Telescope Comparison
Celestron EdgeHD 8" + CGX vs Celestron RASA 8"
The Celestron EdgeHD 8" + CGX is a complete setup. The Celestron RASA 8" needs a mount before it's usable.
First light
Celestron · 203mm · £2,999
The automated deep-sky platform
- 203mm schmidt-cassegrain on a computerised mount with motorised tracking
- Good for: Moon, planets, bright nebulae, star clusters, and deep-sky objects
- GoTo system finds any object in its database after initial star alignment — no star atlas needed
- Tracking motors keep objects centred as Earth rotates — useful above 100×, essential for photography
- 28kg total — requires a fixed garden spot or car transport
Celestron · 203mm · £1,799
The custom-rig optical tube
- 203mm schmidt-cassegrain — optical tube only, no mount included
- 406mm focal length at f/2
- Requires a compatible mount before you can observe anything
- Best for: observers who already own a suitable mount or are building a specific imaging rig
- Not a complete purchase — budget at least £100–300 extra for a mount before observing
The full picture
The numbers that separate these two scopes — and what they mean at the eyepiece.
Aperture
Equal light-gathering. Aperture won't settle this comparison — the mount, focal ratio, and observing experience are what differ.
Focal length
Celestron EdgeHD 8" + CGX's longer focal length reaches higher magnification with the same eyepiece — better reach for planetary detail. Celestron RASA 8"'s shorter focal length gives a wider true field — better for large open clusters and extended nebulae.
Focal ratio
Celestron RASA 8"'s faster f/2 delivers wider fields with any eyepiece — better for open clusters and large nebulae. Celestron EdgeHD 8" + CGX's f/10 provides more magnification per eyepiece — better for fine planetary detail.
Mount type
Celestron RASA 8" has no mount — add a compatible mount before you can observe. Celestron EdgeHD 8" + CGX is a complete ready-to-use system.
Weight (OTA)
Similar optical tube weight. Any portability difference between these setups comes from the mount, not the tube itself.
Optical design
Both Schmidt-Cassegrain designs — versatile, compact, good for planets and deep-sky. Differences come from aperture and mount.
At the eyepiece
| Target | Celestron EdgeHD 8" + CGX | Celestron RASA 8" |
|---|---|---|
| Planets | ||
| Moon | Excellent 203mm aperture and f/10 focal ratio deliver superb high-magnification lunar detail — rilles, central peaks, and subtle shadow gradients | Not recommended Imaging-only instrument with no visual capability; 406mm focal length gives very small lunar image scale even for imaging |
| Saturn | Excellent 203mm aperture and 2032mm focal length resolve the Cassini Division, cloud banding on the disc, and multiple moons | Not recommended No visual use possible; 406mm focal length produces a tiny planetary disc even with high-resolution cameras |
| Jupiter | Excellent Multiple cloud belts, festoons, the Great Red Spot, and Galilean moon shadow transits visible in good seeing | Not recommended Far too short a focal length for planetary imaging; no visual capability |
| Mars | Good At 203mm, polar cap and dark surface albedo features visible at opposition; benefits from steady seeing at these magnifications | Not recommended Extremely small image scale at 406mm; the scope is fundamentally unsuitable for planetary work |
Deep sky | ||
| Orion Nebula (M42) | Good Bright core and Trapezium resolved easily, but 2032mm focal length crops the full extent of the nebula — only the central region fits the field | Excellent 203mm aperture at f/2 captures the full nebula and running man in seconds; HDR blending reveals both bright core and faint outer wisps |
| Andromeda Galaxy (M31) | Moderate At 2032mm focal length, only the bright nucleus and inner core are visible — the outer spiral arms and full extent are well beyond the field of view | Excellent 406mm focal length frames the entire galaxy including companion galaxies M32 and M110 on an APS-C sensor; f/2 speed reveals outer spiral arms quickly |
| Open clusters | Moderate Most open clusters overfill the narrow field; compact clusters like M37 work, but the Pleiades and Hyades are far too large | Excellent Wide field at 406mm perfectly frames large clusters like the Double Cluster and M45 with surrounding nebulosity |
| Globular clusters | Good 203mm begins to resolve individual stars at the edges of M13 and M3; the high magnification suits these compact targets well | Good 203mm aperture resolves outer stars in imaging; short focal length means globulars appear small but well-exposed |
| Faint galaxies | Good 203mm gathers enough light to reveal structure in brighter galaxies — dust lanes in M104, arms in M51 — and the narrow field suits their small apparent size | Good 203mm aperture and f/2 speed reveal faint galaxy groups and tidal streams in modest integration times; small image scale limits detail on individual galaxies |
| Milky Way / wide field | Not recommended 2032mm focal length produces an extremely narrow field — entirely unsuitable for wide-field star sweeping | Excellent 406mm at f/2 is purpose-built for wide-field imaging; captures large Milky Way structures like the Cygnus region in a single frame with extraordinary speed |
Other | ||
| Double stars | Excellent 203mm aperture at f/10 delivers clean diffraction patterns and high resolving power; tight pairs like Porrima and Albireo are well split | Not recommended No visual capability; double star work requires visual observation or very long focal lengths for imaging |
| Astrophotography (deep sky) | Good Flat-field corrector and equatorial GoTo mount make this a capable deep-sky imager, but native f/10 demands long exposures and precise guiding; the 0.7x reducer brings it closer to Excellent | Not applicable |
| Astrophotography (planetary) | Excellent 203mm aperture and 2032mm focal length are ideal for high-resolution planetary lucky imaging with a high-speed camera | Not applicable |
| Large emission nebulae (Veil, North America, Heart) | Not applicable | Excellent The RASA 8's defining use case — f/2 speed with 406mm focal length frames and deeply exposes multi-degree emission nebulae in a fraction of conventional integration times |
| Narrowband imaging (Ha, OIII, SII) | Not applicable | Excellent f/2 speed makes narrowband practical in short subs; requires filters rated for fast focal ratios to avoid halos |
The real tradeoff
Both scopes are capable. The question is which one fits the way you actually observe.
Celestron EdgeHD 8" + CGX
- You'll spend your first clear nights simply looking — Saturn's Cassini Division, Jupiter's festoons, lunar rilles — because this scope is genuinely rewarding at the eyepiece before you ever attach a camera.
- When you do image, you're working at 2032mm (or 1422mm with the reducer), which means autoguiding is non-negotiable, polar alignment must be precise, and your per-sub exposures on nebulae will be long — but you'll pull tight detail out of galaxies and globular clusters that the RASA's 406mm focal length simply can't resolve.
- Setup night involves hauling roughly 25kg of mount and OTA, running a star alignment, polar aligning, balancing, focusing, calibrating your guider — you're committing to at least 30 minutes before your first exposure, and ideally you've built a permanent pier to skip most of that.
Celestron RASA 8"
- You'll never look through this telescope — there's no eyepiece holder, no visual path — so if you want even one peek at Saturn before an imaging run, you need a second scope.
- What you get in return is absurd speed: a 60-second sub at f/2 captures what takes 12+ minutes at f/7, so on a work night you can stack a meaningful dataset on the Veil Nebula or Heart Nebula in under an hour, and narrowband Ha and OIII subs actually yield usable signal in short exposures from a light-polluted garden.
- Your session prep is simpler in one way — no collimation tweaking of a secondary SCT mirror — but more demanding in another: tilt at f/2 is ruthless, your camera and filter choices must be f/2-compatible, and you still need to buy a capable equatorial mount and autoguider separately, roughly doubling the advertised OTA price.
The dark side
Every scope has a personality. Here’s where each one gets difficult.
Celestron
Celestron EdgeHD 8" + CGX
At 2032mm focal length, even 30-second unguided subs will show star trailing — autoguiding hardware and software are a required part of the imaging budget, not an upgrade.
The CGX mount plus OTA totals around 25kg, making this a multi-trip haul to any observing site; realistically this system lives on a permanent pier or in an observatory, not in the back of a hatchback.
SCT collimation shifts during transport and the corrector plate dews up readily in humid conditions — you'll need to learn star-testing, carry an Allen key for the secondary, and budget for a dew shield and heater strip from day one.
Celestron
Celestron RASA 8"
There is zero visual capability — the camera physically occupies the position where a secondary mirror and focuser would be, so this scope cannot be used for any form of eyepiece observation.
Standard narrowband and light-pollution filters produce halos, reflections, and severe gradients at f/2 — you must buy filters specifically engineered for fast optical systems, which are significantly more expensive than their standard equivalents.
Sold as an OTA only at £1,799, but the real system cost includes a mount (£1,000–1,500+), a dedicated astronomy camera, a guide scope and guide camera, and f/2-rated filters — expect the total investment to approach or exceed the EdgeHD + CGX package price.
Which is right for you?
Two different buyers. Two different right answers.
The automated deep-sky platform
Celestron · Celestron EdgeHD 8" + CGX
You want one system that does both — real visual nights on planets and double stars, and serious deep-sky astrophotography of galaxies, globular clusters, and planetary nebulae at high resolution. You're willing to invest the time in polar alignment, collimation, and autoguiding because you enjoy the craft, and you already have (or plan to build) a permanent setup where the 25kg weight isn't a nightly obstacle. If you also want to image planets and the Moon at high magnification, the EdgeHD gives you that option where the RASA simply cannot.
The custom-rig optical tube
Celestron · Celestron RASA 8"
You already own a capable equatorial mount, a dedicated astronomy camera, and a guide setup — and you're tired of stacking hours of long-exposure subs to pull faint nebulosity out of the noise. You image from a light-polluted suburban garden, you want to capture large emission nebulae and narrowband targets in a fraction of the time, and you have no interest in visual observing through this particular scope. If you don't already have the supporting ecosystem of mount, camera, and f/2-rated filters, the total cost and complexity will quickly rival or exceed the EdgeHD + CGX — this is a specialist tool for an experienced imager, not a starting point.
Our verdict
This comparison has a catch: the Celestron RASA 8" is a bare optical tube. You cannot use it without a separate mount — which adds meaningful cost and complexity. The Celestron EdgeHD 8" + CGX is a complete, ready-to-observe package.
For most buyers, the Celestron EdgeHD 8" + CGX is the right choice — you can observe the same night it arrives. The Celestron RASA 8" makes sense if you already own a compatible mount, or are deliberately building a specific imaging setup piece by piece. If I had to choose for a first telescope: the Celestron EdgeHD 8" + CGX, without hesitation.
Celestron EdgeHD 8" + CGX
View Celestron EdgeHD 8" + CGX →Celestron RASA 8"
View Celestron RASA 8" →Deep field: Full specifications
Every data point, for those who want to go further.
Full specifications
Fields highlighted in blue or amber indicate the better value for that spec. Data is manufacturer-stated and may vary.
How much can it see?
| Spec | Celestron EdgeHD 8" + CGX | Celestron RASA 8" |
|---|---|---|
Aperture The most important spec — bigger = more light = better views | 203mm | 203mm |
Focal Length Longer = more magnification potential | 2032mm | 406mm |
Focal Ratio Lower f-number = wider field of view; higher = more magnification per eyepiece | f/10 | f/2 |
Optical Design The type of optics — each design has different strengths | Schmidt-Cassegrain | Schmidt-Cassegrain |
Coatings Better coatings = more light transmission through the optics | StarBright XLT fully multi-coated, EdgeHD flat-field corrector | Fully multi-coated Rowe-Ackermann Schmidt optics |
How do you point it?
| Spec | Celestron EdgeHD 8" + CGX | Celestron RASA 8" |
|---|---|---|
Mount Type The mechanical system that holds and moves the telescope | GoTo (Computerised) | None (OTA only) |
GoToⓘ Computer-controlled pointing — finds any of thousands of objects automatically | ||
Trackingⓘ Motor keeps objects centred as the Earth rotates — essential for astrophotography |
The focuser
| Spec | Celestron EdgeHD 8" + CGX | Celestron RASA 8" |
|---|---|---|
Focuser Size 2" accepts wider eyepieces and gives better low-power views | 2" | — |
Focuser Type Rack-and-pinion is standard; Crayford and dual-speed are smoother | SCT rear-cell focuser (2" visual back included) | Camera threads directly to rear cell (T-thread) |
Size & weight
| Spec | Celestron EdgeHD 8" + CGX | Celestron RASA 8" |
|---|---|---|
OTA Weightⓘ Optical tube only — useful for comparing mount load capacity | 5.4kg | 5.9kg |
Total Weight Full setup including mount — this is what you lug to the car | 28kg | — |
Tube Length | 432mm | 368mm |
Tube Material | Aluminium | Aluminium |
What's in the box?
| Spec | Celestron EdgeHD 8" + CGX | Celestron RASA 8" |
|---|---|---|
Eyepieces Included eyepieces — more is better, but quality matters more than quantity | 25mm Plössl | — |
Finder Scope Helps you locate areas of the sky before switching to the main eyepiece | StarPointer red dot finder | — |
Diagonal Tilts the eyepiece 90° for comfortable viewing — useful on refractors |
Blue highlight: Celestron EdgeHD 8" + CGX advantage · Amber highlight: Celestron RASA 8" advantage · Greyed cells: equal or subjective.