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Ranking 15+ Schmidt-Cassegrain Telescopes in the UK

Rank & ratings last updated by Zane Landers on

Schmidt-Cassegrain telescopes (SCT) were all the rage in the 1970s and 1980s when they were introduced, rivalled only by the Dobsonian telescope in popularity for both newcomers and experienced users. Today, I still see Schmidt-Cassegrain telescopes dominating midsize amateur and research observatories and I commonly see them at astronomy clubs and star parties that I take part in.

However, in today’s world, the SCT faces stiff competition from other telescope designs that are arguably superior in many aspects and thus have less variety than in years past. Gone is the rivalry between Celestron and Meade (which went defunct in 2024). Now none of the other telescope manufacturers besides Celestron offer SCTs.

SCT light path with C6 as base
Schmidt Cassegrain Light Path

Schmidt-Cassegrains use two mirrors—one concave and one convex—and a thin, unusually curved Schmidt corrector to achieve sharp images. This corrector may look like a flat windowpanebut is actually a precise, delicate, and hard-to-replace optical surface.

SCT optics are made in "matched" sets. This means that the corrector is made on what is basically a die. The shapes of the mirrors are then slightly tweaked to make up for any flaws in the way the corrector was manufactured. As such, breaking one of the three optical surfaces means that the other two also have to be replaced.

Most SCTs come in aluminium optical tubes and focus by moving the primary mirror back and forth to adjust the spacing between the mirrors, thus moving the focal plane by huge amounts while not actually moving the mirror very much physically.

A real SCT and its parts
A real Schmidt-Cassegrain cutaway with the parts marked. Image: Zane Landers

Almost all SCTs have standard threads at the back, to which accessories such as star diagonals, focal reducers, or camera adapters can be attached.

I've seen some users also attaching an external Crayford-type focuser to an SCT to provide a slightly stiffer focusing mechanism than the SCT's internal focuser.

What You Should Expect While Buying an SCT

A Schmidt-Cassegrain usually costs at least twice as much as a Newtonian reflector boasting comparable capabilities, if not more, be it a new or used model.

SCTs have very short and stubby tubes. This makes them more portable than basically any non-collapsable reflector telescope of the same aperture. However, the accompanying heavy-duty mount and tripod for an SCT may offset some of this difference in portability.

Because of their internal focusing mechanism and front corrector plate, SCTs are basically sealed internally if caps are kept on the scope.

If the telescope is kept covered, the mirror coatings are at little risk of degradation, provided the instrument is not in an extremely polluted, damp, or dirty environment. The mirror coatings on the oldest Celestron SCTs are over 50 years old, and most will probably last another 50. Most reflectors seldom have their mirror coatings last this long.

If debris or bugs enter our SCT or something breaks internally, solving the problem requires removing the corrector plate, a delicate process that takes steady hands, precision, and all sorts of precautions to re-seat the corrector correctly, or sending the scope back to the manufacturer for loads of money to have them fix it.

How the SCT Design Affects Our Viewing/Imaging Experience

The long focal ratio of SCTs (typically the focal ratio is f/10, with a few f/8 and f/11 models) means they are very easy on cheap eyepieces compared to a fast refractor or reflector, with far less coma, edge-of-field astigmatism, and other problems.

Most SCTs hold collimation better than mass-manufactured reflectors, particularly if the stock collimation screws are kept installed and well-tightened. Replacing the stock collimation screws with thumb screws, which I've seen some people trying, merely exacerbates the need to collimate more often.

Collimating an SCT isn’t insanely difficult but can only be done at night and requires tools and keeping the scope pointed at a bright star. Dedicated laser collimation systems for SCTs are expensive and complicated to use. Collimation only requires adjusting the secondary mirror, as opposed to both the primary and secondary mirrors.

SCTs have basically no chromatic aberration because of their front corrector plate.

SCTs don’t have a spider to hold their secondary mirror and thus don’t produce spikes on bright stars like a Newtonian reflector or some of the other catadioptric designs out there.

SCTs have large central obstructions because of their big secondary mirrors. This makes the contrast lower compared to Newtonians or Maksutov-Cassegrains, which have lower central obstructions.

The Schmidt corrector is thin, so an SCT will acclimate to ambient temperatures faster than a Maksutov-Cassegrain will.

But compared to a Newtonian reflector, a Schmidt-Cassegrain telescope still requires more time to cool down due to the large secondary mirror also needing to cool down and the corrector plate trapping warm air inside the tube.

Even a moderately sized SCT has a huge focal length (typically f/10). For example, Celestron’s C8 8” optical tube has a focal length of 2 metres (2000 mm)! In comparison, a typical 8” Dobsonian reflector telescope has a focal length of only 1200 mm.

At larger sizes, the long focal length becomes a huge issue. A 14” or 16” SCT has a tiny field of view compared to a typical Dobsonian of that aperture.

The long focal length of SCTs means they need more accurate tracking and guiding for astrophotography. An f/6.3 focal reducer helps here.

The long focal ratio of f/10 and such also requires long exposure times, magnifying issues in tracking and guiding when doing deep sky astrophotography. An f/6.3 focal reducer reduces this issue at the expense of possible vignetting with some cameras as well as cost.

But an f/6.3 reducer has its own set of issues.

SCTs actually require a lot of precision to focus due to the extreme curvature of their primary mirrors, which can be a pain when using high magnification or trying to do astrophotography.

To make matters worse, the primary mirror can shift on its rod during focusing, making the target appear to bounce around the field of view. The mirror could also flop over a long period of time, ruining a long-exposure image. This can be alleviated by locking the mirror in place during photographic exposures and/or attaching an external Crayford focuser to the back of the telescope, but either requires a significant amount of monetary expense and/or DIY work.

Older SCTs come on fork mounts or manual equatorial mounts, which require precise polar alignment in order to be used correctly and can be troublesome to aim manually—especially with the narrow field of view of the telescope itself. Newer computerised mounts may be less complicated, but they still frustrate the user and have questionable longevity due to their cheaply made components.

Rank Category: SCTs Under £600

Celestron StarSense Explorer DX 5" Schmidt-Cassegrain
Celestron StarSense Explorer DX 5” PushTo
£541 at FLO
StarSense DX 5" uses a very compact C5 optical tube, which is Celestron’s oldest SCT model in their lineup, dating back to 1971. With an aperture of 125 mm and a focal length of 1250 mm on the surface, it should be comparable in terms of views to a 6" aperture Newtonian reflector telescope. But because its huge secondary mirror blocks 40% of the aperture by diameter, the telescope's actual contrast and resolving power are much lower, and it can only gather light as well as a 4" reflector, not a 6" reflector.

The mount is, of course, easy to use thanks to the StarSense Explorer technology. StarSense Explorer technology shows us where our telescope is pointed in the sky by making use of the camera and gyroscope of my smartphone when it is attached to the mount, and then we have to physically move the telescope accordingly. Unlike GoTo, StarSense Explorer doesn't automatically point to and track the object.

Celestron Astro Fi 5 Inch SCT GoTo
Rank 2
3.9/5
The Celestron Astro Fi 5 is similar to the DX 5" in optics but is placed atop a fully computerised Astro-Fi mount. The mount is controlled exclusively via your smartphone or tablet with Celestron’s SkyPortal app or another app like SkySafari Pro
Celestron Nexstar 5 SLT GoTo
Rank 3
3.6/5

Rank Category: SCTs Between £600 and £1200

The 6" SCT shows us a fair amount of detail on the Moon and planets and performs wonderfully on deep-sky objects, especially under dark skies. I can properly resolve globular clusters and view thousands of galaxies, a few dozen of which have some kind of detail visible in them under dark skies.

Celestron NexStar 6SE SCT GoTo
£1,279 at FLO
The Celestron NexStar 6SE has some of the best value of any SCT package, and I even think of it as a reasonable alternative to a 6” or 8” Dobsonian. The NexStar 6SE is a bit chunkier than the NexStar 5SE but offers significantly more capability at only a slightly higher price and in a slightly larger package.

A 1” increase in aperture may not seem like much to bother with, but in the case of the Celestron NexStar 6SE, I can confirm that it's a much bigger deal than the specs would suggest. The 6SE's C6 optical tube has significantly more light-gathering ability, resolution, and contrast than the 5SE's C5. The optics tend to be made to a slightly higher standard of quality, and the whole tube is negligibly larger in physical size.

I was also able to use the telescope with an f/6.3 focal reducer for photography and a 2” star diagonal for visual, both without suffering from vignetting problems, which I believe provides a huge boost in value too.

The 6SE also uses a beefed-up version of the NexStar SE mount with a taller fork arm. All this being true, the scope is still small enough to carry on a plane with the tube attached to the mount!

As with the 5SE, only a single 25mm Plossl (60x) and a basic 1.25” visual back, diagonal prism, and red dot finder are included, so you’ll want to add more accessories later on to get the most out of the scope.

Celestron StarSense Explorer DX 6" SCT PushTo
Check Amazon Price
The StarSense Explorer DX 6" SCT's C6 XLT optical tube, as seen in the NexStar 6SE, is an excellent telescope, and the StarSense Explorer DX mount provides a sturdy and easy-to-use lightweight mounting for it, though you may prefer a different telescope with motorised tracking or greater aperture. The StarSense Explorer technology, of course, makes finding targets a breeze with this scope.
Celestron NexStar 5 SE SCT
Celestron NexStar 5SE GoTo
The NexStar 5SE is my least favourite Schmidt-Cassegrain out there, as it is a bit small and full of compromises. But I'd say that it does the job for those who must have an SCT for £1000. The NexStar 5SE uses the same Celestron C5 optical tube as the above-mentioned StarSense Explorer DX 5".

The 5SE uses a smaller version of the NexStar SE mount and is controlled with a provided hand paddle. It requires a fair amount of setup, but once working, it automatically slews to any target of my choosing from its database of 40,000 objects and tracks them pretty accurately too.

A built-in equatorial wedge to use the scope in an equatorial configuration for long exposure photography is provided, but I felt that it is of little use due to its complete lack of fine movement adjustments in the mount and the C5 optical tube’s inability to properly illuminate a camera sensor with an f/6.3 focal reducer (arguably necessary for long exposures). You should also note that the 5SE is limited to 1.25” only accessories, despite the ability to physically attach a 2” diagonal.

Celestron Nexstar 6 SLT GoTo

Rank Category: SCTs Between £1200 and £2000

Celestron NexStar Evolution 6 Telescope
Celestron NexStar Evolution 6 SCT GoTo
£1,652 at FLO
The NexStar Evolution 6 adds a lot of bells and whistles compared to the above-ranked NexStar 6SE, but the views are largely the same. The NexStar Evolution 6 uses the same optical tube and hand controller as the 6SE but adds a lot of bonus built-in mechanical features. I also experienced it to be a bit more convenient to set up than the 6SE.

The Evolution mount has clutches, which can be unlocked to point the scope manually if power is lost, a built-in rechargeable lithium-phosphorous battery, and can be controlled with either the included hand paddle or my smartphone/tablet.

The scope also has an eyepiece rack and is slightly easier to assemble and transport. Like the 6SE, I can bring the tube and mount head assembly as carry-on luggage in a case.

It comes with 40mm and 13mm 1.25" Plossl eyepieces, and as with the 6SE, a 1.25” visual back, prism star diagonal, and red dot finder are also included. These accessories are enough to get you started.

Celestron Advanced VX 6" SCT GoTo
Rank 2
4/5
I think that the C6 optical tube is best with either a HyperStar unit or an f/6.3 reducer for deep-sky astrophotography, but it is still a reasonable scope to start with and works well on the Advanced VX mount. However, setting up this relatively small scope on a clunky, big, and complicated mount for visual use is simply overkill in my opinion.
Celestron Nexstar Evolution 5 SCT GoTo
Rank 3
3.8/5
Celestron Nexstar 8SE SCT GoTo
Rank 4
3.7/5
While we'd still call it a decent pick, the NexStar 8SE’s mount is less than ideal due to its rather small tripod legs and lightweight single-arm fork design. We’d recommend stepping up to the 8” NexStar Evolution if you must have an 8” GoTo scope.

Rank Category: SCTs Between £2000 and £2500

Celestron 8" NexStar Evolution Computerized Telescope
Celestron NexStar Evolution 8 SCT GoTo
£2,195 at FLO
The NexStar Evolution 8 is my favourite of the various packages Celestron offers its beloved 8” Schmidt-Cassegrain optical tube, the C8, as. I’d skip over the cheaper but popular NexStar 8SE due to its inadequate mounting. The 8” Evolution model has the same mount and accessories as the above-ranked 6” Evolution, but the included C8 optical tube provides significantly more light gathering and resolving power than the C6 without significantly adding bulk.

The Evolution mount provides a rock-solid support for the 8” optical tube; the same cannot be said of the cheaper alt-azimuth GoTo mounts provided with some other models.

The same accessories as the 6” Evolution are provided with the 8” model. However, the C8 would really benefit from a 2” diagonal and accessories to get the widest field possible at low magnifications, so I’d definitely recommend adding one if you can.

I also like that the 8” Evolution can still be transported on a plane as with the 6” model, but I need to put the mount head in luggage and only bring the tube as a carry-on.

Celestron Advanced VX 8″ SCT GoTo
£2,469 at FLO
The Advanced VX 8” isn’t nearly as compact nor convenient as the Evolution 8, but it offers identical views with the perks of some astrophotography capabilities later on. The Advanced VX 8” is simply Celestron’s C8 optical tube (the same is used in the above-ranked Evolution 8) bundled with Celestron’s Advanced VX German equatorial mount.

The AVX is a computerised GoTo mount that tracks on an astrophotography-friendly equatorial axis instead of an alt-azimuth like the NexStar Evolution. However, setting it up does require more assembly and effort than an alt-azimuth mount.

The whole AVX 8″ SCT package is a bit more cumbersome to transport as well. But once set up, the Advanced VX 8” works great for lunar and planetary astrophotography. For deep-sky astrophotography with a DSLR or cooled camera, a focal reducer and autoguider are necessary to get good results. So make sure to factor those into your budget as well.

Not a lot is included with regard to accessories, and you’ll want to purchase at least a few additional accessories to get the most out of this instrument, whether it’s for visual astronomy or astrophotography.

Rank Category: SCTs Between £2500 and £3000

Celestron Advanced VX 9.25" Schmidt-Cassegrain Telescope
Celestron Advanced VX 9.25” SCT GoTo
£2,849 at FLO
Celestron’s 9.25” optical tube packs just a bit more punch than the C8 but without outgrowing you in the process. The Advanced VX 9.25”, like the 8”, can be used for some astrophotography, though the C9.25 is a bit long in focal length and heavy to be used for long exposures with this mount. The C9.25 is just a bit sharper on planets and gathers slightly more light than the 8” model, but only weighs a bit more.

The C9.25’s slightly different optical design makes it a bit easier to focus, and some claim it has better optics too, though I think this is partly due to the slightly more lax collimation tolerances of the scope.

As with the 8” Advanced VX kit, not a lot is included with regard to accessories.

The C9.25 is about at the limit of what the VX can hold, and as such it isn’t really usable for deep-sky astrophotography, but shots of the Moon and planets are perfectly doable. From my experience, the AVX mount works best with a scope smaller and shorter in focal length than the C9.25, such as a 4” refractor or 6” Newtonian reflector.

Celestron NexStar Evolution 8 EdgeHD with StarSense SCT GoTo
Rank 2
4.1/5
The NexStar Evolution 8” EdgeHD w/StarSense adds EdgeHD optics to the NexStar Evolution 8” package, along with Celestron’s StarSense auto-align technology. Since the Evolution mount isn’t designed for astrophotography, I didn’t benefit much from this improvement. These conveniences are arguably not worth the price tag, but it’s a nice scope nonetheless. More significant is the addition of Celestron’s StarSense auto-aligning system, which aligns the telescope with stars without any input from the user—just set it up, level the tripod, and turn it on. The StarSense system does require a completely clear night sky free of clouds or obstructions such as trees or buildings, however. Additionally, with the StarSense technology active, you are limited to using Celestron’s standard SkyPortal app to control the telescope, which lacks crucial features like a red-tinted display option and far fewer catalogued objects. Otherwise, the performance, operation, and accessories are the same as the regular NexStar Evolution 8”.
Celestron Advanced VX 8″ EdgeHD SCT GoTo
Rank 3
3.9/5
The 8” EdgeHD model is a significant improvement over the regular C8 for astrophotography, though the difference at the eyepiece might be hard to spot. The EdgeHD version of the 8” Advanced VX Schmidt-Cassegrain adds Celestron’s EdgeHD optics, which provide a significantly flatter field and sharper images than the standard C8 8” Schmidt-Cassegrain. It is designed with imaging in mind thanks to its equatorial mount and EdgeHD optics. Though the Advanced VX is a bit on the light side for serious imaging with an 8” telescope, it will do the job. The views are splendid, too. For visual astronomy, you probably won’t notice a huge difference from the regular 8” SCT model besides a slightly improved cool-down time for the optics, but the EdgeHD’s flattened field is helpful for long-exposure astrophotography. As with the regular version, however, for best results, an astrophotography setup really requires a focal reducer, autoguiding, and a polar scope for easy and accurate polar alignment.
Celestron NexStar Evolution 9.25 SCT GoTo
Rank 4
3.9/5
The NexStar Evolution 9.25” is actually a bit harder to grapple with than the Advanced VX 9.25” package, but the actual process of setting it up is a bit simpler, and the scope is overall just a bit easier to use. The NexStar Evolution 9.25” has all of the same features and accessories as the Evolution 6” and 8” models, but with the addition of the C9.25 optical tube. However, the C9.25 is a bit big for the Evolution mount, and the mount has been accordingly beefed up by including a heavy-duty tripod. If you prefer the simplicity and convenience of the Evolution mount compared to the less cumbersome Advanced VX mount, the NexStar Evolution 9.25” is for you.
Celestron CPC 800 GPS SCT GoTo
Rank 5
3.8/5
The CPC 800 is a little less fancy than the 8” NexStar Evolution but comes on a beefier mount and can be used for astrophotography on an equatorial wedge (sold separately).

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