The Seestar S50 smart telescope is a remarkable, low cost device of high quality.
It is a 50mm, apochromatic triplet with a focal length of 250mm, an integral Sony IMX462 sensor with a resolution of 1920x1080 pixels camera is built in, and the whole unit weighs 3 kg. It comes with a solar filter and a built in dualband, broadband (light pollution) filter that can be switched in an out. It also has an anti-dew heater that can be turned on to help avoid dew formation on the objective.
The Seestar S50 is controlled by Seestar software that runs on Android or iOS devices such as smart phone or tablets. It is much more satisfying to use a large tablet screen than a small phone screen, although both work.
Screenshot of the tablet screen running the Seestar software
I will say right now that I wish that there was an SDK that would allow the Seestar S50 to be controlled by other capture software such as our own AstroDMx Capture. However, that being said, at the moment no such SDK exists.
The Seestar S50 can be set to capture 10s, 20s or 30s exposures. The device then live-stacks the images as they are captured. It rejects images and doesn’t stack an image if it has star trails or if the are insufficient stars (usually due to passing clouds). It can be set to save each individual image captured and live-stacked so that they can be independently stacked in other software. Before live stacking begins, dark frames are automatically captured and they are applied in real time to the stacking frames. When a frame is successfully added to the stack, the time is incremented so that it is always possible to see the total accumulated exposure time.
Screenshot of the live-stack of M51 after 10 minutes of 10s exposures have been captured
When the imager decides to terminate the captures, the Seestar S50 saves the integrated image to the tablet device that has been controlling it.
Integrated image of M51 saved to the controlling tablet
It can be set to watermark the image with relevant information. This is a very useful feature.
This is part of the appeal of the Seestar S50. The stacked image is presented in quite an acceptable form suitably labelled. For a casual user or outreach this may be all that is required.
Here are some other examples of integrated images with very modest total exposure times:
If all of the individual images are saved, they will be saved in a folder on the Seestar S50 with a name such as M51 –sub. The interesting and useful fact is that if, say on the next night, M51 is imaged again, the individual files will be saved into the same folder ready to be re-stacked and having more information added to the subject image.
There is a paradigm shift in the way that we think of long exposure times when working with the Seestar S50. Instead of thinking of long individual exposures as we are used to with normal equatorial astro-imaging, we think of accumulated shorter exposures. This harks back to earlier days of amateur electronic imaging at about the turn of the century, with off-chip integration, when software was developed to sum individual 1/50s half frames from very low-lux surveillance cameras into 32bit FITS files using software such as AstroVideo developed by Bev Ewen-Smith of the COAA observatory in the Algarve, or Vega developed by Colin Bowness in the UK. Then frame accumulating video cameras such as Mintrons or the Samsung SDC-435 (SCB-2000), extended this idea to summing the frames into a buffer on the camera for periods of up to 5s or even 10s whilst continually releasing copies of the accumulated image into the video stream at 25fps. In these cases, long exposure times were synthesised by the summing (stacking) of captured shorter exposures. They say that there is nothing new under the Sun and these days this type of work is called EAA (Electronically Assisted Astronomy), we didn’t have a name for it back in the day. The reason for this type of thinking in relation to the Seestar S50 is that it works with an AZ mount. Longer exposures than the 10s, 20s or 30s exposures would allow star trailing to occur within an individual exposure. Although some users of the Seestar S50 leave their scope to stack images of a given object over several hours, others accumulate data by capturing for a shorter period of time at a similar time over several nights (if they are fortunate enough to get several relatively consecutive clear nights.) A combination of these approaches can be used.
Various software can be used to stack the saved (already calibrated) Seestar S50 images: Deep Sky Stacker, PixInsight and Siril and others can be used. Also ZWO’s own ASIDeepStack software works well and can be readily downloaded from the ZWO website. However, it stacks into a 16 bit file rather than a 32 bit file. ZWO’s ASIVideoStack software also works very well for stacking RAW AVI files of the Moon, Sun or planets. It must be said that the Seestar S50 is not really suitable for planetary imaging. Whilst it can be done, the images scale is too small for detailed images of the planets. However, For lunar and solar imaging, the Seestar S50 is ideal.
Image of the Moon as saved to the controlling tablet
Processed image of the 98.2% Moon
Snapshot of the Sun setting over the mountain across the valley
A processed image of the Sun showing lots of sunspots, March 22, 2024
Examples of processed Seestar S50 deep sky images
The Orion nebula
The Pacman nebula
The tadpoles nebula
Central part of the Rosette nebula and the Satellite cluster
M13
M37
The results shown here represent an initial exploration into the capabilities of the Seestar S50 with relatively short total exposures. It is intended to explore the results obtainable from longer individual exposures and longer total exposure times.
Part of the allure of the Seestar S50 is that it is a very portable and easy to use GOTO telescope and mount. It really is a grab and go device that can be taken to alternative sites and be set up and imaging in minutes. Also, the package contains everything you need from a robust carry case, small, stable tripod and even a solar filter.
That having been said, there is a small ecosystem of low cost, 3D printed accessories that enterprising enthusiasts have made available in markets such as eBay and Etsy. These accessories include dust lens caps, dew shields, filter holders and Bahtinov masks. Probably the most essential accessory is a dew shield because the Seestar’s objective lens is not very far inside the tube case. The Bahtinov masks can be useful to achieve perfect focus. Whilst the autofocus facilty is very good, there is a focus facilty that can be invoked, and with the use of a Bahtinov mask, achieve perfect focus on a bright star. Filter holders can be useful if one wishes to switch out the built-in dualband broadband light pollution filter, leaving only the built-in UV/IR cut filter over the sensor, and then use for example, a narrowband dualband filter such as a Ha/OIII filter or a SII/OIII filter. There are even 1.25” to 2” filter converters that can be used to hold smaller filters. We have yet to test any of these accessories other than a Dewshield that we made from a 2” sandwiched filter holder and a short piece of black pipe of the correct diameter that we flocked on the inside with black felt. The device can still hold a 2” filter if required.
Seestar S50 accessories
The accessory which speeds up the setting up of the Seestar S50 is a low cost leveling device that allows the scope/mount to be leveled in moments without having to extend and retract the tripod legs. The Seestar S50 has a built-in leveling system that involves getting two green circles to overlap on the controlling tablet screen. This can be quite awkward, but with the aid of the leveling device, it is both quick and easy. The leveling device fits between the Seestar S50 and the tripod and is installed by simply screwing it onto the tripod and the scope.
Leveling device
The versatility of the Seestar S50 is increased by the fact that it has a Scenery mode for taking images of objects and animals in the landscape. It also has a very useful time-lapse capture mode.
Snapshot of a sheep on the mountainside across the valley
In conclusion, we can say that the Seestar S50 is a serious, low cost, versatile apochromatic telescope system that is quick and easy to set up and use.
