ASIair pro and flat darks for calibration

ZWO ASI2600MC Pro Equipment Calibration
16 replies•1.6k views
Ian Dixon avatar
Ian Dixon avatar
Hello all 

I have been steadily learning how to stack and calibrate my images generated with a ZWO camera (2600 mc pro).   

A great feature of the ASI air pro is that you can shoot flats on auto mode.  The calculations for exposure are made and et voila, you have it.

I recently found this article dealing with how to then shoot flat darks to assist in calibration.

I hope you find this helpful, I did.

kind regards 

Ian


 https://eastwindastro.blogspot.com/2021/03/asiair-autoflat-frame-exposures.html
Rob Calfee avatar
Rob Calfee avatar
I have been using this feature. There has been some weird issues every now and again where the ADU ends up too high or low so I’d still keep an eye on it for every filter. Thanks for posting that article. Didn’t even occur to me to take dark flats that way after regular flats. 

Cheers,
Rob
Ian Dixon avatar
Ian Dixon avatar
Hi Rob, 

You are welcome.   The limitations of this feature is that the exposure time is limited to a max of 10 seconds.  If, for regular flats ,the source is too dim, you can get horizontal lining - but all of that is covered in the article. 

Ian
AppalachianAstroworks avatar
AppalachianAstroworks avatar
@Ian Dixon thanks so much for posting this! It is quite informative as I was curious about what settings to use on the ASIAIR for taking dark flats. The article said to choose either bias or dark when taking the dark flats. Would it be easier to just save them as bias so as not to confuse them with regular darks?

—Aaron
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Ian Dixon avatar
Ian Dixon avatar
Hi Aaron,  Yes absolutely  - I tried this last night after some imaging… saved them as bias frames (really dark flats).   Its logical too, as it fits the algorithm of what most stacking programs do with the frames.

Clear skies,
Ian
AppalachianAstroworks avatar
AppalachianAstroworks avatar
Thanks Ian!

I’ll be using Affinity photo to stack and they have a slot for dark flats. I suppose it makes no difference to the software if I throw them into that slot even if they are technically “bias” files right?
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Ian Dixon avatar
Ian Dixon avatar
It should not.  I think IIRC calibration is (lights-darks)/(flats-bias) and so if one makes dark flats they would replace the bias frames in this formula.   This is the reason that I tried the approach of saving as bias frames.  

Just my thoughts, I will put this into practice today and report back.smile

Ian
AppalachianAstroworks avatar
AppalachianAstroworks avatar
Thanks Ian, I’d appreciate that!
Ian Dixon avatar
Ian Dixon avatar
Well, I can say that the dark flats approach worked nicely.  I restacked and reprocessed with those included and the image was much better corrected. 

https://www.astrobin.com/8bwg1c/E/?nc=user

Best,
Ian
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AppalachianAstroworks avatar
AppalachianAstroworks avatar
Thanks for the update, Ian!  Looks great. 

—Aaron
Lwizzit avatar
Lwizzit avatar
I’ve been searching for this information. Thanks, I just purchased a dark filter, so I can ensure the process.

ill still put the cap on when I can.
Götz Golla avatar
Götz Golla avatar
Hi Ian,

I want to add a little discussion about dark flats. I am using the ASIAIR and the ASI6200MM camera. I found that for exposures of the order of a few seconds, there is no relevant difference between bias and flat dark frames, at least when the camera is cooled.  I therefore dont use dark flats with very good results. Cyril Richard of Siril has also explained this topic better than me: https://discuss.pixls.us/t/siril-enough-with-dark-flats/28298

Since omitting flat darks leads to a lot less work during observation and processing I suggest to carefully analyse your bias and dark frames  and only then decide whether it makes sense to create dark flats. I am sure that there are cameras around which will require dark flats, but I know from practical experience and theory that the newest ASI mono cameras at least have such a low thermal signal when cooled down and no amp glow that this is not necessary.

Greetings

Götz
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Ian Dixon avatar
Ian Dixon avatar
Götz Golla:
Hi Ian,

I want to add a little discussion about dark flats. I am using the ASIAIR and the ASI6200MM camera. I found that for exposures of the order of a few seconds, there is no relevant difference between bias and flat dark frames, at least when the camera is cooled.  I therefore dont use dark flats with very good results. Cyril Richard of Siril has also explained this topic better than me: https://discuss.pixls.us/t/siril-enough-with-dark-flats/28298

Since omitting flat darks leads to a lot less work during observation and processing I suggest to carefully analyse your bias and dark frames  and only then decide whether it makes sense to create dark flats. I am sure that there are cameras around which will require dark flats, but I know from practical experience and theory that the newest ASI mono cameras at least have such a low thermal signal when cooled down and no amp glow that this is not necessary.

Greetings

Götz

Thanks, this is much appreciated.  

Ian
kuechlew avatar
kuechlew avatar
Götz Golla:
Hi Ian,

I want to add a little discussion about dark flats. I am using the ASIAIR and the ASI6200MM camera. I found that for exposures of the order of a few seconds, there is no relevant difference between bias and flat dark frames, at least when the camera is cooled.  I therefore dont use dark flats with very good results. Cyril Richard of Siril has also explained this topic better than me: https://discuss.pixls.us/t/siril-enough-with-dark-flats/28298

Since omitting flat darks leads to a lot less work during observation and processing I suggest to carefully analyse your bias and dark frames  and only then decide whether it makes sense to create dark flats. I am sure that there are cameras around which will require dark flats, but I know from practical experience and theory that the newest ASI mono cameras at least have such a low thermal signal when cooled down and no amp glow that this is not necessary.

Greetings

Götz


Daniel Nimmervoll even takes it one step further for the QHY 268M: (3) BIAS vs. Dark Frames im Praxis Test - YouTube (German only, sorry)

On the other side I find taking dark flats not that much of a pain so currently I don't see a reason to change my workflow.
Anyway as a beginner I stick to the rule: First learn the "proper" way to do it. Only once you master the basic workflow start to experiment and improvise. 
Or in short form: Learn to walk before you start to run.


Clear skies
Wolfgang
BaronRouge avatar
BaronRouge avatar
Hi folks, I followed eastwindastro's excellent guide on this using ASIAIR V2.0 but when I came to do the dark flats it didn't popluate the exposure field with the same exposure as the flats in the way that he suggested. The exposure only has a dropdown picker which means you can't set the dark flats to the same exposure unless your original flats just happened to expose for e.g. 1, 2 or 5 seconds. 

Has anyone else experienced this or am I doing something wrong?
wsg avatar
wsg avatar
Hello Baron. 
I do not follow the updates of the ASIAIR very closely so I am not sure what version you have but if your devise is plastic and not metal you do not have the ability to make flats and dark flats automatically, which is the method described in this year and a half old thread.

If your devise has the Auto flat feature you simply have to reset progress in the sequence after you run Auto flat and change Flat to Dark or Bias and cover your scope.  Do not change any number settings at this point just go back and run the new Autorun sequence.








scott
Supportive
Tim Jordan avatar
Tim Jordan avatar

BaronRouge · Nov 7, 2022 at 02:38 PM

Hi folks, I followed eastwindastro's excellent guide on this using ASIAIR V2.0 but when I came to do the dark flats it didn't popluate the exposure field with the same exposure as the flats in the way that he suggested. The exposure only has a dropdown picker which means you can't set the dark flats to the same exposure unless your original flats just happened to expose for e.g. 1, 2 or 5 seconds. 

Has anyone else experienced this or am I doing something wrong?

15 Dec 2025, and I’m seeing the same as you. Eastwindastro also emphasized the need for bias frames instead of dark flats when using DSLR cameras, but I’ve seen other recommendations to use dark flats instead, particularly when using the Nikon Z6, which is my current camera. I haven’t tried looking in the logs to see if flats exposure is listed there, but since you can’t see the logs in the ASIAir app, it makes the inconvenient painful.

ZWO, it’s time to invest in a user centered design study.

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