The ZWO Seestar S50 is a compact smart telescope with a 50mm apochromatic refractor with a focal length of 250mm (f/5) at its heart.
In an expanding market, it’s the S50’s low price that sets it apart from many of its competitors.
The S50 comes neatly packed in a shockproof carry case with a tripod, USB-C charging cable, solar filter and user/safety guides included.
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There is no lens cap, but the S50’s objective lens is protected when the telescope automatically returns to its parked, off position.
The lightweight, compact design lends itself well to portability.
Fully charged it has a stated battery life of six hours, although this is likely to be less under cold conditions or when the scope’s internal dew heater is turned on.
Connecting it to a USB power bank gave us power to spare over a long night.
The ZWO Seestar S50 is operated via a smartphone or tablet and requires the installation of the designated Seestar iOS or Android app to work.
Connecting our phone to the S50 was nice and straightforward, thanks to the easy-to-follow instructions.
We did discover that connecting to the Seestar’s own Wi-Fi hotspot prevented internet access from our phone.
However, there’s a Station Mode option that connected everything to our home Wi-Fi network, so internet access was restored.
Getting started
The ZWO Seestar S50 has an internal dual-band (OIII and H-alpha) light-pollution filter for imaging emission nebulae.
This worked well even from heavily light-polluted sites – an attractive feature for city users.
The Seestar app automatically selects the light-pollution filter for certain targets, but you can override this if you want to.
ZWO seems responsive to user issues and updates the app and firmware frequently; recent updates include enhanced image stacking.
Once we had situated the S50 outside, the app’s voice prompt requested us to level the unit. This displayed two circles and a digit value on our phone.
The tripod legs can then be adjusted so that the circles overlap and turn green, and the digit value reduces to as close to zero as possible.
How the ZWO Seestar S50 works
Targets can be selected from the Seestar app’s recommendations or via a planetarium-style interface.
Once selected, the S50 moves to its target automatically, mirroring this on the app’s planetarium display.
A few positional tweaks are normally all it takes to successfully centre its target, then ‘Goto success’ is displayed in the app to show it’s ready to start taking pictures.
Exposure lengths of 10, 20 or 30 seconds are available, but we found 10 seconds quite adequate.
The S50 live-stacks each exposure, with the result gradually appearing on our phone, which was thrilling to see.
We took sequences for various targets, ranging from 20 minutes to an hour of total integration time.
Potential problems
One potential disadvantage is the ZWO Seestar S50 narrow field of view compared to some competitors.
It’s also worth noting that because the sensor is in portrait (as opposed to landscape) orientation, larger targets are sometimes truncated or less than optimally framed.
Another thing we noted is that the S50 is altaz-mounted but emulates equatorial motion via software and stepper motors.
The downside of this is field rotation, resulting in noisy corner regions of stacked images captured over long integration times.
However, these are easily cropped off and reduced by stacking sessions taken over several nights.
Astrophotography
The S50’s short focal length doesn’t allow detailed images of planets, rendering only a small, basic view of Jupiter and its two main belts.
However, we found it good for overview shots of the Moon and Sun. Using the solar filter, we grabbed some great images of sunspot groups.
There’s a handy on-screen brightness adjustment to help improve lunar and solar views.
If we wanted to tweak a preset Go-To pointing position, we could manually adjust this via the app. We found this challenging at first and recommend the ‘slow’ speed for precision centring.
In summary, the Seestar S50 offers a fast set-up for beginners and professionals, enabling reasonable-quality imaging of deep-sky and larger Solar System objects at a very competitive price point.
Even better, it’s a lot of fun to use.
Portability
As an all-in-one 50mm refractor with integrated astro camera, the Seestar S50 arrives ready for action.
The sleek, compact and lightweight design is a winning feature: it’s so easy to pack up and pick up that you can be outside and imaging in a short time, grabbing any gaps in the weather.
The fact that it’s so easy to move and set up makes it fantastic for travel, but equally convenient for use at home.
The integrated design is well thought-out, with the internal light-pollution filter providing access to faint objects such as the Horsehead Nebula from polluted sites.
Once locked on to our target, we could retire indoors and disconnect our phone from the S50, reconnecting occasionally to check on progress.
When we were happy we’d spent enough time on one subject, we could simply slew to the next target from the comfort of our sofa.
Despite the automation, the ease of target access is great for evoking genuine excitement about what this instrument can grab next.
Images captured with the ZWO Seestar S50
ZWO Seestar S50 5 best features
Electronic focusing
The S50 auto-focuses on its targets and does this well. There’s an option to display focus adjustments on your device screen, which allows you to manually adjust and record the optimum setting if you feel you can do better. The ability to pinch-zoom a target on screen to magnify our adjustments is also useful.
Dual-band filter
The Seestar S50 is fitted with an internal dual-band light-pollution filter that can be switched off or on. Without the filter, light to the IMX462 sensor passes through an IR-cut filter. The light-pollution filter passes narrowband wavelengths centred on OIII and H-alpha, with pass bandwidths of 30nm and 20nm respectively.
Internal storage
The S50 provides 64GB of internal storage. This is used to save raw videos of the Sun and Moon that can later be stacked using registration-stacking software such as AutoStakkert! Excitingly, there is also an option to save individual FITS files, which can then be extracted and processed using external programs.
Tripod
The S50 comes with a light, sturdy tripod that extends from a height of 275mm to a maximum 363mm. Each adjustable leg has two sections and a rotary locking mechanism is used for levelling
the telescope. The S50 unit is connected to the tripod via a 3/8-inch screw thread.
Seestar control app
The straightforward app for iOS and Android includes a virtual sky atlas, S50 settings options, telescope modes, focus/auto-focus, positional tweaks and access to a user community. It also shows the battery level and acts as the view screen for your live-stacked images. Access to multi-session stacking options (to stack results from multiple nights) is also provided.
Vital stats
- Price: £539
- Optics: 50mm triplet apo refractor
- Focal length: 250mm, f/5
- Sensor: Sony IMX462
- Mount: Altazimuth
- Power: 6,000 mAh battery
- Tripod: Carbon fibre
- Connectivity: USB-C, Wi-Fi, Bluetooth
- Control: Seestar iOS/Android app
- Extras: Dew heater, dual-band OIII/H-alpha filter, 580–630nm solar filter, 64GB storage
- Weight: 2.5kg
- Supplier: 365Astronomy
- Tel: 020 3384 5187
- www.365astronomy.com
This review appeared in the May 2024 issue of BBC Sky at Night Magazine
