Long VS Short Exposures in Astrophotography - Part 1: Broadband Test
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- čas přidán 20. 07. 2024
- Is it better to use long or short exposures when doing astrophotography with a simple light pollution filter? does it really matter? I aim to start finding out by comparing data side by side from 60s and 300s data sets.
/ lukomatico
/ lukomatico
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Celestron RASA 8
IDAS LPS D2 filter
Player One Uranus-C OSC
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Luke, you can drag one of the images "tab" onto the other one in Pix to "sync" the zoom and position to the exact same spot. Just like applying a mask but not below the target "tab" but just on it.
Superb tip mate, thank you so much!! - I'll have to practice that a few times and get my old method out of my head haha! :-D
Clear skies!!
Would be interesting to see a noise comparison video on the Player 1 against a cooled OSC on the RASA. Love your work Luke!
Thank you so much Simon!! - I appreciate the feedback my friend, and hopefully, fingers crossed, something is in the works! :-) clear skies buddy!
Thanks for this! I usually shoot 5 minute subs anyway ;) I do think that the result you show is testament to a good mount, good guiding and proper polar alignment. People with less expensive mounts might see benefit in shooting shorter subs as they then not have to trash so many subs.
Hey Martin!! Hope you're well my friend :-)
Totally agree, great point! - 5m+ subs are great if you can reliably get them, but 1-2m subs will still do the job admirably in all other cases! :-D
Thanks so much for watching buddy,
Clear skies!
This makes complete sense, it’s amazing that bad information gets repeated by experts so often….
Glad you enjoyed it Robert!! :-)
As always Luke a fascinating video. In addition to the obvious win for the 5 min exposures I think it also highlights that I probably don't need to go down to -10°c on my cooled camera. I'm so impressed by the player one camera 👍Great video mate
Hey Paul matey! Hope you're well, I'm currently baking hot lol, I can't cope with this heat!
Definitely think the 5m shots are the way forwards, but more experimentation is ideal I guess, but it's already a clear improvement 👍👍 interesting thought about how deep you need to cool mate, I think you're right!
Great video and comparison Luke, that player one camera looks like a great pairing with the Rasa, super image at the end mate! Clear skies
Thank you Simon mate!! - love the cam, certainly does the biz! :-D
Clear skies buddy, hope you enjoy the sun this weekend!!
Thanks for doing this one. I've always favoured 300s subs but never tried shorter comparison subs to see what the real difference is. saved me the trouble :)
I'm glad you enjoyed it buddy! :-D I always have a ton of fun putting together little off the cuff experiments like this, I certainly plan on doing more!
Hope you have a super week mate, thanks for watching!
Very interesting comparison, Luke! Really enjoyed your video..,as usual. :) As many, I started doing AP with my cheap and non-modified DSLR with no star tracker etc. So I had to make hundreds of very short subs... So this also led to high memory consumption and long processing time for stacking. I'm SO happy to be able to do 5-10min long subs now..and as you have shown it just makes sense to do so, I guess. Clear skies, mate!
Hey Tully! - Thanks very much indeed my friend, it's honestly lovely to read you've been enjoying the videos! :-)
I'm in the same boat really, I do love using longer subs as everything is just seemingly easier and less stress overall (except for guiding!)
I do think in the future when we get near to true zero read noise cameras that we'll likely all be shooting short subs, millions of em! (probably need some form of live-stacking to make it work though?) at that point of camera development it'll be all benefits really and little/no drawback - until then though, a guy can still dream right! :-D
Clear skies mate!
@@lukomatico Haha.. :-D ...sure, I like those dreams! Just the thought to use a camera with zero (or VERY low) read noise.. wow.. This would be something. :)
Hi Luke, another great comparison video. That Player One camera is certainly giving some cooled cameras a run for their money at half the price. The 300sec. exposures look great and a very nice final picture and composition of the Cocoon nebula. Clear skies.
Hey Jon! I'm glad you've liked the video mate, I was actually not sure about putting this out as it seems kind of controversial haha! But, happy I did in the end, - well worth more experimentation too I'd say! :-)
Totally agree by the way, the Uranus is a serious contender for being the budget camera king I'd say!
Thanks for watching 👍👍
You could see the difference right away in the 5 min exposure. Awesome comparison mate. Really enjoyed the video mate!
Thanks so much for watching Ben mate! I'm glad you could see the difference too bud, it was really pretty stark for me looking at the screen directly and not through youtube compression too!
Always a pleasure catching up, glad to see that obsy coming together too!
Clear skies mate!
seeing, transparency, and time of day will make a difference here. the best way to run this experiment would be:
1 set:
2x1 minute exposure
5minute exposure
3x1 minute exposure
and then repeat your sets 15 times to get to 90 seconds, this will help remove this variable
* 90 minutes
I hear you Tyler, for sure that would be a great way to test this from a data collection standpoint :-) Cheers!
Nice video Luke. It's kinda funny... you see the suggestions that advocate shorter subs all over the internet.. yet in every comparison test I've seen like this.. the longer subs always look better. Galatic Hunter did a similar comparison with the same results a couple of years ago. I tried the shorter sub thing a few years ago.. processing 1000+ subs was not fun.. I told myself never again! lol. CS my friend.
Hey James! - Man I absolutely agree, you see the same thing all over - I've done a fair share of it myself to be honest lol!
I'm noticing that if you have the guiding and camera to allow longer subs, it's almost universally a good idea 👍👍
I appreciate you watching and sharing your thoughts mate!!
Clear skies!
Cool comparison Luke, that player one camera sure seems to work well with the RASA. Thanks for sharing the results.
Thank you so much for watching Joe!! :-) I really hope you are doing well my friend 🙏
i've often wondered about the same. i just started 300s (from 120s unguided) exposures (yay for guiding!) and i've already noticed improved details.
thanks, luke!
Good stuff! Thanks for sharing your own experience mate!
I think I'm going to revisit this and see if I get a similar or differing result when my new camera arrives :-) Clear skies!
Hi Luke!
very nice as a test! I just wanted to put a small flat in this approach and conclusions.
With your sampling which is quite wide, and a setup close to perfection (helped or not by the autoguiding), the impact of the other motion blurs will not be seen because it will be smaller than the smallest recordable details , simplifying if it moves inside a photosite we will not see it.
So, we can deduce that with your setup a unit exposure time of 5 minutes is consistent with your entire capture chain, so it's more interesting (but risky, airplane passing, squirrel throwing or other wickedness of the heaven that will make you eliminate this brute).
On the other hand, as soon as the sampling is tightened, other motion blurs can be felt or even distort your unit images so it will be preferable to lower your unit exposure time...
The main thing is to be consistent with your setup! and you are!
Hey there Stephane! It's always a pleasure to hear from you my friend! :-)
I completely agree with everything you've said, 100%! You are the master of your field and a constant source of inspiration in my own astronomy, if anyone can speak to the merits & usage of short exposures and critical sampling, it's you! Your fabulous images are testament to it! :-D
I really appreciate your feedback and thoughts, thank you again,
All the very best and I hope you have a superb week ahead :-)
Clear skies!
So very nice! I prefer the shorter exposure one but we all look at it differently. Signal to noise looks better to me, and the background galaxy's are a great prize 🏆!!
Thanks for the perspective Bill!! I appreciate it bud, we're all different at the end of the day and that's no doubt a good thing! :-D
Clear skies my friend!
Great video Luke.
Thank you!!! :-)
Very interesting! I saw comparisons that had much tighter stars with short exposures but you prove otherwise. I think its not just done with exposure lenghts. The camera, the guiding and the amount of light pollution will influence the result between shorter or longer exposures.
Definitely agree mate, there's so many variables between people's rigs and imaging conditions that finding the right settings will almost invariably involve an amount of personalised testing 👍👍 it was a pretty surprising result for me though! :-D
Thanks for watching!
Hi Luke! Thanks a lot for doing this kind of test! That is very useful 👌
I read on ZWO that you get the full dynamic of the camera at unity gain, which is 100 for ASI533MCpro for example. At zero gain you kind offset the 0 as you will need more photon per read electron. I don't know if I understood well but that is what I understood ^^
Take care ! 😉 Clear skies
Hey there mate! - You're absolutely right for sure! If I had a 533 or 2600 to do this test with I would have ran the whole thing at gain 100 to remove one variable, but unfortunately I had to switch gain/offsets with my IMX585 to allow the test to go ahead with the gear I currently have :-D I hope that explains my reasoning for it a bit better buddy!
Thanks for your helpful comment 🙏
Clear skies!
Hi Luke
It shows that the pixels like to get filled up with more photons with the longer exposure time , as long as the mount can guide for long subs . Conversely if you haven't got the option for 5mins subs then there's not a lot of difference to worry about , without a direct comparison I would be happy with both results . Great work again.
That's a really great take-away from this Steven! - I totally agree that without looking at them side by side I'd have been happy with either too :-) Thanks for the perspective on things my friend!
I have an older C6-N Newtonian I bought for $100 complete and I bought an Explore Science Twilight 1 AZ for it on sale for almost 1/3rd off, so long exposures are off the table. I bought it for stargazing not taking photos. I had only taken it to 250x with a 2x Barlow, it was pretty clear. Unfortunately it had a small line zone that was not in focus at high magnification. The mirrors had some micro-scratches from cleaning with paper towels as well.
I sent the mirrors in for a new aluminize coat to an enhanced 96-97% reflectivity. They tested my primary mirror and it was a very good mirror except it had a small anomaly that was causing the fuzzy zone. To make a long story short they refigured my primary for a good price and Wow! Is all I can say. I'm more into observing and having near perfect views of the Solar System has really kept me up at night. Now I need to buy a really good focuser.
That's great service there and from a very knowledgeable shop I'd say too! It's wonderful they were able to identify and correct the mirror's quirks for you :-)
I actually had some lovely visual views of Jupiter and Saturn earlier this week with my new-to-me Meade LX200 10" SCT - extremely impressed by the star test from that thing too, quality optics never disappoint! :-)
I wish you all the best with your observing my friend, there's some real magic to getting behind the eyepiece and seeing the wonders with your own eyes!
Clear skies :-)
@@lukomatico Thank you and O.W.L. did a great job too. When you consider that for the price of an inexpensive telescope I acquired the optics of a $2500 Takahashi the expense was more than justified. I wished the sky wouldn't have turbulence, but you can't have everything. 🤣
Another great video Luke, and with results pretty much the same as I discovered some time back… although one thing, after about 3 mins you get diminishing returns on your exposure, so not really much point in going beyond that really….this is what I found and also what was proven by the Sharpcap author with his exposure calculator.
I see that Player one are bringing out a range of IMX571 sensor cameras the Poseidon, I hope you get those to rest as I would be very keen, to see the mono version in action…
Keep up the great work….👍🏼
Hey Stewart! Hope you're well mate! :-)
I do wonder where the point of diminishing returns lays for this rig with broadband (narrowband to be determined too!) - as you say I may well already be hitting it at 5 minute subs! Interesting question.
I may well be getting a Poseidon by the way buddy! watch this space! :-D
Hope you have a great week!
Clear skies :-)
@@lukomatico I think you will hit the limit, especially at f2…I did at f5.3, but that was with the QHY268c
Look forward to seeing tests with the new Poseidon….👍🏼
Hmmmm interesting comparison there Luke, when I started using the RASA I only did 60 second subs to begin with at the camera's unity gain, I have upped it to 90 seconds & thought longer subs would create more noise so I may try some longer subs at a later date now but we're packing all out gear so we can go away next week & hopefully some astro imaging to.
Clear skies mate!!
Oh mate, that sounds great! I really do hope that you get some clear skies for next week then, - it looks like the daytime weather should be great at least!! (a little hot mind you!!!) - Interesting to hear about your own experiments by the way, be cool to see if even longer subs work out for ya!
Clear skies mate, and hope you and Nicky enjoy your holiday!
Great job. Would be great to have a 15s comparison as well. Just cause that would be, i think, the threshold for alt-az mounts in general. The difference btw 15s and 30s would be the bang for the buck you get from going EQ
That would have been cool to include! Thank you for the suggestion mate :-) I'll have to revisit this someday
Many thanks, great comparison - I too find that longer exposures lead to better results. Guiding has to be good. Thanks for such informative videos.
My pleasure! I'm really happy to hear you have found the last couple of vids useful Peter, - it's also great to hear that your own findings match mine, that's a useful data point! :-)
Clear skies!
Seems like again each have their differences but nonetheless I would take either image as a great image ! So amazing as always to see you doing your thing man!!
Thank you so much bro!! - I always appreciate your point of view on things! 🙏
Side note : I don't know how you guys manage in Arizona with the heat haha, we're having a heatwave here at the moment and I'm pretty much melting - and yet this is no where near the temps you guys deal with, damn!! 😂🥵
I hope you're getting some clear skies bro!
All the best and as always thank you for your support 🙏
@@lukomatico 😅😅 bro, we stay inside in the air conditioning and it's a no go for our equipment. At least I am not comfortable running my equipment in this heat, even at night its about 35 C . Something about not breaking thousands of dollars in equipment keeps me from not doing astro 😅😭
That player one performs so well on that RASA? Nice image at the end mate. Good demo of the comparison, i have done this myself and always favoured the longer exposures. But cameras are getting better all the time with noise and QE. In the next say 5 years they will be so good that short exp is all you will need. I believe live stacking will be the way forward so you don’t have to worry about all the data you will grab which is really the only downside to short subs ( the sheer number you end up with to process) It also negates all of the issues a lot of people have re guiding. With short subs guiding basically won’t be needed. Well thats my ramblings on it anyways lol. Clear skies mate.
Totally agree Glenn!! - long exposures will end up going the way of the dinosaur for sure, can't wait to see how things do change over the coming decade 👍👍
Thanks so much for coming and watching buddy, hope you have a super weekend and enjoy this sun! :-)
I use Sharpcap's smart histogram to determine exposure length. It dynamically measures current sky conditions to determine the best exposure length based on the time available you have and your camera sensor analysis. I use it as a guide and end up using something that is close to an existing dark library exposure I already have. :-)
Well it gives 5-15 second exposure times for bortle 7-9.
Thanks B! - I've used it fleetingly in the past, I may have to give it another check and maybe it would outline good starting points for a future experiment! :-)
Cheers for watching and commenting buddy, clear skies! :-)
Nice job Luke! Since I started this hobby (back in the film days) I’ve never quite decided on an optimum exposure time for my setup. Your analysis demonstrates quite vividly that, although subtle, longer exposures are the ticket. Two questions: 1.) in severely light polluted skies, would shorter exposures have an advantage? 2.) Do you imagine that splitting the difference and exposing for 150 seconds would yield results somewhat midway between the 5 minute and 1 minute results? Are these things that predictable?
Once again, you produce interesting, illuminating, and practical topics…do keep up the great work.
Thank you Joe!!
Very interesting comment mate, I appreciate it!
I reckon that short subs do of course still have a lot going for them, easier to guide, less painful to toss away bad subs, etc - but the longer subs have the key thing, better signal to noise ratio!
As to going inbetween and getting an 'inbetween' result, it should work yeah! That said, there will no doubt be a point of diminishing returns along the way somewhere, perhaps I'd already hit it with 5m subs? Perhaps not though, I'd need more testing to confirm that one! :-)
Thanks so much for watching mate!
These data tests you’re doing are fantastic. In this particular instance you’re using a scope that’s fantastic at short exposures. I’d expect your results would be drastically wider across a slower rig.
Hey Garnett! - I hope you're keeping well buddy! :-)
I definitely have a lot of fun doing these kinda off the cuff tests, it keeps my interest high and I feel like I continue to learn things each time which is nice! - I'm glad you're enjoying them mate, truly I am!
I happen to have just acquired a much slower scope with which I could revisit such a test(Meade LX200 10") I share in your expectations that this would lead to a more dramatic difference for sure! - It may make for an interesting video to try and find out!
Thanks for watching mate, I hope you have a superb week ahead!
Clear skies :-)
We have always known that 90min exposure is better then 90x1min exposure ,given perfect camera . But if camera is not perfect then it depends , and there is no one set point , depends on target , what you do , what you shoot , how you do it . Throw dithering in there , and things may change a bit , but longer is always better , but not always practical
Well said Pavle! Very true my friend :-) It's always a good idea to test these things out for yourself!
Clear skies!
Great job! I am impressed by your work.
The result is exactly opposite to my expectation. Theoretically, the short-exposure image should be better than the longer-exposure one, since the gain difference between two is 9 times while the readout noise difference is 6 times. Roughly speaking, one can expect the same S/N ratio from low and high gain images of the same total exposure, if the readout noise of low gain equals Sqrt(R), where R is the gain ratio between two. Maybe there is something else we don't know going on.
One thing I suspect is the thermal noise effect since you are not using a cooled camera. May I know the sensor temperature of the two imaging sessions?
Thanks again for your great video.
It's interesting that you chose to run with different gains for the two datasets as that brings a variable into play that has not been accounted for. With out any familiarity with your camera I am wondering if the higher gain on the shorter exposures has impacted on the noise level and the resolution of the image.
Hey Allan! - an added variable, true! - a necessary one though I thought, just to make the test somewhat fair 👍
Exposures of 1 & 5 minutes at the same gain on this setup would disadvantage one or the other - either 60s being too poorly exposed at zero gain, or 5m being whited-out at 200g
I hope that better explains my rationale for the experiment parameters my friend, I should perhaps have stated that during the video!
Thanks for watching and clear skies!
Ah man this is so the question we all ask ourselves when we're setting up to image! what sub length shall I take? ? Thanks for taking the time to add some clarity to this question, the 300sec zero gain pics are cleaner and more detailed. I must say though I would be delighted with either which bodes well as I received a certain ZWO camera with a certain Sony sensor this week cough cough. Your fault but I thank you for it Luke ;) :D
Haha!! - that's brilliant Chris, I think you'll love it mate! :-D mine's been awesome fun from day 1 👍
Congratulations and I can't wait to see your images come rolling in! :-D
I always appreciate you watching matey, thank you!
Well, time for me to get back to the hard task of sitting around melting and moaning about how hot it currently is! 😂🥵
@@lukomatico Thanks Luke! Well I managed a few test shots last night as well as it being the first time using an ASI Air Plus!! (Wow!) I was grinning at how easy it made things, especially finding objects and guiding. The sensor temp was 20 degrees so considering it has no cooling the results were remarkable! I think it may be all the astro cam I need :) Yeah the heat, I have a marine aquarium which I'm watching like a hawk, I might need to setup a fan blowing on the water if it gets any hotter. Take it easy mate and have a good week :)
As far as I can tell longer exposures and less light pollution are always better regardless of what camera you use. I never try to image where I live because I'd have to spend so much on filters. I just decided it was better to save the money I might spend on filters and use it for gas money and drive to west Texas. I live in the Houston area so it's at least 425 miles to get to bortle 1 skies. I know that's not an option for most people but in my case it's worth it. It's an astronomy adventure and I have the advantage of camping, possibly swimming and always beautiful scenery. It's also a chance to see parts of the country I've never seen and meet new interesting people. Clear skies.
That's a really cool way of looking at it Carl, and no doubt an approach that brings you much joy, which in the end is really what this is all about! :-)
Thanks for the perspective my friend, clear skies!!
@@lukomatico You bet! Always glad to share.
You certainly are getting great results with these cameras, especially for being uncooled. Seems to be a good pairing with the Rasa.
Thanks Dave! - it's been a challenge recently with the heat but the setup is going great!! :-D
Hope you are keeping well buddy 👍👍
@@lukomatico All good Luke, made it home on Thursday, tried one night on K2 comet, but the dew one!
@@DavesAstrophotography Oh that's rough mate! - glad to hear you're back safe though! 👍👍
i am really looking into EAA with the Asiair live stacking
Ioptron az pro mount, Celestron c8 with 6.3 reducer
and zwo 294mc pro... should be fun, experimenting is the best part of doing this 👊👍
I really think you should go for it! :-)
I absolutely agree that it'll be great fun, not only with the results but also learning the kit 👍👍
Thanks for sharing buddy! :-) good luck!
Great comparison, Luke! Thank you very much for another helpful video!
Please, why did you use the IDAS LPS D2 instead of your IDAS NBZ filter?
Thanks and CS, Stephen
Hey there Stephen!! - thanks so much, really glad you liked the comparison 👍 I used the LPS rather than NBZ as a bit of an experiment really, I wanted to see how it'd look on this target! :-) I'm back to using the nbz now though for my next project 👌
nice video. i made the same observation with my gear
Good to know mate, thank you for sharing!! :-)
This is a great/fun topic (esp. when you move to a faster scope). Interesting I see different results (although in all honesty I have not put much time into a proper comparison). I know I’ve gone from 600sec (~F4.7) to 120-180sec (F3.3) and things are *still* so much better that I’m considering moving to even shorter (90s). I know Chuck (who got an APOD with his RASA8?) is a fan of many-short vs less-long - but he does suffer from very bad light pollution. One point is that many shorts will give you a lot more useable data since you’ll be less likely to hit guiding/clouds/satellites/focus issues…
Actually I think Chuck may use even smaller exposures - something like 30s?
Hey Duncan! There's definitely a lot of great points there, and many arguable reasons for shooting shorter rather than longer subs! :-D
I guess the key thing is that eventually the short subs will catch the SNR of the longer ones, but you will need more total integration to make them match it seems, - definitely one of those subjects where some personalised testing is required to fine tune I reckon 👍👍
Thank you for watching and sharing your experience mate, it's interesting to read and highly valued! :-)
Clear skies!
He does often use subs of around that length yeah 👍 Works for him, that's for sure! :-)
Ive discovered with my EdgeHD 11 in my Bortle 8, backyard I get the best results imaging most broad band (galaxy) objects with 90 - 120 sec. exposures to avoid light pollution build up. When imaging narrow band (nebulae) objects I find 600 sec. subs gets me a nice bunch of data. :)
That's a great point of reference there Tom, thank you for sharing! :-)
I'd love an edge11 someday by the way, congratulations on such a superb scope! 👍👍
Clear skies :-)
Hi Dr Robin Glovers talk on subframe exposures were determined by the cameras read noise, light pollution and your preferred tolerances. His take was that there is little to gain on longer subs but, more with shorter ones. What are your thoughts on this?
Hey mate! - I've watched Dr. Glover's talk a good few times now, really great video! - I think the gap between long and short subs is now very close, closer than it's ever been really. Short subs are nice sometimes because they can have additional sharpness, but long subs tend to smooth out noise slightly easier when stacked - it's all tradeoffs imo! :-) Cheers!
Gain 0 always feels like lost photons to me. But interesting this beats the same integration time of shorter exposures at a much lower gain. I would not have expected that. Another interesting comparison would be 2-3 mins at unity gain. I wonder if the sweet spot is what’s the longest you can expose at unity gain without saturating those buckets. This should maximise all the photons that arrive.
That's an interesting question Tom! There's got to be a sweet spot for sure, and a point of diminishing returns too you'd expect right? It's worth more experimentation for sure - an interesting subject I reckon! :-)
Thanks so much for watching and giving a great comment buddy, clear skies!
yeah interesting, Thanks!
Cheers mate! :-)
Hi Luke this is a question I've been wondering about too. The longer exposure differently looks better to me. Just wondering if even longer exposures say 10 minutes or longer would show even more detail? Seems like we are going back 30 year when we used to take photos on film for hours, the limiting factor used to be how long you were prepared to manually keep a star on the crosshairs lol.
Thanks again for making these videos
Hey Anthony! - that's a great line of thought mate, I wonder where the point of diminishing returns is? Maybe I already hit it at 5m, or maybe 10m+ really would be notably better, it's certainly worth thinking about, thank you!! 👍👍
I definitely don't envy the folk who had to sit there manually guiding in a freezing cold field or something, haha!! :-)
Thanks for watching buddy!
That's a good assumption. Though there are other factors that we have to take into consideration: satelites, airplanes, bugs, my aunt passing by... you get my point. With a proper cooled camera of course you can achieve exposures of even 45 minutes or so (I heard from somebody that actually does this but with a CCD, and actually he pointed out that he prefers this way of imaging, because in one shot he can see how the image is going to turn out).
To be very blond, the maximum I have achieved (but with a modded DSLR) is 400 seconds on a SCT, tried to expose more, since I was in a bortle class 3 site, but did not see any difference with the 400 second exposures.
Anyway. If you're in a not so light polluted place which is fairly dry, I believe you can happilly do 10 min exposures.
Cheers to both of you!
@@enriqueboeneker That's good info Enrique! Thank you for sharing and offering another point of view :-D
I'd love to get out somewhere truly dark one day (bortle 3 or lower?) and try that for myself too, I bet it's amazing! :-)
Aah but Luke. I'm still thinking that shooting at high gain makes for less good images (as we might expect) and the jury is still out on the effect of exposure length? What I do know is that 100 gain is optimal (on paper) for my camera and I just dial that in without thinking. I know also that I should try bin 2 if the seeing is bad, but I generally wont set up on those nights, as it takes an hour to setup. The biggest issue I face is Schipol airport traffic. So for exposure, I've settled for 60 or 120 - just because losing 300+s in one go is too painful. With these settings I'm happy to take what I can get. When I started we were boosting film to 1600asa and delighted with the tiniest hint of a dustlane in a grainy black and white print of andromeda, so what this modern kit can do from the middle of the city lights just continues to blow me away! Like your setup. Love what you're doing!
Hey mate! - I guess you may be using a 2600 or similar? If so, I used to use mine at gain 100 always too - worked great! :-)
I reckon a lot of this side of astronomy comes down to personal preference and ultimate goal for the images, as you say there's advantages to short subs - less painful to throw one or two away for sure!
Thanks for watching mate!
P.S - I can only imagine how different astronomy feels from your start point with film to now - what an amazing "development" if you'll excuse the pun! :-D
Clear skies!
@@lukomatico Good guess - I'm using an asi 533MC now. Yes, the scene has changed a lot in 50 years. My very first shot involved a Zenit B SLR bought new for 27 quid - hard earned from a weekend job shelf stacking. I attached it to my 4" f/12 newt on an undriven mount, using elastic bands and fine focussed by moving the secondary prism and trading off collimation. Film was Ilford PAN F 50 asa. I used my planisphere as a shutter over the aperture to avoid shake, aiming for 1/5th sec. I got an amazing series of lunar eclipse shots at prime focus thanks to the darkroom at the air cadets. Its all a bit different nowadays, but the thrill when it works out is the same! But what's really cool is that kids can still do it the old fashioned way without spending a lot of pocket money (you can still buy pan F even).
Uranus-C - check!
Idas LPS D2 - check!
RASA 8 - pff, man, so far away! 😜
Haha! :-D it's a great scope for sure, glad to hear you've got the camera and filter by the way! I hope you are enjoying it 👍👍
@@lukomatico I can’t complain though. Do have a “mini-RASA” a Rokinon 135 mm f/2 lens which will definitely use. Just going to try now with my “normal” rig (ED80 triplet) the camera on the Sun, lets see if I can put it to work. Cheers!
I’d like to see the comparison with 0 gain on both
0 gain 60s subs and 0 gain 300s subs right? That's something I could maybe do at some point yeah!
Thanks for watching and clear skies buddy! :-)
Awesome work, much appreciated! Just to be sure: the first set was 90 minutes of 60 second subs. The second set was 300 seconds (with a gain of zero, interesting). So the first set has an integration time of 1,5 hours, but I seem to have missed what the 5 minute exposures are. I assume 90 minutes of 300 seconds exposures? So for set 1 you stacked 90 subs (at what gain?) and for set 2 you stacked 18 subs?
That's right Sander! 90m total in both cases, just the sub length and gain were the variables in the experiment 👍 (aside from some uncounterable variables too, such as some atmospheric variance through the test etc)
Clear skies my friend!
@@lukomatico Why wasn't unity gain or a least the same gain used? Makes the comparison NOT equal??????????
I can see your argument Charles, but it's simply not how you'd use this camera in reality, so why force those constraints on it during the test?
If you tested 60s subs vs 300s subs at the same gain setting, then provided that the 300s shots aren't overexposed then they will always be better from a purely snr standpoint, that's a given, instead though by using real-world settings like this it gives a better comparison as we can now see how the data looks when the camera is used with reasonable settings.
While there are cameras out there with which you could make a 1-1 comparison the likes of which you describe, 60s vs 5m subs at unity for example, this camera isn't one of them when paired with the RASA.
Hi Luke, nice comparison ! 😊
How did you manage darks with your Neptune ?
Thank you David! I'm glad you liked it my friend 🙏
Regarding darks, I don't use them with this camera :-) I just make sure to frequently dither my exposures instead! 👍
I hope that is useful to you, thank you for watching!
@@lukomatico Very useful, thank you ! I have the Uranus and do darks with it but with more or less success. I will manage my dither more properly ! 😊
Every set up has threshold exposure. Exposure time below threshold strongly introduces noise. Exposure above threshold have little contribution to noise reduction.
Use narrow band filters drive threshold to at least 2 min. For example, threshold for my set up and location is just 10 sec. Addition of narrowband filters make it 4 min.
Altogether, comparison of 1 and 5 min, when narrow band filters in use, will produce dramatic difference. 5 and 10 min will show minuscule difference.
Hey Ana!
I agree for sure, there's always a sweet-spot for exposure - that said, it's finding it that's the trick! :-)
Here in my bortle 7 skies most calculators online would suggest a far shorter exposure than I actually use for both broadband and narrowband work, - they're certainly not erroneous for everybody but for me their suggestions give highly sub-optimal results, - It's always worth actually testing these things out in the real-world as without a scientific analysis* of your whole optical system you simply can't plug in every detail required to make a truly accurate calculation :-) (*some examples being: true measured sky brightness - total optical system etendue/transmission - batch-to-batch variance on filter bandpasses - per-wavelength sensor response variations etc - it's just not realistic to do all that unless you're a scientific organisation!)
Thanks so much for taking the time to watch and comment, I really appreciate that you'd do that!
All the best & clear skies! :-)
@@lukomatico Sharpcap does exactly this. It measures brightness, analyzes your sensor and gives you results, which have been tested and they worked. My one is also bortle 7. Sharpcap recommends 3.5 min with asi294mc and l-extreme on c8 f/10. As an extreme example. We have 75 miles away bortle 2 place. Software recommended whooping 40 min subs. My mount will not handle even 2 min for my scope.
@@anata5127 That's a great point Ana! I guess if you were using a mono system you could run the 'brain' tool for each filter and figure out some optimal exposures quite quickly, - nice!
I'll have to try this out, I'll see what sharpcap suggests as an exposure and test those values vs standard 5m subs for example 👍
Thank you very much for the tip & suggestion! :-)
Clear skies!
@@lukomatico Brain does not work on mono. Here some extrapolation from color camera needs. Thus, I have both 294mm and 294mc.
In my opinion, most critical in getting low noise is overall exposure time. I have started astrophotography from EAA only recently in March 2022. Targets look great in 20-40 min. Then more I added overall exposure time, then more details I saw. Now, I have a target (m57) to which I add more and more exposure time with strict selection of FWMH
Hey Ana! That's very interesting to note, thanks again for your feedback!
It sounds like due to your mount and desire for high resolution imaging you may want to try lucky imaging too, check out some of the pictures taken by Exaxe on astrobin for great examples! :-) 👍
I can offer to help with a quantitative noise assessment if you are interested, in addition to how they look on screen
The conference talk by sharpcap developer, glover, talks about balancing the shot noise from light pollution with the read noise of the sensor determines balance of exposure duration with number of images.
Hey Brent! I appreciate the offer buddy, cheers! :-)
RE: Dr. Glover's talks - I must admit I've watched and digested the info a good few times over, it all seems to make perfect sense - at least in theory anyway! I guess careful testing would be needed to see if the theory can be applied in practice though!
Thanks for watching :-)
Nice video Luke. I was curious to see whether it lined up with my testing. Apologies in advance if I'm teaching you how to suck eggs. Taking fewer, longer exposures also means you're stacking less noise, while still reaching your desired SNR. Your computer also has less pre-processing to do (especially if you have to drizzle your data which is very computationally intensive). Longer exposures also means you're far more likely to swamp any read-noise, dark current or sky noise as in your case - you got a cleaner image with higher SNR. I've always preferred the zero-gain, longer exposure approach for nothing more than the much higher dynamic range and full well depth that result from low gain exposures. As a side note, longer exposures also mean you can drop your offset as you're much less likely to have zero value pixels and each well is more likely to register an authentic average real-world value. I'd say your cleaner background was primarily down to sky noise, or lack thereof in your longer subs image. Light hits your sensor at different times, like raindrops falling onto a piece of paper. It won't all be covered at the same time. The more times your sensor registers few photons coming from the same place, the more likely the ADC is to register a pixel value higher than the background and noise value. With shorter exposures, you are likely to register less photons as not as many will hit the sensor in the same place during the same exposure... Higher SNR in longer exposures also means there's more breathing room between your signal and the noise floor, so you have much higher contrast in your mage after even a Screen Transfer Function. I really hope that makes sense.
Hey there Rick! - it all makes perfect sense mate yeah! :-)
I'm familiar with the concepts behind astro imaging, which, in an odd way, made this result slightly more confusing! - I'd expected that in a photon-rich scenario like this, imaging with the rasa and a very broad LP filter, that there should be very little difference between the two sets as neither are photon limited, or constrained by read noise as a result - at least that's what the usual math would suggest right? It appears this test set was behaving a little more like a true photon-limited/read noise limited scenario, like Narrowband for example - which leaves me wondering what part of the test I had so wrong lol!! :-D ah well, more testing required, it'd be nice to figure out the point of diminishing returns eventually at least, for both my usual filters 👍👍
Thank you so much for watching and leaving such a high quality comment mate, I really do appreciate it!
Clear skies!
@@lukomatico Cheers mate. On the contrary, I thought your test was very good. The conclusion you came to was what I would have predicted as because whatever else is going on in the scene, so long as your LP isn't too crazy, you're still collecting the odd photon on longer exposures which increases the likelihood of cumulative photons adding something to the pixel well increasing it's data value. This is far less likely to happen on shorter exposures, no matter how many you take. Say for example, you have something in frame that's 5e-/ADU, but you're only registering 3e-, that pixel will never register a value above background when read by the ADC. Obviously the numbers wouldn't be so small, but I hope someone can benefit from the information. Keep up the good work and clear skies to you too, especially now astro-dark isn't far away.
Thank you Rick! - I just re-read my message - sorry if it came across like I'd implied you thought my test was poor or something buddy, I didn't mean it that way! :-)
It's a subject that really interests me for sure, I've had a lot of fun in the past playing with lucky imaging, where as you'll no doubt know, dealing with shot noise and very low signal levels is the norm - but of course as you note in your message, when you reach the scenario where per-sub your signal/noise ratio is just barely positive then stacking efficiency is low, taking a lot of subs and a lot of total integration to approach the signal of fewer, longer subs!
There's got to be a sweet spot I'd guess, and a point of diminishing returns - it'd be interesting to find out where they actually lay though! 👍👍
Thank you again, and I totally agree it's great to have quality info in the comments for people to digest! :-)
Clear skies buddy!
@@lukomatico Cheers. Funny you should mention diminishing returns. I'm working on an East and West Veil Nebula mosaic. Total integrated exposure time will be about ~60 hours, so data collection is somewhat... time consuming and frustrating at times. I'm taking 5 minute subs as that gives me an ADU high enough to swamp the read noise and only about 3% of each sub is sky-noise. I started to see diminishing returns after about 80x 5min subs, but I'm doing 100 per channel per panel anyway. Once I have all the data captured for each channel, I'll publish the results as I have a feeling I'm going to hit diminishing returns far quicker with Oiii and Sii when compared to Ha.
@@rv3211 Wow!! - That sounds like a heck of a project Rick, I'd love to see it when you are done!
Good luck capturing the rest of the data and I applaud your dedication my friend! :-)
Clear skies!
Great video. I'm new to this game.ive got a wiliam optics gt81 with the wiliam optics 50m guide scope with the zwo 294 camera just wondering if you could tell me what to set my gain at.
The 294mc pro is always best at 120 gain.
Hey there Craig!
Thanks so much for your kind comment :-)
It sounds like you've got a lovely rig there, congratulations!
Re: your question about gain, as the other commenter mentioned, 120 is a great setting for the 294 sensor, no real reason to go below it 👍👍
@@lukomatico thanks buddy ill get it out tomorrow if it says clear & give it a shot. Thanks for the info
Did you ever try a 5 minute unity gain exposure test, for example my asi533mc-p would be 100. Why did you choose zero?
Hey mate! - Good question! - I did indeed test that, but the images can be a bit blown out in places, likely due to the smaller dynamic range of my camera and the speed of the rasa. - re: why gain zero, - I'd seen great results from other folk shooting with rasa/hyperstar etc at gain 0 (with other cameras), so thought to add it to my little test! - it worked well I must say!
I hope to change to a new cooled camera soon (PlayerOne's version of the 2600) so will likely go back to using gain 100 myself too as it worked great with my old 2600mc pro :-)
Hope that helps!
Thank goodness the 300s subs were better...otherwise we've all wasted a lot of time tweaking our guiding and whatnot. There are advantages to shorter subs, but none related to image quality. Thanks for the comparison!!
Thanks Kevin!! I agree, there's still advantages to short subs but if absolute image quality is your goal it still seems long subs are unbeatable even with today's cameras! (or maybe something is flawed in my testing, making the results skew so heavily toward long subs?)
Thanks for watching!! :-)
Luke, I always think of you as a Pixinsight guy, but on this project you use APP for stacking. How come you don’t use WBPP?
Hey mate! :-)
I've been a bit of an APP convert for the last 9 months or so when it comes to stacking! I find WBPP a bit cumbersome by comparison, and APP tends to give a smoother output I think from the same data set!
Hope that explains my reasoning mate!
Clear skies 👍
What's the best Telescope to pair with the Sony A7 IV? My budget is below $2000.
That's a tough question mate! Do you want to do wide field or more narrow field imaging? With a full frame sensor to support you'll be able to get something like an askar fra500 at that price point perhaps and have a nice setup capable of using that sensor size :-) if you want a longer focal length scope though it may be a bit more difficult
Hope that helps
Why would the flats work better on the 5 minute subs vs the 60s?
Did you use same gain for both or not? If not what were differences?
Hey there! - I used different gains & offset values for each experiment - the 60s set were at gain 200, offset 20 - the 300s set were at gain 0, offset 5
I hope that helps! :-)
@@lukomatico Why different?
Hey Charles! - it made sense to use an appropriate gain like you would when imaging normally for each exposure length to avoid blowing out the image completely, and/or to avoid favouring one set of exposures or the other 👍
If I had a camera with a deeper full well capacity I could redo the experiment with the same gain for both I reckon,
Hope that helps explain my choice!
Clear skies! :-)
Ey up dude 👍🏼 Awesome what that camera can do 👍🏼 super impressed 👍🏼👍🏼 I’m seriously thinking of buying as I’m on an old full spectrum canon 1100d (with a filter) and I don’t wanna fork out for a James Webb Astro cam (sensor was at 27 degrees other night 😱) 😂 do ya reckon it would work well with a 72ed? Guiding is 0.8 tops to 0.6 low (eq3 pro) my pictures with the dslr are decent but lack the details….random question but….what do ya think dude?
Hey there buddy! Hope you're doing well! 👍👍
I reckon if the cam fits your needs in the rig you have then absolutely go for it mate! - it's a lot smaller sensor than the DSLR of course, but it's cleaner, more sensitive and doesn't need darks etc - I really like the thing 👍
If you ever see yourself using an Asiair or something then you might wanna go for the zwo version of the 585, but if that's not for you then I do reckon the Player One version is the best one 🙏
Hope you have a cracking weekend in all this sun mate! :-)
@@lukomatico cheers dude 👍🏼 thanks for taking the time to reply 👍🏼 you too have a good weekend sir 👍🏼
90 reads each with read noise vs 18 reads with read noise.
Optimal sub length depends on the camera read noise as well as the light pollution. There is this excellent talk by Dr. Robin Glover about the longest reasonable sub-exposure time, depending on your sky brightness and the read noise of your CMOS camera.
czcams.com/video/3RH93UvP358/video.html
Hey there bud! - I've watched that one a good few times over the years haha, great video!
It's a bit of a balancing act to get a truly optimal subexposure length because as the video mentions, you need to consider the read noise of the camera for a given gain setting, your sky brightness, any filters used thus reducing sky brightness and also optical system throughput so you can determine how long you need to go before you've completely swamped read noise etc in your image background values, which sharpcap's "brain" function can figure out reasonably well - finally I guess you need to determine how many exposures you'd like to stack for a given project, I'd not want to take 60s exposures for 10 hours for example, and be stuck dealing with 600 light frames! :-) I'd much sooner be dealing with 60x10m subs personally, otherwise stacking can take literally a day to complete (or not complete at all, running out of available memory, crashes etc)
Clear skies!
I did something similar recently with my OSC, comparing 10min vs 2min exposures with broadly similar results. However my main issue with the longe exposures was throwing away more images due to planes, satellites and atmospherics. Light pollution from street lights and the moon was also more pronounced. So while I was quite impressed with how little background noise there was and the better detail in the 10min exposures, overall I doubt I’ll take such long subs again because I threw away so many. Maybe I’ll try with 5min exposures next time.
Hey Jeremy! - That's interesting to hear mate, good to know the results were rather similar for your experiment too!
I totally hear you about the pain in throwing out those long subs, it's a real PITA to actively watch yourself lose a 10m shot in the last minute or so too due a passing cloud or such, haha!
I definitely think it's worth further experimentation though, you should eventually settle upon a happy medium and get the best of both worlds ideally - at least that's what I'd like to do :-)
Thank you for watching mate, and I hope you managed to add to your recent M16!
Clear skies :-)
@@lukomatico I’m getting there mate, gradually adding data. I’m up to around 15 hours of usable data now and I’m perhaps starting to get into the realms of diminishing returns, but I’ll stick at it for a while yet. It’s a challenging target from my location but who wants easy 🤔.
Sorry… I am going with many short exposures with high gain with my setup.
Totally understandable Mario! There's a lot of advantages still to the short exposure approach for sure 👍👍
Clear skies my friend! :-)
sigh.. never getting 5 mins from a sky guider pro :(
I wouldn't worry about it too much mate! - just expose as long as you reasonably can and stack 'em up!
I'm sure the results will be great 👍
Good luck!
@@lukomatico ha yes... I think I am getting good results for the kit I have.. but always trying to squeeze that little extra :)
Me with a pair of 10x binoculars and a iPhone 😢😢😂😂
Haha, it's better than nothing buddy! :-D Thanks for watching!
ρɾσɱσʂɱ 👌
Thank you my friend!
Really interesting. You might like this video from SharpCap on setting gain values czcams.com/video/ub1HjvlCJ5Y/video.html. It's a bit dry but worthwhile.
Hey Paul! Hope you are well mate :-) I've given that a watch a few times aye, great suggestion!! I was just really surprised with how this test turned out, it seems to fly in the face of the conventionally accepted knowledge!
Hope you have a great weekend buddy!