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Problems with creating MasterFlats


(@ggalbch)
White Dwarf Customer
Joined: 1 year ago
Posts: 26
Topic starter  

Hello,

I tried to create this afternoon MasterFlats and MasterDarkFlats from my freshly taken flats and dark flats and the MasterFlat that was created does not look right. The histogram is all pushed to the right. Never seen this before. The flats and dark flats were taken as always in NINA.
The first two images show a single flat taken few days back and the second is the MasterFlat created out of those 30 flats.
The next two images show the single flat from today and the MasterFlat that came out of APP. The exposure time for the flats and dark flats match.
I loaded them correctly in APP and ran calibration under "automatic" as always. I afterward also tried to run them under "average" with sigma rejection and got the same result. 

image
image
image
image

I am confused what possibly I am doing wrong.
I am looking forward to any help.

Thank you
Georg


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(@wvreeven)
Galaxy Admin
Joined: 4 years ago
Posts: 2035
 

@ggalbch Hi Georg,

That certainly looks strange.

Posted by: @ggalbch

The exposure time for the flats and dark flats match.

Are the exposure times for all flats (and therefore dark flats) the same?

Wouter


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(@ggalbch)
White Dwarf Customer
Joined: 1 year ago
Posts: 26
Topic starter  

Thanks Wouter for responding.

I double checked the files and yes, the times match up for all files.
With the ALP-T filter, exposures came out at 7.01sec

image

And with the L-Pro filter, exposures were at 2 sec

image

 I am looking forward to hearing form you soon.

Sincerely,
Georg


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(@wvreeven)
Galaxy Admin
Joined: 4 years ago
Posts: 2035
 

@ggalbch In your first post, which filter do the first two images correspond to and which filter the other two?


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(@ggalbch)
White Dwarf Customer
Joined: 1 year ago
Posts: 26
Topic starter  

@wvreeven 
Hi again. The first two images (first is a single flat fits file - second is the resulting MasterFlat) are from collected flats a few days back with ALP-T filter.
The following 2 images are of the last flats taken yesterday also with ALP-T filter (the first is again a single flat fits file and the second is the resulting MasterFlat). I did not include images of the L-Pro filter run but the histogram of the MasterFlat is there also pushed to the far right.  

If you want me to upload the files, please let me know. Thanks for your help.
Georg


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(@wvreeven)
Galaxy Admin
Joined: 4 years ago
Posts: 2035
 

@ggalbch Hi Georg,

Yes, please upload 5 flats and 5 dark flats of both sessions and please indicate which session is which. Let me know here when the upload is done and I'll have a look. Upload instructions are at the top of each forum page.

Thanks, Wouter


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(@ggalbch)
White Dwarf Customer
Joined: 1 year ago
Posts: 26
Topic starter  

Wouter, thanks again.

How and where do I upload the files? It has been a while since I uploaded large files...

Thank you 
Georg


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(@wvreeven)
Galaxy Admin
Joined: 4 years ago
Posts: 2035
 

@ggalbch Instructions are on the top of each forum page. Go to


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(@ggalbch)
White Dwarf Customer
Joined: 1 year ago
Posts: 26
Topic starter  

Thanks
The files have been uploaded. The Folder name is GeorgGAlbrecht_MasterFlatProblem and I have zipped them by filters. 3 Zip files in total.
I am looking forward to hearing from you soon.

Cheers
Georg


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(@wvreeven)
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Joined: 4 years ago
Posts: 2035
 

@ggalbch Thanks for the upload. Not quite the folder name I requested but I managed to download them.

I am confused. The start of this thread is about differences in master flats based on flats taken on two different nights. All flats of those two nights were taken with an ALP-T filter. I requested 5 files of each set. Now I see that you uploaded one set of ALP-T flats, one set of L-Pro sets and one set of UV-IR flats. Why did you do that? Isn't the purpose of your request to find out what is different between the two sets of ALP-T flats? Can you please just upload 5 flats and dark flats of each set of the ALP-T filter so I can see what the difference is and if I can reproduce your issue?


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(@ggalbch)
White Dwarf Customer
Joined: 1 year ago
Posts: 26
Topic starter  

@wvreeven 

In my original post I didn't specify what filter was used other then the MasterFlat came out with histogram pushed to the right. In my follow up message I explained the images I attached which were from the ALP-T run only and the exposure times to be the same. I mentioned ALP-T and L-Pro there and afterwards found that the UV/IR filter yelled the same result. All my attempts to create MasterFlads yelled the same outcome, no matter which filter. Therefore I uploaded all three sets of filters, ALP-T, L-Pro and UV/IR.

Apologies for my dislexia and not seeing you had specified a file name. Sorry.

I will now upload ALP-T flats/darkflats from the older run where MF has histogram in the center and the new flats/darkflats from 2 days ago where the MF came out with histogram pushed to the right - with the file name you suggested.

Cheers, Georg

 

 

 


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(@wvreeven)
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Joined: 4 years ago
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Posted by: @ggalbch

Apologies for my dislexia and not seeing you had specified a file name. Sorry.

I am sorry for my response, Georg. We have many people who upload data and I was merely trying to keep track of that all. Like I wrote, I downloaded the data just fine.

Thanks for explaining that all your flats seem to suffer from the same issue. That should give me more data to look into. Did anything change between taking the two sets of flats? Any updates of software or drivers?

Thanks, Wouter


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(@ggalbch)
White Dwarf Customer
Joined: 1 year ago
Posts: 26
Topic starter  

No worries Wouter. I should know better to read emails more careful knowing of my little problem 🙂
Of the second upload, the first Flats/DarkFlats with the MF histogram centered, were created in the APP Beta3 version and the new Flats/DarkFlats with MF histogram pushed to the right were created in the APP Beta4 version. I updated APP to Beta4 beginning of September. I have not had any driver updates lately and only the usual NINA Beta updates that come every 4-5 days... But the single flat subs do look "normal" if I compare flats from now with 1-2-3 months back.
It's just the MasterFlats that are much, much brighter.

Now, I did some additional work and ran one of the latest Flat/DrakFlat ALP-T series this morning and looked at the histogram in APP under different settings and I wanted to show you this...

MasterFlat with 15% BG, 5% sigma, 2.5% base

image
image

Same setting with normalized BG (here the MF looks familiar)

image
image

Here with no stretch and no normalized BG

image
image

And lastly, no stretch and with normalized background.

image
image

The histogram here actually looks like where I would expect it to be.

Hmmm... Honestly, once I saw how the MF came out and showing histogram pushed to the right, I actually didn't run any integration. Just didn't want to loose time on my computer. But maybe I should and see what the outcome is...
So, how about you let me do that and I report back to you how it calibrated and also integrated the images? If they come out properly, we don't have to go further. Deal?

I let you know later this afternoon.

Cheers, Georg


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(@wvreeven)
Galaxy Admin
Joined: 4 years ago
Posts: 2035
 

@ggalbch Deal!

Meanwhile, the "no stretch and no normalized BG" histogram looks what I would expect the histogram of a flat to look like. The three colors separated with the highest response in green and the lowest in blue. I am not sure what camera you use (I don't think I asked you yet and it looks like you didn't write it in any of your comments but I may have missed that) but in case you have a ZWO camera, its drivers should allow you to set the "white balance" of the red and blue channels. ZWO sets it to 52% and 95% respectively causing the blue channel to usually be between the red (lowest) and green (highest). So it looks to me like the flats were taken correctly.


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(@ggalbch)
White Dwarf Customer
Joined: 1 year ago
Posts: 26
Topic starter  

Hi Wouter

In the mean time APP crunched away on the data and produced an nice stacked image. That's for all the panicking when looking at the FITS file displayer from ZWO, Dahhhh...
I think that there must be something wrong there how it displays the fits and shows the histogram. Something must have changed...
I was pretty much sure that either I had chosen a wrong setting in APP or taken really shitty Flats. By the way it's an ASI183MC Pro, the camera in use.

So I think we can set this one to sleep. Thank you so much for your help.
Much appreciated.

Clear Skies, Georg

 


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(@wvreeven)
Galaxy Admin
Joined: 4 years ago
Posts: 2035
 

@ggalbch I am glad this turned out to be a storm in a glass of water 🙂 


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