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INDI Library v1.9.8 Released (29 Sep 2022)

Bi-monthly INDI Library released with new drivers and bug fixes.

Dark Flats

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Replied by Peter Sütterlin on topic Dark Flats

Well, Flat Darks are not different from other Darks, is it? But if you only want to easily see which type they are, just add the exposure time or a timestamp to the filename for those type of darks?
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1 year 11 months ago #61994

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Replied by Giles on topic Dark Flats

As an ASI camera user, who seems to be getting poor results using Flats at all I would like to suggest a couple of changes:

1. Flats - An option to set the number of significant digits for the exposure time, for instance, I don't want an auto-calculated exposure time of 0.534323 seconds, just make it 0.5 seconds, or 0.53 seconds.
2. Dark Flats, would be nice to have a check box in Flats to say also create Dark Flats, then when all the flats (after going through all the filters) in the sequence are done, bring the pop-up to cover the scope, allow user to select OK, and rerun the Flats sequence again (but without autocalculating the ADUs for each filter and just using the exposure time used for the flats.).

For (2) - it would be good if I only have to remove the flat light source and cover the scope once in the whole process (8 filters in the wheel).

The above would help me enormously in testing with different ADUs.

I seem to get best results with just Darks and Bias, despite having a ZWO camera (although it is a Pro, so has the 256MB buffer).
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1 year 11 months ago #62042

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Replied by Alex Varakin on topic Dark Flats

I take flat darks in Ekos as just regular darks and feed them into Weighted batch processing script and it figures out that these darks apply to flats because they have same exposure. Never felt a need for special feature in Ekos
1 year 11 months ago #62333

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Replied by Giles on topic Dark Flats


If you use the auto-ADU feature for your eight filters in your filter wheel, then all your flats have different exposure times, like 0.54723 seconds or similar. It is a real pain to construct another 8 jobs with each filter having the exact same exposure time, you have to note down 8 x exposure times, each with around 5 significant digits.

And, yes, I could do 0.55 seconds and reduce the number of significant digits, but my processing software complains that the exposures for dark flats are different from light flats.

I can see this is not so much an issue for one-shot-colour users, but for those composing LRGBHaOiiiSii images, it is a bit of a pain.
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Last edit: 1 year 11 months ago by Giles.
1 year 11 months ago #62340

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Replied by Nick Birkett on topic Dark Flats

Yes I agree. My 10c worth:
What I do is take Flats using the auto-exposure option in "Calibration Options". After the flats are complete I double click on each of the
flat jobs and edit them by changing Flat to Dark then click the tick button. I then have a set of Dark jobs that have an identical exposure to the Flat jobs (and don't forget to switch off the flat light and cover the scope - yes !!).
But it would be a nice feature if I could just click an option eg copy flat jobs to darkflat jobs . This might also save me having to rename all the resulting Dark frames as DarkFlat which I do just to keep things tidy. Not a critical option but a nice one to have I'd say.
8 months 3 weeks ago #79226

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Replied by Jasem Mutlaq on topic Dark Flats

What would be an intuitive option? Add Flat job, then create a dark flat immediately afterwards?

i.e. if we have LRGB flats, do we make it L flat, L dark flat, R flat, R dark flat.. or LRGB flats, then LRGB dark flats? any advantages or disadvantages?
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8 months 3 weeks ago #79227

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Replied by Giles on topic Dark Flats

That would require a lot of covering and uncovering the telescope if done manually.
I would prefer doing all filters for flats, then converting the sequence to dark flats.

Then I just have to arrange light source once, and scope cover once.
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8 months 3 weeks ago #79228

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Replied by Nick Birkett on topic Dark Flats

If the Flat->Dark option was after the last flat job it could convert all flats to darks and then you would only have to turn off flat light and cover scope once (like doing it manually). eg option : (Copy all flat jobs to darkflat jobs). I guess the problem would be that the exopures of the flats are only known once the flats jobs are instigated (using the auto exposure option).
8 months 3 weeks ago #79230

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Replied by Alexander Weis on topic Re:Dark Flats

I take darks less often than flats and have to cover the scope manually so it is typically not a sequential workflow for me. I rather have a dark library and then take flats using the same camera settings. So a transfer option from a dark library entry to create a flat job with the same settings with a default number of exposures would be my 10c for such a workflow.

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8 months 3 weeks ago #79233

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Replied by Giles on topic Re:Dark Flats

Dark Flats are distinct from Darks.

Dark Flats are Dark Frames with the exposure setting set to the same as the filter matching Light Flats.

They are used as an alternative for Bias frames with cameras that have issues with Bias frames (e.g. all ZWO CMOS cameras).

A Full set of calibration frames would include:

Darks (same exposure length as the normal light frames)
Flats (set at exposure length to match a particular low ADU)
Bias _OR_ Dark Flats (Bias are dark frames with very low exposure times), but ZWO cameras don't manage Bias frames very well, so it is recommended that they use Dark Flats.

This thread is about making it easier to make Dark Flats once you have created a set of the Flats with the auto-ADU setting in kstars.
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8 months 3 weeks ago #79234

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Replied by Nick Birkett on topic Re:Dark Flats

Flats taken using the auto setting are typically different exposures every time you do them (depends on the exact strength and position of the light source) so dark library is not useful here.
Also DarkFlats use same exposure as corresponding flats so typically only a few seconds and not long exposures like Darks for light frames.
You could then do your flats and then hit a button and redo all the jobs as DarkFlats.
If "Change Flat jobs to DarkFlat jobs" was an option then you don't have to use it.
8 months 3 weeks ago #79236

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Replied by Alexander Weis on topic Re:Dark Flats

Thanks for summing up the definitions. I have a CMOS camera and I was clear. The topic of the thread in my view started rather to include "dark flat" in the dropdown for exposure jobs.

I use a controlled artificial light source for flats. With this I used the function to find good exposure times in Stellarmate only once per filter/scope/camera setup. Since then I always use the same (rounded value) exposures time for flats and the corresponding (flat) darks.After this one off determination of the exposure time the workflow is then separated for (flat) darks (I use a library) and flats (every session). So I don’t take darks in every session. A bit lazy but works and saves time.
Standard setup: EQ6R, Williams Megrez 72- ASI 533MC -ZWO EAF, 50 mm viewfinder - ASI 120MM
8 months 3 weeks ago #79237

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