The Optical Tube
The Evolution 6 optical tube is the Celestron C6, which is a 6” (150mm) f/10 Schmidt-Cassegrain with a focal length of approximately 1500 mm. Due to the nature of SCT focusing systems, this may vary slightly depending on what accessories you are using. Like all Schmidt-Cassegrains, you adjust the focus by turning a knob to rack the primary mirror back and forth, and attach accessories with threaded adapters to the back, which can accept standard 1.25” or 2” ports or a camera T-ring.
The C6 is the latest and second-smallest of Celestron’s standard SCT models, having been released as recently as 2006-the original Celestron 5, 8, 11, and 14 were released in the 1970s, with the C9.25 following in the 90s. The C6 offers much more light gathering capability and resolution than the smaller C5, which it has largely sidelined on account of the C5’s large central obstruction, lack of HyperStar capability, and negligibly different physical size.
The C6 doesn’t really suffer from mirror flop like larger Schmidt-Cassegrains on account of its small size, and the focal length of 1500mm isn’t too claustrophobic. Though the C6 will vignette somewhat with 2” eyepieces or an f/6.3 reducer, you’re limited to about a 1 degree field of view, which is about what you get with the included 40mm Plossl eyepiece. This is not the widest field a 6” can provide, but it’s enough for most viewing purposes.
You will have to collimate the C6 from time to time by adjusting the secondary mirror. Contrary to popular opinion, collimating an SCT is not a particularly difficult or worrisome process, and you definitely do not need to send the scope back to the retailer or manufacturer to have them do it for you. You just need to adjust the 3 small screws on the secondary mirror housing while pointed at a bright star or artificial point source until everything appears concentric; our collimation guide offers more information and details. The aftermarket thumbscrews, or “Bob’s Knobs” advertised and recommended by some to make collimation easier, are unnecessary and actually lead to the scope holding collimation more poorly, requiring more frequent adjustment to keep the scope aligned.
The C6 optical tube attaches to the Evolution mount via a standard Vixen-style dovetail bar secured to the side of the tube, which means you can also put the C6 on a variety of other manual or electronically-driven mounts if you so desire.
The NexStar Evolution 6 includes two 1.25” barreled, Plossl eyepieces: a 40mm unit providing 38x and a 13mm ocular providing 115x. These are fairly good quality eyepieces and are enough to get you started, though you’ll almost certainly want more. A 1.25” prism star diagonal and a threaded visual back are provided with the Evolution 6 to accept these eyepieces.
For a finder, the Evolution 6 includes a simple red dot unit, which is really all you need to line the telescope up with a few bright stars and let the GoTo system take over.
Attaching a 2” diagonal to the Evolution 6 is technically possible, but ill-advised due to the balance problems a 2” diagonal and eyepieces will induce, as well as the fact that they will likely vignette with the Evolution 6 due to the C6 optical tube’s small baffle size.
The NexStar Evolution mount, at first glance, is a relatively simple affair—just an altazimuth fork arm with left-right, up-down pointing capability and computer-driven motors like the other Celestron NexStar telescopes. However, there’s actually quite a bit more going on than that, though how much of Evolution’s features are actually useful to most hobbyists is debatable.
For starters, the Evolution mount has clutches on both the altitude and azimuth axes, so the telescope can be pointed manually. However, you have to keep the clutches locked when operating the telescope’s motors. Using the telescope manually with the mount powered on will ruin the alignment of the mount to the night sky and thus all slewing/tracking accuracy. Without any slow-motion adjustments, etc., the manual movement of the mount is too jerky and inaccurate to let you actually use the telescope without powering it on.
Next is the built-in battery. Rather than having to deal with a separate power supply, charging it, connecting it to the Evolution, and worrying about the cord wrapping around the scope and/or unplugging itself-or burning through scores of disposable batteries-the Evolution mount has a built-in lithium battery, specifically a LiFePO4 unit. The charge lasts around 12 hours or so at best with a new battery. This might be a problem if you plan on going anywhere and plan on long observing sessions without access to reliable electricity to recharge the mount with. Running the mount’s WiFi also drains the battery faster.
LiFePO4 batteries are very safe, hold charge well, and last longer than a typical lead-acid battery pack or regular lithium-ion unit, but they don’t last forever. The supplied units in the Evolution mounts are not exactly the highest-quality units around and are only rated for 1000–2000 charge cycles, which might sound like a lot, but is still finite. Eventually, these batteries will fail. Some users with scopes around 5 years old are already reporting problems, and replacements cost $125 if you’ve had the scope for over 2 years or bought it used. It’s questionable whether the scopes will be serviceable forever, and the scope basically requires the battery to run; external power can run the mount forever, but it has to go through the battery in order to do so. So you’re going to have a bricked mount eventually, at which point you’ll have no choice but to put the optical tube on something else.
The Evolution mount is advertised as being more useful for astrophotography than the cheaper alt-azimuth mounted instruments from Celestron. In practice, it really isn’t going to compete with an equatorial mount, even if you put it on a wedge to track properly for long exposures. The high-quality worm gears in the Evolution do make for a more elegant experience when using the scope, however, as motions at high power are less jerky and the scope sounds like a high-tech device straight off the Starship Enterprise as opposed to a dying garbage truck as it moves around the sky. The gears will also last longer than cheaper mounts, though this is somewhat obviated by the limited battery lifetime outlined above.
Unlike many mounts, which are supplied with a calculator-like hand controller or simply a built-in WiFi network, the NexStar Evolution comes with both a hand controller and a built-in WiFi network. Thus, you can run the scope either off your smart device with the free SkyPortal App-or preferably SkySafari-or just with the controller. However, even if you mainly control the scope with your phone or tablet, you probably want to keep the controller around as it provides information on things like battery charge that are not available in apps. To actually use the mount, all you need to do is get the scope pointed at two reference stars, confirm them, and then it’ll automatically track and slew to whatever you want. You can select objects in the hand controller’s database, search for them in the app, or just tap on your screen to select and point at something.
The Evolution mount has two supplied accessory trays-one between the tripod legs and one on the mount head below the scope. In most cases, you’re better off keeping your stuff in a proper case and with a small side table to rest your extra gear on; leaving exposed gear on the tripod or mount head is a recipe for disaster, or at least for everything to get dew all over it in short order.
Lastly, the Evolution mount can accept any telescope with a Vixen-style dovetail thanks to its universal dovetail saddle, though you should make sure whatever you put on it can both balance properly and achieve clearance above the base of the mount, which limits you mostly to short, small instruments such as other catadioptric optical tubes.
Should I buy a Used Celestron NexStar Evolution 6”?
If you can find one in good condition with a reliable battery and electronics, there isn’t really anything wrong with buying a used Evolution 6”, but these scopes depreciate in value more over time due to the battery degradation and should be priced accordingly. Some of the oldest units are getting close to a decade old now.
As with any telescope, make sure the coatings on the telescope’s mirrors and corrector plate are in good condition; scratches on the corrector are acceptable but cracks are not. Bugs and detritus inside the telescope can be cleaned, but are a hassle. Make sure the focuser moves smoothly, and, of course, do your best to check that everything works well with the mount if possible.
The NexStar Evolution 6” is certainly a nice telescope, but there are some other options you might want to look over regardless of whether you are a beginner, looking to upgrade, or looking for a convenient and portable package.
The main reason we have mixed feelings about the Evolution 6” is largely due to the fact that, for all its bells and whistles, at the end of the day, you are really just getting an overly-equipped 6” telescope. Other 6” computerized telescopes exist at lower prices. There are better options than a 6” computerized telescope, including larger computerized instruments at this price, and it’s questionable if a 6” telescope is able to really show you enough to benefit from a GoTo mount in the first place.
- The Celestron NexStar 6SE quite literally duplicates the Evolution 6” in form and function. You can purchase a WiFi dongle for it for under $150, stick on a cheap lithium-ion battery for power, and get some nicer eyepieces while you’re at it. There is no difference in the views, setup and operation, or portability compared to the Evolution 6”. In fact, the 6SE is a bit lighter.
- A 6”, 8” or 10” Dobsonian will offer superior views to the Evolution 6”, doesn’t have any components to fail, doesn’t need power, and is easier to set up.
- The Sky-Watcher 8” and 10” GoTo Collapsible Dobsonians work manually, but also have full GoTo capability with a WiFi/app interface just like the Evolution.
- A 12” manual or computer-aided Dobsonian is also an option, albeit bulky and awkward to deal with. Truss-tube, collapsible, and GoTo units are also available for a higher price.
- If you’re interested in astrophotography, something like the Advanced VX 6” Newtonian from Celestron, or an a la carte setup built up from a variety of parts from different manufacturers, is a better choice.
- If you’re dead set on the Evolution line, we’d recommend at least spending a bit more on the 8” Evolution model, which doesn’t have a lower cost equivalent in Celestron’s other lines (the 8SE is wobbly and undermounted).
Aftermarket Accessory Recommendations
The NexStar Evolution 6” costs a lot of money, and as such, it wouldn’t be wholly inappropriate to spend a lot of money on accessories. But with a focal ratio of f/10, cheap eyepieces will do just fine, and you’re limited to 1.25” oculars anyway.
A 9mm “gold-line” will provide 167x with the Evolution 6”, which is a pretty good magnification for viewing the Moon, planets, and small deep-sky objects such as globular star clusters or planetary nebulae, along with double stars. You can also get a 6mm goldline, which will provide 250x-about the most you ever want to use. Using a power greater than 250x to 300x will merely give you a fuzzy, hard-to-focus, and dim image with no appreciable gain in detail compared to lower powers. On nights of poor seeing, even 200x might be too much magnification to get a consistently sharp image.
Something in the 18-25mm range to fill the gap between the stock 13mm and 40mm eyepieces is also a good idea for medium power. The Agena 18mm Starguider is our favorite pick in this category, providing 83x with the Evolution 6”.
The last optical accessory we recommend picking up is a UHC, or ultra high contrast nebula filter. By selectively permitting light from very specific wavelengths, UHC filters blacken the sky background and enhance the contrast of certain nebulae, which can help reduce the effects of light pollution and provide a slightly better view even under pristine skies. It won’t help with other deep-sky objects, however, so you should always try to observe under dark skies for the best possible views. The Orion 1.25” UltraBlock is our preferred recommendation for a UHC filter and can be threaded either onto the scope’s included star diagonal or any of your eyepieces individually.
Additionally, a dew shield for the Evolution 6” is de facto necessary if you plan on observing for any significant length of time, and also shields the scope from bugs, stray light, and curious hands-the former means you’ll actually get superior contrast at the eyepiece with the dew shield versus without it under most circumstances.
What can you see with the Celestron Nexstar Evolution 6?
The NexStar Evolution 6” can show you a lot, both within the solar system and of faint deep-sky objects, and its GoTo system means it takes less time to locate the latter for viewing.
You’ll have no trouble seeing the phases of Mercury and Venus with the Evolution 6”, though little else is visible on either of the interior planets. The Moon shows details just a few miles across under good seeing conditions, and you can locate thousands upon thousands of mountains, ridges, valleys, rilles, and of course craters. Mars’ ice caps are easy to see, and when the planet is at or close to opposition for a few months out of every two years you can easily see various dark markings covering the planet along with dust storms if any occur.
Jupiter’s cloud belts are easy to see with the Evolution 6”, along with the Great (but not necessarily red) Spot and its 4 largest moons: Io, Europa, Ganymede, and Callisto, which each appear as tiny disks and can be seen transiting across the giant planet, casting black shadows behind them pretty much every other day that the planet itself is visible.
Saturn’s rings are easy to see with the Evolution 6” at low power; pop in a high power eyepiece and the Cassini Division within them can be spotted too, along with a few cloud belts on Saturn itself and a handful of its moons. Uranus and Neptune are bluish star-like points on all but the best nights, with Uranus’ moons just out of reach due to their low brightness and Neptune’s moon Triton proving to be quite a difficult catch. Pluto is, similarly, just a bit too dim to spot with the Evolution 6”, though you’d have trouble distinguishing it from a faint star anyway.
The Evolution 6” has just enough aperture to resolve globular clusters like M13 and M15. Some globulars have different concentrations of stars than others, and some appear out-of-round, like M92. Others, like M13 and M22, have dust lanes. Don’t expect color, however, and you’ll need high magnification to resolve the stars clearly. Planetary nebulae, like globular clusters, excel even under less-than-ideal conditions, and the smallest ones may show colors. Open clusters are harder to fit in the Evolution’s narrow field of view, but sparkle with dozens or hundreds of colorful stars.
Dark skies are needed for viewing galaxies and most nebulae with any telescope. Under light-polluted conditions, the Evolution 6 will be able to locate a handful of barely-visible smudges if you can see them at all. But under dark skies, the Evolution 6” can begin to show you the spiral structure in some of the brighter galaxies and can reveal clusters with dozens more.
Emission nebulae like the Orion Nebula look great with the Evolution 6”, particularly if you use an aftermarket UHC filter to enhance the view and can get out into dark skies. Many also have star clusters embedded in them.