Celestron CGX 925 SCT Review: Recommended Scope

The C9.25 XLT Optical Tube

The Celestron CGX 925 SCT package features the Celestron C9.25 XLT optical tube, a 9.25” (235mm) f/10 Schmidt-Cassegrain telescope with a focal length of 2350mm, which can be reduced to 1480mm and f/6.3 with the Celestron f/6.3 focal reducer or to an f/2 470mm system with a Starizona HyperStar kit, the latter configuration being similar to the Celestron 8” RASA. 

The Celestron C9.25 XLT is one of the company’s best-selling Schmidt-Cassegrain telescopes, offering a significant increase in light-gathering and resolution over the 8” SCT, while still being fairly compact and portable. The C9.25’s slightly different optical configuration from the other Celestron SCTs features more weakly curved primary and secondary mirrors, which produce an unusually long tube but reduce the issues of coma and field curvature, while also improving collimation and manufacturing tolerances (essentially by magnifying errors less).

Collimating the C9.25 XLT is fairly easy, and involves adjusting three screws to tip and tilt the secondary mirror. This is a fairly infrequently-required process, and our collimation guide explains more. Focusing the C9.25 XLT, as with all of Celestron’s Schmidt-Cassegrain telescopes, is achieved with a knob at the back of the telescope, which moves the primary mirror and shifts the focal plane dramatically. This design can cause “image shift,” where the view appears to rock back and forth as the focus is adjusted, but newer C9.25 XLTs don’t have much of this problem. However, over long time spans (such as a few hours during a photographic exposure), the mirror can flop on its support and cause blurry stars as the frame either tilts or shifts out of focus. This is a major disadvantage for those who want a no-fuss astrophotography setup; the EdgeHD 9.25 has locks to prevent the problem and, as such, is a better choice for deep-sky astrophotography.

Accessories such as visual backs, focal reducers, and camera adapters can be attached directly to the SCT threaded port at the back of the C9.25 XLT’s tube. The C9.25 XLT bundled with the CGX 925 package comes with a CGE-style dovetail rail to fit the CGX or any other mount compatible with a CGE or Losmandy D-style plate, along with holes at the top drilled for a second dovetail and a carry handle on the back of the tube for easy transportation.

Accessories

The CGX 925 package includes a 9×50 finderscope, – much better than the 6×30 finder included with the CGEM II 800 SCT, though still not as good as a larger 60mm or 80mm finder. The scope also includes a 2” visual back, a 2” prism star diagonal, and a 23mm focal length, 2” diameter Luminos eyepiece with an 82-degree apparent field of view, yielding 102x and a true field of 0.8 degrees – slightly smaller than the angular diameter of the full Moon – with the C9.25 XLT. You will still want additional eyepieces for the C9.25 XLT, offering higher and lower magnifications for a wider field of view.

The CGX Equatorial Mount

The CGX is Celestron’s premium equatorial mount, designed to be a major improvement over the CGEM II in terms of mechanics, stability, and software features. The CGX has a stated weight capacity of 55 lbs, which means that it can handle up to 27-28 lbs of equipment for imaging purposes. As such, it has plenty of margin for handling long-exposure astrophotography with the C9.25 XLT telescope and f/6.3 reducer or f/2 HyperStar conversion, as well as any additional accessories such as a guide scope, camera, or dew heater. The CGX is a much better choice for dedicated imaging than the CGEM II and competes well with other mounts in its price range, such as the Sky-Watcher EQ8-R or the Losmandy G11. Our review of the CGX goes into further detail about its advantages and drawbacks when used for imaging.

The CGX has a dual dovetail saddle capable of accepting Vixen, Losmandy, and Celestron CGE style dovetail plates, the latter being used with the provided C9.25 XLT optical tube. The CGX uses a standard ¾” (20mm) counterweight shaft and comes with two 11 lb counterweights to balance the C9.25 XLT, with plenty of margin for additional weight from accessories. You can connect the mount to your PC with a USB cable and control it with software such as NINA via ASCOM drivers, and a standard ST4 port is built in for an autoguider, which you’ll need for deep-sky imaging with the CGX and any telescope. Additionally, the CGX mount allows you to connect Celestron’s add-ons such as the StarSense AutoAlign, SkySync GPS, and SkyPortal WiFi adapters. You can power the CGX with either AC or DC connectors, and a cigarette lighter DC cord is provided with the mount.

The CGX is not easy to set up for visual or imaging use, as it is very heavy and bulky – the tripod alone weighs 19.2 lbs, and the mount head weighs 44 lbs. After balancing the optical tube, adjusting the counterweights, and leveling the tripod, you can polar align with a polar scope or Celestron’s All-Star Polar Alignment method. With the NexStar+ hand controller or a suitable WiFi adapter/smart device, you align the mount with the sky. Simply center several alignment stars in the eyepiece and confirm them to complete the alignment process. You can then automatically slew to and track anything you select in the mount’s 40,000 object catalog.

Should I buy a Used Celestron CGX 925 SCT?

I think a used CGX 925 package can be a great deal, as older CGXs are identical to newer ones except for some cosmetic changes. Check to make sure that the mount powers on and operates smoothly, and that the C9.25 XLT telescope is free of corrosion or damage to the mirrors and corrector plate, which requires replacing the whole telescope or optical set to fix. Missing accessories, a missing hand controller, or a missing counterweight/bar are easily replaced but should accordingly result in a price reduction on a used item.

Alternative Recommendations

The Celestron CGX 925 SCT is a powerful telescope for the money, but it is not the most economical or convenient for any particular task. Deep-sky astrophotographers should consider a separate mount and optical tube package such as what’s outlined in our rankings, or at least upgrading to the EdgeHD 9.25 for serious imaging work, while for visual use or planetary imaging, we’ve picked a few options that might be a better fit:

• The Apertura AD12/Zhumell Z12/Orion SkyLine 12 offers almost double the light-gathering power and 30% more resolution than the CGX 925 SCT and includes a wide-variety 
• The Sky-Watcher 12” Collapsible Dobsonian is fairly compact when disassembled thanks to its collapsible tube and is available in both manual and GoTo versions, with the latter allowing for manual aiming thanks to its FreedomFind encoders.
• The Celestron CGX 800 EdgeHD is a better choice than the CGX 925 for deep-sky astrophotography, as it has a flatter and wider field of view, mirror locks, and no field curvature or coma at the edges of the field. It is also cheaper and lighter than the CGX 925 SCT, but of course has less aperture and resolution for visual use or planetary imaging.

Aftermarket Accessory Recommendations

The standard Celestron 0.63x focal reducer is necessary for any deep-sky imaging with the C9.25 XLT. It screws onto the back of the tube ahead of your camera or adapters and brings the scope down to f/6.3 and a focal length of 1480mm. You can also use a focal reducer for visual astronomy with the C9.25 XLT, but a 2” star diagonal and eyepieces are usually the preferred choice for achieving a wider field of view. Alternatively, a Starizona HyperStar will enable you to shoot with the C9.25 XLT at 470mm focal length, which increases tolerance for tracking errors and provides a very wide field. However, this option is expensive, and you are limited to using certain one-shot-color CMOS cameras and small sensor sizes with this configuration.

The C9.25 XLT can handle up to 400-500x magnification on a steady night, and you’ll want to be able to achieve a range of magnification with additional 2″ oculars, starting with a low power eyepiece such as Apertura’s 38mm SWA (62x) or Explore Scientific’s 30mm 82-degree (78x). The latter will have vignetting towards the edges of the field of view with the C9.25 XLT but offer a roughly 1-degree unvignetted true field. Additionally, a good UHC nebula filter, such as the Orion UltraBlock, will improve your views of nebulae with the C9.25 XLT under almost any conditions.

For higher power eyepieces, you can either use 2″ oculars or switch to 1.25″ ones with a suitable adapter. Explore Scientific’s 14mm 82-degree (168x) or, alternatively, a 15mm redline/goldline (157x) are both excellent choices for medium power eyepieces. Explore Scientific’s 6.7mm 82-degree (350x) or, alternatively, a 6mm redline/goldline (392x) are both great options for high power eyepieces. You could also use a medium-power ocular with a Barlow lens in lieu of a high-power eyepiece if you are planning on getting a Barlow for planetary imaging purposes anyway. 

The C9.25 XLT can benefit from the use of a dew shield to prevent condensation from forming on the front Schmidt corrector plate. Dew can not only obstruct views/images, but its contents – namely trace acids and other chemicals from industrial processes or pollen – can damage the StarBright XLT coatings or even the glass itself composing the corrector. Additionally, adding a dew shield can help reduce stray light entering the telescope, improve contrast, and protect the corrector plate from accidental touches and fingerprints. A flexible dew shield is inexpensive, can be rolled up for storage/transport, and is all that most people will need. However, a heated plastic or metal dew shield may be necessary for more humid climates. 

A polar scope, PoleMaster, or StarSense Pro are a must for the CGX, regardless of what you are using it for, as accurate polar alignment cannot be otherwise obtained except with All-Star Polar Align. Additionally, either an AC adapter or a rechargeable power supply such as the Celestron PowerTank Lithium Pro is necessary to use the CGX.

For imaging, a motor focuser and Bahtinov mask are highly recommended for use with the C9.25 XLT; Starizona’s HyperStar conversion is also available to bring the C9.25 XLT to f/2. However, the 9.25” RASA already includes this conversion and is cheaper, so a HyperStar is probably not worth purchasing. You will also need an autoguider setup in the form of a suitable guide camera and either a guide scope/off-axis guider for deep-sky astrophotography.

What can you see?

The C9.25 XLT telescope has a relatively small maximum unvignetted field of view of 1 degree when using either a 2” wide-angle ocular or 1.25” eyepiece and f/6.3 reducer, which is much smaller than the 2-degree field of view that 8-12” Dobsonian telescopes can achieve but about the same as that of a regular C8 XLT.  While larger open star clusters and nebulae may not be ideal to view with the C9.25 XLT as a result of this limited field size, some of the smaller open star clusters are spectacular in the eyepiece, as are many of the brighter globular star clusters from the Messier catalog, which display individual stars at high magnifications. Smaller planetary nebulae like the Ghost of Jupiter Nebula and Cat’s Eye Nebula show many details and colors, while larger emission nebulae such as Orion (M42), the Lagoon (M8), and the Swan (M17) can still be seen in great detail, especially under dark skies, and are further enhanced with a UHC filter.

Under light-polluted skies, galaxies viewed through the C9.25 XLT or really any telescope will appear as little besides washed-out smudges and are often hard to see at all. However, if you transport the telescope to a darker location, you can begin to resolve details such as hints of spiral arms, dust lanes (by far the easiest details to observe on account of their high contrast), and H-II regions in brighter galaxies from the Messier and NGC catalogs. Additionally, you can observe many galaxy groups and the various huge galaxy clusters in Virgo, Leo, Fornax, and Coma Berenices.

With the C9.25 XLT, you can get stunning views of the Moon and planets. The phases of Mercury and Venus, as well as dark markings and polar ice caps on Mars, are clearly visible. Jupiter’s cloud belts and the Great Red Spot show up sharp and colorful, with its four Galilean moons visible even at the 9×50 finder. At high power during frequently-occurring transits, the C9.25 XLT reveals their small disks along with their shadows moving across the planet’s cloud belts. Saturn’s rings, cloud belts, and a handful of moons are visible. The Cassini Division in Saturn’s rings can also be observed on a typical night of good seeing, as well as the Encke gap on an exceptional night. Uranus and Neptune show little besides their tiny round disks, with a couple of Uranus’ moons barely visible and Triton showing up fairly conspicuously next to Neptune. It is technically possible to observe Pluto with a 9.25” telescope like the C9.25 XLT under dark skies, and the CGX will easily locate it for you, but Pluto is already on the verge of being too dim for the most seasoned observers to spot and will continue to lose brightness as it grows more distant from the Sun.

Astrophotography Capabilities

If you’re looking to use the C9.25 XLT and CGX for deep-sky astrophotography, it can produce good results with almost any camera if an f/6.3 reducer and a suitable autoguider are used. A Starizona HyperStar will enable you to shoot with the C9.25 XLT at 470mm focal length, which increases tolerance for tracking errors and provides a very wide field. However, this option is expensive, and you are limited to using certain one-shot-color CMOS cameras and small sensor sizes with this configuration.

If you’re looking to do planetary imaging, the C9.25 XLT telescope is a great choice – though of course, a larger scope can resolve more under good seeing conditions. To make the most out of the C9.25 XLT for planetary imaging, you’ll need to pair it with a 2x to 3x Barlow lens, which boosts its focal length to between 4700mm and 7050mm for optimal image scale. You’ll also need a high-speed planetary video camera, such as the ZWO ASI224MC (which also doubles as a guide camera) and a laptop. With this setup and good seeing conditions, you can take beautiful photos of the Moon, Venus, Mars, Jupiter, and Saturn.