Celestron NexStar 4SE vs NexStar 8SE

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Written By: Zane Landers
Category: Learn

The Celestron NexStar 4SE and Celestron NexStar 8SE are the smallest and largest telescopes in the Celestron NexStar Special Edition (SE) lineup. The NexStar 4SE is the only one of the four telescopes in the NexStar SE line (4SE, 5SE, 6SE, and 8SE) to be a Maksutov-Cassegrain rather than a Schmidt-Cassegrain, as well as the only one with a built-in diagonal rather than standardized rear threads and a visual back.

The NexStar 4SE and 8SE have little in common besides their similar mount designs and onboard software. The mount and tripod each is equipped with are drastically different in design; the optical design is different; and the 4SE is fundamentally designed for different purposes than the 8SE. The two are also our least-recommended picks out of the NexStar SE lineup, thanks to the relative lack of capabilities offered by the 4SE for its price and the fact that the 8SE is simply too big for its relatively flimsy mount and tripod to hold steady.

Celestron Nexstar 4SE Maksutov vs NexStar 8SE SCT
ScopeApertureMount TypeMax FOVMaximum MagnificationStabilityQuality

Bottom Line

The NexStar 4SE and 8SE are actually good telescopes, but the GoTo mounts and tripods that both sit atop are poorly suited for the job. The 4SE’s mount is too big and time-consuming to deal with, while the 8SE is lightweight and wobbly. The NexStar SE mounts are also rather outdated and lacking in features compared to newer GoTo mounts with features like Wi-Fi and built-in slip clutches. While the NexStar 8SE, of course, boasts massive performance advantages over the much smaller 4SE, neither is a telescope we’d particularly recommend to beginners or seasoned astronomers. They simply aren’t worth the money. Consider purchasing the NexStar 6SE instead, or perhaps a different telescope design, such as a Dobsonian.

Optics Comparison

The NexStar 4SE is a Maksutov-Cassegrain telescope that uses a spherical primary mirror, a convex secondary mirror, and a corrector lens. Maksutov-Cassegrains’ corrector lenses have a meniscus shape, similar to a contact lens, with a concave surface on one side and a convex surface matching its curvature on the other. The 4SE is like most Maksutov-Cassegrains in that the secondary mirror has the same curvature as the corrector. This means that instead of a separate piece of glass, the secondary mirror is an aluminized reflective part of the corrector. The light then reflects through a hole in the primary mirror. The Maksutov-Cassegrain design works best when designed to produce focal ratios above f/12, which means it’s no surprise that the 4SE is an f/13 instrument with a 1325mm focal length given its 4” (102mm) aperture.

Light path of Gregorian Maksutov Cassegrain
Maksutov Light Path

Schmidt-Cassegrain telescopes like the NexStar 8SE are similar to the Maksutov-Cassegrain in basic design and utilize a similar pair of spherical concave and convex mirrors. However, they substitute the Maksutov meniscus lens with a thin, almost-flat piece of glass called a Schmidt corrector, which can be mass-manufactured out of cheap sheet glass without the need to grind and polish two faces of a very thick piece of specialized and likely expensive crown glass. The secondary mirror sits on an adjustable cell attached to the middle of this corrector.

The NexStar 8SE uses the Celestron C8 telescope optical tube, which has been around since the 1970s. This telescope is sold atop a variety of other mounts from Celestron, and its universal Vixen-style dovetail bar means that you can use it on practically any mount you wish. Optically, the C8 is an 8” (203mm) diameter f/10 Schmidt-Cassegrain telescope with a resulting 2032mm focal length. The main difference between a C8 made today and one made in 1970 is that the new C8 XLTs have better optical coatings and a secondary mirror that can be taken off, which lets a Starizona HyperStar system be used. The HyperStar converts the C8 XLT to an f/2 Schmidt camera optical configuration for astrophotography, though you’d need to use it on a different mount than the one provided with the 8SE.

The NexStar 4SE accepts only 1.25” eyepieces. It uses a built-in flip mirror star diagonal instead of the more common approach of a standard screw-on visual back/adapter that holds a removable 1.25” star diagonal. There is a threaded rear port on the 4SE to use when the flip mirror is toggled off, but it is largely useless and not worth buying the required adapters to attach anything to it.

The 1.25”-only eyepiece format combined with the 4SE’s 1325mm focal length limits the maximum true field of view with a low-power eyepiece, such as a 32mm Plossl, to 1.2°, or about two and a half times the apparent width of the full Moon in the sky. A 1.2° field isn’t terribly narrow, but compared to a wide-field 4” telescope, it is far more constraining if you are trying to view large nebulae or open star clusters, which under a dark sky constitute the majority of the interesting deep-space objects you can spot through a smaller telescope.

The pointless flip mirror attached to the back of the NexStar 4SE is also a concern when it comes to longevity. Over time, if this mirror were to corrode or get damaged, there is pretty much nothing you can do about it unless the manufacturer is still willing to service the telescope. More immediately concerning is that the mirror does not always return to an exactly 45-degree angle when the “flip mirror” knob is turned back and forth, which causes the telescope to basically go out of collimation, blurring and vignetting the view. The tilt of the optical path when this happens also means that the view at the eyepiece is suddenly out of sync with the apparent position of the 4SE’s mount and/or red dot finder. This can be a nuisance if you are not aware of what is going on, and fixing it may require taking apart the whole flip mirror housing.

The NexStar 8SE is not technically constrained to 1.25” eyepieces/diagonals thanks to its universal rear SCT threads, but the undersized interior baffles inside the telescope mean that anything with a field stop of over 35mm—or about a 1° area of sky—will be vignetted to some extent. So in practice, both of these telescopes are limited to a similar maximum field, and the C8 is debatably worth using with 2” oculars.

Both the 4SE and 8SE use a moving-mirror focus system, which means that the eyepiece/diagonal doesn’t physically move back and forth when you adjust focus but rather the primary mirror does so inside the telescope. The disadvantage here is that in some cases, the mirror can shift around and wobble as you adjust focus, leading to an apparently bouncy image. At high magnifications, your target may appear to move out of the field of view, making precise focusing difficult. Fortunately, neither the 4SE nor 8SE typically have this problem in abundance.

In terms of performance, anyone with a basic understanding of telescopes would know that the C8 XLT/8SE offers twice the resolving power of its half-sized cousin and about four times the light-gathering power on account of offering four times the surface area with its primary mirror. This means that the 8SE offers vastly brighter views of deep-sky objects than the 4SE. Likewise, on high-resolution targets like the Moon, planets, or double stars, the 8SE reigns supreme as long as you’ve properly collimated it—a seldom-required process that our collimation guide explains in detail. Speaking of collimation, the 4SE can also be collimated with 3 small screws at the back end of the tube, but unless you literally drop the telescope tube, it is unlikely to need such adjustments.

The only performance advantages of the 4SE over the 8SE would come under suboptimal conditions. If you haven’t had the time to let your scope adequately cool down for high-power observing, the 4SE is much quicker to acclimate to cold nighttime temperatures for sharp images. Likewise, the smaller aperture of the 4SE means that on a night of very bad atmospheric turbulence, the larger 8SE has to look through more columns of rapidly moving air and thus may present a blurrier view (though the view through the smaller telescope will still be sub-par). On nights when the sky is steady and you aren’t in a rush, the 8SE will prove superior to the 4SE on high-resolution targets, and it is always far better for deep-sky observing.

Accessories Comparison

The NexStar 4SE and 8SE both come with a red dot finder for aiming manually and aligning their mounts’ GoTo systems. You also get a single eyepiece with each, Celestron’s 25mm “E-Lux” 1.25” Plossl. This eyepiece has a ~52° apparent field of view, therefore yielding 43x and an approximately 1° field with the 4SE or 81x and a 0.64° field with the NexStar 8SE. The 8SE also includes a 1.25” thread-on SCT visual back and a 1.25” prism star diagonal to insert your eyepiece in, while the 4SE’s built-in flip mirror obviates the need for either of these items.

The single 25mm E-Lux Plossl eyepiece provided with the NexStar 4SE and 8SE works fine thanks to the slow focal ratio of both telescopes, but doesn’t yield the maximum field of view possible with a 1.25” ocular like a 32mm Plossl. And of course, 43x or 81x is hardly enough magnification for optimal lunar and planetary views, for which magnifications of at least 100-200x are ideal. However, both of these telescopes are expensive enough that aftermarket eyepieces are hardly much of an additional cost, and it’s almost always assumed that you already possess or will obtain more eyepieces when you buy pricier telescopes anyway.

Mounting Comparison

At first glance, the NexStar 4SE and 8SE appear to share the same mount and tripod, but the 6SE/8SE mount is significantly beefier than the smaller 4SE/5SE mount.

The mounting supplied with the 4SE and 5SE has a built-in “equatorial wedge,” allowing you to nominally convert the telescope to an equatorial configuration. Besides the fact that it has no side-to-side adjustment and no fine-tuning mechanism for the latitude setting bar, it is rather unclear as to why you would use the 4SE or 5SE in this manner. Neither the 4SE optical tube nor the NexStar mountings are exactly capable of being used for deep-sky astrophotography, let alone designed to do the job well.

The NexStar 8SE uses a tripod and mount head that outwardly resemble the 4SE mount but with a longer fork arm and a beefier tripod. The 4SE/5SE mount uses 1.25” diameter tripod legs, while the 6SE/8SE mount uses 1.5” legs. Still, this is not enough to properly support the 14-pound C8 XLT optical tube. Even with the tripod legs retracted all the way, the 8SE is considerably bouncy, which makes focusing at high magnifications rather frustrating; the vibrations and wobbles also reduce its automatic pointing and tracking accuracy over time.

Ironically, the NexStar 4SE suffers from essentially the opposite problems of the 8SE when it comes to the design of the mount and tripod. The NexStar 4SE optical tube weighs a mere 6 lbs, but the 4SE mount and tripod weigh about 20 lbs by themselves, and the fork arm of the mount is rather wide. This makes the telescope extremely heavy and cumbersome for a mere 4” aperture. Full GoTo, i.e., the ability to point automatically at faint deep-sky objects, is also not particularly necessary for a telescope designed mainly with the Moon and planets in mind and only capable of revealing the brightest and most familiar deep-sky targets. A simple clock drive like the Sky-Watcher Virtuoso uses is really all you need for a small Maksutov-Cassegrain telescope.

Both the 4SE and 8SE use the Celestron NexStar+ hand controller to operate their mount’s tracking/pointing features, though you can plug in an aftermarket Wi-Fi dongle if you would prefer to control either telescope with your smartphone or tablet instead. The NexStar+ hand controller is fine, but the design of these devices has not fundamentally improved since the late 1980s. In any case, the NexStar 4SE and 8SE have not significantly changed since 2007, and apart from their new orange paint job and a switch to an inferior tripod, both have been offered since 2003 as the NexStar 4GT and 8i, respectively.

Unfortunately, unlike newer GoTo mounts, the NexStar mounts do not have clutches or dual encoders, meaning that you cannot aim them manually. A full leveling and star alignment procedure must take place to set up tracking, let alone the GoTo functions. This is especially annoying with the 4SE, which should be a “grab n’ go” telescope. In practice, the time it takes to set up the NexStar 4SE’s mount, as well as its considerable weight, obviates the convenience of its lightweight, compact Maksutov-Cassegrain optical design.

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