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Flats seem to dim? (Lumix S5)

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#1 Whereisclearsky

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Posted 03 March 2024 - 03:57 AM

Hi,

 

I'm using Lumix S5 with Sigma 40mm F1.4.

 

My flats seem too dim even though the histogram is way to the right, like the peak is outside histogram.

 

Here is what ADU values I get with 1250 ISO, F2.2 and 1/250s:

 

https://i.imgur.com/uGeIP02.png

 

Do I need to get them much brighter?



#2 Tapio

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Posted 03 March 2024 - 04:33 AM

Just use them (+bias) in calibration.

If they correct vignetting and dust motes they are fine.


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#3 Whereisclearsky

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Posted 03 March 2024 - 04:36 AM

Just use them (+bias) in calibration.

If they correct vignetting and dust motes they are fine.

I don’t know if they will that’s the issue.

I’m afraid they might be too dim.



#4 sharkmelley

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Posted 03 March 2024 - 04:41 AM

Your flats are absolutely fine.  You are overlooking the fact that you have a 14-bit camera, so when you import the data into PixInsight the values will all be in the range 0-16383.  In other words, 16383 (or thereabouts) is the saturation level and you want your flats to have a mean value of approximately half of that i.e. 8000


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#5 Whereisclearsky

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Posted 03 March 2024 - 04:53 AM

Your flats are absolutely fine.  You are overlooking the fact that you have a 14-bit camera, so when you import the data into PixInsight the values will all be in the range 0-16383.  In other words, 16383 (or thereabouts) is the saturation level and you want your flats to have a mean value of approximately half of that i.e. 8000

Should I take lights+flats+flat darks or replace flat darks with bias?



#6 sharkmelley

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Posted 03 March 2024 - 05:01 AM

Should I take lights+flats+flat darks or replace flat darks with bias?

Flat darks are not necessary for DLSR/Mirrorless cameras.  Use bias frames instead.



#7 Whereisclearsky

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Posted 03 March 2024 - 05:05 AM

Flat darks are not necessary for DLSR/Mirrorless cameras.  Use bias frames instead.

Btw I have seen your older thread where you made script for Nikon concentring rings,

so you think it would be possible to do for Lumix S5?



#8 sharkmelley

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Posted 03 March 2024 - 05:49 AM

Btw I have seen your older thread where you made script for Nikon concentring rings,

so you think it would be possible to do for Lumix S5?

The script I wrote was designed as a repair to data affected by a specific fault in Nikon's lossy data compression. 

 

It's not yet clear to me what kind of raw processing causes the Lumix S5 rings


Edited by sharkmelley, 03 March 2024 - 06:06 AM.

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#9 Whereisclearsky

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Posted 03 March 2024 - 06:33 AM

The script I wrote was designed as a repair to data affected by a specific fault in Nikon's lossy data compression. 

 

It's not yet clear to me what kind of raw processing causes the Lumix S5 rings

It annoys me that I don’t know what settings to go for exactly to avoid the rings.

Do you think I could do some test lights without having access to sky/stars?



#10 sharkmelley

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Posted 03 March 2024 - 06:55 AM

My general advice for working around problems with coloured concentric rings is to shoot at a relatively high ISO (e.g. ISO 1600 or greater) and adjust your exposure time so the peak of the back-of-camera histogram is approximately halfway across.  Flats should be shot at the same ISO and with the back-of-camera histogram further to the right.


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#11 Whereisclearsky

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Posted 03 March 2024 - 11:43 AM

My general advice for working around problems with coloured concentric rings is to shoot at a relatively high ISO (e.g. ISO 1600 or greater) and adjust your exposure time so the peak of the back-of-camera histogram is approximately halfway across.  Flats should be shot at the same ISO and with the back-of-camera histogram further to the right.

With 1600iso and 1/2 histogram wouldn’t some objects like m42 be overexposed?



#12 sharkmelley

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Posted 03 March 2024 - 12:40 PM

With 1600iso and 1/2 histogram wouldn’t some objects like m42 be overexposed?

Almost certainly if you expose so the histogram peaks halfway then M42 and other bright objects will be overexposed.  But it's quite normal for the core of M42 to be blown out, even when shooting "normally".  Most people combine the blown out exposures with a set of much shorter exposures that don't blow out the core.



#13 Whereisclearsky

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Posted 03 March 2024 - 12:42 PM

Almost certainly if you expose so the histogram peaks halfway then M42 and other bright objects will be overexposed.  But it's quite normal for the core of M42 to be blown out, even when shooting "normally".  Most people combine the blown out exposures with a set of much shorter exposures that don't blow out the core.

But then the less exposed images will have rings of power. smirk.gif



#14 sharkmelley

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Posted 03 March 2024 - 12:45 PM

But then the less exposed images will have rings of power. smirk.gif

You will use only the bright core of the less exposed images.  That's the way it's usually done.



#15 Whereisclearsky

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Posted 03 March 2024 - 12:48 PM

You will use only the bright core of the less exposed images.  That's the way it's usually done.

I know I asked before but do you think I could try replicating the rings

without access to clear skies?

 

Like maybe shooting a black large sheet or something.



#16 sharkmelley

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Posted 03 March 2024 - 12:56 PM

Yes, you can shoot flats at different exposure levels and at different ISOs to replicate the rings.  That's exactly how you helped me diagnose the original problem in this post.



#17 Whereisclearsky

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Posted 03 March 2024 - 12:59 PM

Yes, you can shoot flats at different exposure levels and at different ISOs to replicate the rings.  That's exactly how you helped me diagnose the original problem in this post.

I meant shooting lights like that to see what ISO and shutter speeds doesn’t produce rings.

This camera btw has dual gain iso but I doubt it has anything to do with it.



#18 sharkmelley

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Posted 03 March 2024 - 01:11 PM

OK, let me rephrase what I said.  Yes, you can shoot flats at different exposure levels and at different ISOs to replicate the rings determine what ISOs and histogram levels don't produce rings.



#19 Whereisclearsky

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Posted 03 March 2024 - 01:20 PM

OK, let me rephrase what I said.  Yes, you can shoot flats at different exposure levels and at different ISOs to replicate the rings determine what ISOs and histogram levels don't produce rings.

But if I try to do 30s long flat at higher iso it will be way overexposed right?



#20 sharkmelley

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Posted 03 March 2024 - 01:25 PM

But if I try to do 30s long flat at higher iso it will be way overexposed right?

It's not the exposure length that matters.  It's the position of the back-of-camera histogram that's important.


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#21 Whereisclearsky

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Posted 03 March 2024 - 02:15 PM

It's not the exposure length that matters.  It's the position of the back-of-camera histogram that's important.

I have tried shooting some flats at multiple ISO and exposure times to keep the histogram peak in the middle.

 

Would you be able to take a look please?

https://mega.nz/file...tXzLXbbLJeAirx0

 

Or at least explain how to do it? I read your previous posts but I'm not understanding lots of it. lol



#22 sharkmelley

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Posted 03 March 2024 - 03:39 PM

Sure, I'm happy to take a look.


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#23 sharkmelley

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Posted 03 March 2024 - 05:36 PM

I have tried shooting some flats at multiple ISO and exposure times to keep the histogram peak in the middle.

 

Would you be able to take a look please?

https://mega.nz/file...tXzLXbbLJeAirx0

Was the back-of-camera histogram central? When I open these in Photoshop, the histogram is well over to the right - about 1/4 from the right-hand edge.  Maybe there's a difference between the way the Lumix S5 renders the data compared with Adobe's engine.

 

In any case, the good news is that none of these images had any hint of rings and the histograms didn't have the same regular spikes.  I think you can go 1 stop lower in exposure and still avoid the rings.


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#24 Whereisclearsky

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Posted 04 March 2024 - 04:10 AM

Was the back-of-camera histogram central? When I open these in Photoshop, the histogram is well over to the right - about 1/4 from the right-hand edge.  Maybe there's a difference between the way the Lumix S5 renders the data compared with Adobe's engine.

 

In any case, the good news is that none of these images had any hint of rings and the histograms didn't have the same regular spikes.  I think you can go 1 stop lower in exposure and still avoid the rings.

Thanks for checking. bow.gif

Yes the histogram on camera's display was always around the middle.

 

Here is how Apple Photo's sees it: https://i.imgur.com/DsmlxYA.png

 

As for flats I should try to target 8000ADU right?



#25 Whereisclearsky

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Posted 04 March 2024 - 04:24 AM

Also I wonder why at one point the histogram peak goes white instead of yellow?
https://imgur.com/a/1Ot3QO0

I have also tried 2 darker flats if you don't mind looking, these surely should have rings, otherwise I would be really confused. grin.gif

https://mega.nz/file...RNWzmRaSRL-V3j0




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