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INDI Library v2.0.6 is Released (02 Feb 2024)

Bi-monthly release with minor bug fixes and improvements

Dark Flats

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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.
2 years 2 months 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.
2 years 2 months 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.
2 years 2 months ago #79237

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Replied by Nick Birkett on topic Re:Dark Flats

So if it is an option then you you are not forced use it. So what is the issue ?
As far as I know there is such an option in other software (eg NINA unless I am mistaken), so obviously
something that some people would use.
The following user(s) said Thank You: Alexander Weis
2 years 2 months ago #79238

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Replied by Nick Birkett on topic Dark Flats

Hi Jasem. Creating DarkFlat directly after each Flat would be a pain as others have said. Something along the lines of:
If auto exposure flat is selected, then
If DarkFlat later selected in dropdown, add tick box to this to say "clone all previous flat jobs to match"

This would just automate the task of going through the completed flat jobs and editing them into darks (DarkFlats).

As I said somewhere else this is a nice to have rather than essential.
I think NINA has this (I don't use NINA so could be wrong), so someone must be using it.
2 years 2 months ago #79239

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Replied by Jasem Mutlaq on topic Dark Flats

Ok I'm just trying to find a way that's intuitive and not confusing to users. Say we add all the flats, then SOMEWHERE a button is there to create the dark flat from whatever flats in the list?
2 years 2 months ago #79241

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Replied by Alexander Weis on topic Re:Dark Flats

Hi Nick, my post was a reply to Giles but crossed in the timeline with yours. I have no issue aat all if this was addressed to me. My first post in this thread highlighted that for users of flat panels the option to build a job from a dark frame might be useful. So just the other way around in order. That for me doesn't exclude the other idea but only highlights that depending on the equipment used for taking flats there is not just one direction for creating jobs with settings based on existing images.So variable exposure times using the auto function in Stellarmate: Transfer settings from flat to a dark job
Fixed exposure times when using flat panels: Transfer settings from dark to new flat job
2 years 2 months ago #79242

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Replied by Nick Birkett on topic Dark Flats

Yes. I think the problem is that if you use auto-exposure flats then exposure times are only available after the flats have been executed.
Whereas if you are not using auto exposure then you would need to just use the exposures as is. So I guess the logic would firstly require
that (1) Flat jobs already exist. (2) If auto flats where used then exposures would have to wait until flats had been done, (3) Auto Darkflat
has been selected. Maybe I'm making it sound too compiicated ?
2 years 2 months ago #79243

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Replied by Paul on topic Re:Dark Flats

Nick,

You have highlighted what I found, the exposure length would "randomly" change.
I decided to go back to setting fixed exposure lengths for my flats as I could then automate taking both flats and flat darks.

Paul
2 years 2 months ago #79254

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Replied by Nick Birkett on topic Re:Dark Flats

Yes exactly that's why if there was a button to automate the DarkFlats then it would no longer be an issue.
My method at the moment is to reset the flat jobs and then edit them by simply changing Flat to Dark. I don't see why process cannot be automated.
If you have one scope, one camera ok, but with multiple scopes, cameras and filters it can get tedious to manage.
Using auto exposure Flats can guarantee a good exposure every time with no trial and error - especially if you don't have an accurately reproducable flat light eg daylight or an led panel held at some non exact distance.
2 years 2 months ago #79256

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Replied by Alexander Weis on topic Re:Dark Flats

If you are using e.g. a T-shirt in the twilight in combination with the auto exposure function for flats, the resulting exposure time will vary naturally between sessions.

How about the capture module would offer the option to read the capture settings from an existing file? If one uses the auto exposure for flats you could read out at any time later what is needed for darks that correspond to a flat.

When using fixed exposure times and a dark library like I do, this could be used the other way round to create flats in line with existing darks.

There might be other use cases, when you perhaps want to add more exposures of the same target after a while. A sample from the previous series could serve as a reference to recall the exposure parameters - reducing the risk to set a parameter wrong accidently.
.
Just a thought to keep such a potential extension simple to follow and flexible beyond the single use case of flats->flat darks.

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2 years 2 months ago #79257

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Replied by Paul on topic Re:Dark Flats

Nick,

You would need some way of determining how many flat darks are required for each exposure length which could take a considerable time when the exposure keeps changing. You don't want to do the darks until all the flats have been compiled.
An assistance would be to have a lock option, where once the correct exposure has been determined for the filter it could remain at that exposure. After all flats have been exposed then the darks could optionally be created based on the previous exposures.

Paul
Last edit: 2 years 2 months ago by Paul.
2 years 2 months ago #79259

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