Short vs Long exposures for Astrophotography: Comparing several 1-hour stacks
ฝัง
- เผยแพร่เมื่อ 29 ส.ค. 2024
- * There is a typo in the video "20x300" is actually "12x300".
Written post with Patrick's comparison: www.galactic-h...
Patrick's Astrobin: www.astrobin.c...
In this third video of the "Galactic Experiment" series, we compare four different master lights of the Rosette Nebula. One is made up of 60 frames each 60 seconds, then we have 30x120s, 12x300s and finally 4x900s. What looks better?
* There is a typo in the video "20x300" is actually "12x300".
Other Galactic Experiments: • Galactic Experiments
Like our channel? Support Galactic Hunter: / galactic_hunter
Become a lifetime member of the Galactic Course: www.galactic-h...
Learn more with our books: www.galactic-h...
Prints available: www.galactic-h...
Galactic Hunter was created by Antoine and Dalia Grelin, a stargazing couple from Las Vegas, NV. We do our best to publish entertaining and helpful Astrophotography content, through videos, written tutorials, books and more. The main goal of this TH-cam channel is to help as many beginner astrophotographers as possible in this difficult yet rewarding hobby. We hope our content will help you reach new heights in your deep sky imaging journey!
Website: www.galactic-hu...
Facebook: / galactichunter
Instagram: @galactic.hunter
#GalacticExperiment
Starting Astrophotography, a complete guide: www.galactic-h...
Beginner DSLR Astrophotography Equipment Guide: www.galactic-h...
Full list of our equipment: www.galactic-h...
The equipment you see in most of our videos:
[Purchasing equipment through these affiliate links helps support our channel at no cost to you!]
Monochrome Camera: ASI 1600MM Pro - bit.ly/2pbF7c0
OSC Camera: QHY128C - bit.ly/349UYry
DSLR Camera: Canon 7D Mark II - amzn.to/2RDeDcq
Reflector Telescope: bit.ly/2NgKcYm
70mm Refractor Telescope: bit.ly/31TtraT
115mm Refractor Telescope: bit.ly/3aOfPCZ
Mount 1: Orion Atlas Q-G Computerized GoTo Mount - bit.ly/2Jr3ZD9
Mount 2: MyT Paramount - bit.ly/2MG51NG
Other:
Guiding: ZWO ASI 290MM MINI - bit.ly/2MRTmvt
Coma: Baader MPCC Mark III Coma Corrector - bit.ly/2WlEV5M
Acquisition: ASIAir - bit.ly/2QJj46e
Deep Cycle Battery: amzn.to/2G6PULe
This is excellent! I will be referencing this video on the website 🙂 Cheers guys
That's awesome Trevor thanks we appreciate it! 🤟🏻
Great job with the experiment!
Thanks Nico!
That is some serious dedication and I can see how much you like astrophotography in general! Really appreciate your work!
Thanks Ray, yes we dedicated a night for this experiment, it was fun to do :)
The really striking thing is how little difference there is. Particularly when you consider that the autostretch may not have done exactly the same thing in all cases.
Have you taken into consideration how your target was moving while imaging? If your target was rising during thise 4 hours it would make sense for the later data sets to be superior regardless of exposure lengths used.
Yes that was also a concern, we waited until the Rosette was about 35 degrees high before imaging it, but yes because we imaged from the backyard it probably got way better when it was at its highest point so that would affect the experiment as well.
So it basically looks like longer exposures usually result in better overall contrast, but at the increasing risk of damage to the stack due to bad or damaged frames.
Really useful and a def thought provoker. Thanks guys. Clear skies.
Thank you!
Ah yes thank you!!!! I've been asking for this lol. I love this!
Awesome!
You can't just STF Stretch each image individually and compare, you have to apply the *same* exact stretch to each image and then you'll see the real differences. This is why your 300s pic was mostly red compared to all the others.
Love this! Super helpful to see this. I'll be sending a lot of people to this video!
Thank you Jeff!
Wow! Thank you for doing this! I was surprised at the 2 minute interval quality!
I am surprised there is so little difference but I agree the best results would be a stack of many long exposures
Yes, in the end it's all 1 hour long so in a way I'm not surprised there isn't too much difference, it would be interesting to see the same experiment with a full night worth of exposures 🤔
Exceedingly long exposures will raise the noise while diminishing the returns on signal. There is a tipping point that longer exposures will no longer overcome the noise. It depends on the sum of the sources for all your noise.
Great video! I've always kinda wondered what the difference would be...nicely done.
Thanks!
I love these type of experiments. Thanks for doing this!
On my recent Rosette nebula image, using my Nikon D810a, Skywatcher Esprit 100ed with an Optolong L-Pro clip-in filter, I did 10-minute exposures at 400iso. Over 3 nights, I think I got about 70 subframes. I'm convinced, longer is better. When I stretched the data, it didn't fall apart and had excellent signal to noise.
Thanks for showing this video. I just started autoguiding and I noticed a significant increase in light pollution gradient across my subs when I ramped up from 120s to 300s. I wonder if it becomes more even with longer subs, but I'm always weary of the wind as you say which can ruin that sub! More experimenting I think!
Great work!! For me, it is better the 4x15min image. But all of them are beautiful. Congrats.
Hi, thanks for this comparision. In theory their should not be a big difference between 120s sub and 900s subs if you use a CMOS Camera. I think the main difference you see in the pictures are the incoming night/darkness and the difference of height of the object in the sky.
Regards
Andreas
Thanks Andreas and yes that makes complete sense!
Great info.
Just a quick note on the math: 300 seconds is 5 minutes like you said, but 20 frames is not an hour, it's an hour and 40 minutes. You would need only 12 frames for an hour.
Yes that was a typo in the video but it was a stack of one hour for sure :)
Salut!
You mention on the beginning of the video that we are looking at pure lights stacks.
What strikes me is that you don't have darks then, therefore the heat noise necessarily goes up, probably accounting for that noisy result on the last stack.
However the longer the exposure, I assume the lower the iso/gain setting was, so the more dynamic available for post-processing, resulting in better contrasts, colors etc...
I'd probably go for something less prone to errors as 15mn, but maybe 7 to 10 would be a good balance, depending on the set-up!
Great analysis. Thank you. I have a lot of trees, planes and other random obstructions so, with the short viewing times, I generally go with the 3 min subs. It seems to work out well for me.
I love the depth and the color in the 15-minute version. I'm sure you're right--stacking more is going to lower that noise floor!
Great candid vid. One point, 20 x 300s exposures = 1h40. So if it definitely was 20 exposures that sort of means you can't count that lot of subs due to having far more exposure overall. It would have to have been 12 subs.
Thanks and yes that was a typo error done during editing, it was 12 subs for sure.
Very nice , some of us can’t auto guide yet , either skill level or mount issues and a redcat will do longer exposures then a 8” sct with a 6.3 focal reducer corrector. Like I have . But 15 minutes wow that’s crazy . Was surprised on the results of the 5 minute one . Great work thank you .
Thank you Dan!
I lived in Vegas 2009 and camped at lake mead with my 11”sc and goto . Only visual though . Great dark site .
Robin Glover have a presentation about this, there is a certain limit where there is minimal gain in quality if you increase the exposure limit further.
4x the exposure reduces noise by half. The only thing that is diminishing is the time we have available. =)
I think double the exposure time is more like stacking two pictures using addition mode. So that's why the 4x900s looks brighter than the 60x60s. Maybe if you stack images using other modes, the difference between final images would be tinyer ?
For me the clear winner was the 5min subs. They were the cleanest.
I can only assume you changed the gain/ iso between the different sets to keep the histogram the same. I don't have an autoguider so am pretty limited on my exposure length. This video shows that the gain after 1minute it pretty limited. Thanks for sharing. 👍
Watching this video again . I now image with a asi 294mc pro and use Nina. Good by hand control. Two hours of 5 minute exposures with the L pro and the whirlpool came out so nice. Tonight the bubble nebula.
The whole video - nicely done with good information. I liked 900 x 4. I wonder if I could get a shot 900 seconds long without a problem? Thank you for doing this. Now it’s my turn ...
I like the idea but I don't know why you stuck with it knowing that the auto stretch makes the images incomparable. I think you should've gone back and fixed that before finishing the video. I also think you need calibration frames for a proper comparison.
Again, thanks for sharing, pair of two!
Look. I think that to have a better evaluation for long vs medium/ short exposures, you should include the following variables: bortle class, haze/smog, gain/offset or ISO and how these impact in the histogram level and, therefore, your exposure time and end result.
I believe dark skies allow you to expose more and as a result to maybe get more information. Light pollutted skies, on the other hand, limit severely your exposure times per shot.
Actually, after writing this it came to my mind that there might be some targets that might be extremely difficult (if not impossible) to shoot (for example galaxies), no matter what the exposure time you might use, from a suburban or city location.
Anyway, thanks again for sharing, guys. I enjoy very much your videos.
Not sure if you mentioned stacking 60 files will take a lot longer to process and eat up more disk space? And also more overhead, image download and much more dithering.
Great video. TH-cam is filled with how to videos on all the same stuff, but very little actual practical examples of various settings on the same thing. This is really useful. Did you keep the same camera settings between the shots such as gain? And did you have a filter installed?
Thank you Steve! Yes we used Unity Gain for all the shots. Same temperature as well. Triad Ultra filter.
You might consider showing us the histograms of subs. Really short exposures will have a lot of noise and the histogram peak will be way to the left. Too long of an exposure will shift the histogram peak way to the right. A Goldilocks exposure will have the peak about a third of the way from the left. That way you don’t record too much light pollution, skyglow, or saturate the sensor with bright stars and you also have a better signal-to-noise ratio to begin with than when you are using very short exposures.
I would have to vote for the 300 seconds exposure as Dahlia says, one flash of light, a gust of wind, or a passing satellite, the data frame would be lost. The longer the subframe, the greater chance for corruption possibilities.
Great video, what I normally do is find a dark bit of sky , run sharpcap brain ( need to do the sensor analysis first ) , use unity gain , give it how many hours I want to run it for , my Altair Astro 26c hypercam TEC , gets values of gain 100 optimal black levels of 396 , which I tough was crazy , but it does not clip any data now , my last measure for ngc 7822 was 233 s subs
Pourquoi vous ne faites plus de videos en français, c'était tellement bien !...les videos techniques sont très difficiles à suivre avec les sous-titres (approximatifs) !...dommage !!...j' étais un abonné fidèle de votre chaîne en français, mais depuis qu'il n'y a que des videos en anglais, j'ai été obligé de me désabonner, moi qui attendais toujours vos vidéos avec impatience !!..
Désolé mais malheuresement c'est juste impossible pour nous de tout faire en deux langues 😩Avant on ne faisait qu'une video tous les 2 ou 3 mois donc c'était possible.
@@GalacticHunter Moi aussi j'adore vos vidéos, seulement l'anglais et moi .. bah ça coince un peu.. Mais je m'y met doucement. C'est vrai que plus de sous-titres serait cool pour nous ;)
Petite question, tu es originaire d'où dans l'hexagone? La prochaine fois que je retourne à Vegas, je passe vous voir!
Continuez comme ça, même en anglais c'est cool de vous suivre!
Sorry if I missed it, but how was the histogram adjusted with all these?
It would be interesting to remove one or two images from each, to see the difference between them to in a real life scenario.
I mean, obviously there won't be any real difference between stacking 59 images or 60 images, but what's the difference between stacking 4*900s and 3*900s? Would that be noticeable?
Great stuff, I do think it would be an interesting experiment if you had chosen a target with a lot of fainter and darker outer dust clouds and gasses like Simies 147 or Barnards 7 or maybe the Tarantula.
Cool Experiment!
Great dedication! I have found the same to be true.
Hi guys! i have a Nikon D3500, 30" is the maximum exposure time... its 30 seconds enough?
300x20 is 1 h 40mins or was that an error in the editing of the text
you should run your images through a calculator to give skybackground quality and snr readout,some of these tools give you the optimal exposure time . atm i can't remember the tool, i'm guessing your optimal exposure is around 3-5 mins
That convinces me that taking as many short pictures as possible with your stacking gear is the way to go. Taking 15 min long pictures isn't worth the imaging hassle with sat trails, wind and small vibration accidents.
Great video good info for us beginners. Can I ask does the iso obviously change on each scenario ?
I'm pretty sure they changed it considering the difference in exposure time for max and min. I'm guessing that for the longest exposure the gain was turned all the way down
Good morning, thanks for the video, I would go with 2, can you do a video on iso?
This is great. Thanks for sharing. Trial and error I guess eh haha!
15-min rules. Great post
I think I like the 120s the best of all from a benefit to hassle ratio. As mentioned 15 minutes is a long time for something to go wrong, wasting a lot of data gathering time. Also the lack of subs to stack really makes the noise an issue.
The 5 min sub being such an outlier is a puzzle to me. It's the darkest red by far, but also the least sharp of them all.
Isn't the best way to determine exposure lengths by looking at the histogram of a sub after capture? Get the graphs to the right without clipping them?
There's so much to every aspect of this hobby.. Here's another I watched last night, there's a formula to everything! But for now i just want to watch the world burn, and wing it haha
th-cam.com/video/n1RbyswFUqs/w-d-xo.html
Come on.... I need to wait 15 minutes per exposure... how do you even wait that long?????
Simple, eat dinner, then come back to it :D
Well in that case I can set it up for hours of exposre lol
I’ve had a lot of success between 5-8 minutes. Personally I haven’t tried longer than 8 yet because I’m still just using a DSLR
Merci pour cette vidéo. Très intéressant.
There's math to decide that. In short, you take 8% of your fullwell for the flat exposure time. You take a test light on the target to achieve 85% of your fullwell on the brightest pixel. Finally you take a dark for the same seconds as it took to reach the 85% fullwell and determine its max pixel. Subtracting your dark and flat from the light should leave at least 50% of your fullwell. If it doesn't, move both your dark and light slightly up or down to refine to 50%
For Galaxies and Globular Clusters and some Nebulae that have bright cores, these images will not lead to good results. The long exposures will just blow out the centers of the main object. I been struggling with this issue as a NOOB. Can you create an experiment that shows us NOOBs what the best approach would be for this very, very common issue. Nebulae are easy, LOL.
I would go with the picture that's closest to what it is supposed to look like
If you're at >1500mm focal length, and are relatively fast, short=more details.
Isn't comparing only lights unfair? Thermal noise and RMS is not the same
Great video! I am a little baffled though, what about star saturation? I would have thought that at same gain and aperture, a 15 min sub would blow star cores completely? Would like to hear your comments on that. Thanks for the video!
Looking at the numbers Patrick showed, the stars got a tiny bit larger at 15min, but with good astronomy cameras they really don't get blown up unless the focus is off.
@@GalacticHunter Thanks for taking the time to reply...
maybe you should try short expo with high gain try to reduce the readout noise and make the sensor more senstive
you canot compare if you don't subtract RN from the light frame, the subject signal must be alone for the swamp extraction. i thinks...
There is a video that RoRo posted talking about changing sub exposure lengths based on light pollution (shorter in higher LP) What are your thoughts on that variable?
In a Bortle 4/5 area I have recently started with ASI1600 MM Pro, previously using Canon 70D (mod). I have done 5 mins and 15 mins for 1.5 - 2.0 hours. Despite the pesky satellite trails I prefer the 15 mins, when weather conditions permit.
You should be shooting 100+ frames with that camera to gain back dynamic range since it's only 12bit (this also helps with rejection of satellite trails). 5 minutes would be better at empirically improving your data. This video is incredibly misleading as the only thing it showcases is how PixInsight applies difference levels of stretching at different exposure lengths, and NOT how good the data actually is.
Looking at Patricks excel chart, something here is odd. Your star count dropped big time at 300s. The star count should increase with exposure time "in theory". Where there high clouds during this part of test?
No idea, I did not see any clouds but that does sound likely!
At 900 sec you got a better separation on the background
Why do people do these comparisons and not use blink? Side by side is not a good comparison.
I don't know why people dislike...
seems to me like anything past 300 seconds might have too much atmospheric distortion and like mentioned, if something goes wrong for a single sub that's a lot of time lost
If you look at Patrick’s analysis, you might reshoot your five minutes exposure because the five minute exposure data has less stars than 2 minute and 15 minutes and FWHM, eccentricity, number of stars are significantly different and don’t follow the trend. Unfortunately your data sort of like a typical night imaging, there are better periods of clarity than others
Very interesting indeed, maybe there were some thin passing clouds when shooting that batch 🤔
Great video! What would the iso equivalent of your camera setting be?
I'm still a newbie at this, but do you have to change your gain settings for the longer exposures in order to avoid oversaturation?
Thats just great, so I stick to my 2 or 3 min exposures :)
Very informative, thank you.
I was wondering if you used same f stop on camera with the different exposure times?
Thanks, with a camera lens yes always use the lowest possible f/number without sacrificing the shape of the stars on the edges
300 sec is 5 mins x 20 frames = 100 mins ie 1 hr 40 minutes ?
I would shoot a lot of 3-5 minute exposures at 50-60%% gain. Why? 1) I was recently shooting 180s exposures at Bortle 4 location and literally every other sub had satellites and/or airplanes in them. I can not afford to throw away 1/5th of my subs if I were shooting 15+ minute exposures. 2) looking at read noise chart for my camera, the read noise at 250 (of 500) is 3 times lower than at "unity gain" of 120 and only 10% higher than at full gain, so you still have full dynamic range with *almost* the minimal possible read noise. 3) lesser effect of imperfect polar alignment and guiding errors 4) more frequent dithering. IMO 15+ minute exposures are too risky and the difference in noise between 15 minute and 3 minute exposures is a lot less than 1 minute and 3 minute exposure.
Also in your video I noticed that there's background gradient in shorter exposures. That's, I believe, because you started your experiment with shorter exposures when the object was lower in the sky and finished it when it was more overhead, so earlier set of subs had more sky glow on the horizon and more atmospheric dispersion than longer exposures when the object was high in the sky. So it's not a fair comparison. Perhaps try the same experiment over 4 different nights at approximately same ascension or otherwise same seeing conditions.
It would be interesting to see the image histograms.
How happy are you with the ASIAIR Pro? We have it since couple weeks and like it a lot.
Will you guys also make a review/video of ASIAIR too? 🤩
Great comparism with the exposure lenght, so in generell as longer as more details, but rather for dimmer targets.
Have a great day, cheers
Thanks, we had issues with the ASIAir pro at first (it came with a corrupted SD card) but now we fixed it and love it. We just wish the WiFi was stronger. Not sure about a review, not planned yet but maybe :)
@@GalacticHunter you point out a weak point 😅🙈 the wifi is great when you just stand very near, its a pity the didnt use a stronger antenna. We bought a flat LAN RJ45 Cable 20m for the ASIAir Pro, so the speed for downloading is faster and best, we can stay inside the house in freezing winter ☺️
Couldn't do it with the constraint on a backyard in the suburbs and the target going behind a tree or a house and loosing 15 minutes of 1 frame. My 25x300 seconds are very hard to distinguish from my 125x60 seconds. Even if I get 5 frames ruined, I still got plenty to work with . Plus the ISO needs to be cranked down or not even possible to take it down far enough with a DSLR and having light pollution. But yes, I can see doing 15 on a dark site with no obstructions and absolutely sure there won't be any clouds.
You knnow you dont have to just guess exposure time, sharp cap has a sensor analysis tool, then you go to the histogram and measure with scope, filters attached and it will tell how long subs need to be, otherwise you will just fill pixels with light pollution and gains from longer expourses are neglible..
Interesting, we don't use Sharpcap, that's a great feature
Would love you guys to do an eq vs alt alz difference with the same object, as lots are now using alt alz mount to do DSO imaging. And getting reasonable shots, due to fast modern cameras, sure your limited to 30 secs, but can still do multi short exposures and using software to de rotation image. Its so often said by those in astrophotography dso imaging cannot be done on an alt alz mount, but proven wrong.
It is not proven wrong by any stretch. A good, solid equatorial mount is going to beat an alt-az mount. Every. Single. Time. Fast, modern cameras? Huh? What does that even mean? Your exposure limit is not just a hard and fast 30 seconds. It's completely dependent on the location of your target in the sky. What is this magical "de rotation" software? Typical stacking software will align the images, but at the cost of rotation, forcing you to crop a bucketload of the image.
Can you get images using an alt-az setup? Sure. Are they going to be as good as images created using an equatorial mount? Nope. Here's a prime example for you: Narrowband imaging. Good luck taking that 5-10 minute Oiii sub with your alt-az mount. Oh, that's not a fair comparison? Fine. What are you going to do with a DSO that fills the frame? Oh, that's not fair, either? OK. So, you're extremely limited in the types of targets you can shoot, and you will, by your own statement, only get "reasonable shots". Why, again, would you choose an alt-az mount as the basis for your astrophotography?
Number 3: Text says 20x300sec=6000sec=100min=1h40min
you state 12x300 at the end of the video which equals 1h. 😊
Things to consider, I usually stick to 120 or 180sec. rarely 300sec.
Haha I knew we got some math wrong 😅Each stack was a total of one hour for sure though :)
@@GalacticHunter you got me confused for a while 😊
Is someone's car alarm going off in the background like 7min in?
yes
I have a question guys, if I already have a single stacked tif file of 3 hours (180 x 60 sec) and want to add 3 more hours (another 180 x 60 sec) is it necessary to re process the entire 360 raw files or can I add the first stacked tif file to the other raw files in DSS ? Thanks.
You can stack multiple sessions with the tabs at the bottom. Personally, I’ve only done it once and I currently trying to find out if I can just combine stacked images or if I should save the data and re-stack them all. Only problem is I’ve deleted the flats for them. SMH
@@jedidiahwest4619 thank you. Once I got all the data, tomorrow I will check if it works
You want a bigger telescope and I would go shorter exposure.
Top, merci
Nice
What equipment did you use to take these pictures?
Raptor 61 / Atlas EQ-G / ASI071MC / Triad Ultra
This is not very meaningful because the recording conditions have changed. Second from theory there should be no difference at all so you should be able to explain why there is a difference and I predict it's not basically because of the different recording times..
hello guys, great work.. I was wondering though have you guys been able to figure out the any relationship between short and long exposure? I mean like to get the equivalent image of a 900s sub you need x 1s subs .. your experiment shows that a 1:1 factor doesn't work. But there must be a magic factor. In other words, in order to get the same result as a 900s exposure you will need 10x more 1s subs ... i hope i explained it right
Hi, are you using the same gain for each set ?
Yes Unity Gain
You get more light with longer exposures. Stack a few of those and itll be better than more but shorter exposures.
only up to a point, after that you're just collecting more light pollution or you're saturating stars and filling the full well capacity of the camera. Total data is what matters, not exposure length (to a point).
@@Phillyo118 well yea..
Thank you so much for this comparison! Very (!) helpful!
I want to refer to a very in-depth talk of the founder of SharpCap about the theory of exposure time - noise - number of subs - TIET - camera types... Make sure to check it out: th-cam.com/video/3RH93UvP358/w-d-xo.html
I'll link your comparison in the video-description of my stacking-video (covering the math-side of the topic).
Clear skies to both of you!!
-Chris
How is 300x20 = an hour.........
Typo
Great video guys. Thanks for taking the time to do the analysis. I always love to see the differences with exposure times to get a feel for detail. My camera is cooled, so noise isn't too bad, but like Dahlia said with super long exposures, one gust of wind or some guiding glitch can waste a lot. I like the 5 min exposure time. I shoot with OSC and 5 minutes with Optolong L-Extreme worked pretty well. I recently shot the Rosette and with 75 stacked 5minute subs and the detail was decent, with low noise. Cheers. www.astrobin.com/full/u88xr5/0/
Thanks for the link. Nicely done! So far I have had the best luck with 5 min exposures too. Just beginning in the hobby.
@@cryptojihadi265 good luck 😀. Just start slow and be patient.
but just think of how much hard drive space you save!!! 15 min subs for 8 hours = 32 shots. vs 2 min subs for 8 hrs = 240 shots....Gigabytes had up a lot faster. I would think you can get away with better guiding (more forgiving) with a 275mm Raptor, vs longer scopes....which would allow for longer exposures as well. right?
Haha yes that's why we do 5 or 10m exposures now for most objects instead of 3 minutes like before. And yes guiding doesn't even matter that much with the Raptor it's so wide.
The longest I can do on my alt-az mount is 20 seconds subs. Sad.
Are you guys serious, where is your match. Last time I check one hour is 60 minutes and only 12 frames of 5 minutes each. You took 5 minute exposure and staked 20 of them this is 100 minutes which almost 2 hours. you need to stack 12 images for a 1 hour.
Read the description... 🤦🏼♂️