Long VS Short Exposures in Astrophotography - Broadband 

As I'm sure you know, if the stars are oblong, there will always be less fine detail. If the system is blurring the stars into a other than round shape, then it is doing the same with the fine details as well.

I also did a similar comparison a while back, I shoot in Bortle 3-4 and the dark sky really works well with longer subs, but not too long. For instance, I have found out that 300s LRGB and 600s SHO gives me the most detail. Drop lower and I start losing fine detail, go higher and there is no gain in any detail, it actually seams there are worse results since external factors (such as wind) have higher impact on overall sub quality in longer exposures. I think the sky darkness as well as aperture size and speed are all three very important in deciding the sub frame length. Great video as always.

Hey mate, You are a right legend! Thank you for sharing your tips and experiences here at RU-vid-You sure are gifted at this universal hobbie we all share a strong affection for. Your talent and dedication is most appreciated and your presentations are extraordinary. May you continue such exceptional work well into the future buddy. Sending you many blessings and light from Australia!

Thanks for giving over a very rare clear night to do this for your viewers. Much appreciated

The one on the right definitely seems to have more detail and contrast ... at least to me. Maybe not when zoomed in on the tiny galaxy, but for sure when zoomed out all the way.

I recently tried pushing my humble 102mm scope as hard as I could by using a 1x flattener and 294m in bin1. The small well depth and small sampling of 0.67 meant I chose 30s exposures to combat seeing and guiding errors. I was ablt to throw out 25% of the exposures and ended up with a much better stack than I anticipated.

The way I see it. The more subs you take the lower the normalised noise floor of the image. As long as you expose long enough to bring fine details slightly above that noise floor, then your good. So then it becomes a balancing act. Too long exposures and you don't get as many subs and therefore have more noise but stronger signal. Too short exposures you get many subs so lower noise floor but a weaker signal so might lose details to the normalisation process. I personally find for emission nebulae 300s is enough, granted I'm using a very sensitive cooled camera. For bright wideband stuff like Orion, Galaxies etc, 60s or even 30s is enough. 60 would blow Orions core out for me. Awesome testing!!! Really interesting video

One thing i think is a benefit with shorter exposures is that when seeing conditions are a bit poor as they often are in Florida’s west coast, the images tend to be a slight bit less blurred. The comparison between the faint galaxy in those pics looks similar to what can be experienced.

Processing time and data storage, overall data collection efficiency etc. they can sway me away from too short of a sub.

good comparison luke! i think the things like elongated stars and satellite trails aren’t a shortcoming of your comparison here, i feel like it’s an important thing to include because that’s exactly the risk you take with longer subs. less chance for dithering to help out, less of a loss if you lose a frame to a wind gust or guiding spike, et cetera. for those who want to dive deeper, Deep Sky Detail has a great video on Signal to Noise Ratio And Number of Subframes, i’d recommend checking it out for a better more fundamental understanding on how many and how long your subs should be! and clear skies luke!

Great video Luke. I tend to stick to shorter lengths - max 2 or 3 mins - only because of satellite trails, and other unknowns 😂

So many starlink satellites now unfortunately makes shorter exposures almost a necessity. I took 100 exposures of Markarian's Chain the other night and more than half had either an aeoplane or satellite trail 😒

Interesting comparison. I think the "the longer, the better" is just a legacy of the times where cameras had a LOT more noise and much lesser quantum efficiency. Personally i opted for the 2 min exposures, because I never was able see any benefit on going to 3 min, 5 min or 6 min exposures. Tried several times and always went back. That way if i really have to drop a picture its less exposure times trashed. More pictures also mean more dittering. Last but not least , even if your mount tracking is PERFECT, you should always consider the wobbling of the atmosphere ... if you have a lot of jet stream on the night, the start would wobble a lot, causing bigger/elongated stars. Here shorter exposures would help. I'm not an expert, and my rig is much cheaper than yours, but i think a more modern approach is not "the longer exposure possible until stars become elongated", but the opposite one: "as short exposures as possible until noise start to increase". I have a touptek 26000kpa ( the same you presented some time ago ), and 2 mins is PLENTY to keep the noise down.

AWESOME video, Luke. You addressed so many things I had been wondering for a very long time. Absolutely fantastic content my friend!

As always Luke, a solid walktrough processing images. Thanks mate👍

Interesting, thank you for taking the time to do this comparison and sharing the results.

I do live stacking for public outreach at a local observatory. We live-stack and project to a large screen outside the obsevatory. We have an old, home-brew large (30”, F5) Newtonian, with rather poor tracking, so the exposures are limited to 20s max. We get great results with the short exposures. I can take the captured fits and post-process with PI for even better results. We do end up using higher gain that is ideal, but a few blown-out stars don’t bother me.

Interesting. I normally go 4 to 15 seconds in Sharp Cap. I get bored waiting for the next update.

Very interesting, Luke. Nice work!

Great job Luke. I always find myself debating exposure times. Seeing the differences are so…well, subtle, I think I can rest more easily knowing that whatever I do and whatever I get, it’s all going to be fine. It’s always good to go back to basics in this hobby.

Really interesting. Thanks for taking the time to do this experiment. I've found that a sort of sweet spot is often around 3 minutes, especially with OSC. Star colors seems to be very decently perserved, and detail in the background doesn't seem to take a hit. Downside is that it will increase the number of individual subs by 8 pr hour. When you have projects often spanning 20+ hours, those extra subs all add up both in terms of processing time and storage. As an example using a camera that produces 51mb fits: - 20 hours of data using 300s subs = 240 files / 12gb - 20 hours of data using 180s subs = 400 files / 20,5 gb Of course... a way around that is to take say 15 minutes worth of 1m subs only for the stars.

Great video! Interesting test, careful and fair comparison, fascinating result. Personally, I liked the increased contrast and color on the longer exposure, but you noted everything that I could see and reached a very fair conclusion. Your presentations are consistently impressive and the reason I subscribe!!

You've answered this age old question that I've had! Thank you!

What I found out is that in most cases it's enough to shoot 120-180 seconds shots at broadband (OSC) and 180-300 on Narrowband (like the L-Ultimate). Most of the times I shot 30 seconds shots for the stars. To many different exposure times, will make the processing traject longer :) Nice video by the way !!

Nice job Luke, as always. My sense is that the shorter exposure / more frames stacked image has smoother noise, but the other seems to have slightly better colour AND slightly better contrast. I think the lesson for us all is to get a minimum of 20 frames to stack, with exposures that are as long as our gear AND environmental conditions will allow for that still deliver perfectly round stars. In other words, the answer to the question is, as always "it depends!!!"

Thanks Luke for another great video. I love the comparison of the two exposure lengths. Both images are very nice. My way of thinking is that from a more light polluted sky setting the shorter exposures are going to be the winner. I'll have to test this out with my scope also. Thanks again and clear skies. Ray

Hi Luke. Great vídeo. I am a traveller which usually means polar alignment every Session. I have also mostly favored toward shorter exposure as every minute you spend in polar alignment means less data and less signal. I Wonder If you could do a similar test but with the following two sets: 1) 60x1min, good polar alignment, qnd 2) 5x10min, excelent PA. The 10min diff would simulate the extra time one would spend on perfect PA.

Great one my friend!! That noise comparison we have to thank to Poseidon's performance, a monstrous camera with almost no noise, if you did that comparison with amp glow sensors that would be a huge win for the shorter side!! Clear skies man!!

I have found surprising results lucky imaging some DSO's with my 24" dob, getting a pleasing result of M42 in a bit over 2 minutes. This is an interesting topic for sure. Damo

Fantastic video Luke. I love real experiments like this rather than BS opinions that people often spew out. You learn much more and there are always surprises. Cheers

Thanks for your effort!

Hey Luke! Thanks for making this video! This really shows the pros and cons for short vs long exposures. I had been doing experiments and your observations align with what I have discovered. The to get the best of both worlds I have started taking very short exposures for detail and longer exposures to bring out the contrast and faint dust. The biggest advantage for shorter exposures is less reliance on your tracking, especially for smaller objects. Clear Skies mate!

Excellent video. Surprised me with the results.

Hi Luke intresting experiment like you say not much in it both images look good , the only down side I can see is the amount of hard drive space and processing time the shorter sub would take up, would be interesting to see how this same experiment on the Quattro , thanks again Luke for taking the time to make these videos

Excellent comparison Luke which shows the problem that most of us face in that longer subs may have a slight edge in some areas but, satellites and wind conditions can reduce the ability to take advantage of them. I have been pondering this myself as I'm now imaging from a bortle 3/4 area but on top of a hill in Scotland which is more often than not fairy windy. I'm currently designing my obsy and it's making me lean more towards a rotating dome style structure rather than a roll-off-roof to keep wind issues down to a minimum.

Nice idea for an episode, thanks for sharing! For NB I like longer 5-10min and Broadband 2-3 min exposures. I find the cores of most galaxies. Start to get out of hand after three minutes.

Excellent experiment! Would love to see a narrowband version of this experiment.

Really interesting comparison Luke and the result was not what I was expecting. I suspect though it would be a win for the 10 minute subs over say a 3 hour session ? A future video on exposure lengths re a faint galaxy might be interesting ? I would guess that's where the 10 minute subs would shine but with the improvement in camera sensors that could well be wrong ? My only other suggestion for a future video would be a pixinsight comparison of an image processed entirely with default settings vs the other dialed in ? Anyway mate great video 👍

Really interesting. I've recently switched to 1 min to 90 second subs as I need a LP filter to go further in my Bortle 4 skies and that makes everything come out with a blue hue that I find hard to remove. The other advantage of 60-90 second subs is that I don't need guiding, which keeps my set-up nice and simple (and yes, less satellite trails and lost subs when they're shorter). Thanks for doing this test. I am planning to buy blur and noise exterminator soon and will use your links.

Nice video as always, Luke ! Great comparisson, showcases nicely, that exposure time isn't really a factor anymore with these modern sensors. Read noise was always an argument for longer exposures, now you can tailor your exposure length to other parameters, like the amount of data your pc can handle, satelite trails elimination with stacking algorithms etc. I have settled at 180 sec exposures for OSC data and 300 sec for dual narrowband, works well in my bortle 5 skies and stacking doesn't kill my old pc. Clear skies Luke !

Great video, thank you!

Another stellar presentation Luke, thanks for doing this as its a question that has been lingering for a while now. The question has resurfaced now that I've started shooting in mono with SHO filters. From what I could see in the video, I think the added stacks give the shorter subs the edge in regards to minor detail. Not to mention the issue of guiding that many of us run into as you noted. I think there is a sweet spot that needs to be found with a minimum number of subs. I would definately love to see a similar test done with SHO as well as a rough outline of needed ration of Ha vs Sii vs Oiii. I've been going with a 1:2 ratio for Ha vs Oiii and 1:1.5 for Ha vs Siii, but I'm not sure if that's a good benchmark. Again - THANKS!

Fascinating. I like how you showed both images at multiple stages. A variation to test can be doing the same comparison with a ccd on a slow scope. I think the difference will be drastic because of the much higher read noise associated with ccd sensors.

Glad you did the comparison. Besides avoiding data processing headaches, the only reason for longer subs is avoiding camera read noise. With a F2.2 scope from low Bortle 7 on a broadband target and the IMX571 sensor in high gain mode, I believe the read noise is swamped to less than 5% of total noise with anything over about 2 seconds. I have a spreadsheet on read noise calculations and so with 1 minute subs in your situation, you are still way way beyond camera read noise playing any material part in that test situation. I shoot 6-8 second subs on an F3.65 12” Unguided Dobsonian and so I’ve done the math to know when read noise raises it’s head and believe me, you are still not even close to having it matter. You could have done 10 min, 1 min, AND added 6 second (1/10th again) and other than the pain of stacking 1000 subs, you would not have had a read noise issue, but I bet the image would have been a bit more detailed still. (Oh, and I own PI for post processing but stack with SIRIL as it’s so blazingly fast)

I did a 10min test on Tarantula and compared it to my usual 5min subs, I can say I did collect a lot more data, but also collectted a lot more satellite trails as for in the Southern Hemisphere it is busy to the south, so the shorter exposures allow me to get clean subs without too many getting satellite trails. Was cool to see the target clearly without having to stretch the 10min sub.

Great job luke cheers mate.

Great video, Luke. Would love to see one where the gain and offset is the same and the only differential is exposure time. P.s. If you're using OBS Studio (if that's what you're using) it's still a hair out of sync with the audio to video. Hit me up for a link if you don't know how to fix it.

Thanks for doing this. I see more stars on the Left... I see more resolution on the Left... stars appear brighter on the Left.

Interesting vid Luke. Thanks for taking the time to do this. Your viewers, and myself, might be interested to see the results from slower scopes. I also noticed you changed the gain and bias settings. This is a "black art" area most astro imagers fumble about with. It might be worthwhile making a vid how you set these. Again thanks

I feel like there should be proper dark and flat processing of the images to compare rightfully.

I wished I actually had the time to test 10s, 1min, 3 min and 5min exposures. For 10s we know thanks to Astro Biscuit that the davabtage is that you can do basically lucky imaging and get better resolution not having to chase the seeing. But you need a sky with very low light polution. Next new moon I'm hoping to go to a Bortle 3 sky and shoot some OSC BB and NB. For NB I'll shoot 5min exposures but for BB I don't know if I'll go with 10s to not clip the galaxies of Markarians Chain or go longer.

Good comparison Luke, I would certainly be happy with either of those images. To be honest I'd never really given that much thought to this, I have just taken longer exposures if using narrowband filters and shorter ones when imaging broadband targets. I know that's not very scientific but looking at the various images that appeared in the media and on-line when I began taking an interest in astro photography that was the overall impression I was given about how other people were doing it. From your comparison I would say there really is hardly any difference, though I would tend towards the shorter length exposures simply because there appeared to be less noise.

Great video Luke. Really interesting. I'm left wondering about mono now. So with a colour camera you found that the longer subs gave better colour but less detail. What would that mean for a LRGB setup? Where in effect colour is derived from the contrast and detail recorded in the Luminance channel or perhaps even the contrast and detail in all four mono channels. Looking forward to the next videos in this series.

If we don't take short enough exposures we'll never have reason to go buy more hard drives :)

An advantage to more shorter subs that you don't mention is that if you're undersampled, you can't drizzle with only six subs, but sixty is more than enough. Also, the combination of drizzling and BlurXterminator, if you're even slightly undersampled, is better than BlurXterminator alone. Of course, if you had many hours of integration time (i.e., more subs), the longer subs could also take advantage of this too.

Im just blown away with how much detail you got with 1 hour of data. The Rasa is amazing. From this I would go for 2 or 3 min or maybe 5.

Excellent video as always Luke. I would like to see this example demonstrated on a faint object with very low surface brightness, using NB and a long focal length, say f7 or longer e.g. OU4 (Squid Nebula). Let's see and example where the relatively few photons counted over the different exposure times really compete with the noise (The dark current noise generally increases at a slower rate than the light signal). In this video, the dark current noise is greatly drowned out by the local LP and half moon.

I would be interested in another test. I too am impressed with the latest software and, as a practitioner of EAA i like to keep my total exposures down to 30 mins so i can move on to other targets during an evening. I use 60s subs. I would be curious to see a 30min comparison vs your 60min vs something even longer to just see how well short runs can now match up with the “all nighters”… 👏👍

Hey Luke, it’s something I’ve been thinking about lately, but you’ve kinda made my mind up! I normally shoot 10 min subs, but have lost quite a few, due to aircraft and wind, so maybe dropping to 5 mins or even 3 would be better! One thing to think about though, have you got enough memory on the pc, my 2600 mm camera files are 50mb each regardless of sub length, so more subs means more space taken up on the pc, also I will have to do more calibration frames to match the new sub length (I’m lazy!) But still I think it’s worth doing! Thanks for sharing mate👍 Clear skies!

Great comparison, Luke. I'll have to try some tests of my own with my ASI 2600mm pro/SW 100mm Esprit. I image from a Bortle 2 area but still seldom image over 3-minute sub for LRGB targets.

Hi Lukomatico. Nice comparison video! I wonder how do you setup the offset value, a I couldn't quite follow the way to do it. Thanks

Thanks!

I thought it was a comparison between long vs short, but this is long vs very long exposures. For me, short exposure is

Excellent experiment, really well detailed explanation, I personally use between 2min and 5min exposure depending on the target, but you are daring to use 10min exposure with the RASA11 🥵, you are the master good job!!!!😅💪🏻

Very nice comparision Luke. Could you also try 1sec sub(lucky image) comparision with longer exposure?

I think the longer yours subs, the more your mount and seeing will work against your final resolution. Thats why the 60 1 min stack resolves that tiny galaxy better. My motto? Dont go over 2 min with broadband but take lots of shorter subs.

Thanks Luke! I wonder if zwo did the same experiment when they were developing the seestar s50. I know their choice of 10sec exposures were mostly to get rid of the field rotation from it being alt/az but so far I'm pretty impressed with it for what it is. I managed to get a few subs of NGC 3621 in an attempt to get that new supernova, sn2024ggi from my precarious position on the peak of my roof. I was only willing to risk myself going up and down the ladder in the dark with the seestar with its lucomatico dew shield and a tablet. It did a lot better at getting images up there in the breeze than I thought it would. I'm at 39 degrees Latitude so it was pretty low on the horizon at about 16-18 degrees (hence, getting on the roof to get over the trees...). Now I just need to get off my backside and process those subs... All of that is to say that I worried about the exposure length being so short that I was wasting my time, so I'm glad to see you run this experiment with your experience... I'm just a beginning imager so thanks again, it helps! /Dave 👍👍

Interesting comparison mate I tried longer subs with my RASA last year & got more data regarding dusty areas on galaxies but sacrificed colour by blowing it out so I generally don't take it any further than 3 minutes. Maybe I'll try again sometime,,,, clear skies

I like them both... but I favor the left just slightly better. Nice video comparison Luke👍

Great video Luke. Ive just started to drop my sub lenght to 2 mins. Seems to me like i get less noisy images. Plus you can get a couple of subs where the seeing had gone great. Longer subs maybe gets spread. Clear skies my friend

Interesting comparison. I shot the Whirlpool myself last week, and I happened to go with about 60*3 minute subs, and there wasn't the world of difference between mine and either of yours. I might have a bit more detail in the dust lanes in 5195 in the final image, but then it's probably because I went a bit more extreme with BlurXTerminator. I think perhaps people sometimes obsess a bit much about the exposure time, and you need a comparison like this to show that it often doesn't matter at all in a lot of cases. But of course it does depend on what you are trying to capture too. It would be interesting to see a comparison where different sub times does make a big difference though, if there is such a case..

Hi Luke. Assuming tracking/guiding wouldn't be a problem, and that you gather more than 15-20 individual frames, I would say that the longer subs, ironically (or maybe not) gave out a better star shape and star contrast. If you check out the stars present in the arms of the galaxy, I think you can see that they are sharper, as they contrast better with the spiral arms, and also, again maybe ironically, they are rounder. Perhaps blur x-terminator can do a better job in correcting the shape/PSF of the stars for a stack made up of longer exposures... just assuming... I think the real difference would be for narrow-band imaging, where fainter signal is simply not being picked up by the imaging sensor on shorter exposures, in comparison with longer ones, and also where background signal and camera noise play a much more important role in the final product. All in all, it is an excellent test for an ongoing debate: who was first ? the chicken or the egg ? :D All the best and good luck with the channel.

I think if you got a lot more of short and long exposures you would get better results with long

Not sure if anyone has done it well not that I could find. Could you test f2 vs normal filters in both LP and DB filters. So the reason behind the test request is how well do they work or don't work for certain speeds. So no filter, LP and DB at f2, f5~6 and f10. (depending on what OTA's you have) I think it would be very interesting to see the difference in the 9 images or lack of maybe???

Very good

Very nice comparison, Luke! This seems to be an ever-present question among astrophotographers. It's honestly a minimal concern for me, and I hope I didn't miss this in your video, but was there a large difference in time for calibration and stacking in PI? I'm wondering about a session that have a lot more total exposure time and how each technique would 'stack up'. 🙂

Hi Luke, I assume that you did not drizzle for the 60x short exposures, right? It would make sense for a fair comparison. But on the other hand, if you did, it would be another big advantage for short exposures? Keep going with your great videos!

Cutting off from the video a bit early… but some comments on what I did see. An auto-stretch is a very poor way to compare two datasets like this. Little shifts in light gradient, or aspects of the stacking artifacts you didn’t remove prior, will result in different auto-stretches. Deeper data may also be stretched more, resulting in a background that looks noisier when it may actually be cleaner. You’d need to take steps to normalize the two frames for visual comparison or, for a real analysis, use Subframe Selector. Also, when people thing about fewer longer subs vs more short subs, they’re usually thinking about under-exposure. But what you’ve done is engaged the dual gain stage on the camera vs native, where the dual gain stage is actually a bit more optimal in terms of signal vs noise. And you’ve well-exposed both examples. This would normally mean the shorter exposures produces the best signal vs noise in the final image, while the 0 gain option is a sane one because it still performs very well but allows you to use something like the RASA without an utterly insane amount of subs. For a slower telescope, you would almost always want to shoot it at the dual gain stage. If you wanted a good comparison for what people are usually considering, turn on the dual gain stage, capture a set of subs which are fully exposed (cutting shy of clipping desirable highlights, as you say) and compare that to a series of much shorter exposures. Like 2 minutes vs 30 seconds or whatever (maybe 0 gain is saner with the RASA if that’s all you have to compare). That will produce a very different set of parameters for the experiment. A couple gotchas on this experiment, too: the shorter subs suffer more with heavier light pollution as fainter signal is all the more mixed up with the light pollution, and also, a sensor which is extremely clean like you’re using is going to perform much better in this experiment at the short range than a messier one with higher sensor noise, banding, etc. You’d also want to make sure both datasets have enough subs for rejection algorithms to be efficient.

Very interesting video! And I appreciate you made this video too after the "integration time" one! I have the same sensor, IMX571C, but in Touptek sauce, what's the difference in the two gain values you mentioned? I only used 100 on 5mins subs on an F4 system, but probably should I change somthing? How can I determine the best value?

Great job on this one Luke! I personally stick between 1 and 5 minutes and usually average more like 2. That is mostly because I don't trust my mount all that much and it hurts me to think about throwing way 10 minutes of data due to trailed stars. I would love to see this test repeated with a scope around f/5 to see if there are any differences when you aren't using an ultra fast optic

I’ve been wondering about this recently Luke so thanks for the video. Would love to see a comparison with the new Askar 120 if you have time. I take 3min subs but wonder after watching this if I’d be better going with 1 or 2 min? Not sure if the slower f7 scope makes a difference with the choice of time? Cheers Simon

Excellent and interesting comparison Luke. Good job! I've been having trouble with guiding due to EQ-5 dec issues. Now this shows me that I'm not really missing out by cutting back to 1 min unguided (for now). Of courese I'll be addressing these issues when the weather permits...

I know you probably like the red border around your RU-vid thumbnails because it sets them apart from others but unfortunately it's the same colour as the red line that appears under thumbnails of videos once I've watched them and it would be easy for me to skip over a new video. I think it's the reason why not many people do it.

Great job Luke! I’m a little thrown off, why playerone vs Zwo 571 cameras have different readout charts. I thought 100gain was start of high gain mode? Should it be 125? I have Zwo what’s the difference

I try for ten minute subs and to get as many hours in as I can on a target but you do get to a point of diminishing returns. I shot some 7200 second subs on M57 in Ha, as it has a lovely Ha detail. The longest I have collected data on one target was Melotte 15, a total of 70 hours and 20 minutes.

Thanks

Excelente!! Would have loved to have seen the SNR numbers on each master ?

top job pal

Do you feel the switch to low read noise mode helped even the odds for both sides? I feel without it the experiment might have been quite different.

Nice job, but I think your comparison is not very fair because we have to combine at least 25-30 subs to minimize many types of noise. It would be great if you will compare 3-4 hrs total exposure. 24*10min and 40*1min. Thx.

Great video Luke! It brings to mind something I can’t get my head around. If I have sixty 1 minute subs, when they are stacked is the resulting image still a 1 minute exposure in reality? Simplistically, haven’t all the subs been added up and divided by sixty?

Very interesting experiment. My own conclusion is 'compromise'. Nice calm night go for five minute subs, not so calm go for one to three minute subs. If it's really breezy . . . watch Star Trek reruns.

ru-vid.com/video/%D0%B2%D0%B8%D0%B4%D0%B5%D0%BE-3RH93UvP358.html&t Above link is to a discussion from Robin Glover creator of SharpCap and way to calculate minimum exposure time using smart histogram feature of SharpCap Pro based on various criteria to give roughly equivalent quality when stacked. Shorter subs obviously mean you are handling more data, but shorter subs mimimize impact of periodic tracking errors due to wind, overall tracking accuracy, or other items resulting in fewer discarded sub-exposures. This is another way to ensure the sub-exposure length you select is above the minimum required to balance the various items that impact overall quality (sky darkness, read noise, thermal noise, etc.)

Good video. Why do you use 100 and 200 for your offset levels? I leave mine at 20 or 30. Wondering if I’m doing something wrong.

Bonita la toma de la galaxia remolino buen procesado

Quick question : did you adjust sensibility/gain on the 1m exposure to "compensate" the shorter exposure time?

Could you in theory mix the short and long subs together for a hybrid to get rhe best of both?

Hi, I did the math on your set up and your "ideal" sub length in Bortle 7 at f2 and 300nm (visual spectrum) bandwidth is just 0.9 seconds. You could effectively do lucky imaging so you might like to try it again one evening with 2, 5 or 10 second subs vs. 1 minute over a 15 minute period. If you can do an hour great but you're going to have a LOT of stacking :-) The data below if for a 2600MC as I don't have your camera details to hand but let me know if you'd like me to run them and I plug 'em in. ---------------- Environment ---------------- Star Magnitude: 11.0 Background magnitude: 18.30 Bortle: 7.0 Seeing FWHM: 3.0 arcsec ----------------- Exposure ----------------- Sub Exposure: 60 secs Number of subs: 60 Total Integration Time: 60.0 mins ------------------ Filter ------------------ Filter Bandwidth: 300 nm Wavelength: 550 nm ---------------- Noise Calcs ---------------- Background signal: 45.4 e⁻/sec/px Electrons per sub: 2,723 e⁻/px Sub background noise: 52.2 e⁻/px Sub thermal noise: 0.04 e⁻/px Sub read noise: 1.25 e⁻/px Sub Total noise: 52.20 e⁻/px Stack Total noise: 404.35 e⁻/px One long sub total noise: 404.23 e⁻/px Extra noise: 0.03 % Ideal @ 5%: 0.3 secs Ideal @ 2%: 0.9 secs ----------- Telescope: EdgeHD 11 ----------- Type: Reflector Focal Length: 559 mm Aperture: 279 mm Focal Ratio: 2.0 Central Obstruction: 95 mm Total area: 542.2 cm² -------------- Telescope Calcs -------------- Image scale: 1.39 arcsec/px Field of View: 2.41 x 1.61 deg Airy Disk: 2.68 µm Airy Disk anglular FWHM: 0.42 arcsec Airy Disk linear FWHM: 1.13 µm Dawes limit: 0.50 arcsec Rayleigh limit: 0.50 arcsec Niquist limit: 2.78 arcsec ---------------- Pixel Data ---------------- Flux from star: 1.435e-15 W/m²/nm Star flux (telescope): 1.292e+06 photons/px Star signal: 1.176e+06 e⁻/px Total FWHM: 3.0 Central pixel (Seeing): 17.1 % Central pixel: 16.8 % Central pixel signal: 198,100 e⁻ Central pixel ADUs: 835,400 Central pixel Value: 1.00 Signal noise (cp): 445 e⁻ Background flux: 2,993 photons/px Background signal: 2,723 e⁻/px Background noise: 52.2 e⁻ Centre pixel noise: 454 SNR: 436 ---------- Camera: ASI 2600MC Duo ---------- Type: Colour Resolution: 6,248 x 4,176 Size: 23.5 x 15.7 mm QE: 91 % Pixel size: 3.76 µm Bin: 1 Image Scale: 1.39 arcsec/px Gain: 100 Temperature: -10 °C Read noise: 1.25 e⁻ Full well: 15,811 Dark current: 0.00070 e/s/px eGain: 0.23717 e/ADU

Do you think having a RASA 11" with a 26mp camera was the reason why the results were very close? Do you think a C8 SCT with a ASI071MC Pro or maybe a ASI294MC Pro would show similar results between a 1 minute and 10 minute, maybe not the quality of your results, but in the context of those two cameras. Thanks

Long time no speak Luke (sorry mate, have drifted away from astro to bird photography). I'd be curious to see 5 min subs from a dark sky site with low to no winds.