Getting the Most from the ZWO Seestar S50 - Specs, Tips and Tricks

My first impressions of the new ZWO Seestar S50 smart telescope including specifications, tips and sample images.

My current astrophotography equipment is so big and heavy, and with my limited sky view and light pollution, I constantly feel like I cannot be bothered to go outside with it. I wanted something small, portable, and quick to set up. The Seestar S50 is going to change things.

ZWO Seestar S50 Specifications

So, let's first talk about the Seestar S50 specifications. The telescope is a 50mm f/5 apochromatic triplet lens refractor, which is connected to a 2.1-megapixel Sony IMX462 CMOS sensor with a resolution of 1936 x 1096 pixels (usable image resolution of 1920x1080). This is all mounted on a compact alt-az Goto mount. The telescope features a built-in light pollution filter and dew heater, which can be activated from within the app.

Also included in the box (which doubles as a lightweight carry case) is a short but functional carbon fibre tripod with extending feet. There is a USB-C cable for charging and connecting to a PC or Mac and a solar filter. The Seestar S50 battery has a rated capacity of 6000mAh, and the battery life is about 6 hours.

If all this wasn't enough, the telescope not only has a Goto system with tracking, but it can also use plate solving to accurately locate objects, lens autofocus (with manual override) and can even stream video feeds whilst in solar, lunar or scenery modes!

The telescope can operate in deep sky mode with or without the light pollution filter, a lunar mode for the Moon, solar mode with the provided solar filter which you have to attach manually, and you can also use the telescope in scenery mode for terrestrial viewing. You can record AVI video files for solar, lunar and scenery modes, and scenery mode even lets you record time-lapse.

Ready to Image Right Out the Box?

The Seestar S50 is ready to start imaging out of the box, although I'd recommend putting it on charge first.

Getting started is easy. Screw in the included tripod (it has a 3/8" tripod screw thread, to use a photographic tripod, you need a 1/4" to 3/8" adaptor), place it on a reasonably level and stable surface, point it in the rough direction you want to image and turn it on. The USB-C port is on the back of the telescope.

Open the app on your phone and tap to connect, which will prompt you to enter your phone's WiFi settings, where you can connect to the telescope's access point. Once connected, the app will show a level calibration where you can adjust the tripod feet to level the scope. The leveller tool aims to adjust the tripod legs until the circles turn green. You don't need to get the numbers to 0.0, but the closer you get to zero, the less compensation the scope will have to make; thus, the tracking will be more accurate. Once complete, it's ready to start imaging!

First thing I did was to click lunar and go to the Moon since it was bright and easy to see. The Seestar quickly sprang into life, slewing around to get to the Moon. I did a quick autofocus, then I watched the live view of the Moon in my hands within 1 minute of putting it on the table. One tap and I've captured a pretty good photo of the Moon.

My next target is a personal favourite, the Orion nebula, so I keyed in M43, again a quick slew, and I'm looking at the nebula on my phone's screen. The preview screen has about a 1-second exposure on the refresh, so you can see brighter objects in the preview to help with composition. You can also use the star map to make changes to the position.

These were all captured on my first night; I was so excited and impatient I wanted to get as many objects as possible, so I didn't give them long enough exposures that they needed. Even with short exposure times, they still show how good the telescope is.

Imaging deep sky objects is as easy as pressing the red record button. The camera will start capturing 10-second exposures and automatically live-stacking them into a single image. If any star trails are detected, it will automatically reject them so they won't be included.

Autofocus works pretty well most of the time; however, I found the focus can be a little out for planetary and when there are few stars in the field of view. Minor adjustments were needed only via the manual focus controls. For help with manual focusing, you may wish to see my guide on using a Hartmann mask with the Seestar S50.

On my first night out, the battery lasted around 3.5 hours, but that was in -7° C and with the due heater running. The Seestar is rated down to -10° C. You can easily connect a charger cable for longer sessions.

Seestar S50 Stacking and FITS Files

When you connect the Seestar S50 to a computer via the USB cable, you will see a list of folders, one for each target, and within that, a raw Fits file and preview jpeg.

The app will also save a JPEG copy of the stacked and stretched image to your phone for easy sharing.

In the settings screen, you can enable a feature that will save each frame in FITS format so you can manually stack them in the software of your choosing later. I highly recommend that you enable this because on my third attempt at a nebula, after 35 minutes of exposure, an aeroplane flew right through the centre of it. The whole lot was ruined because this was stacked in one image. If I had the individual files, I could remove that one frame with the aircraft trail and restack the rest. The Seestar S50 has 64GB of onboard storage, plenty for a night viewing. A single FITS file comes in at around 12MB, so you can easily get many nights worth of images.

Limitations, Drawbacks and Tips on Using the Seestar S50

I have had some issues with tracking and star trailing. When using the goto function to locate an object, it wouldn't track very well, so I'd have to go back and go to the object again, after which it would track properly. Also, on quite a few targets, it started to reject frames for star trails after 15 minutes, and after 20 minutes, virtually all the frames were rejected. Again, using the goto function to realign solved this. Hopefully, this software issue will be resolved in the next version. Also, check the level of the scope. The closer to 0.0 you can get it, the more accurate the tracking will be.

Update: I have had some success raising the scope to 90° then doing the levelling again. It probably gets slightly off balance when in the 90° position, which throws off the level adjustment. If your initial level was low enough, it might not make a huge difference, but if you only levelled to 1.7, for example, it could tilt to over 2, which it cannot compensate for automatically.

Because the Seestar S50 uses an Alt-Az mount, there are restrictions on the angles at which it can operate and the maximum duration of a session. Firstly, any objects above 85° elevation will not image. This is because an Alt-Az mount is physically unable to track objects in this region due to the way it is aligned and the motion of the stars in the sky. For this, you need an equatorial mount. Also, the longer the exposure, the closer to 85°; you will encounter field rotation, where the edges of each exposure are cropped and rotated as they are stacked. The result is an unpleasant spiral of images. Again, this is a limitation of Alt-Az mounts, which equatorial-mounted telescopes do not suffer from.

Because of the sensor's shape and size produces images in a long, vertical format roughly the same size and resolution as a standard phone screen. While this aspect ratio may take some time, it is ideal for sharing and viewing photographs on social networking platforms.

The Seestar's restricted field of view is, in my opinion, one of its most significant limitations. This is particularly noticeable when photographing huge objects such as the Andromeda Galaxy. With an imaging window of around 1 degree (60 arc minutes), you can capture only a portion of the galaxy simultaneously. That being said, 250mm is an acceptable balance for most targets, with the scope able to capture targets as small as the crab nebula with some clarity, although objects with a diameter in the 20-50 arcminute range are best.

Some images can have lots of noise for no reason. This is due to how the Seestar calculates the dark frames and the usage of the dew heater. The first time you start imaging, you will see a message indicating that it optimises the enhancement process; the process takes about a minute. The Seestar gathers data for the dark frame subtraction - sensor noise during this process. If the scope hasn't had time to acclimate to the ambient temperature, or you later turn on the dew heater, the dark frames will be invalidated since sensor noise is directly linked to the sensor temperature. Consider allowing the scope to cool down outside for 10-15 minutes before starting, and if you turn the dew heater on, allow 10-15 minutes and run the enhancement improvement again.

Conclusions

The Seestar S50 smart telescope is so easy it feels like cheating. However, as I say to my photography students, the best camera is the one you have with you. My current astrophotography equipment is so big, heavy, and complex that it takes me at least an hour to get everything in place, connected, polar aligned, and imaging. Usually, then the clouds come in. All the hassle of setting up and taking in, with very limited views of the sky and lots of light pollution, means I rarely take my scope out.

The Seestar S50 can be set up and imaged within 2 minutes, perfect for travelling and quick imaging sessions between clouds. I can carry it out in one hand, place it on the table, do a quick level using the spirit level in the app, select my target and start imaging. Easy peasy, lemon squeezy.

So with the Seestar S50, you have a small aperture and a short focal length scope, but what you lack in size you more than make up for in ease of use and portability, and the software is so easy to use ANYONE can get great astrophotography results!