I didn’t mention this in the video but I took dark frames for 12 months before watching a Peter Zelinka video that suggested they’re not necessary. I tried it out and darks add no value to my images, but that’s not to say they won’t add value to yours, it needs to be tested. There are lots of threads on forums on this with the same information that I have put in this video. Darks in general are not needed with a DSLR, but dithering is absolutely crucial. This won’t be true for everyone, however so please do test it.
I tried both and my images look better when I subtract dark frames. You have to shoot dark frames in between light frames or right at the end of the series so that the temp. of your sensor does not vary much.
Thanks for the tip. I've just reprocessed an image without darks and it turned out better than my first attempt. There was less colour noise in the image.
An interesting topic for sure. I like how you prefaced this by stating that every camera is different. My DSLR for example absolutely needs dark frames, and that is one of the main reasons I am looking more and more into a cooled, dedicated astronomy-camera. It is really annoying having to cut your imaging-time short by an hour or more (longer exposures), just to take pictures with the lens cap on. This is not a problem when I'm in my backyard, as I just tend to hide it somewhere and go to bed, but out on dark(er) locations, that's not really an option.
Just a thought to add to this. I capture my images with APT and it lets me know the sensor temperature. It does this for my light frames as well as my calibration frames including the dark frames. I take my dark frames on evenings that are cloudy. I then build a library of dark frames separated by degree Celsius. I then can match those with the light frames when I take them based on the temperature. Not sure if this would be helpful to anyone but it seems to work very well for me.
@@alanalain4884 yes and the time it takes for the second image makes the gap needed for the time lapse to work. If I need a longer gap between shots I use an intervalometer. That's the beauty of using LENR in a time lapse - a ready-made gap and cleaner images 😃
One possible solution may be to not take dark frames after your session. Since dslr cameras are not cooled, the temperature in the sensor kind of builds up every time you take a picture. So effectively you end up with dark frames with lets say 2-5 degrees apart from the lights. So either you take the dark frames on the field when the camera is properly/passively cooled and matching roughly the temperature when you started your session or anywhere else with the same ambient temperature. It's just an idea. Also some people use master frames and keep them for six months and then renew what do you say about that ?
Never seen such discussion before, but I've tested with my mirrorless camera and the moon, the background is clearly better when I stack and subtract dark frames.
I'm completely new to all of this. I just received delivery of an EQM-35 mount and plan on using my DSLR for now. Will hopefully get some time this weekend to shoot something. I'll probably take darks and then stack both with & without. Since I'm so inexperienced, any image I can get would be an epic achievement for me. Thanks for the video.
I’m a noob. I’ve been imaging since January and thought I was dithering the entire time and this video made me check. I have not been lol. Excited to try without darks as they are my least favorite part of imaging. Thanks for doing your videos!
Hey Nick. Thanks for your thoughts and info on this. I found it useful and I'm going to try this soon. I'm thinking of getting my dslr modified probably end of summer when the dark nights come back in. I've been impressed with your images since I found your channel and I'm ready for my own journey and it's going to be exciting and I've had help and advice Thanks for sharing this interesting video and stay safe buddy!
Congrats on your video. Nice, I liked it. I generally do three or four darks before and another three of four after shooting, stack them, and flatten the darkest pixels to remove the noise, leaving only the stuck pixels and amp glow. This works for me. I'll have to try your dithering technique to see what I think. While not taking dark frames might seem like a good idea, as you suggest in your video, dark frames are way superior (in my opinion) for removing hot or stuck pixels, and amp glow than using the dithering technique. So what I think is best (and I do) is to use the dark frame ONLY for stuck pixels, amp glow, etc, but remove the noise. This just requires preparing your darkframe using an image processing software (like photoshop), and you do not need dozens of dark frames, only a small ammount saving time. Time seems to be what you are most concerned about. Regarding the temperature, you cantake a few dark frames before and some after your light frames. OR wait until your camera wamrs up completely. I have noticed mine warms up only so much after about 15 minutes aprox, after that it remains pretty constant. It's a pity I can't measure the sensor's temperature some how, but the casing temperature is in fact a good indication of what the inside of the camera is like. If the outer casing remains constant for a long period of time, well probably so is the inside. Don't you think? Good work and good luck.
Intriguing. Depends on the camera and how hard you push it. Could also argue you save time with higher iso and using darks. I can get away with no darks and just dithering with my Sony A7, but on my crop sensor Sony A6000, with a higher pixel density, I get some crazy crazy artifacts. Nice video!
Dark frames only add noise on my Canon 60d. I dither, and I use bias and flat frames. I've measured noise with and without temperature matched dark frames, and even temperature matched darks increase noise. Don't skip bias and flat frames though!
That will get interesting. Let me grab some snacks before I post my point of view :-) Good point and if the quality improvement is not that big I would go for that and maybe even use the saved time for some additional light frames. But this needs to be tested. First what is the difference in the master dark with just slight differences in the temperature. So do dark frames fit the noise pattern of the lights even if the temperature if a few degrees off. Next thing is that in a DSLR the sensor heats up during your imaging session due to the constant usage. It creates a balance between the heat that is created by the usage and the heat dissipation cause by the ambient temperature and I would expect the temperature settle at a certain value after some time. Taking your dark frames at the end of the session (with not much time between light and dark frames) should end up with dark frames having more or less the same temperature. Some cameras also save the temperature as raw value in the image files what could help find dark frames with matching temperatures. So I would politely disagree to the general message that dark frames are useless with a DSLR but I agree to the fact that it is more complex compared to cooled camera with a fixed temperature of the sensor. Happy to discuss this further and see some test data. Cheers form the "main landmass" from a guy who missed to shoot the super moon yesterday 😩 😉
It’s a great point of view and thanks for the comprehensive reply. It absolutely does need to be tested, which I hopefully made clear in the video. I’ve certainly found that they add no value to my images at all and having been involved in various forum discussions lots of other people came to the same conclusions. Having said that, each user is in a different situation and so there will inevitably be use cases where darks are useful with a DSLR. Cheers 🙂
Just tested that and analyzing my images in Pixinsight, the Stack with Darks has slightly more noise, than without. I'm using a Rebel T7/EOS 2000D, and Darks literally make my images either worse, or don't help the slightest. Tested multiple times with weather below 5°C, not sure how it will turn out once it's a warm summer night though, but we'll see :) For now, I won't be taking anymore darks, as for my camera they make things worse
Yesterday I had a quick imaging session with M51 Whirlpool Galaxy to test this. I got 15x3min Lights, 15 Darks, 20 Flats and 30 Bias. I used 3px dithering in guiding. And the result is very interesting. Actually for this session it worked really good for me without darks. If you want I can send a screenshot of that comparison.
Hi Nick, as you've seen on twitter I have been trying out your method shown in the video of taking no darks, I have tried this before but didnt achieve great results but this time its been a revelation as I think the more light subs you take the better the inage is. I did try processing the same images with darks and have to say the no darks were easily better, thank you I think this is the way forward for me, I can add more light frames now, there are bound to be some hot pixels and I haven't dithered either, maybe the az gti mount compensates 🤷, keep up the fantastic work and clear skies 👍
If you haven’t converted your mount to EQ mode, you don’t need to dither an AZ mount as it isn’t rotation corrected so everything is moving a few pixels every minute by physics. For free :-)
@@jml7916 yep, since my reply I have converted to eq mode and now dither with my asiair pro, guide with my zwo asi120mc-s and image with my zwo asi 294MC pro 👍
Correct me if I'm wrong, but I guess there's another issue with taking darks without controlled sensor temperature. The sensor's temperature rises and balances at some point while imaging light frames, but when I put the lens cap on and proceed taking darks, doesn't the sensor's temperature drop shortly after a few dark frames since it is no longer revealed to the open sky? Just a thought, I'm interested in what you guys think. By the way, what is the point of ruining the actual imaging time just for darks? The lens cap is put on, so I believe one should be able to safely take darks until like civil twilight without worrying about light getting through.
This is cool... but it would have been cool that on your side you'd gave us one image comparison to better illustrate your observations. Thank you nontheless for this insight.
In my case without dark frames my DSS results with a picture in which when enough contrast in levels is applied you can see hot pixels that are grouped and indicative of a drift in my tracking (no guiding here for now) Darks always removed them very well. But I always use up all night dark sky for imaging and capture my calibration when sun starts to rise so it's only a matter of getting less sleep for me.
BTW, the ad that RU-vid inserted at the end of your video was for Affinity Photo 1.9 which has an excellent calibration routine for applying darks, flats, flat darks, and aligning and stacking images. It seems to work very well.
depends on camera. i find darks really help with my sony a7r3 (mirrorless). while its not cooled and i'm not aware of the temperature delta, there are still some noise patterns that clean up well from dark subtraction.
Hi Simon. I truly think the title of this video should be "Why, I stopped taking dark frames" thus why I cannot agree with all of your comments. Dark frames are & will always be necessary in some part of calibration, especially when using a dslr. Unfortunately dithering alone will not calibrate out all thermal / pattern noise created by the sensor. General consensus from seasoned imagers recommend the use of dithering in conjunction with a few carefully taken dark frames.
Interesting video as ever, Nick. Thanks for putting it together. My experience so far has been mixed. With my modded 450D, darks seem to help a bit but not game changing; as I always do them outside immediately after an imaging session, it doesn’t add any burden for me except the extra time in DSS. Never convinced the impact is always worth it, but it definitely does detract. With my MK1 6D, if I’m doing any stretching of the image at all I definitely need darks. I’ve only got a Stat Adventurer mount so I can’t dither (at least on purpose; I suppose inaccurate tracking is a form of dithering!!). Stretching the output from my 6D without darks reveals weird colourful pixel-snakes in the image, which only seem to disappear once I’ve subtracted darks. So I think, in my very limited experience, it depends on the camera. As the dark capturing process doesn’t interfere with image capture for me, I’m happy to continue. But if you could find a way to eliminate flats from the process, Id be in your debt forever!! I find them a massive faff!!
I stopped taking darks with my DSLR after hearing Trevor jones from astro backyard mention in an offhanded comment that he didnt either when using a DSLR. I tried it and have better pics because of it. The image of Carina that I use as my icon is done without darks
I wouldn't say the *consensus* is that you don't need to take darks with a DSLR. It's an idea that's being floated, and I think it depends somewhat on the performance of the camera, more likely to be true with newer DSLRs (the ones I call "third generation," Nikon D5300 and later). You're right that dithering (and also cosmetic correction) get rid of hot pixels effectively. The experiment is worth doing, because the time taken by dark frames is appreciable. They have to be in the imaging session in order for the temperatures to match.
Thanks for your comment Michael. It’s certainly camera dependent. In hindsight I probably should have mentioned that creating a dark library is a good solution for the mismatch of temperature
@@AstroExploring Actually let's keep the question open, because you're onto something. With newer sensors, the pixels are small enough that a star is never a single pixel, and Cosmetic Correction can distinguish hot pixels from stars. I still get a benefit from dark frames, but it's much smaller than 10 or 15 years ago.
I created a library of darks in the garage and freezer iirc. Though if I didn't have a matching library, I did start skipping them, especially when it was cold out.
As I remember you get less noise when ambient temp is cold v warm. I skip the darks if shooting in sub zero. Use darks during warm summer nights and now will skip the darks.
Glad to see someone call out this myth. With DSLRs and mirrorless cameras, I find separate darks almost always add more noise than they remove, usually in the form of colored spots or dark holes, as they will never, ever match the temperature of the lights. I see differences in thermal noise from image to image as the sensor temperature is always changing. In my experience, whether darks are needed at all depends hugely on how cold or warm the night is. They may not be needed at all in winter, but in summer lights can be peppered with thermal noise specks that I’ve found can only be thoroughly removed using LENR darks in the camera, as only those darks will match the lights closely. Darks taken at the end of the night or from a library never will. Subtracting them adds noise, or at best replaces one form of noise - bright specks - with another - dark holes. Users of Canon full frame DSLRs (not mirrorless R cameras) have a dark frame buffer that allows 3 to 5 lights to be taken in quick succession before the LENR dark kicks in and locks up the camera. So that speeds up acquisition, as long as you are controlling the camera via the shutter port not via USB. But you are right - people should test, as YMMV! And if you do take darks, however they are shot, you do not need to take bias frames. Not with any CMOS camera. Even makers of CMOS cameras such as ZWO say that. Bias frames are a holdover practice from linear CCD cameras for scaling library thermal frames taken at different temperatures. So that’s another “wisdom” that needs to go away. In testing calibration sets with and without bias frames I’ve found they make no difference at best. But don’t take my word for it! Test! This all needs to be tested, with the results presented as evidence, as only results matter. Not anyone’s received wisdom, authoritative assertion, or hand-me-down practice. i.e. “everyone knows that ..” But I’ve found that with DSLRs and mirrorless cameras a lot depends on the ambient air temperature. What works in winter may not work in summer. And what works for a new camera might not apply to an old one. Thanks! Clear skies!
I don't see the issue, take your darks immediately after you take your astro shots, sensor temp isn't going to change since it's already stabilized from taking the main shots.
If your mount has no active guiding control and only a motor to compensate the earth rotation , then your exposure time is limited anyway. Over time your images (10, 50, 100 or even more) have small offsets to each other. That again has a similar effect as dithering. So, no need to dither, when you don't have a pixel precise guiding.
@@AstroExploring I can't agree with this. You need darks for hot pixels, amp glow and pattern noise if you don't dither, even if it doesn't fully calibrate out thermal noise.
I experimented with this in PixInsight with the Weighted Batch Preprocessing script, and got a strange result: If I left out the darks for the main images, my flats were either not applied or under-applied. (I tried putting in the flat darks as darks, and alternatively as bias, and got the same result either way.) The script created a normal-looking master flat and claimed to have applied it. I'm trying to figure out what was going on. I would have thought that putting in the flat darks as bias frames (which they are) would have made everything correct. Thoughts, anyone?
I got sick of amp glow so I bought a asi533 last night from flo because there was 1 left lool, might be put off with the square chip though, hopefully not. Anyway, my dslr has had a good run but amp glow is getting more frequent, the problem I face that I hope you do a video on or have already somewhere is how do people image dso's and they have multiple colours in them. I have a optlong LP filter that makes everything reddish, so far the ring and dumbell have come out with different colours using DSS but wizard, crescent, veil, monkey head all are just red.
I'm considering the asi533 as well due to amp glow concerns and had the same worry about the square sensor. But seems like most like it as framing is easier.
Certainly an interesting topic. I am yet to try a stack without darks. I have a Canon 100D which has a particularly noisy sensor so I have created a number of Master Darks at different ISO levels. I tend to do these by popping the camera in the fridge for an hour or so (or 6...) with an intervalometer set, usually after my imaging session. This seems to work ok in winter as the temperature outside is often similar to the fridge... Yet to consider some summer darks. I'll re-process some data and see how it compares. I too had read this on forums but am yet to bite the bullet. Considering flat's are a must what are your views on bias frames?
It’s definitely worth trying it out for sure. Bias frames I do find useful but others recommend dark flats instead of bias. I haven’t used them too much but didn’t notice a significant difference and bias frames are easier so I stuck with those for now
My takeaway also, the video suggests that because your online images don't use dark frames, this is sufficient evidence that using dark frames is not required. Maybe your images would look better if you used darks (taken at the same time as lights). Not trolling, but if you're looking to improve the quality of your educational instructional videos, that stuff is important to put in the video.
Hi Andy, thanks for the comment. What I didn’t make clear in the video is that I took darks for over a year, using a variety of methods (between lights, before lights, after lights) before stopping taking them altogether. I hopefully made clear in the video that it won’t work for everyone, nor will it work for every camera. The title is a bit clickbaity so I hope you’ll forgive the sweeping generalised statement that it makes. I don’t expect everyone to agree with it, because everyone’s experience will be different
Thanks for clear video Nick. My question is, is it worthwhile doing dithering with a Star tracker? (I don't currently have a guide scope or camera) Or should I wait until I get a more stable GEM such as HEQ5?
@@hangerbird I have a star adventurer and use its mechanical dithering capability, there is some maths you need to do to get the correct dither value. I then do not use darks on the assumption that the mechanical dither reduces the noise anyway.
I couldn’t say whether it’s worthwhile or not with the SA as I’ve never tried it on a star tracker before but it’s certainly worth giving it a go just to test if nothing else
If dithering what calibration frames would you recommend, lights flats bias , or lights flats dark flats or as above but load the bias as a dark frame too as well as calibration with flats ?
I use flats and bias personally. I see discussions around using dark flats over bias frames but I’ve never dabbled too much in dark flats to really offer a verdict on that
Interesting video! I've had limited benefit from darks with Milky Way images, but when pushing deep space files the difference can be substantial, and the same lights stacked with darks vs without, are vastly different. What complicates this is that some software detects and removes hot pixels from some raw file formats and not others, for instance my Canon files never show hot pixels (even though they'll be there, but removed), but my Sony (mirrorless rather than DSLR but same idea) has a huge number of hot pixels so for foreground stacks darks become pretty much essential, depending on the camera/file type.
Hey, Nick! Well it turned out that at least in the experiment I performed yesterday, your advise turned out to be right. I didn't miss the dark frames at all. On the contrary, I managed to get more detail out of the data I had. I tagged you on Twitter so you can see a comparison. Thanks so much again!
