Why Buy Dobsonians, and Why We Recommend It?

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Written By: Zane Landers
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Category: Learn

There are a wide variety of telescope designs and types that you can go out and purchase. Many people are drawn to the elegance and simplicity of a refractor or the stubby but still familiar-looking catadioptric telescopes atop spindly equatorial (EQ) or fork mounts. However, if you’re aiming to get close-up views of star clusters, galaxies, and our Solar System, the right telescope for you is the unassuming Dobsonian, which to many people resembles a cannon more than an astronomical instrument and probably isn’t the first thing that comes to mind. If you’re interested, we have a Dobsonian buyers’ guide that has all the product recommendations.

Examples of different type of telescope mount combinations

The Dobsonian telescope is a Newtonian reflector atop a simple altitude-azimuth (alt-az) mount that pivots up and down and left-to-right. Usually when we talk about telescopes, we refer to the optical configuration and mount separately; in a Dobsonian, the two are inseparable. A Dobsonian telescope is pretty much always a Newtonian reflector combined with a simple alt-az mount.

Dobsonian telescopes were designed with the idea of putting more aperture, that is, a larger diameter main mirror to collect more light from distant objects, into the hands of amateurs as cheaply and easily as possible. They do this by using an extremely simple mounting made out of common materials (wood and plastic), which uses few precision parts, combined with the simplest optical configuration available for a good telescope. This means that the body of the telescope can be easily fabricated with basic hand or power tools at home, while the primary mirror can be ground on your kitchen table. Of course, the simplicity here extends to mass-manufactured instruments, which are able to be made out of laser- or CNC-cut wooden parts and cast metal fittings. Even a poorly designed commercial Dobsonian is vastly sturdier and of better quality than most undermounted, low-quality “hobby killer” telescopes on tripods that are sold in large numbers to beginners in both online and offline shops alike.

From a telescope’s cost perspective, the Dobsonian tends to be more economical than any other telescope configuration available to amateur astronomers. The only way you are realistically ever going to possess an instrument larger than 12” or so is if it is a Dobsonian (preferably a truss tube), and it’s easy to see why when you look at the massive mountings required by most other telescope designs.

Dobsonians are also the easiest telescopes to computerize due to their perfectly balanced nature. Dobsonians utilize the laws of physics alone to balance and require no clutches, lubricants, or, ideally, any counterweights to move smoothly around the sky.

Lastly, Dobsonians tend to be the most portable telescope design and thus occupy many listings in our portable telescope product guide. A collapsible or truss tube Dobsonian 10” or smaller in aperture fits in a passenger seat or even a large suitcase, while compact car owners can still accommodate a 16” or even 20” instrument without help setting it up or worrying about a lack of space. This is important since the best quality views through any telescope are often out in the countryside, i.e., far away from city lights.

Performance of Dobsonians Compared to Others

Fundamentally, Dobsonians offer better performance at the eyepiece than any other telescope design because they are able to be larger than most other optical designs without suffering from an extremely high cost, a narrow field of view, or portability issues.

Optical Performance: Why Newtonian Reflectors Are the Best

Newtonian reflectors are fundamentally the only way to obtain a telescope over 16” in aperture, and in the case of most people, a Newtonian/Dobsonian is the only affordable way to get even a 10” telescope. The larger your telescope’s aperture—that is, the primary objective lens or mirror—the more you can see. A larger mirror has more resolving power and collects more light from distant, faint celestial objects than a smaller one. Area scales with diameter, so a 12” telescope has 4x the light-gathering power of a 6” and twice the resolution.

Generally, if possible, we recommend starting with a 6–10″ or maybe 12” telescope. This is problematic when you consider that the only option besides a Dobsonian/Newtonian that fits the budget of most people might be a rather unwieldy computerized Schmidt-Cassegrain. Why? Well, let’s go over the three main competitors to the Newtonian reflector among amateur astronomers.

Refractors are celebrated for their sharp, contrast-rich views, primarily because they don’t have a central obstruction like many reflectors. However, as their size increases, their practicality dwindles rapidly. Refractors exceeding 6″ in aperture become unwieldy. Their weight surges, they demand larger mounts, and the cost escalates exponentially due to the precision required in crafting large refractor lenses free of imperfections. The need for a long focal length to avoid optical aberrations of the lens leads to a very long tube and a narrow field of view, making the telescopes harder to aim and limiting what can be observed with them. Refractors beyond 8″ are virtually nonexistent in the amateur market due to these impracticalities.

Maksutov-Cassegrain (Mak) and Schmidt-Cassegrain (SCT) telescopes are the other popular optical designs you’re likely to have up for consideration. Maksutovs are great scopes, but, like refractors, the cost associated with manufacturing the front corrector lens and their limited field of view prevent instruments over 8” or so from being practical and make 6-7” Maks unwieldy. So what about the Schmidt-Cassegrain? Well, Schmidts get very heavy and expensive past the 11-12” mark, and they also suffer from a narrow field of view at these sizes. Well, what do we mean by a narrow field of view?

A typical Newtonian reflector, and by extension, a Dobsonian, `has a focal ratio somewhere between f/3 and f/8 (usually f/6 is the limit). A typical 8” Schmidt-Cassegrain has a focal ratio of f/10. A typical 8” Maksutov or refractor, if you can find one, has a focal ratio of f/12 to f/15. All of these telescopes can only be used with up to a 2” format eyepiece.

The focal length dictates the magnification and field of view with a given eyepiece. You can use a longer focal length eyepiece to decrease the power of a long focal length telescope, but the physical area of the maximum field of view is a constant 2” across. So an 8” Dobsonian can cover a 2.2° or so area of sky, while an 8” Schmidt is limited to 1.3° (actually often 1° due to vignetting issues in most 8” Schmidt-Cassegrains). An 8” Maksutov-Cassegrain or refractor might not even have a field of view of 1° across! But what does this mean for views at the eyepiece?

Objects in the night sky often cover a surprisingly large area. The Moon spans not more than 0.5° of our sky, but nebulae like the Orion Nebula and open star clusters like the Pleiades can span one or two degrees across. The Andromeda Galaxy spans a mighty 3° from end to end! So a telescope with a wider maximum field of view allows you to take in the entirety of these objects at once, rather than just a small window. It is also easier to find objects by hand if you are starting out with a larger field of view. Combining a large aperture with the widest possible field of view is ideal for the best possible views of deep-sky objects for a variety of reasons.

This isn’t to say that Newtonians are perfect. Newtonian reflectors have diffraction spikes on bright objects, an issue that refractors and most catadioptrics don’t have. They also have coma at faster focal ratios, which requires a coma corrector to compensate for. However, all in all, Newtonian reflectors deliver fewer compromises at larger apertures than most other telescope types.

Dobsonian Mount: The Best-in-Class Mount

All of what we’ve said so far applies to Newtonian reflectors. So what makes the Dobsonian mount so special? The simplicity of the Dobsonian mount is ideal from both a cost and ease-of-use standpoint.

Equatorial mounts, while providing precision tracking of celestial objects on a single axis, come with their share of challenges when paired with larger Newtonian reflectors. As the aperture size increases, the length and weight of the telescope optical tube escalate, making the setup top-heavy and demanding a robust (and often expensive) mount to maintain balance. Furthermore, the setup becomes more cumbersome, potentially requiring ladders for eyepiece access for even an 8” or 10” instrument. For these reasons, while equatorially-mounted Newtonians can be perfect for specific tasks and smaller apertures, they become impractical for larger sizes. Here, the Dobsonian mount, with its alt-azimuth design, steps in as the optimal choice. It keeps the mirror, and thus the eyepiece, as low to the ground as it can be while also minimizing the rotational movement of the eyepiece as the telescope is aimed around the sky. This keeps the eyepiece easily accessible, whether you are aiming near the horizon, straight up, or around the celestial pole. The same cannot be said of a German equatorial mount.

Dobsonians are also easier to adjust by hand than an equatorial mount. The alt-azimuth nature of the Dobsonian mount is more intuitive, while the lack of slow-motion cables means you simply push on the side of the telescope to make pointing or tracking adjustments. The Dobsonian mount is perfectly balanced and moves with buttery-smooth motions when pushed; you won’t overshoot your target or have trouble making tracking adjustments to keep it in the field of view at higher magnifications. Dobsonians also stay put when you let go of them, instead of oscillating back and forth like an equatorial mount might.

Cost-Effectiveness of Dobsonians

Dobsonian telescopes are unrivaled in their cost-effectiveness for the given aperture. The optics of a Newtonian reflector are cheaper to manufacture than any other telescope design, while the Dobsonian mount is extremely cost-effective to build compared to a robust fork mount or German equatorial design, especially at larger sizes.

Given that the larger the telescope, the more you can see, the fact that a Dobsonian is by and large the only affordable ticket to apertures over 10-12” and is substantially cheaper for all but the smallest apertures should be pretty noteworthy. Amateur astronomers who observe with large and spectacularly capable telescopes usually own super-sized Dobsonians in the 20-40” aperture range.

ApertureCost (Dobsonian)Cost (EQ Newtonian)Cost (Achromat Refractor)Cost (SCT/Mak)
4”$150$200$250$300
6”$300$600$1000$1000
8”$700$1500$5000?$1500
12”$1200~$4000$10000?$4300
16”~$3000~$8000??????$19000

Portability of Dobsonian Telescopes

Dobsonian telescopes, at their core, consist of two primary components: the optical tube and the mount. Unlike more complex telescope setups, which usually involve a tripod to level and a half dozen different pieces of hardware to assemble, a solid-tubed Dobsonian is dead simple to take with you. When you’re ready to transport the telescope, it’s often as easy as separating the tube from the mount. Dobsonians don’t require a power supply, vibration suppression pads, counterweights, mounting rings, or other accessories like many other telescopes can, which also means there’s simply less stuff to bring with you on a night of stargazing. They also don’t really need a dew shield like you might for a refractor or catadioptric telescope.

Moreover, because the Dobsonian doesn’t rely on a tripod, it naturally takes up less floor space when not in use, unless you are able to store your tripod on a shelf somewhere convenient. Many people do not like how “bulky” these telescopes appear to be, but in actuality, a heavy-duty tripod for a substantially smaller telescope takes up more room than a typical 10” Dob. You can also completely ignore the idea of a carrying case or padding; most Dobsonian owners don’t even bother to wrap the tube in a towel or blanket. These are fairly sturdy and robust instruments.

Modern innovations have seen the emergence of truss or collapsible tube designs in Dobsonian telescopes. These designs allow the optical tube, which can be the bulkiest part of the telescope, to be collapsed or disassembled into more compact segments. This modularity further enhances the Dobsonian’s portability and ease of storage. When not in use or during transport, these segments can be neatly packed away, saving a significant amount of space.

The truss tube designs usually result in a fairly compact “rocker box” or base, and if not, many commercial truss tube telescopes have a base that can be packed flat without the use of tools to reduce volume further. When transported, the cuboid nature of the sub-assemblies of the telescope maximizes packing efficiency and means that you usually don’t need any kind of case or padding besides for the stowed truss poles.

While it might seem counterintuitive, even larger Dobsonians, with apertures up to 40″, have been designed with portability in mind. Due to the Dobsonian telescope’s inherent simplicity and the modular nature of truss designs, these larger telescopes can be broken down into manageable components. With a suitable vehicle, a single individual can transport these pieces and roll the heavy mirror/rocker box on wheels down a ramp in and out of the car or trailer. Once at the observation site, assembly is straightforward, and the telescope can be set up with relative ease by just a single person in no more than 15 minutes.

Ease of Construction

Dobsonians are the easiest telescope to build, whether it’s yourself at home or on an assembly line. Part of this is because they are Newtonian reflecting telescopes. Only the primary mirror is a complex optic, and a parabolic primary mirror is far easier to grind and polish than a complex lens or multiple curved mirrors. The secondary mirror is a flat mirror that’s easy to mass-produce. The mount of a Dobsonian can be made entirely out of plywood, apart from the plastic bearing surfaces.

Even if you’ve bought your own Dobsonian, the ease of fabricating parts for one is still an important aspect of these telescopes. You can make a new base for your telescope if your old one is damaged or you find it too heavy. You can fabricate your own bearings or replace the laminate/pads on your telescope if you don’t like how it moves. You can also easily add hardware to the sides of the base, such as wheels, eyepiece racks, a tablet stalk, etc., just by drilling holes and tapping in wood screws.

Longevity

Arguably the most critical component of a Dobsonian or Newtonian telescope, the primary mirror, is impressively durable. With proper care and maintenance, protected aluminum mirror coatings can last anywhere between 50 and 100 years. Cheaply-done “enhanced aluminum” still lasts around 20 years or so. The quartz overcoat on mirror coatings staves off physical abrasion and chemical corrosion, while the aluminum itself takes decades to oxidize and eventually corrode off the glass.

Moreover, if the need arises, recoating the primary mirror is a fairly affordable endeavor. For enthusiasts keen on DIY solutions, silver recoats can be done at home, although silver does have a propensity to tarnish and will need attention roughly on an annual basis. Interestingly, the secondary mirror of most telescopes, due to its upside-down orientation during proper storage, generally lasts even longer without the need for recoating.

Unlike Schmidt telescopes, which have a thin corrector that can shatter, or other designs that possess a vulnerable, thick, and expensive lens at the front, the primary mirror of a Newtonian reflector sits at the bottom of the tube. The secondary is not nearly as at risk if the telescope is dropped, etc., and can be replaced for a fairly low cost if it is somehow damaged.

Dobsonian telescopes shun complexity in favor of user-friendly mechanics. They avoid complex mechanical parts that might be challenging or expensive to replace. Most of the telescope’s components can be repaired or replaced using common hardware, making maintenance accessible and cost-effective. The Dobsonian mount, renowned for its simplicity, can be reconstructed from scratch without much hassle.

Finally, Dobsonians are also designed to be tough. Minor dents to the tube, for instance, typically don’t affect performance. Similarly, the particle board mounts of mass-manufactured scopes can swell, warp, and otherwise deviate slightly from their original shape without losing functionality. Even if the coatings or mirrors sustain minor damage, the performance drop at the eyepiece through a telescope is usually negligible, and recoating is a straightforward process, as mentioned above. In fact, even computerized Dobsonians, if faced with electronic failures, can typically still be operated manually to no detriment.

Zane Landers

An amateur astronomer and telescope maker from Connecticut who has been featured on TIME magazineNational GeographicLa Vanguardia, and Clarin, The Guardian, The Arizona Daily Star, and Astronomy Technology Today and had won the Stellafane 1st and 3rd place Junior Awards in the 2018 Convention. Zane has owned over 425 telescopes, of which around 400 he has actually gotten to take out under the stars. These range from the stuff we review on TelescopicWatch to homemade or antique telescopes; the oldest he has owned or worked on so far was an Emil Busch refractor made shortly before the outbreak of World War I. Many of these are telescopes that he repaired or built.

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