How many Frames Do We need To Bring Out Most Details Of A Deepsky Object Like Faint Nebulas? - Forums

Hello and welcome I'd like to ask everyone experienced in this or knows how many frames we need to take to bring out most of the details from a deep sky object like those that are nebulas and are faint.
I'm been hunting for a faint deep sky object since the previous year, the Witch Head Nebula with my Seastar S50 telescope, however.
Even I collected 800 frames of data. I can't bring out every detail from this kind of nebula in siril.
Does anyone have experience in this or know how many frames or data we need to bring out all of the details of a nebula like this?
I just guessed that if we have 500 frames, that is the amount where you can bring out the most details of the deep sky object well mostly from a galaxy but not a nebula.
Can anyone tell?

I think that even with all of the "right" information, you can only get an estimation. I've used programs like StarTools 4 to estimate SNR for given portions of an image (faint objects, main extent of an object, brightest regions). Without spending as much money as SkyTools, grab the ultimate version of astrobin subscription to:
1) search the witch head nebula with the advanced search function
2) sort results by integration time
3) "add filter" by bortle scale +/- 1

If you want to be even more specific, add a filter for telescope type (RASA, traditional SCT, RC, Newtonian, etc.) There's no focal ratio option as of now.

This will show you images that match your sky quality/equipment and give you an idea of how much time you will need to spend on an image given your goal (faint nebulosity).

keep in mind we process things differently (I'm usually more on the aggressive side when it comes to stretching and will employ more noise reduction that some are comfortable with). These differences make it difficult to place a number on how much time you will need, but I think you can get pretty close using astrobin's advanced search function.

Short answer, as many as possible.

It is not the number of frames, per se; it is the total integration time that needs to be maximised, as a factor of signal to noise ratio => scope resolution, FOV, light pollution, etc.

With the Seastar S50, I assume that the sub length is about 10s, so 800 pictures is about 2 hours and 15 minutes, which is very little for a faint nebula. You should aim for many (really many) hours to maximise the signal and manage noise.

It also depends on the object that you image, the dimmer the object or parts of the object, the longer you need. You need lot of patience and persistence in this hobby

Generally speaking, I find 3-6 hours is enough integration time for relatively bright objects like galaxies. 12-16 hours is usually enough for fainter objects like dim emission nebulae. 16-32 hours is usually required for dark nebulae and IFN. This is with a ASI 6200MC in a f/4.6 system doing ~50% L and ~50% RGB subs. YMMV.

When I started imaging, I would rush and start stacking images after an hour or two with varied success. Now, I will normally integrate after 3-4 hrs more as a proof of concept and then decide from there if I need more integration time or not. Some targets I've imaged over several nights to get enough images that I'm happy with the result.

The speed / f-ratio of your telescope will also have an effect on how much integration time you need.

Richard Mak"s comments above is really sound advice. The quality of the image that can be attained is dependent upon collecting as many useful "signal" photons as possible. This is dependent upon your optics (50 mm is actually quite small for deep sky astrophotography) although its f number of 4.9 is relatively fast, most scopes are f/6 to f/11. While SNR of the final image goes as the square root of the number of images (the SNR of 25 stacked images is 5 times higher than an individual image) this doesn't determine the number of photos the system can collect. The number of photons is determined by the optics (size and f/number) and the exposure time of each image. I believe the maximum exposure of the S50 is ten seconds so this will limit the number of faint photos that can be collected. For nebula I typical employ exposures of 300 seconds for broadband filters and 600 seconds for narrowband filters. The number of useful photons you can collect is also dependent upon your sky brightness. I shoot in Bortle class 4 skies which works with my exposures and f7.7 setup.

Stacking a lot more images doesn't increase the photon counts within your stacked images - you need to have the ability to capture images with longer exposures - more images will only reduce the noise within your images allowing you to see more detail but only if you can collect enough target signal that is above the noise floor. A bright sky will add more background photons than target photons so the contrast of the images will tend to be low.

A scope of 80 to 120mm with a independent CMOS camera on a reasonable mount is typically the starting point for astrophotography. The seastar S50 is not what I would start with but makes a reasonable viewing scope with it live stacking on your cell phone.

Michael

Richard Mak:
It is not the number of frames, per se; it is the total integration time that needs to be maximised, as a factor of signal to noise ratio => scope resolution, FOV, light pollution, etc.

With the Seastar S50, I assume that the sub length is about 10s, so 800 pictures is about 2 hours and 15 minutes, which is very little for a faint nebula. You should aim for many (really many) hours to maximise the signal and manage noise.

It also depends on the object that you image, the dimmer the object or parts of the object, the longer you need. You need lot of patience and persistence in this hobby

So you mentioned needing around 1,000 to 2,000 frames, or maybe even 5,000? I often struggle to maintain consistent exposure times because the weather sometimes forces me to end a session. This means I have to restart everything another time.

Jon Main:
Generally speaking, I find 3-6 hours is enough integration time for relatively bright objects like galaxies. 12-16 hours is usually enough for fainter objects like dim emission nebulae. 16-32 hours is usually required for dark nebulae and IFN. This is with a ASI 6200MC in a f/4.6 system doing ~50% L and ~50% RGB subs. YMMV.

So I'm guessing 12 hours could be equal to 2000 sub-frames right?
I almost have 1000 so not sure that would be the right amount. It could be more to it then.

I would stop thinking in terms of how many sub frames, that's the wrong approach. As Richard mentioned, it's the total exposure time that matters. If you can get 5 or 6 hours of imaging done in a night. That's total exposure time not time spent shooting as that's never one to one, there's always overhead. You will be in ok shape for the bright objects. Really faint objects or details will take much longer meaning you will have to combine data taken over two or three or four nights. The right number of subs is the number you need to get the results you want.

Szijártó Áron:
Jon Main:
Generally speaking, I find 3-6 hours is enough integration time for relatively bright objects like galaxies. 12-16 hours is usually enough for fainter objects like dim emission nebulae. 16-32 hours is usually required for dark nebulae and IFN. This is with a ASI 6200MC in a f/4.6 system doing ~50% L and ~50% RGB subs. YMMV.

So I'm guessing 12 hours could be equal to 2000 sub-frames right?
I almost have 1000 so not sure that would be the right amount. It could be more to it then.

Generally speaking, every time you stack your data and decide that it's not good enough you need to double what you have. Ie. You stack 1h of data and it's noisy so you get a total of 2h. You stak that and it's still noisy so you get 4h. It's still a bit too noisy so you get 8h. You stack that and you are happy with the results. You are now done.

Tony Gondola:
I would stop thinking in terms of how many sub frames, that's the wrong approach. As Richard mentioned, it's the total exposure time that matters. If you can get 5 or 6 hours of imaging done in a night. That's total exposure time not time spent shooting as that's never one to one, there's always overhead. You will be in ok shape for the bright objects. Really faint objects or details will take much longer meaning you will have to combine data taken over two or three or four nights. The right number of subs is the number you need to get the results you want.

You might be right. I usually started to capture this object last year; I didn't get far, though, so I started to work on it more at that moment.
It's been now 2 or 3 nights of data I've collected yet. But might try to get more as I can each night. If the weather lets me to do so.
Right now as I checked with stacking the current 800 frames. I only managed to bring out some parts of the nebula, but not all of it. So, I'm guessing I'm almost there to bring out more details from the nebula.

Szijártó Áron:
Richard Mak:
It is not the number of frames, per se; it is the total integration time that needs to be maximised, as a factor of signal to noise ratio => scope resolution, FOV, light pollution, etc.

With the Seastar S50, I assume that the sub length is about 10s, so 800 pictures is about 2 hours and 15 minutes, which is very little for a faint nebula. You should aim for many (really many) hours to maximise the signal and manage noise.

It also depends on the object that you image, the dimmer the object or parts of the object, the longer you need. You need lot of patience and persistence in this hobby

So you mentioned needing around 1,000 to 2,000 frames, or maybe even 5,000? I often struggle to maintain consistent exposure times because the weather sometimes forces me to end a session. This means I have to restart everything another time.

Hahaha, welcome to the club....

I started with a Canon EOS R, lens, tripod, 2 second exposures with an intervalometer.... (if you collect even two hours' worth of data, you will get impressive results that way)

At the end of the day it is the total integration time that you have to maximise, until you get a result you are happy with.
This is not a competition, you (at least I) do it for yourself. Keep going on the same target as long as you find it fun => you get a picture you like. Then pick a new target and move on. You can always add more data later, if you feel like it. DSOs don't change much, even on year scales...

Save all the data and integrate them off the Seastar, there are good videos on youtube. Check out a fellow Hungarian, Space Koala. She has a good video about Seastar mosaics, stacked off device.

While the number of frames that you stack can improve the SNR of the image, it does nothing to increase the "signal", it just averages out the noise. If the signal is at or below the noise floor no amount of stacking will bring out more detail. For Example, 1000 images at 10 seconds each giving an overall integration time of 10,000 seconds or about 2.8 hours is not going to give the same counts per pixel as 50 images at 200 seconds each. The counts per pixels in the second case will be approximately 20 times higher. Assuming the sky background is not too bright this will provide a net increase in SNR for each image and about a 7 times improvement for the stack of 50 images. In the first case you would think that the SNR of the stack of 1000 images would be 32 higher than each image, because the signal is in the noise you won't see that much improvement over the individual images.

Also each frame has bias (readout noise) so again if the signal is weak the readout noise will degrade it if you don't calibrate your images. Also, thermal noise is a function of exposure time and also needs to be calibrated out with dark frames.

Astrophotography is about recovering a small signal (the faint nebule), relative to all the noise factors, to arrive at a image that has both good Signal (S) and good SNR need enough images to reduce noise and enough integration time per image to get the desired signal above the noise floor. !0 second exposures will not get you there. High SNR without an adequate S will not provide a very impressive image.

I don't want the original poster to despair thinking that because he is limited to 10 sec. exposure, he can't get a good result, he can. I commonly use 15 sec. subs with good results. Noise is random, signal is not.

I generally figure about 10 hours of exposure as a minimum for anything. Faint objects I go for 30-40 hours. But it depends on the weather. I get what I get, which is usually clouds and poor seeing, so I can't count on getting the amount of time I wanted.

I got a very good image of the Witches Head nebula with just 3 hours of data. Unsure whether you’d get the same result with a Seestar.

Tony Gondola:
I don't want the original poster to despair thinking that because he is limited to 10 sec. exposure, he can't get a good result, he can. I commonly use 15 sec. subs with good results. Noise is random, signal is not.

There's still the noise floor that you have to overcome, this was especially problematic with old CCD's.

I think the biggest factor here would be the quality of the skies OP is imaging in. An hour in a B1 new moon sky is worth 27-36 hours in a B8-9. With a such a huge difference, the subexposure times don’t really matter. OP mentioned hunting, if they can get their S50 to a dark sky, the Witchhead should show up nicely with just 2-3 hours of data.

Kyle Cerniglia:
Tony Gondola:
I don't want the original poster to despair thinking that because he is limited to 10 sec. exposure, he can't get a good result, he can. I commonly use 15 sec. subs with good results. Noise is random, signal is not.

There's still the noise floor that you have to overcome, this was especially problematic with old CCD's.

CCD are a totally different ball game, requiring long sub-exposures for a number of reasons. In the CMOS world it's just not needed.

Szijártó Áron:
Hello and welcome I'd like to ask everyone experienced in this or knows how many frames we need to take to bring out most of the details from a deep sky object like those that are nebulas and are faint.
I'm been hunting for a faint deep sky object since the previous year, the Witch Head Nebula with my Seastar S50 telescope, however.
Even I collected 800 frames of data. I can't bring out every detail from this kind of nebula in siril.
Does anyone have experience in this or know how many frames or data we need to bring out all of the details of a nebula like this?
I just guessed that if we have 500 frames, that is the amount where you can bring out the most details of the deep sky object well mostly from a galaxy but not a nebula.

Szijártó Áron:
Hello and welcome I'd like to ask everyone experienced in this or knows how many frames we need to take to bring out most of the details from a deep sky object like those that are nebulas and are faint.
I'm been hunting for a faint deep sky object since the previous year, the Witch Head Nebula with my Seastar S50 telescope, however.
Even I collected 800 frames of data. I can't bring out every detail from this kind of nebula in siril.
Does anyone have experience in this or know how many frames or data we need to bring out all of the details of a nebula like this?
I just guessed that if we have 500 frames, that is the amount where you can bring out the most details of the deep sky object well mostly from a galaxy but not a nebula.
Can anyone tell?

Several factors are involved and extracting detail from a nebula. Light pollution, phase of the moon, quality and size and temperature of the sensor, aperture, reflector versus refractor, accuracy of tracking, dithering, sky quality, number of dark and bias frames used, exposure settings, and your ability to post process. For any given observation of a given nebula, I don’t think anyone would be able to say that there is a minimum or maximum number of frames to capture to get the best data. I just purchased the Dwarf3 smart telescope and took 194 frames of M42. With just a little post processing for contrast and color, I think it turned out just fine.

Kevin Wilcox:
I got a very good image of the Witches Head nebula with just 3 hours of data. Unsure whether you’d get the same result with a Seestar.

Well, I now had 800 frames which was 2 hours. I merely managed to bring out only the outer interior or whatever you call it of the nebula.
So, how many frames did you collect under these hours? I right now have 1000 frames, although I might need to get more exposure time if I really can.

I would think that two hours would just be a starting point for this object.

Szijártó Áron:
Hello and welcome I'd like to ask everyone experienced in this or knows how many frames we need to take to bring out most of the details from a deep sky object like those that are nebulas and are faint.
I'm been hunting for a faint deep sky object since the previous year, the Witch Head Nebula with my Seastar S50 telescope, however.
Even I collected 800 frames of data. I can't bring out every detail from this kind of nebula in siril.
Does anyone have experience in this or know how many frames or data we need to bring out all of the details of a nebula like this?
I just guessed that if we have 500 frames, that is the amount where you can bring out the most details of the deep sky object well mostly from a galaxy but not a nebula.
Can anyone tell?

Szijártó Áron:
Kevin Wilcox:
I got a very good image of the Witches Head nebula with just 3 hours of data. Unsure whether you’d get the same result with a Seestar.

Well, I now had 800 frames which was 2 hours. I merely managed to bring out only the outer interior or whatever you call it of the nebula.
So, how many frames did you collect under these hours? I right now have 1000 frames, although I might need to get more exposure time if I really can.

Targets like witch head are feint, relatively very feint. 2 hours just won't do it

Moonlight will ruin it too.
I have beginnervgear, bortle6 and won't even attempt this. Even When new moon and no clouds

It's not about frames it's about data (raw hours of it).

I saw a video once that claimed there is a square root relation between signal to noise and the amount of hours you put into it. So to double your signal to noise ratio, double the amount of exposure hours. I can't remember who made the video, but it was an interesting watch. I'm sure there's a lot of factors at play that change that relation, such as seeing, bortle location, etc, but it's a general rule of thumb.

So if you don't get the faint details at 16 hours, your best bet would be to continue until you gather 32 hours. Going for 20 hours will only marginally help. Then if 32 hours is not enough, you gather 64 hours of data. Then 128. Then 256, etc.

Now that would mean you'd have to put exponentially more work into it which may be impossible depending on your personal situation and location. But some times the only thing that helps is more hours, even under Bortle 1 skies. But there are options, like collaborating with other people or have multiple scope setups at home, to gather more data in a shorter amount of time.