Review: ZWO Seestar S50

ZWO’s Seestar S50 smart telescope is an all-in-one portable astrophotography set-up with beginners in mind, designed to make imaging as simple as possible. Sounds great, but what’s it like from a city? Let’s find out…

First impressions

I was excited to hear about ZWO’s plans to release a smart-telescope. There are a few available already from other manufacturers, like the Vespera and DWARF II, but ZWO are big players in the astrophotography world. I like their kit and use some, including an ASIAIR Plus and 2600MC Pro camera. They’ve got a lot of experience with making equipment affordable and user-friendly, so the signs were positive from the start. Then the price was announced: £539 (from FLO). If you’re new to astro then this might seem expensive, and while it’s certainly not cheap, it represents remarkably good value for the hardware. I’m not the only one to think so, as these Seestar units have been flying off the shelves, leading to long delays. Lucky I got in there early and was a day #1 pre-order direct from ZWO!

Hands-on with the Seestar S50

The Seestar is well packaged in a kind of tough polystyrene case. It’s lightweight and fairly sturdy. The case has a little carry handle and clips to keep it closed, but no lock.

Open the case up and it comes with nearly everything you need:

• The Seestar S50 itself;
• Small tripod;
• USB C charging cable;
• Instruction manual;
• Solar filter.

It’s well designed and everything looks great. It feels like next-generation tech. I was impressed that ZWO had squeezed a tripod into the case, and the inclusion of a solar filter was welcome.

The telescope is made from a hard plastic, which keeps the weight (and cost) down, but is prone to scuffing. These telescopes won’t look pristine for long. However, it’s the lens that needs to be kept in good condition, and the telescope tucks that out of harm’s way when not in use so no lens cap is needed. It’s a neat solution.

It’s all very well thought-out. There’s an in-built dew heater, and even a basic dualband filter to help with imaging narrowband targets. An internal battery is rated for six hours, and in my experience that’s about right, although this will vary based on your conditions — very cold temperatures and use of the dew heater will drain the battery faster. You can recharge it, or even directly power it, from a simple USB power bank. ZWO state that the Seestar will work if the temperature is between -10 and +40 degrees C, and charging can take place between 0 and +40 degrees C.

I said that nearly everything needed is included. To complete the package you’ll need a smart device to run the software and display the images. To clarify for any complete beginners, the Seestar isn’t a conventional telescope with an eyepiece that you look through; it’s entirely digital, so you need a smartphone or tablet to control it and view images.I tried running the Seestar app on a Windows laptop using the Android emulator BlueStacks, but couldn’t get it to work due to Bluetooth issues. Someone tech savvy in this regard may have more luck.

It’s fairly easy to set the telescope up. The Seestar screws on top of the tripod, you extend the legs if you want, and then power it up. Actually, that last step did initially throw me. I pressed the power button and the lights came on… but then nothing. After some experimentation I realised that pressing the power button activates the battery indicator lights; to turn the unit on you need to hold the power button down for a few seconds.

Connecting to the Seestar was quick and easy, using its own WiFi connection. You can also use Station Mode, where the Seestar connects to your home network, thereby extending its range and allowing you to use the internet and Seestar at the same time.

Then an issue: a message flashed up saying that the Seestar wasn’t level. Two circles were displayed, and it’s like a mini-game to adjust the tripod’s position and leg length to get the circles to overlap, thereby indicating that it’s level. The tripod is the weak link, as it’s rather small and fiddly to adjust in this way, but given the good value of the whole kit, as well as its portability credentials, it would feel churlish to criticise too harshly.

The user interface is good on the whole, although not intuitive enough that a user — especially a beginner — would be able to work everything out right away. There are some quirks and it can be hard to find the option to do exactly what you want. For example, it took me a while to find how to turn the dew heater on. And would a beginner even know when they should be doing this? Also, upon entering the sky map (where you can scroll around and choose targets) it started with a view of the southern hemisphere. Oh, and even after using it extensively for several weeks, I’m still not sure of the best way to actually get images onto my main computer. Hook the Seestar up to it using a USB cable? Email saved images from my phone to myself? Finding pictures to transfer is harder than it should be.

I do have another gripe with the Seestar’s app. The images used throughout, such as in the object catalogue, are stock images taken with other telescopes, and as such are generally much better than you’ll realistically achieve with the Seestar. Check out this image of Jupiter, for example:

Maybe it’s not such a sin for a page explaining opposition, as in the example, but if you’re a beginner and aren’t sure what views you’ll actually get through the Seestar, showing images taken using high-end imaging rigs are misleading. I think it’s basically the same as cheap telescopes putting photos taken by the Hubble Space Telescope on their boxes. You’ll see what Jupiter actually looks like through a Seestar S50 later in this review.

First light

On the first clear night I eagerly selected a target. The Seestar sparked into life, slewed to the object, focussed, and began gathering data. This is without any alignment process, other than levelling the telescope. If you’re old-school then you’ll know how impressive this is. No three-star selection, fine tuning, polar alignment. The Seestar just does it all, using plate-solving (taking photos of the sky and cross-referencing with star charts saved in its internal memory) to point in the right direction. It’s very, very good, and works even through the light pollution of a city.

Talking of city lights, how does it fare at imaging deep sky objects? The Seestar takes 10-second exposures, and automatically stacks them to make a longer integration. It does this in real-time, meaning you can see the image get better before your very eyes.

Here’s a single 10-second exposure of The Double Cluster:

That’s not bad. But what if we keep collecting light?

This is two hours of data. The Seestar app automatically takes all the data, combines it, and displays an integrated image. We can see lots more stars, and better colour too. This is to be expected, as long integration times are essential for combatting light pollution. The Seestar’s algorithm decides whether a particular 10-second exposure is worthy of adding to the live stack. During my testing about 1/3 of the exposures were deemed to be poor quality and were discarded, so a two-hour integration may actually take you closer to three hours.

Here are some other example photos.

55 minutes on The Andromeda Galaxy. We can see the bright core really well, and some dusty lanes. You can boost the brightness in the app, but the image shown here is just using default settings. Remember, this is from a city centre, and I think it’s pretty good. With properly dark skies you’d get to this level of detail much faster, but I always recommend thinking of urban astrophotography as a marathon rather than a sprint.

This image does demonstrate a limit of the Seestar S50 though: you can’t rotate the telescope or sensor to adjust the framing. Ideally the sensor would have been 90-degrees to where it was, meaning the whole galaxy could fit the frame. Alas, I had to be content with chopping the edges off the galaxy, and having dead space at the top and bottom of the image.

What about something very faint?

Here’s 90-minutes on The Iris Nebula. We actually see some detail in the nebulosity, which is impressive. But it also demonstrates another constraint, which I think is the biggest limitation of this telescope for the city astrophotographer. Drumroll…

What’s the catch?

…drumroll continues… field rotation. Higher-end imaging systems tend to use equatorial mounts, which track objects in arcs (right ascension / declination) as they move across the sky. However, the Seestar uses a simpler altitude-azimuth (up down / left right) approach. This means that a target seems to twist in the sky over a night. This can be seen clearly in the image above: look at the top-left and bottom-right corners. That’s the result of field rotation. You might get away with it for small targets right in the centre, but something that fills your entire frame? Probably not.

Just how big an impact this will have depends on your target’s location in the sky and how long you’re imaging for. But the bottom line is that field rotation makes it very challenging to complete multi-night projects that are necessary for really high quality images from a city.

Does that mean the telescope is a bust for urban astrophotographers? No, but we need to be aware of its limits.

Narrowband

Many astro targets give out most of their light in narrowband wavelengths, and the Seestar S50 comes equipped with an internal dualband filter to help get the best images of these objects. These filters also handily block lots of light pollution, which is good news for city imagers. The particular dualband filter used in the Seestar has fairly wide bandpasses, so isn’t exactly premium, but given that a high-quality dualband filter can cost almost as much as an entire Seestar, I’m not complaining!

Here’s The Pacman Nebula with just five minutes of integration. The level of detail is good for such a short time, but due to the object’s location in the sky some extreme field rotation artifacts are creeping in already.

And 30 minutes on The Cocoon Nebula. I think this is really quite good from a city centre, and all it took was a few clicks.

Solar System targets

What about planetary imaging? The Seestar S50 has a focal length of 250mm and an aperture of 50mm. This isn’t really sufficient for getting good photos of planets, but it is possible to glimpse some details. Here are pictures I took of Jupiter and Saturn:

You can just about make out some details, but don’t expect breathtaking results. This telescope is designed for deep sky targets, and that’s where it performs best.

Let’s turn our attention to the Moon and Sun, which are two targets so bright that they’re not really affected by light pollution. The Seestar app has a lunar mode, and this produces good results. Here’s a 10-second video, so it’s giving a real-time view. Look carefully and you can see shimmering caused by the light passing through Earth’s atmosphere.

What about that solar filter? It works surprisingly well, although my Seestar did have trouble finding the Sun in the first place, so I had to move it using the app’s manual controls. Here’s another 10-second video:

Conclusions and recommendations

It’s time to draw these thoughts together. First, I’m going to rate the Seestar compared to the four main tenants of my Urban Astrophotography approach:

Make it as easy as possible to collect data.
Yes, for sure, the Seestar S50 is excellent in this regard.

Develop image processing skills, because they’re as important as the data you collect.
You can actually do this with the Seestar. The default option is for the Seestar to do some basic processing automatically to produce an integrated image, but there’s an option to save all the exposures (subframes). If you do this then you can process the data yourself in whatever software you like, such as PixInsight.

Aim for long total integration times.
This is where the Seestar falls down. Field rotation makes it very challenging for the kind of integration times needed for high quality city astrophotography — but basic imaging is certainly achievable.

Have fun!
This depends on what you count as fun. If you like imaging with a minimum of hassle, then the Seestar gets top marks. If you’re the kind of person that likes tweaking all the settings and modifying their kit, then the Seestar might fall short for you.

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So, should you buy a Seestar S50 for astrophotography from a city? That depends on what you want from it.

If you’re a beginner and want to dip your toe into the hobby to find out if it’s for you, then I think that the Seestar S50 is a brilliant option. It’ll give you a good taste of astroimaging, and you can save all the subframes to have a go at processing too. It’s as gentle an introduction to the hobby as you’re going to get. You could even use it not just for conventional imaging, but for Electronically Assisted Astronomy (EAA), which is essentially making short integrations of just a few minutes to glimpse targets you’d never be able to see through a telescope eyepiece from a city. If you find that the Seestar’s not for you, then the second-hand market is going to be very receptive to these units for a long time, so keep it in good condition and you’ll be able to sell it on without much trouble. I get asked for beginner telescope recommendations fairly regularly, and from now on I’ll be pitching the Seestar S50 as an option that should be seriously considered. That’s probably ZWO’s strategy with the Seestar, actually: treat it as a gateway drug into astrophotography, and then converts will spend the big bucks on ZWO hardware later on.

What if you’re a beginner but you’ve got deep pockets and really want to go all-in from the start? You might find the Seestar S50 to be a bit limiting. Perhaps a more conventional imaging rig would better suit you. In terms of a telescope, I recommend an Askar FRA400 — but note that telescope alone costs about twice as much as the entire Seestar S50 kit. Add in a mount, camera, plenty of accessories, and you could likely buy eight or more Seestars! That’s not an exaggeration; the Seestar really is good value. However, following this traditional route will not only give you headroom for much higher image quality, but also provide you with a solid understanding of the concepts that underpin astrophotography. This is because you’ll need to comprehend aspects like mounts, balance, alignment, filters, guiding, and countless more that the Seestar takes care of automatically. This knowledge is powerful indeed, and it’s useful to understand concepts from first principles. You won’t get that to a deep level with a Seestar.

And finally, what if you’re an experienced astrophotographer that already has an advanced imaging rig? Then the Seestar is a harder sell, but still potentially useful. I’m going to use mine as a portable set-up for if I ever manage to travel to darker skies. (I don’t ever move my main rig to dark skies — see Controversial Opinion #5). You won’t produce images that rival a more professional setup, but you can still have fun. It’s also a great tool for outreach from a city, and I’ve written a guide to using the Seestar for outreach star parties here.

Final thoughts

There are a few extra things I want to flag to round out this review.

• I think ZWO should receive credit for pumping our firmware and app updates at a furious pace. Not just bug fixes, but whole new features. While writing this review, a new update has dropped that introduces, among other things, a timelapse mode. Already I’m thinking it might be fun making a video of sunspots moving over the course of a day.
• A focal length of 250mm may make you think that this is a wide-field instrument, but it has a tiny sensor, so your actual field of view is pretty small. Coincidentally, almost exactly the same as my Askar 130PHQ 1000mm telescope combined with ASI2600MC Pro APS-C camera.
• The Seestar has a “Scenery mode” for terrestrial use, but I haven’t tried this yet.
• Thinking back to my earlier comment about a more traditional imaging rig being better at teaching you first principles and the basics, I can’t help but wonder if that will become a thing of the past. There’s no denying the power of these smart telescopes, and perhaps they’ll become the standard in the near-future. In which case, knowing how to polar align may become obsolete knowledge. That’ll make some people sad, but I say embrace the future! We’re not at that stage yet though…
• There are lots of clever people out there playing with Seestar units, and I expect mods and hacks to appear that boost its capabilities.
• I wish ZWO had a way to allow proper framing of a target, combined with negating field rotation. You can’t really do that with an alt-az system, such as the Seestar uses, but — and I’m thinking aloud here — is there a creative solution? Maybe mount the camera sensor on some kind of automated Lazy Susan that physically rotates it to counteract field rotation? That might be impossible, but if a future-generation Seestar unit can overcome this issue and allow for easy multi-night imaging projects, that would be a real game-changer for urban astrophotographers. Come on ZWO, I believe in you!

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Other Urban Astrophotography content you may be interested in…

Guide: Using a Seestar S50 for public outreach star parties
OSC vs Mono from a city
Gallery of images taken from a light-polluted city centre
How to get long integration times
10 controversial opinions

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Seestar S50 gallery

All images taken from a Bortle 8 city centre, and are direct from the Seestar (no extra processing).

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