Telescope Comparison
ZWO Seestar S50 vs ZWO Seestar S70
The specs are close. The experience isn't.
First light
ZWO · 50mm · £539
The app-native deep-sky imager
- 50mm sensor-based smart telescope — no traditional eyepiece
- Connects to a smartphone app; the app selects, slews to, and stacks targets automatically
- Best for: faint deep-sky objects — galaxies, nebulae, star clusters built up over minutes
- Not for direct eyepiece viewing — every view is delivered on a phone or tablet screen
- 2.5kg compact all-in-one unit
ZWO · 70mm · £699
The app-native deep-sky imager
- 70mm sensor-based smart telescope — no traditional eyepiece
- Connects to a smartphone app; the app selects, slews to, and stacks targets automatically
- Best for: faint deep-sky objects — galaxies, nebulae, star clusters built up over minutes
- Not for direct eyepiece viewing — every view is delivered on a phone or tablet screen
- 3.2kg compact all-in-one unit
The full picture
The numbers that separate these two scopes — and what they mean at the eyepiece.
Aperture
ZWO Seestar S70 gathers 2× more light. On bright targets — Moon, Saturn, Jupiter — you won't notice. On fainter targets — dim galaxies, faint globular clusters — the gap is real.
Focal length
ZWO Seestar S70's longer focal length reaches higher magnification with the same eyepiece — better reach for planetary detail. ZWO Seestar S50's shorter focal length gives a wider true field — better for large open clusters and extended nebulae.
Focal ratio
Focal ratio is not meaningful for smart telescope sensor systems — the optics are optimised for the built-in sensor rather than interchangeable eyepieces.
Mount type
Same mount type — setup experience and ergonomics will be similar. Differences lie in build quality and included accessories.
Weight (OTA)
Similar optical tube weight. Any portability difference between these setups comes from the mount, not the tube itself.
Optical design
Both sensor-based smart telescopes — no eyepiece, app-controlled, live stacking. The differences are in sensor size, aperture, and companion software quality.
At the eyepiece
| Target | ZWO Seestar S50 | ZWO Seestar S70 |
|---|---|---|
| Planets | ||
| Moon | Moderate Full disc fits the frame well, but 50mm aperture and 250mm focal length limit crater-level detail compared to even budget visual scopes | Good 70mm aperture captures good surface detail, but short 350mm focal length means the disc is small on the sensor and fine detail is limited |
| Saturn | Challenging Rings detectable via stacking, but 250mm focal length renders the planet very small on the sensor | Challenging Rings identifiable but very small at 350mm focal length — minimal detail beyond basic ring structure |
| Jupiter | Challenging Disc and main cloud bands visible after stacking, but limited detail at this aperture and focal length | Challenging Disc and Galilean moons visible, but 70mm aperture and 350mm focal length yield a tiny disc with little cloud band detail |
| Mars | Not recommended Tiny disc even at opposition — 50mm aperture and 250mm focal length cannot resolve surface features meaningfully | Not recommended Sub-70mm effective resolution and very short focal length make Mars a featureless dot even at opposition |
Deep sky | ||
| Orion Nebula (M42) | Good Fast f/5 optics and 250mm focal length capture the full nebula extent with good colour and structure after stacking; aperture below 80mm limits fainter outer regions | Excellent Fast f/5 ratio and 350mm focal length frame the full nebula beautifully — stacking reveals extensive nebulosity and colour |
| Andromeda Galaxy (M31) | Excellent 250mm focal length frames the full galaxy beautifully; dust lanes emerge within minutes of stacking | Excellent 350mm focal length captures the full extent of the galaxy including outer halo — a signature target for this scope |
| Open clusters | Excellent Short 250mm focal length provides wide field of view — Pleiades, Double Cluster, and similar targets fit the frame perfectly | Excellent Wide field at 350mm frames large clusters like the Double Cluster and Pleiades perfectly |
| Globular clusters | Challenging 50mm aperture cannot resolve individual stars; globulars appear as fuzzy concentrated patches even with extended stacking | Challenging 70mm aperture cannot resolve individual stars — globulars appear as soft glowing patches even with stacking |
| Faint galaxies | Challenging 50mm aperture limits light gathering — small and faint galaxies show cores only, with little structural detail | Moderate Stacking compensates for the modest 70mm aperture, revealing shapes and structure in brighter galaxies, but faintest targets require long integration times |
| Milky Way / wide field | Excellent 250mm at f/5 is ideal for sweeping star fields and large nebula complexes | Excellent 350mm at f/5 is ideal for sweeping star fields and Milky Way structures |
Other | ||
| Double stars | Not recommended No eyepiece for visual splitting, and 50mm aperture with 250mm focal length cannot meaningfully resolve close pairs on the sensor | Moderate 70mm resolves wider doubles but close pairs are beyond its Dawes limit — and the imaging-only output is not ideal for double star work |
| Astrophotography (deep sky) | Good Fully automated GoTo and tracking with integrated camera at f/5; alt-az field rotation limits long integrations, and 50mm aperture caps faint-target performance | Good Integrated GoTo and tracking with f/5 optics and automated stacking deliver strong deep-sky results; limited by 70mm aperture on faintest targets and lack of manual processing control |
| Astrophotography (planetary) | Challenging 50mm aperture and 250mm focal length produce a very small planetary disc; stacking helps but cannot overcome the resolution limit | Challenging 70mm aperture and 350mm focal length produce very small planetary discs with minimal detail |
| Solar imaging | Good With the included or optional solar filter, the Seestar captures sunspot detail and solar granulation automatically — a unique feature at this price point | Not applicable |
| Emission nebulae (with dual-band filter) | Not applicable | Excellent Built-in dual-band filter isolates Ha and OIII, making targets like the Veil, Rosette, and Heart nebulae accessible even from light-polluted skies |
The real tradeoff
Both scopes are capable. The question is which one fits the way you actually observe.
ZWO Seestar S50
- You'll fit this in a backpack and set it up anywhere in under two minutes — perfect for spontaneous observing sessions from your garden or a car park.
- You'll watch the Andromeda Galaxy and Orion Nebula resolve beautifully on your phone screen as the stacking algorithm does the heavy lifting, but you'll hit a hard ceiling on anything smaller or fainter.
- You'll spend almost nothing on accessories or learning curve, but you'll accept that planets and double stars simply aren't in your telescope's wheelhouse.
ZWO Seestar S70
- You'll get 40% more light-gathering power and a longer focal length, so faint nebulae and distant galaxies reveal more structure and colour after the same integration time.
- You'll still pack it away easily and rely entirely on app automation, but the S70 rewards slightly longer observing sessions — 15–30 minutes per target yields noticeably better results than the S50 can manage.
- You'll pay £250 more for meaningfully deeper targets and better resolution on wide-field objects, but you're still locked into the same no-eyepiece, screen-only experience.
The dark side
Every scope has a personality. Here’s where each one gets difficult.
ZWO
ZWO Seestar S50
No eyepiece — this is purely a digital imaging device with no visual observing capability.
50mm aperture severely limits resolution on planets, small galaxies, and faint deep-sky targets compared to traditional telescopes or the S70.
Field rotation occurs in longer stacking sessions due to the integrated alt-az mount, capping total effective integration time on some targets.
No manual control over sub-exposures, gain, or calibration frames — the app handles everything automatically with limited user override.
Entirely dependent on ZWO Seestar app and WiFi connection; app updates or connection drops render the telescope unusable.
Internal dew heater draws battery power, reducing runtime in cold or humid conditions.
ZWO
ZWO Seestar S70
No eyepiece — all viewing is via the app on a phone or tablet, no visual observing option.
70mm aperture limits resolution on planets and the Moon compared to even a modest visual telescope.
Short 350mm focal length means planets appear as small discs, unsuitable for detailed planetary imaging.
Processing handled entirely in-app with limited manual control — dedicated post-processing requires exporting stacked files.
Integrated design prevents upgrading individual components; sensor, optics, and mount form a single unit.
Battery life may not last a full long winter session without an external power bank.
Which is right for you?
Two different buyers. Two different right answers.
The app-native deep-sky imager
ZWO · ZWO Seestar S50
You'll love the S50 if you want to learn astrophotography in the absolute easiest way possible, live in a light-polluted area where its integrated filter earns its keep, and you're happy to travel light — this is the grab-and-shoot camera telescope that asks nothing of you except a clear sky and two minutes. You're not interested in visual observing, planetary detail, or faint galaxies; you want Andromeda, the Orion Nebula, and open clusters to look good on your phone, and you want the whole experience to feel effortless.
The app-native deep-sky imager
ZWO · ZWO Seestar S70
You'll love the S70 if you're willing to spend an extra £250 for genuinely better deep-sky results and don't mind slightly longer integration times to unlock fainter nebulae and more structure in galaxies — you want to feel like you've accomplished something, not just pointed at a target. You're still a beginner or impatient observer who wants zero manual control, but you value richer images enough to accept the S70's marginally longer setup and session commitment. This isn't for you if you want visual observing, planetary detail, or the absolute tiniest footprint; it's for you if you want to take home images that make you want to come back outside next week.
Our verdict
These two are closer than most comparisons on this site. The spec differences are genuine — mount type, focal ratio — but neither is the wrong answer for a typical observer starting out.
If I had to choose between them: the ZWO Seestar S50 is the scope most people will be using regularly six months from now. The ZWO Seestar S70 rewards you more once you know what you're doing — it's worth revisiting after your first year.
ZWO Seestar S50
View ZWO Seestar S50 →ZWO Seestar S70
View ZWO Seestar S70 →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 | ZWO Seestar S50 | ZWO Seestar S70 |
|---|---|---|
Apertureⓘ The most important spec — bigger = more light = better views | 50mm | 70mm |
Focal Length Longer = more magnification potential | 250mm | 350mm |
Focal Ratio Lower f-number = wider field of view; higher = more magnification per eyepiece | f/5 | f/5 |
Optical Design The type of optics — each design has different strengths | Smart Telescope | Smart Telescope |
Coatings Better coatings = more light transmission through the optics | Multi-coated ED doublet objective | Multi-coated ED doublet objective |
How do you point it?
| Spec | ZWO Seestar S50 | ZWO Seestar S70 |
|---|---|---|
Mount Type The mechanical system that holds and moves the telescope | Integrated | Integrated |
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 | ZWO Seestar S50 | ZWO Seestar S70 |
|---|---|---|
Focuser Size 2" accepts wider eyepieces and gives better low-power views | — | — |
Focuser Type Rack-and-pinion is standard; Crayford and dual-speed are smoother | Motorised electric focuser (auto-focus via software) | Motorised electric focuser (auto-focus via software) |
Size & weight
| Spec | ZWO Seestar S50 | ZWO Seestar S70 |
|---|---|---|
OTA Weightⓘ Optical tube only — useful for comparing mount load capacity | 2.5kg | 3.2kg |
Total Weightⓘ Full setup including mount — this is what you lug to the car | 2.5kg | 3.2kg |
Tube Length | 270mm | — |
Tube Material | Aluminium alloy with polycarbonate housing | Aluminium alloy with polycarbonate housing |
What's in the box?
| Spec | ZWO Seestar S50 | ZWO Seestar S70 |
|---|---|---|
Diagonal Tilts the eyepiece 90° for comfortable viewing — useful on refractors |
Smart features
| Spec | ZWO Seestar S50 | ZWO Seestar S70 |
|---|---|---|
Built-in Camera Records and stacks images automatically — no separate camera needed | ||
App Controlled | ||
WiFi | ||
Battery Included | ||
Sensor | 1/2.8" Sony IMX462 CMOS | 1/1.8" Sony IMX585 CMOS |
Sensor Resolutionⓘ Higher megapixels captures finer detail | 2.1MP | 3.8MP |
Blue highlight: ZWO Seestar S50 advantage · Amber highlight: ZWO Seestar S70 advantage · Greyed cells: equal or subjective.