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How Many Exposure Times Need For Better Image?

ZWO Seestar S50 Beginner Deep Sky
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Szijártó Áron avatar
Szijártó Áron avatar
Hello and welcome. I'd like to ask everyone who uses Zwo Seastar S50 and has experienced that. How many exposure times do we need to get better images? I saw a video about exposure times but did not watch it, so I first have to know if anyone who is experienced and knows how much exposure is the best that shows exactly the desired image and how long we need to wait for it.
I am currently trying to see any changes when im try to plan the deep sky photography but sometimes when I'm in the middle of the stacking an error pops up that says the stacking has failed due to not enough stars or getting stars trails. 
So, does anyone know how long we have to wait to get a better image?
D. Jung avatar
D. Jung avatar
Depends on the target and your level of light pollution. 
The SNR doubles with 4 times the exposure, so you need to wait longer and longer to get better results.
Anywhere between a couple of minutes for the brightest objects to 100h+ for the faintest.
​​​​​
Don't expect too much from the seastar and maybe watch those videos…
Tony Gondola avatar
Tony Gondola avatar
longer is better in deep sky photography…
kurt ragsdale avatar
kurt ragsdale avatar
The more time you can put together the better it's going to look. I got over 4 hours on m 51 in light polluted skies here. It helps a lot to get to darker skies. I can start to some the elephant trunk at the apartment complex here around 30 minutes but I'm not going to put up here until I can get more at the other darker sky site around here. I got more detail on m 27 at the darker sky site close to here with 30 minutes there than the hour and half here at the apartment complex.
Wim van Berlo avatar
Wim van Berlo avatar
The question is put too general in my opinion. If in stead, the question is put as "how many exposures do I need to reach my objective with this target?", you will get a more definitive answer. 4× longer exposure time will get you double snr, in theory. But what snr do you need? If you want an image of the main region of the Orion nebula, you'll need much less time than if you want to capture ifn around M81. People sometimes talk about the point or rule of diminishing returns, but with the sqrt(N) relationship, there is no such point. But there always is a point of "now I'm pleased", or "now I want to move on".

just my opinion on the matter.

cs,

Wim
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Jan Erik Vallestad avatar
Jan Erik Vallestad avatar
I think you've already been told in a previous post but I am going to repeat one major issue which is field rotation. For how long are you trying to image the same object on a given night? With this equipment you will be limited to a rather short amount of time per object, per night. So ideally you would either have to modify it (which defeats its purpose IMO) or shoot different targets and repeat their sequence each night at approximately the same time. 

After some time field rotation will make the star alignment harder and there will be fewer stars available that overlap. Could this be what you are seeing during the live stack? A dedicated stacking software will do a much better job, but the resulting image will become very small due to cropping.

IMO the Seestar basically is a cheap and fun entry level piece of equipment. Out of the box it's not meant for deep, high resolution images. At the very least it requires lots of planning, patience and quite possibly modifications to avoid field rotation. 

Perhaps someone that actually own one might be able to chime in and confirm whether the Seestar has trouble doing live stacking with too much field rotation. If not you may get better advice on ZWO's own forum or their Seestar FB group.
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ScottF avatar
ScottF avatar
It really depends on your objective, as pointed out above—for example, M27, the Dumbbell Nebula. You can get a pleasing image of the main body without a significant investment in time. But if you want to capture the Ha and OIII in the wings around the core, you need to invest more time. 
I'd check out potential targets and see what others have done here. If you see a nice image that takes only a few hours to achieve, then it's likely a good target for you. But some amazing images here take over 50 hours to achieve. That's not a target to consider with a Seestar.
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D. Jung avatar
D. Jung avatar
Astrophotography definitely has some pay 2 win aspects. If you don't spend money, you need a lot of patience, and you can't get all the good stuff.
Szijártó Áron avatar
Szijártó Áron avatar
I think you've already been told in a previous post, but I am going to repeat one major issue, which is field rotation. For how long are you trying to image the same object on a given night? With this equipment you will be limited to a rather short amount of time per object, per night. So ideally you would either have to modify it (which defeats its purpose IMO) or shoot different targets and repeat their sequence each night at approximately the same time. 

After some time field rotation will make the star alignment harder and there will be fewer stars available that overlap. Could this be what you are seeing during the live stack? A dedicated stacking software will do a much better job, but the resulting image will become very small due to cropping.

IMO the Seestar basically is a cheap and fun entry level piece of equipment. Out of the box it's not meant for deep, high resolution images. At the very least it requires lots of planning, patience and quite possibly modifications to avoid field rotation. 

Perhaps someone that actually own one might be able to chime in and confirm whether the Seestar has trouble doing live stacking with too much field rotation. If not you may get better advice on ZWO's own forum or their Seestar FB group.



So this all depends on how long u can do this and depends on the level of the light pollution. Im recently on green level light pollution according to the seastars light pollution map. But the green field is cant be that bad right? I mean it acceptable for deep sky imaging. So the only disadvantage here is the field rotation I guess.
Jan Erik Vallestad avatar
Jan Erik Vallestad avatar
Szijártó Áron:
So this all depends on how long u can do this and depends on the level of the light pollution. Im recently on green level light pollution according to the seastars light pollution map. But the green field is cant be that bad right? I mean it acceptable for deep sky imaging. So the only disadvantage here is the field rotation I guess.



Yes, in your case I would be most worried about field rotation I think - although I don't know where on ther bortle scale you are, or how the Seestar measure these things. Keep track of how long it takes before field rotation becomes a problem, then it's all a question of how much FOV you feel comfortable sacrificing in the end result. But as I understand it you probably should repeat the imaging sequence at the same time for several days to accumulate enough hours of exposure. Just how it is with the Seestar I'm afraid, unless you mod it of course.
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Szijártó Áron avatar
Szijártó Áron avatar
Szijártó Áron:
So this all depends on how long u can do this and depends on the level of the light pollution. Im recently on green level light pollution according to the seastars light pollution map. But the green field is cant be that bad right? I mean it acceptable for deep sky imaging. So the only disadvantage here is the field rotation I guess.



Yes, in your case I would be most worried about field rotation I think - although I don't know where on ther bortle scale you are, or how the Seestar measure these things. Keep track of how long it takes before field rotation becomes a problem, then it's all a question of how much FOV you feel comfortable sacrificing in the end result. But as I understand it you probably should repeat the imaging sequence at the same time for several days to accumulate enough hours of exposure. Just how it is with the Seestar I'm afraid, unless you mod it of course.

Just checked and according to seastars LP map it is green or dark green which stands for the rural level of light pollution of 4. Im assuming its enough to capture bright objects the least.
Jan Erik Vallestad avatar
Jan Erik Vallestad avatar
If it's bortle 4 you should be good to capture most objects, depending ln equipment of course.
kurt ragsdale avatar
kurt ragsdale avatar
I put in punch color to get rid of the obvious field rotation in my see star pics. I use zwo software planetary stacker to put different nights of the objects pics together and denoise it with Siril data adaptive dual domain denoising but some objects take several hours to get enough of it out and you have to figure out how long it can go without blanking out your work.
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