Celestron Nexstar 8SE vs. 8″ Dobsonians

While the Celestron NexStar 8SE offers modern features and automated tracking, the 8″ Dobsonians bring simplicity, a larger field of view, and stability to the table. Though our analysis will lean towards the advantages of Dobsonians, especially considering certain challenges with the 8SE, it is crucial to approach this comparison with neutrality and a clear understanding of the needs of individual astronomers.

The NexStar 8SE is, simply put, a bad buy compared to an 8” Dobsonian. For one thing, any good 8” telescope puts up the same views, and the NexStar 8SE, with its computerized features, comes at a price roughly double that of a standard 8″ Dobsonian as of the time of writing (September 2023). If it’s “bang for your buck” that you’re after, an 8” Dobsonian obviously wins before we even get into anything technical.

But the investment doesn’t stop at the initial purchase. To truly optimize the NexStar 8SE experience, one often finds themselves needing to invest in several accessories that a Dobsonian owner can safely ignore. These might include a power supply, vibration suppression pads, a dew shield to prevent moisture accumulation, and, of course, several additional eyepieces since the 8SE includes only a single low-power ocular to get you started. That’s before you even consider switching to running the scope off your phone/tablet with a costly aftermarket Wi-Fi dongle. You are unlikely to be happy with your NexStar 8SE setup without spending nearly the price of an entire 8” Dobsonian telescope just to accessorize it, or over $2000 USD in all.

In contrast, an 8″ Dobsonian offers a straightforward, immersive experience without the necessity for any upgrades at all, besides perhaps a better finder or a couple of eyepieces. Its design is robust, and its manual operation fosters a hands-on connection with the cosmos. Manually aiming a Dobsonian is not as difficult as it might seem at first. With a little practice and the aid of a star chart or astronomy app, even beginners can swiftly navigate between stars and find deep-sky objects with ease. For many, manually tracing the night sky and discovering the cosmos without the constraints of having to scroll through a database or deal with an alignment procedure is a much more relaxing and rewarding experience, too.

Optics Comparison

The Celestron NexStar 8SE is a product of Celestron’s refined C8 XLT optical tube design. Drawing inspiration from the original C8 telescope launched in the 1970s, the updated version boasts advanced features like HyperStar compatibility and the renowned “StarBright XLT” optical coatings.

The C8 is a Schmidt-Casegrain telescope, or SCT for short. The heart of the C8 comprises an 8” (203mm) f/2 spherical primary mirror paired with a small secondary mirror. This secondary mirror is convex and elevates the telescope’s focal ratio by about 5x to f/10, thus stretching its focal length to 2032mm. At the tube’s front end is a Schmidt corrector plate, a thin plate of optical glass meticulously crafted to rectify spherical aberration produced by the primary and secondary mirrors while also anchoring the secondary mirror in place.

A typical 8″ Dobsonian, such as the Apertura AD8, employs an 8″ (203mm) primary mirror akin to the C8 XLT. However, its mirror has a parabolic curve; most 8” Dobs employ an f/5.9 or f/6 primary mirror and thus have a focal length ranging between 1200-1250mm.

Both the NexStar 8SE and an 8” Dobsonian are nominally capable of accepting both 1.25” and 2” eyepieces, though the 8SE vignettes with most 2” oculars and doesn’t come supplied with a 2” visual back or diagonal to accept them.

As for views? It’s a toss-up. The C8 XLT optical tube has a larger secondary mirror than most 8” Dobs, which leads to it gathering less light than an 8” Dob in theory, but not by much. The benefits of the StarBright XLT multi-coatings on the corrector, as well as the drawbacks of it absorbing/reflecting light entering the C8, are both negligible. A Dobsonian usually has diffraction spikes on bright stars and planets, but the C8 XLT’s larger obstruction smears fine detail a bit more. The spikes on stars through a Dobsonian tend to be only on the brightest ones anyway, and it’s purely cosmetic. Deep-sky objects look identical through either, apart from magnification and field of view differences with different eyepieces.

The C8 XLT is not known to be the pinnacle of optical perfection, but neither are the mass-manufactured 8” Dobsonians. Some Dobsonians come from the same factory as the C8 and other SCTs and are made by the same people with similar tooling and materials. There are rarely bad examples of either, though both tend to suffer principally from slightly rough (overpolished) optics if there is a defect.

At high magnifications, the use of a quality eyepiece, as well as allowing for proper collimation and cooldown time, are generally more important factors in deciding the performance of either telescope design than any meaningful unit-to-unit variation.

Collimation Requirement Differences

Collimation, the process of aligning a telescope’s optics for optimal performance, is an integral aspect of telescope maintenance. While all telescopes will require collimation at some point, the process varies between different models and optical designs.

SCTs like the 8SE/C8, once properly collimated, tend to hold their alignment relatively well unless subjected to significant jarring or rough handling. However, it’s good practice to check collimation periodically, especially if the telescope is transported frequently. Collimating an SCT requires pointing the telescope at a bright star and adjusting the tip/tilt of the secondary mirror, which can be tricky to get right.

Newtonian telescopes, such as 8″ Dobsonians, have a two-fold collimation process that involves adjustments to both the primary and secondary mirrors. Collimation tools, like a collimation cap or a laser collimator, make the process straightforward, even for beginners and in the daytime.

An 8″ Dobsonian is robust in maintaining its collimation. While it’s always advisable to check alignment before observational sessions, especially if the telescope has been moved, many Dobsonian users find they only need to collimate their scopes occasionally, and usually only the primary mirror needs to be tweaked. The secondary mirror in a Newtonian reflector rarely goes out of alignment. If it does, it’s typically due to significant trauma or mishandling and shouldn’t need adjustment again for a long time.

Field of View Comparison

The typical 1200mm focal length specification and 2” focuser of any good 8” Dob offers a broad maximum field of view up to 2.25°, or about 4.5 times the angular diameter of the Moon, with a 2” eyepiece. It’s worth noting, though, that the periphery of this view might display some coma; a coma corrector will slightly reduce the field to approximately 2° or 4 full Moons across, but renders all of it nice and sharp to the edges.

The field of view of the C8 XLT is quite a bit narrower, both due to its longer 2032mm focal length and physical constraints. The original design of the C8, which was carried over to the present, is optimized for a field of view of about 35mm (1.4″), which equates to the dimensions of traditional SLR film or the present-day “full-frame” camera sensors. Back in its early days, the 1970s, 2″ eyepieces weren’t as prevalent as they are today, so Celestron’s designers only bothered to widen the telescope’s interior baffling to illuminate a 35mm circle. Consequently, when a 2″ eyepiece boasting over a 35mm field stop is introduced to the C8 XLT, vignetting occurs, limiting the maximum field of view to 1° or so – about twice the angular diameter of the full Moon. Using an f/6.3 reducer does not allow a wider unvignetted field than this, just a shrunken but narrow view at lower powers.

Accessories Comparison

The NexStar 8SE doesn’t include much to get you started—just a red dot finder to aim/align the telescope, a 1.25” visual back and star diagonal to put your eyepiece in, and a single 25mm Plossl eyepiece, which yields 81x with the C8 XLT optical tube. You don’t even get a power cable for the mount.

The 8SE will require at least 3 eyepieces to get the full range of useful magnifications that the telescope can offer, as well as a rechargeable power supply (or wall adapter), a dew shield, and probably vibration suppression pads, in addition to any sort of DIY solution to improve the wobbly mounting. And that’s before you factor in personalizations like thumbscrews for collimation or a Wi-Fi dongle to replace the stock hand controller and allow one to operate the telescope over a modern smartphone app like SkySafari.

The exact accessories provided with 8” Dobsonians vary based on the make and model, but you usually get either a 9×50 finder scope or an acceptable red dot finder of some sort. None of these are actually what we recommend—a reflex sight such as the Telrad or Rigel Quikfinder is much more comfortable and usually more intuitive—but all of them do the job. You also get at least one low-power eyepiece, and manufacturers tend to throw in some sort of usable collimation tool too. Usually the minimum included eyepiece is a 25mm Plossl of at least acceptable quality, yielding 48x or so.

Most telescopes are rarely provided with a full suite of accessories, but since these are often a matter of personal preference and budget, it doesn’t matter much. The Apertura AD8/Zhumell Z8 and their 10″/12″ counterparts are some of the few scopes, let alone Dobsonians, that come close to offering a complete set of necessary accessories out of the box, and they would still benefit from a medium-power eyepiece and a better high-power ocular of some sort.

Mounting Differences

The Celestron NexStar 8SE features an alt-azimuth single-arm mount, a larger variant of the NexStar SE mounts. It consists of a single-armed mount head that bolts to an adjustable steel tripod. The same mount is used with the NexStar 6SE. It features a Vixen-style dovetail saddle to allow for quick, tool-free removal and interchangeability of telescope tubes.

The NexStar 8SE tripod’s legs are sturdier with a 1.5” diameter as compared to the 1.25” legs found in the 5SE/4SE model, and the form arm is taller.

Unfortunately, the NexStar 8SE mount is incapable of supporting the C8 XLT optical tube’s weight effectively and wobbles even at fairly low power. The primary limitation is the mount’s single fork arm, largely constructed from plastic, which lacks the necessary rigidity. Additionally, the 1.5” tripod legs, although thicker than some of their predecessors, tend to be shaky and can twist under the combined weight of the C8 XLT tube and the mount head. This lightweight design results in a top-heavy configuration for the 8SE, compromising its overall stability.

Being computerized, the 8SE mount offers automatic tracking of celestial objects. It can automatically slew to specific stars, planets, and other celestial objects stored in its database, making it easier for beginners to locate objects in the night sky. It will then track to keep these objects in the field of view as the Earth rotates. The GoTo system requires alignment at the start of each observing session via the provided NexStar+ controller, which you use to operate the mount. Swapping the controller for an aftermarket Wi-Fi dongle is also an option.

In contrast, Dobsonian mounts are characterized by their simplicity. Built on a rocker-box design, they rest directly on the ground, using a rotating base (azimuth) and a cradle for the optical tube that allows vertical movement (altitude).

Dobsonian mounts are typically bulkier due to their low center-of-gravity design, but this ensures stability. Known for their sturdiness, Dobsonian mounts offer great durability and resistance to wear and tear. The absence of electronic components reduces potential points of failure. Their low center of gravity and substantial base provide significant stability, making them less prone to vibrations and shakes. And even if you destroy the rocker box of your Dobsonian, it’s easy to build a new one in an afternoon with just a jigsaw and plywood.

Many of the 8” Dobsonian telescopes on the market aren’t ideally designed when it comes to the mounting; they’re usually unnecessarily large and made of chipboard, altitude bearings are rarely big enough, and sub-optimal materials like roller bearings or nylon pads are substituted for proper laminates and Teflon. Nonetheless, they’re rock-solid even at high magnifications, and though it may require some fiddling with the bearings, these telescopes are easy to steer around the sky, offering buttery-smooth fine motions without the use of gears or electronic components.

To the uninitiated, the prospect of manually aiming a Dobsonian telescope might seem daunting. The idea of “star-hopping” – navigating the night sky using stars as reference points to locate celestial objects—can appear complex, especially when compared to the automated convenience of computerized mounts. However, the reality is that star-hopping, once learned, is an intuitive and rewarding experience for many astronomers.

Critics will point out that in areas with significant light pollution, the number of visible stars is reduced, making star-hopping more challenging. However, this brings up an inevitable counterpoint. In heavily light-polluted areas, there are few to no “faint fuzzies” visible to necessitate a computerized mount’s guidance. In such environments, the primary targets are going to be the Moon, planets, prominent double stars, and a few bright star clusters or nebulae, all of which are relatively easy to locate manually.

Differences in Astrophotography Capabilities

In our comparisons of the 8SE to other computerized telescopes, we’ve left out astrophotography since they are all about equally usable for planetary imaging and useless for deep-sky astrophotography. However, since one of the supposed selling points of the NexStar 8SE over any manual telescope is the ability to take photos, we thought we’d elaborate on this as well as how a Dobsonian is actually not much worse for planetary imaging.

The first thing you might ask is, wait – isn’t the NexStar 8SE usable for long-exposure astrophotography? Well, not exactly.

• At f/10, the NexStar 8SE is notably slow for deep-sky imaging. The majority of astrophotographers prefer faster systems for capturing distant galaxies, nebulae, and star clusters. To somewhat counter this issue, there’s the option of an f/6.3 reducer. While it brings the focal ratio down, it also brings with it an added cost.
• Mirror flop sometimes ruins long exposures with the regular C8 XLT optical tube, which is why the astrophotography-oriented EdgeHD 8 version of C8 has mirror locks.
• Edge-of-field aberrations and vignetting can somewhat limit camera choices with the 8SE/C8 XLT with or without a reducer.
• The altazimuth design of the 8SE mount is fundamentally not cut out for long-exposure astrophotography. Altaz mounts are prone to a phenomenon known as field rotation over extended exposures, which can distort celestial objects in images. Once you use the 8SE in EQ mode on a wedge, it further compromises the system’s stability. The setup becomes increasingly top-heavy, heightening the risk of vibrations and shaky images.
• Even more concerning is the mount’s inherent instability. Wobbliness becomes a serious concern, especially when trying to achieve long exposures where even minute vibrations can blur the image.
• There is a possibility of using the Celestron NexStar 8SE with a HyperStar at f/2 or with an f/6.3 reducer for electronically-assisted astronomy (EAA), which involves live-stacked short exposures, or for very short-exposure deep-sky images. However, this is costly and extremely limiting in what you can do compared to just using the C8 XLT on a better mount or employing some alternative telescope/mount combination for the job.

All of the issues above can be solved – more or less – with enough time and money thrown at the problem, but you’re either simply remounting the 8SE or spending so much money that you could have just gone with something else in the first place.

An 8” Schmidt-Cassegrain is hardly a good choice for first-time astrophotographers – our articles on choosing an OTA and mount explain more. If you are insistent on using the C8 XLT optical tube for deep-sky astrophotography, mounts like the Sky-Watcher EQ6R are inherently designed with astrophotography in mind and represent a more worthwhile investment in the long run.

What about planetary imaging? Contrary to what one might assume, the manual nudging required with a Dobsonian for planetary imaging isn’t significantly more taxing than dealing with the 8SE’s wobbly mount/tripod. Since planetary imaging utilizes short exposures on video, the precision required for tracking is less stringent than in deep-sky photography. By taking a vast number of frames, you can then use a program like RegiStax or AutoStakkert to select the clearest images (those captured in moments of steady atmospheric seeing and free of vibrations), then stack/process them for a crisp final image. 

As long as the target is somewhere in the field of view of the camera, you’re good to go. The 8SE’s poor-quality tracking and vibrations mean that the amount of frames you will lose to drift or wobbles is not going to be much different than attempting to finesse tracking with a Dobsonian mount by hand.

A sturdy tracking mount – be it a heavier-duty tripod for the 8SE or a GoTo-equipped Dobsonian – is a much more satisfactory experience than attempting to use the 8SE or a manual 8” Dob for planetary imaging, but again, neither are stopped in their tracks by their mounting limitations.

Like upgrading the C8 XLT to a different mount, there is a solution if you already own a manual Dobsonian but desire some motorized tracking capability, be it for planetary imaging work or less hassle during observation sessions. An equatorial platform can be placed beneath a Dobsonian, granting it up to ~45 minutes of tracking ability before requiring a reset. These platforms can either be crafted at home out of plywood or bought from various aftermarket sellers for a few hundred USD. An equatorial platform does not significantly decrease the stability of a Dobsonian and will not interfere with aiming it manually, either.