Thanks for the well thought out explanation. I have watched many calibration videos over the past 4 yrs. But your teaching skills are much better than most. Clear skies
Is this correct? Darks already contain bias so if you use dark frames you do not need to subtract bias from the lights. Bias or dark flats are need for flats.
That’s right! You wouldn’t need both! Workflows that use both are aimed at optimizing dark frames i.e. scaling them in case they were not taken correctly
This is, I believe, the first video I have seen of yours. I like your rice and plate algorithm. You are clearly smart and thorough. I think I'll be watching more.
Great tutorial. Thanks for that. I'am among the lazy fraction of astrofotographers, who try to restrict the calibration work to the indispensable minimum, which really matters in the final picture. Flats are indeed indispensable, specifically for fast optics, the other depend on the camera and the ambition for the final picture. You have supplemented what I exercise after long experimental experience with solid scientific justifications.
Some older ccd's require longer duration flats, or they record a shadow of the shutter. (KAF8300 sensors are a good example) What's really bad is when the "dust" moves over time during a session (mostly a DSLR problem). Flats just make it worse. I tried a round of low ISO flats, had to shoot a set of bias frames to calibrate the flats in PixInsight. I wasn't exploring it for long term use, just trying to clean up some borderline data. It did work but it's more cumbersome than it's worth. Better data is the solution (and sometimes a better camera).
oh no! Dust that moves around really sounds like the most horrible problem that you can't calibrate out. At that point you just hope it moves around enough to get rejected (kidding)
Greetings from India ! Many congratulations! 🎉.Your gear selection is simply amazing just like your knowledge on the subject and ability to explain the technicalities in simpler terms.
Is it necessary to be perfectly focused before taking flats? I've been running an autofocus beforehand, but would rather just skip that, and start the night directly with taking flats, and dark flats.
Great job! You don’t just clobber us with knowledge, but back up and justify your views. Very clear explanation. One thing I would like to hear your opinion on is dark frame calibration with a DSLR or other non-cooled camera. Achieving a consistent temperature is obviously a challenge. How important is this, and what are the best practices for creating temperature-matched dark frames?
Thank you so much for saying that! I use a dark library for my mirrorless camera and I try to take dark frames for each 5-degree increment. There is no perfect solution because the temperature is not controlled, but if it’s close enough it will provide a benefit over just nothing.
Excellent discussion of the needed exposure time for flat frames. I had the striping problem you described but didn't know the cause. Experimentation with neutral density filters between my light panel and telescope solved the problem by lengthening my exposure times. But until I saw your video, I didn't know why very short flat frame exposures were causing the problem. Well done!
With my 183mc pro to fully remove the amp glow (that can creep back in stretching), I rotate the camera 180 degrees half way through the session. If I take light flats (I don't), how would this work as I am changing the imaging train mid session?
If your darks are correct you should be able to calibrate them out perfectly without needing to do this rotation. A reason they may not work is for example if light creeps in while you’re taking darks. I noticed this with my 183MM Pro - light was leaking in somewhere. Now I do darks with the cap on, inside a box, under the bed in a dark room. It sound ridiculous but it works. I don’t see how rotating the camera would be beneficial - it flips by 180° anyway during the meridian flip. If you do decide to rotate the camera you’ll need to take flats in both orientations and calibrate each light with the correct flat.
@@the_space_koala If there is a meridian flip, then yes, rotation is unnecessary (that is how I discovered this trick). The amp glow is so bright on mine there is very little signal under it and artifacts keep creeping back in. I regularly use 300 or 450sec exposures and have at least 35 matching darks. I will follow your advice and increase this to 50+ next session.
This is the clearest and best presented explanation of calibration frames I have seen. A lot of materials found on forums are just recipes (good and bad) presented either without reason or with faulty reasoning. Thank you SK.
Please make a tutorial for mobile astrophotography..bytw. I'm a mobile astrophotographer now but i about buy a new telescope edisla astra 100 and i already captured milky way galaxy,orion constellation, scorpion, etc constellation, star trails,venus,moon, Jupiter, Sirius and lots of stars
Could you put together a simple chart with the different types of frames on the left horizontal axis: darks, flats, bias, dark flats. And across the type such attributes as temperature and ISO (and perhaps others) and a check in the corresponding box if that attribute affects that type of frame. The goal here is to understand what is a "library" of calibration frames. To rephrase, does a library need to have a master bias frame for each ISO and temperature? Currently I'm sticking with ISO of 1600 but my camera is not cooled. This really is a nice video because it tells us *why* we are taking each type of frame.
I know about these concepts only because I have been doing it for a while. But, this is a very good information and clear explanation for anyone who is starting new
I'm glad you started making these longer videos to explain things. How do you build up a library of master darks? Don't they have to be taken every time? I missed something, I think. I'll watch the video again. Also, if you every feel like making a video explaining proper ISO/gain settings for DSO imagining, I don't think I'd be the only person who would greatly appreciate that.
Darks can be reused over and over! The only one that’s session specific is the flat. For the dark library you just take them for each temperature you want to shoot at - in case of a cooled camera. For a non-cooled camera you’ll still do the same but as you can’t control the temperature you try to take them at each 5-degree increment as the weather allows and then later use the one that is closest to the current temperature. I have been known to take darks in my fridge for the fall-winter 😁😁
Calibration success rate depends on camera. For advanced cameras from such companies as FLI, QHY, etc. calibration works no matter how it has been done. On other hand, ASI294-created lights very tough to calibrate.
Excellent video, your the first who actually said when you don’t use darks you still need to calibrate lights with the bias instead. One other fyi, you said calibration is really important for astrometry when measuring star brightness changes, I think you meant photometry, Astrometry measured position, photometry measures intensity, great presentation
May be this smart Space Koala might convince me to take calibration frames 😊Up to now I have only taken calibration frames for my ASI294MC Pro. To get rid of the the amp glow this camera unfortunately suffer from. For other cameras, including mirrorless, I feel the quality usually are OK. The "lights" are more affected by atmospheric conditions to be "perfect" anyhow in my sessions up to now.
If you use your mirrorless with a lens you can also just take a series of calibration frames and reuse them! I for one don’t remove the lens of my mirrorless often so I can even reuse flats between sessions sometimes! And you can create a dark library for each like 5 degree increment in temperature and reuse those as well!
I really liked your video. If I could offer a constructive comment I would suggest you try to eliminate some of the jump cuts. There are so many it makes watching the video very difficult over an extended period. That said, your content was very well presented.
Ooh, sounds like a fun little game. Let's see how close my understanding is prior to watching the video, and then see how far off I was afterwards. So, I think: * Darks: these serve to map the hot pixels of your camera, and potential thermal artefacts (e.g. a hot component close to the back of the sensor artificially illuminating some pixels). * Flats: these map things like dust specks on the lens and potentially cold pixels that don't react to incoming light. * Biases: this is the hardest one. I'd say thermal interference is probably one of the things it captures, but I have no clue why these should be required if you already have darks. Alright, onto the video! 😁
* Darks: Alright, amp glow and dark current, forgot about those. 😅 * Flats: right, vignetting. Although, TBH, even with flats, I still get some vignetting after stacking in Siril using lights/darks/flats/biases. No clue why. * Biases: so, I was way off, it seems. * Dark Flats: never used them. The script in Siril that I use doesn't require them. The extra details w.r.t. mirror flip, rolling shutter, ... are good info. Never even considered those.
@@EvenTheDogAgrees haha I got the notification about your first comment immediately so I was interested in seeing what you think about the video :D Glad you found it useful
@@the_space_koala Yeah, I'm actually interested in the math behind all these operations, especially in the context of astrophotography. Are there any decent resources you'd recommend?
@@the_space_koala There's something unclear to me. The new mirrorless cameras, no old DSLR technology/sensors, like the new Sony cameras without star-eater problems (Sony A7rv, A7CII, A7Cr), should have basically no dark-current issues because they use cutting-edge sensors. Also they have very low noise, and cooling might not that critical. Aside emission nebula, these cameras in real life can perform as well as dedicated astro-cams for galaxies, clusters, and reflection nebula?
@@santiagomadruga4298 these modern cameras are definitely up there with the Astro cameras, but I think part of the issue is that if you don’t cool them the will heat up to 40-50 degrees sometimes during a long exposure and at that temperature you will start experiencing some of these problems anyway
if you search for "EL Sheet" you can order pre-cut circles from Amazon or any Chinese website - you also have the option of ordering it already with the inverter attached which has a 12V input. For the acrylic I just custom ordered from a small Italian company called Plexishop. The important thing is order it more opaque than you think you'll need it - you can always expose your flats longer, you can't make them shorter if it's too bright :D
