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Seestar S50 - first light and review

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#1 Rasfahan

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Posted 03 October 2023 - 07:58 AM

Introduction

I've bought this as a possible integrated, ultra-portable AP kit, so this review is heavily skewed towards that usage. Personally, I have no interest in EAA - I prefer to do full-fledged AP, using all postprocessing tools available, or just put an eyepiece into a telescope at a dark site. The Seestar S50 was delivered to me yesterday, and to my surprise the night was clear until about 2:30 am.

 

Delivery
The Seestar was sent from China and arrived within 4 days at my doorstep. Logistics were handled by FedEx which gave detaild tracking information and handled all customs formalities - it's a rarety that I don't have to pick up packages from China at the customs office. So, very good on ZWO to provide adequate and correct customs information.

 

Packaging
The Seestar comes in a cardboard box which contains another suitcase-like box made from styrofoam. The fit to the scope and tripod is tight. Time will tell how sturdy it is, but to me it seems a very safe transport box. I'ld be comfortable even putting it into check-in baggage.

 

Contents
The box contains the integrated mount-and-telescope, a small carbon tripod, a 1m USB-A to USB-C cable, a solar filter and a quickstart manual. The carbon tripod legs can be used shortened for a height of about 25 cm or extended to about 50 cm. When the telescope is mounted it is sturdy enough to not tip over and very rigid towards bending motions but not quite as resistant towards applied torque. The filter is a foil filter in a plastic ring. I'll describe the telescope in detail in the other sections.

 

Hardware
Overview
The S50 is a compact, integrated telescope, ALT/AZ goto mount, CMOS OSC camera, AP computer and rechargeable battery. Setup is very quick: Assemble mount/telescope and tripod, power up the Seestar, connect to the inbuilt WIFI, follow instructions to level the tripod and go shoot. It takes literally a couple of minutes.

Battery
I don't know the capacity of the battery, but it can't be more than 80Wh. Due to the small size of the telescope and the uncooled camera, it will power the Seestar for at least the advertised 6h. I didn't have need for the dew heater, though.

 

Mount
The integrated ALT/AZ mount has some play/backlash in the ALT axis which lead to streaked stars in about 20% of my exposures. DSO gotos are fast and accurate.  The object was kept centered during the whole 2.5h run, but I assume it is recentered after each image for platesolving.

 

Camera
The Seestar S50 comes with an IMX462 OSC sensor. It is a small sensor with small pixels and high QE: The sensor dimensions are 5.6 x 3.2mm, pixel size is 2.9µm  and a QE of about 90% at 500nm and about 82% at the h-alpha wavelength. Although the read noise is only 1.1e- at unity gain, the small pixels mean it isn't as low per area as some other chips. As a special feature the bayer matrix becomes basically transparent in the near infrared. This means it is a great chip for solar, (especially h-alpha) or planetary observation and very decent for EAA. For DSOs, a larger sensor and higher full-well capacity would be desirable. In addition, the chip is mounted with severe tilt.

 

Optics
ZWO advertises the Seestar as a "triplet apochromatic". They provide no information about the design or the glass types used. It is here, unfortunately, that the savings made to meet the price point are the most obvious: The scope shows severe trefoil astigmatism. The CA at the higher end of what one would call "apochromatic" even with the inflationary use in advertising - and from the colors I got on the Gamma Cas nebulae, I would assume that the UV/IR-cut filter included by ZWO cuts the blues quite short. Even with all that, the stars are quite small (1.8 px FWHM). The small chip is illuminated almost 100%, so together with the closed design flats can be skipped - FPN really isn't a concern here, considering the optical and mechanical problems.

 

Software/Usage
ZWO wants to access a huge amount of private data (including position tracking, contacts, profiling, etc.) so I'ld recommend picking up a cheap smartphone just for this app. ZWO also uses a plethora of open source software while blatantly violating their license.
The app and scope software seem rock solid - I encountered no bugs. The pairing process is straightforward and quick (download the APP, power on the scope, press connect in the APP, press reset button on scope. You start off with a welcoming screen with four modes (solar, lunar, "stargazing - basically DSO" and landscape). The moon wasn't up when I was, so I skipped that. I'll certainlly be testing the landscape mode for birding.

 

Solar
I only briefly tested the solar mode. During my initial trial it had problems finding the sun - but then it was only 10° above the horizon and partailly obscured by clouds. Once centered, it tracked the sun perfectly until sunset.

 

Stargazing (DSO)
The interface certainly is geared towards EAA: You pick an object, the telescope slews to it and centers via platesolving. The standard catalogs are included (Messier, NGC, IC, Sharpless) and you can pick your coordinates as well as slew the scope manually. It then shows an autostretched, debayered image every 10s. Selecting the record button, it will autostack these images in the liveview. The stacked images are saved to your phone when you stop live stacking. In the options, you can enable the S50 to also save every sub as a FITS-file. The recording will continue even when the smartphone is disconnected from the Seestar. position. Image saving is associated with a significant overhead - 2.5h of observing time put out 1.5h of subs.
The subs can be transfered to a computer via USB - the S50 shows up as an external disk. It is from these that I produced the Gamma Cas image below. An integrated light pollution filter can also be inserted into the light path - this happens automatically if you select a nebula from the catalog. Autofocus runs quickly (10s) and accurately. There is no sequencing functionality: You're limited to 10s exposures taken with the selected filter and the selected focus position.

 

Summary
For the price, you get a very nicely integrated package for those that prefer ease of use to image quality: An ALT-AZ mount comparable to a Skywatcher AZ-GTi, a carbon tripod, a 50mm semi-apo, a 1/2.8" uncooled astro camera, a rechargeable battery with 6h battery life and a mount computer. The software is very stable but geared mostly towards EAA currently. I am cautiously confident ZWO will add further features in coming updates, but prefer stability to featuritis. The whole software/hardware integration works very well, setup is easy and quick. The one thing I would wish for is better quality control: Unpinched optics, less tilt in the sensor and tighter gearing would go a long way here - it's really what's holding this setup back from producing great instead of mediocre images.

 

Postprocessed Image:

Astrobin link:

get.jpg?insecure

 

Aberration inspector (single frame):

Aberration Inspector single.jpg

 

 

Aberration Inspector (stacked):

Aberration Inspector.jpg

 

FWHM (single frame):

FWHM.jpg

 

Eccentricity (single frame; just for completeness, not useful at the small FWHM):

Ecc.jpg

 

Solar (single shot):

IMG_0083.jpeg


Edited by Rasfahan, 03 October 2023 - 07:58 AM.

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#2 airscottdenning

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Posted 03 October 2023 - 09:41 AM

Wow, excellent review! Best I've seen of S50 by far. Thank you very much for doing this. 


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#3 dciobota

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Posted 03 October 2023 - 10:24 AM

Nice review and impressive images as well from something less than $500 nowadays. I'm sure someone getting started in the hobby would be thrilled to get the gamma cass pic you got.

My only objection to the rig is that it looked rather large in Cuivs review. An azgti with a camera and 135mm lens and a mini tripod like I have seem smaller to me.
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#4 Rasfahan

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Posted 03 October 2023 - 10:58 AM

Nice review and impressive images as well from something less than $500 nowadays. I'm sure someone getting started in the hobby would be thrilled to get the gamma cass pic you got.

My only objection to the rig is that it looked rather large in Cuivs review. An azgti with a camera and 135mm lens and a mini tripod like I have seem smaller to me.

Thanks for the compliment - I think the image would be further improved by more integration time. I had planned for 4h, but clouds came in after 2,5h and the overhead with image download cut the whole integration time short to 1:40h. But yes, had this been one of my first images three years ago, I would've been thrilled.

 

It's not bulkier than the AZ-GTi + 135mm. Even with the case, it'll easily fit within carry-on luggage. Depending on the camera you'll get better images with the 135mm, have a better upgrade path and it'll come apart for storage and reuse of components  - but here in Europe the kit (Samyang 135, ASI462MC, AZ-GTi, mini carbon tripod, EAF, mini PC or ASIAir) will cost four times what the pre-order S50 cost and more than three times the current (inflated) local price.  Here's a comparison pic. Note the 135mm is without a camera and mount:

IMG_0530.jpeg


Edited by Rasfahan, 03 October 2023 - 10:59 AM.

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#5 dciobota

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Posted 03 October 2023 - 11:12 AM

Oh now that gives much better scale, thanks! It's not nearly as big as it looked in Cuivs video. Maybe it was the perspective of something. It's almost small enough to fit in a backpack if I were still doing that. Nice.

#6 HotRod217

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Posted 03 October 2023 - 11:39 AM

It's better for solar imaging than I thought.



#7 Rasfahan

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Posted 04 October 2023 - 02:10 AM

Oh now that gives much better scale, thanks! It's not nearly as big as it looked in Cuivs video. Maybe it was the perspective of something. It's almost small enough to fit in a backpack if I were still doing that. Nice.

Yes, it looks very bulky on photos. I needed three attempts to convey the right impression. It'll easily fit a hiking backpack if you want to carry an additional 2.5kg with you - I'ld prefer my image-stabilised binos for stargazing when hiking.

 

 

It's better for solar imaging than I thought.

Yes, that works pretty well, the small pixels help here. Looks to be clear today, so I might try add some shots with the sun higher up.


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#8 tarbat

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Posted 04 October 2023 - 10:05 AM

In case you haven't seen these posted elsewhere, these are the results of my 2 weeks ownership of a Seestar. All images are straight from the Seestar, no post-processing.  This is really a good introduction to EAA for beginners, or even an experienced user who wants an ultra-portable rig to take to deep sky sites.  Stacked FITS files also available at https://drive.google...6yX?usp=sharing

 

composite
 
EDIT: And after some basic post-processing in Siril.
 

 


Edited by tarbat, 04 October 2023 - 11:15 AM.

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#9 Rasfahan

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Posted 04 October 2023 - 03:55 PM

Yes, it's great for EAA, I think. Especially with the very quick setup - the ultimate grab&go.


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#10 tarbat

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Posted 05 October 2023 - 08:42 AM

I'm no expert on the analysis of optics, but I did a quick analysis on my Seestar S50 using Siril's aberation inspector and PSF tool that can estimate sensor tilt.

 

Aberation Inspector - stack of 600 sub-exposures

 

aberation

 

Sensor Tile

 

sensor

 



#11 Rasfahan

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Posted 05 October 2023 - 09:42 AM

I'm no expert on the analysis of optics, but I did a quick analysis on my Seestar S50 using Siril's aberation inspector and PSF tool that can estimate sensor tilt.

 

Aberation Inspector - stack of 600 sub-exposures

 

 

 

Sensor Tile

 

Due to the field rotation, you can‘t use stacked images to check for tilt or optical aberrations, you need to check a single shot. Unfortunately, the aspect ratio is very high in that chip, so ASTAP will only measure the central part and is rather useless here.



#12 tarbat

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Posted 05 October 2023 - 10:21 AM

Due to the field rotation, you can‘t use stacked images to check for tilt or optical aberrations, you need to check a single shot. Unfortunately, the aspect ratio is very high in that chip, so ASTAP will only measure the central part and is rather useless here.

Thankyou.  So using the Siril command "seqtilt sequencename" I ran the sensor tilt command on the sequence of 600 subs. Results:

 

Stars: 115, Truncated mean[FWHM]: 2.45, Sensor tilt[FWHM]: 0.13 (5%), Off-axis aberration[FWHM]: 0.15

 

sensor

 

 

And Aberation Inspector on a single sub-exposure.

 

aberation

Edited by tarbat, 05 October 2023 - 11:00 AM.


#13 Rasfahan

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Posted 05 October 2023 - 01:58 PM

The tilt is measured the same as in ASTAP - this is due to the aspect ratio of the chip. Also, you can‘t well measure tilt on a stacked frame if you have field rotation or a meridian flip is involved.

The single shot shows approx. the same astigmatism as my sample.

#14 Mills543

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Posted 03 November 2023 - 04:52 PM

Nice review! Thanks. I have one coming and looking forward to using it. Would you happen to know if multiple phones can be connected at once? Thinking about using it with my students. I teach Earth Space at a high school.

#15 Nancy.yao@ZWO

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Posted 06 November 2023 - 09:14 PM

Mills543, on 04 Nov 2023 - 05:52 AM, said:

Nice review! Thanks. I have one coming and looking forward to using it. Would you happen to know if multiple phones can be connected at once? Thinking about using it with my students. I teach Earth Space at a high school.

It can connect two mobile phones at the same time


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#16 apearce

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Posted 16 November 2023 - 07:36 PM

Hi

 

A great review!  You mention that you can "pick your coordinates".  So does that mean that you can enter an RA and Dec into the app and it will slew to that position?  You also state that the images can be transferred to your PC via USB.  In the manual, I don't see a USB port, although I must admit that the product manual is not that detailed.

 

Regards

Andrew



#17 Rasfahan

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Posted 16 November 2023 - 08:59 PM

Hi

 

A great review!  You mention that you can "pick your coordinates".  So does that mean that you can enter an RA and Dec into the app and it will slew to that position?  You also state that the images can be transferred to your PC via USB.  In the manual, I don't see a USB port, although I must admit that the product manual is not that detailed.

 

Regards

Andrew

You can not directly input RA and DEC coordinates but need to use the catalog. It seems to include many (all?) NGC and SH2 objects at least - weather has been atrocious here so I haven't played around with it a lot recently. Once you select an object from the catalog you can move freely around in the sky atlas, so if an object is not listed you can still move to it.

 

The Seestar does has an USB-C port that can be used to access the files.



#18 apearce

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Posted 16 November 2023 - 09:30 PM

You can not directly input RA and DEC coordinates but need to use the catalog. It seems to include many (all?) NGC and SH2 objects at least - weather has been atrocious here so I haven't played around with it a lot recently. Once you select an object from the catalog you can move freely around in the sky atlas, so if an object is not listed you can still move to it.

 

The Seestar does has an USB-C port that can be used to access the files.

Thanks for getting back to me.  So for example, if I was trying to locate a variable star to image, I would have to try and find the nearest NGC object and then there is the ability to manually adjust the position of Seestar to the variable star position (if I knew where it is in relation to the Star Atlas?).  I have seen images taken by others which show 15th magnitude variable stars, which is quite impressive.  I presume that the scale of the Star Atlas is sufficent such that you knew where to offset from a known NGC object, say a couple of fields of view, to locate a variable star?



#19 tarbat

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Posted 17 November 2023 - 04:07 AM

So for example, if I was trying to locate a variable star to image, I would have to try and find the nearest NGC object and then there is the ability to manually adjust the position of Seestar to the variable star position (if I knew where it is in relation to the Star Atlas?).

Yes, you'd select a target that's in the SkyAtlas catalog, and then move the RED box over the area of the sky that you want to image and press SYNC.

Attached Thumbnails

  • 1.jpg

Edited by tarbat, 17 November 2023 - 04:08 AM.


#20 Rasfahan

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Posted 17 November 2023 - 04:10 AM

Thanks for getting back to me.  So for example, if I was trying to locate a variable star to image, I would have to try and find the nearest NGC object and then there is the ability to manually adjust the position of Seestar to the variable star position (if I knew where it is in relation to the Star Atlas?).  I have seen images taken by others which show 15th magnitude variable stars, which is quite impressive.  I presume that the scale of the Star Atlas is sufficent such that you knew where to offset from a known NGC object, say a couple of fields of view, to locate a variable star?

I just checked with the app - the catalogs are NGC, IC, SH2 and Messier - but they do not contain a lot of the objects. I had assumed they were filtered by visibility but that is not the case. You can select any of the objects in the database and the freely move to your desired object. A RA/DEC grid can be enabled to make this easier. I‘ld prefer free input of the coordinates, but that‘s not possible currently.
 

You can download the app and use most of it including the sky atlas without connecting to a Seestar to test it out if it meets your needs.

 

15mag should be unproblematic, much higher mags should be possible. The 10s images that are stacked are reasonably clean, the stacking algorithm works well enough and the Seestar dithers, so you‘re not read-noise but sky limited. Interesting idea to use it for variable star measurement, I might get involved in this.



#21 SeymoreStars

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Posted 23 November 2023 - 10:31 AM

What's the polar alignment routine like? A photographer friend of mine got one and I will try to help her remotely.



#22 SeattleStars

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Posted 24 November 2023 - 02:29 AM

What's the polar alignment routine like? A photographer friend of mine got one and I will try to help her remotely.

Alt/Az no polar needed.


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#23 SeymoreStars

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Posted 24 November 2023 - 11:13 AM

Alt/Az no polar needed.

Okay is there a 2 star alignment routine or the like to know where the device is pointed?



#24 tarbat

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Posted 24 November 2023 - 11:18 AM

No need, it’s all automated.  Put the Seestar on its tripod, turn it on and select a target, and it uses automated plate-solving to align itself and find the target.  All you need to do is remember to autofocus.

 

Okay is there a 2 star alignment routine or the like to know where the device is pointed?


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#25 SeymoreStars

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Posted 24 November 2023 - 11:19 AM

Thank you tarbat.




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