window aimed at the sky, making it extremely intuitive to align and use. A budget-friendly Cheshire collimation tool will make collimating the Messier 8″ Dobsonian considerably easier as well, and you’ll absolutely want it for sharp high-magnification views. And while expensive, the dual-speed upgrade for the Messier 8” Dobsonian’s focuser can make getting sharp views at high magnification a little easier.
Last but certainly not least, a narrowband UHC/OIII nebula filter is highly recommended for almost any telescope, including the Messier 8″ Dobsonian, to enhance contrast on nebulae like Orion and reveal previously unseen detail and structure. This is particularly helpful if you are observing under light-polluted skies. For use with 1.25” eyepieces, a 2” UHC filter will screw onto the Messier’s provided 1.25” adapter, and it will of course attach directly to the 2” extension tube or any 2” oculars you may have purchased.
What can you see?
The Bresser Messier 8” Dobsonian, like any quality 8” Dobsonian, is a versatile instrument capable of providing views of various celestial objects. Even under light-polluted conditions, this telescope can unveil a diverse range of open star clusters, such as M11 and M35, individual stars within globular clusters, like M13 and M15, and numerous double stars, many of which are challenging to split at high magnifications and/or offer vivid coloration.
The quality of a telescope’s views of most deep-sky objects largely depends on the level of light pollution in your area. Suburban light pollution can essentially eliminate galaxies altogether and significantly impair nebulae, while highly light-polluted skies will make viewing everything but star clusters a frustrating task. For optimal viewing of galaxies and nebulae with any telescope, moderately dark skies are necessary and you will see more the better your sky conditions are.
With the Bresser Messier 8” Dobsonian, you can observe hundreds of colourful open star clusters and several dozen globular clusters, most of which can be resolved into individual stars using a high-magnification eyepiece. Nebulae such as the Orion Nebula (M42) are detailed and bright even under mediocre skies and are further enhanced by a UHC filter. The Veil Nebula is spectacular under dark skies with a UHC or Oxygen-III filter, and you can also pursue numerous colourful planetary nebulae. The Bresser Messier 8” Dobsonian can, fittingly, rather effortlessly display all of the galaxies in the Messier catalogue, and under optimal conditions, you can begin to discern a few features in brighter and more detailed galaxies. The spiral arms of M51 begin to be revealed with an 8” scope at medium magnification, while the dust lanes in M82, M64, and the enormous Andromeda Galaxy (M31) are strikingly apparent due to their high contrast.
The Bresser Messier 8” Dobsonian’s supplied solar filter will allow you to safely observe the Sun, though you’ll need to make sure it is unable to be blown or knocked off the scope and fasten it securely before use; never look through the telescope or its 6×30 finder at the Sun without a filter. The white-light nature of this solar filter means you’ll be able to see sunspots, the granular texture of the Sun’s photosphere, and any solar eclipses; flares/prominences require a specialized hydrogen-alpha scope to see except during an eclipse. An 8” telescope is quite frankly overkill for observing the Sun, however, since atmospheric turbulence (caused mostly by the Sun itself) is severe enough to limit resolution to that of a 4” or so instrument much of the time anyway.
Additionally, the Bresser Messier 8” Dobsonian can offer superb views of Solar System objects, including the Moon’s numerous craters and mountain peaks, and the phases of Mercury and Venus. The scope can reveal a few dark markings on Mars along with the planet’s polar ice caps and any dust storms, though you’ll have to wait for Mars to be favorably close to Earth to clearly resolve any of these surface features. Jupiter’s cloud belts, the Great Red Spot, and its four prominent moons are visible through the telescope. These moons appear as tiny disks alongside their jet-black shadows when they transit in front of Jupiter, causing an eclipse over the planet’s cloud tops.
Saturn’s rings and the Cassini Division in them are no trouble for the Bresser Messier 8” Dobsonian to resolve, the latter requiring a high-power eyepiece along with the planet’s cloud bands. You should also expect to see several moons around the ringed planet. Uranus is a bluish-green disk, easily seen in the Messier 8” Dobsonian’s 6×30 finderscope. A few of its moons are visible with an 8” telescope, but in practice a larger instrument is required to see them. Neptune can be spotted with the 6×30 finderscope but appears as a deep blue smudge at best in the telescope, though its moon Triton is fairly easy to see accompanying it. Pluto requires dark skies to be seen at all, and realistically, an 8” telescope is no longer enough to see it as the dwarf planet has continued to dim as it gets further away from the Sun for the foreseeable future.