The C9.25 Optical Tube
The NexStar Evolution 9.25 telescope features Celestron’s C9.25 XLT optical tube, which is a 9.25″ (235mm) Schmidt-Cassegrain telescope with a focal length of 2350mm and an f/10 focal ratio. The C9.25 XLT is an updated version of the original C9.25, which came out in the 1990s. The mirrors and corrector plate have new coatings that let more light through. Compared to the smaller C8 XLT/NexStar Evolution 8, the C9.25 has about 34% more light-collecting surface area and 16% more resolution—not a huge gain, but certainly enough to be noticed at the eyepiece.
Schmidt-Cassegrain telescopes use spherical mirrors and a thin Schmidt corrector plate to make sharp images in a small tube assembly. This makes it possible to fit a very long focal length into a very short and stubby tube. The curvature of the C9.25’s mirrors is slightly weaker than that of a normal Schmidt-Cassegrain telescope, which gives the C9.25 a distinctively long tube and slightly less stringent tolerances for collimation and optical quality, which allows it to achieve images that are often sharper than is to be expected for a telescope of its size, especially when compared to other brands like Meade. The C9.25 XLT also has the added feature of being compatible with the Starizona HyperStar system to turn it into an f/2 Schmidt Camera.
Like most Schmidt-Cassegrain telescopes, the C9.25 XLT’s focus is adjusted by turning a knob at the back, which slides the primary mirror along a threaded rod inside the tube. This can sometimes cause “image shift” when focusing, especially at high magnifications or when imaging, which can make the object being observed appear to move within the field of view (and smearing long-exposure images). However, this issue is usually minimal with the C9.25 XLT.
It is also important to collimate the C9.25 XLT’s optics from time to time by adjusting the secondary mirror. It is generally not recommended to replace the built-in Philips head screws with thumb screws like “Bob’s Knobs”, as thumb screws may not be tight enough to maintain proper collimation and may be too tempting to adjust even when your alignment is already good. Collimating a Schmidt-Cassegrain telescope is not difficult and can be done relatively quickly, as explained in our collimation guide.
Like most Schmidt-Cassegrain telescopes, the C9.25 XLT has a threaded rear port designed to fit a variety of SCT accessories, such as focal reducers, star diagonals, and camera adapters. I appreciate that the C9.25’s baffle tube is big enough not to vignette with a 2” eyepiece, unlike the smaller C8 or C6 XLT telescopes.
Accessories
The NexStar Evolution 9.25 comes with two Plossl eyepieces with 1.25″ barrels: a 40mm eyepiece that offers 59x magnification and a 13mm eyepiece that provides 181x magnification. The 40mm has an apparent field of view of 43 degrees, while the 13mm has an apparent field of view of 52 degrees. These eyepieces are of decent quality and will suffice for getting started, although you may want to purchase additional eyepieces later on, along with perhaps a focal reducer or 2” star diagonal for a wider field of view. The Evolution 9.25 also includes a 1.25″ prism star diagonal and a threaded visual back to accommodate these eyepieces.
For finding celestial objects, the Evolution 9.25 comes with a simple red dot finder that will allow you to align the telescope with a few bright stars and then let the GoTo system take over for you. This type of finder is all you need for a computerized telescope such as the Evolution 9.25
The Celestron NexStar Evolution Mount
The NexStar Evolution mount is the largest of the various GoTo, single-armed alt-azimuth fork mounts Celestron sells for beginner telescopes. With a Vixen-style dovetail, you can attach the C9.25 XLT or other optical tubes to it, as long as the other optical tubes are well-balanced and don’t touch the base of the mount when the mount is pointed high into the sky.
The NexStar Evolution mount can be controlled either with the provided hand controller or with your smartphone or tablet (though you have to pick one or the other). To control the Evolution with your smart device, you simply connect to the mount’s WiFi network and use the free Celestron SkyPortal app or another app such as SkySafari Pro. The NexStar Evolution must be aligned on a few bright stars, regardless of how you interact with it, before it will begin automatically tracking and slewing to objects.
The NexStar Evolution mount has a LiFePO4 lithium battery built in. This eliminates the need for a separate power supply and the hassle of charging it, connecting it to the Evolution, and worrying about the cord getting tangled around the scope or unplugging itself. This is a useful feature, but the battery may not last long enough for long observing sessions without access to electricity to charge it. Additionally, running the mount via a smartphone over WiFi will drain the battery faster than if you stick with the hand controller.
It is uncertain whether the NexStar Evolution mounts will be serviceable indefinitely, and the Evolution mount requires electricity to go through the battery to run; external power can run the mount indefinitely, of course, but it must go through the battery to do so. Eventually, the battery will fail after a couple thousand charge cycles, and the mount will be unusable, at which point you will need to use the C9.25 XLT optical tube with a different mount or replace the battery. If and when Celestron discontinues or stops supporting the Evolution, these mounts will be useless door stops when they finally kick the bucket. LiFePO4 batteries like the ones in the Evolution mount are very safe and do last longer than lead-acid or regular lithium-ion batteries, but as with any modern electronics, the NexStar Evolution mount just isn’t built to last. The earliest-made units are already beginning to fail.
I notice that NexStar Evolution mount is different from most other alt-azimuth GoTo mounts made by Celestron due to its clutches on both the altitude and azimuth axes. This makes it possible to manually point the telescope. However, you must keep the clutches locked when using the motorized movement of the telescope. If you try to use the telescope manually while the mount is powered on, it will disrupt the alignment of the mount with the night sky and compromise the accuracy of tracking and slewing. In any case, without any fine adjustment cables or gears, manually moving the mount is too bouncy and imprecise to use the telescope effectively without powering it on.
As previously mentioned, the NexStar Evolution mount is a one-armed fork design. The C9.25 XLT optical tube is much heavier than the smaller C8 and C6 optical tubes supplied with the NexStar Evolution, and as such, Celestron provides a much bigger and heavier-duty tripod borrowed from the CPC and CGX mounts for use with the Evolution 9.25. This tripod is sturdy, but it’s quite heavy and takes up a lot of space in the car. The fork mount itself is also still a little wobbly despite the rock-solid tripod, and the C9.25 may have trouble clearing the base of the Evolution mount with a 2” star diagonal when pointed nearly directly overhead. While the NexStar Evolution 9.25 is certainly a decent package, the mount is definitely on the small side for what is needed for the C9.25 XLT, and the Advanced VX 9.25” SCT package is arguably more portable as well as steadier and free of clearance issues.
Should I buy a Used Celestron NexStar Evolution 9.25?
If you come across a used, complete Celestron NexStar Evolution 9.25 at a reasonable price, it may be worth purchasing as long as you thoroughly check it over. But you should avoid Schmidt-Cassegrain telescopes with broken front corrector plates because they can’t be fixed or replaced without replacing all of the optics, which can cost more than just replacing the telescope’s optical tube. If the NexStar Evolution mount is not functioning, you should expect to pay less for the package, but the Vixen-style dovetail on the C9.25 XLT optical tube means it’s easy to attach to another mount, such as another Evolution or Advanced VX. You should also check to make sure that the mirrors in the C9.25 XLT optical tube are free of corrosion and that the front corrector plate is free of fungus, which can permanently damage the glass and thus impair views. Accessories that come with the NexStar Evolution 9.25 are not very expensive to replace, so missing accessories are not a big deal.
Alternative Recommendations
The Celestron NexStar Evolution 9.25 is not ideal due to the limitations and awkwardness of its mount; we’d recommend considering the C9.25 Advanced VX package or a Dobsonian instead, if you can get one.
Under $1500
- The Apertura AD12/Zhumell Z12/Orion SkyLine 12 has significantly more aperture and, therefore, better performance than the NexStar Evolution 9.25 with a shorter focal length and wider field of view. The Dobsonian mount is sturdy and easy to use, and a variety of high-quality accessories are provided with the telescope.
- The Apertura AD10/Zhumell Z10/Orion SkyLine 10 is similar to the NexStar Evolution 9.25 in terms of deep-sky and planetary views, but it’s more portable than the Evolution 9.25 or a larger 12” solid-tubed scope. It is simple to set up and use and can be easily carried by one adult. Like the AD12/Z12, you get a nice accessory bundle provided too.
- The Explore Scientific 10” Hybrid Dobsonian lacks the accessories of the Apertura/Zhumell Dobsonians but is far more compact and features a superior mount design, with similar performance to the Evolution 9.25 and a wider field of view. The Explore Scientific 10” Truss Tube is essentially an upgraded 10” Hybrid with a dual-speed focuser and built-in cooling fans installed.
$1500-$3000
- The Sky-Watcher 12″ Flextube Collapsible Dobsonian is more compact than a standard 12” Dobsonian and likewise features an enormous leap in capabilities compared to the NexStar Evolution 9.25, without the complexity of a true truss tube. A GoTo version is also available with WiFi control like the Evolution 9.25, as well as the ability to be aimed freely manually too.
- The Explore Scientific 12″ Truss Tube Dobsonian is similarly compact in its design to the 10” model with the same great features and even more light-gathering capability. However, it needs some DIY modifications to perform at its best.
- The Celestron Advanced VX 9.25” SCT features the same optical tube as the NexStar Evolution 9.25 but is lighter, sturdier, and more portable, if perhaps a bit more complicated to set up and assemble on account of its equatorial mounting.
- The Celestron NexStar Evolution 8 is smaller than the Evolution 9.25 in aperture, but it’s a lot lighter, steadier, and the C8 XLT optical tube doesn’t lose too much capability compared to the C9.25. The 6” Evolution model is great too, albeit quite small and lacking in capabilities compared to the Evolution 8 and 9.25.
- The Celestron Advanced VX 8” SCT has some capabilities for deep-sky astrophotography unlike the NexStar Evolution models, though few advantages otherwise.
- The Celestron Advanced VX 7” Maksutov’s Maksutov-Cassegrain optics offer similar performance on the Moon, planets and double stars to the NexStar Evoluition 9.25, but for deep-sky viewing it is less capable.
Aftermarket Accessory Recommendations
The NexStar Evolution 9.25 is expensive, so you should accordingly have a high budget for additional accessories. Regardless of exactly what you end up purchasing for eyepieces, we recommend purchasing a 2” diagonal, such as the Apertura 2” dielectric mirror star diagonal, which screws directly onto the back of the NexStar Evolution 9.25’s optical tube. The stock Plossl eyepieces work well, but we recommend adding at least a wide-angle 2” low-power eyepiece like the Apertura 38mm SWA (62x), which offers a much wider and more immersive field of view (70 degrees vs. 43 degrees) than the stock 40mm E-Lux Plossl eyepiece at a similar magnification, allowing you to achieve a true field of about 1.1 degrees across in the sky, or 2x the width of the full Moon.
A high-power eyepiece in the 6-12mm focal length range like the Explore Scientific 8.5mm 82-degree (276x) is worth adding to your kit for viewing the Moon, planets, and double stars with your Evolution 9.25. The NexStar Evolution 9.25’s C9.25 XLT optical tube can also work well with cheaper Plossl and wide-angle eyepieces like SWA, SuperView, and goldline/redline oculars. The NexStar Evolution 9.25 can handle up to 500x magnification with perfect seeing conditions, although 300x is the typical upper limit, even on nights with good seeing, which can be rare.
We also recommend purchasing a UHC nebula filter, ideally in a 2” size that can be screwed onto a 1.25” adapter for use with either size eyepiece. The Orion UltraBlock is a good choice in this category, and it greatly improves the contrast of nebula views regardless of your overall sky conditions. However, as always, your best views of all deep-sky objects, including filtered views of nebulae will be obtained from dark skies free of light pollution.
A dew shield is essential for the NexStar Evolution 9.25 or any Schmidt-Cassegrain telescope. The thin Schmidt corrector plate cools down to below ambient temperatures quickly at night, and will attract dew easily, especially if you set up the telescope for more than an hour or two in even a relatively dry environment. The dew shield also keeps immediate sources of stray light and moonlight out of the telescope, improving contrast at the eyepiece, and prevents people or insects from accidentally touching the front corrector plate. A non-heated dew shield is sufficient for drier climates, but those in especially humid climates may want to consider a heated dew shield, which requires a simple dew heater controller to be used. In this case, it may also be advisable to get dew heaters for your eyepieces that can be plugged into the same controller.
What can you see?
The NexStar Evolution 9.25’s C9.25 XLT optical tube has enough light-gathering power to provide great views of deep-sky objects. Open star clusters, such as M35, M11, M46, and M38, are visible through the NexStar Evolution 9.25 regardless of light pollution levels due to their brightness. However, larger clusters like the Double Cluster, the Pleiades (M45), or the Beehive (M44) do not fit within the narrow field of view of the NexStar Evolution 9.25. With the NexStar Evolution 9.25, you can use high magnification to see the individual stars at the centers of globular star clusters such as M3 and M22, and observe their different shapes and structures, such as M13’s “Propeller” dust lanes or the tightly-packed core of M15. However, dimmer globular clusters may remain unresolved or simply can’t be seen at all in more light-polluted skies.
Galaxies and large nebulae are severely affected by light pollution, but the NexStar Evolution 9.25 can still show you the bright Orion (M42) and Lagoon (M8) nebulae even under relatively bright skies. Dark skies and/or a UHC filter improve the visible details and contrast in these nebulae, and allow you to observe other emission nebulae, such as the Swan (M17).
A filter does not help with galaxies, and under light-polluted skies, few are visible. Those that are still visible under brightly light-polluted skies lack detail, as the fainter regions have been washed out. However, under dark skies, the NexStar Evolution 9.25 can show you thousands of galaxies, including hundreds of individual objects in the Virgo Cluster, the dust lanes in galaxies like M82 and M104, and even hints of spiral arms in M101, M51 and M33 to skilled and patient observers.
The NexStar Evolution 9.25 will also be able to show you a variety of planetary nebulae. The NexStar Evolution mount will easily guide you to them, allowing you to see the greenish color of the Cat’s Eye nebula, for instance, or the well-known Ring (M57). The larger Dumbbell (M27) and Helix can be seen especially well under dark skies and/or with a UHC nebula filter.
The NexStar Evolution 9.25 is also well-suited for observing planets. The phases of Venus and Mercury are easily visible. The NexStar Evolution 9.25 provides spectacular views of the Moon, with the ability to see details just miles wide on a clear night. Thousands of mountains, craters, and ridges are easily visible regardless of the Moon’s phase or poor seeing conditions. When it is close to Earth and viewing conditions are acceptable, the NexStar Evolution 9.25 can show the polar ice cap of Mars and reveal dark markings on its surface. Jupiter’s Great Red Spot and its vivid cloud bands are also visible through the NexStar Evolution 9.25, and its moons can be clearly resolved as they transit in front of the planet next to their inky-black shadows.
As with any decent telescope, the NexStar Evolution 9.25 is capable of showing the rings of Saturn, along with the Cassini Division on a steady night, and the optics are good enough that the telescope may even reveal the Encke gap in the rings to scrutinizing observers on a steady night. Saturn also displays brown-beige cloud bands and around half a dozen of its moons. The teal disk of Uranus can be resolved through the NexStar Evolution 9.25, and it may be possible to glimpse one or two of its moons too, though they are very dim and close to Uranus’ glare. Neptune is often difficult to distinguish from a star, with the Evolution mount’s GoTo system helping to locate it amongst a sea of similar-looking pinpoints, and its moon Triton can be seen close by. The NexStar Evolution 9.25 can also show you Pluto as a faint, star-like pinpoint under dark skies.
Astrophotography Capabilities
The Evolution mount is barely adequate for the C9.25 XLT optical tube for visual use, and consequently, for deep-sky astrophotography on a wedge, the mount is not stable enough or accurate enough for imaging with the C9.25 XLT at its native f/10 or with an f/6.3 reducer. Using the telescope atop a wedge with the Starizona Hyperstar f/2 conversion kit, suitable cooled CMOS camera, and autoguiding should be acceptable, but there are much simpler, cheaper, and easier-to-use setups for shooting at 470mm focal length.
Fortunately, planetary astrophotography with the NexStar Evolution 9.25 is a pretty straightforward affair, thanks to the less stringent tracking requirements and lack of a need for a wedge. A good Barlow lens and high-speed planetary imaging camera, along with a laptop and capture software, are all you need for high-quality images of the Moon and planets.
