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Stack is noisy  

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(@skanker)
Main Sequence Star Customer
Joined: 6 months ago
Posts: 26
December 17, 2018 17:34  

Hello!

Last weekend I've made some pictures of comet 46P Wirtanen and M45.

Canon 6D - Samyang 135mm - ISO 1250 - F3.2

The stack in the drive folder consists of 5o pictures ( + 20 darks 30 flats 30 bias)

https://drive.google.com/drive/folders/1lejQi18FL-0NlBh55dOCepqeS4uF0gM4?usp=sharing

In my opinion the noise is to strong in the final stack... I've also tried to stack the lights in Photoshop ( median) and the result was much cleaner compared to the APP version!

Did I do something wrong in APP?

CS Gernot 

 

This topic was modified 3 months ago by skanker

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(@vincent-mod)
Black Hole Moderator
Joined: 2 years ago
Posts: 272
December 19, 2018 02:04  

So could you post the 2 end results next to each other as pictures? It's very likely a difference in stretching for background versus signal (and the processes between the two are very different).

So looking at the stack in APP, I can see there is no correction made during calibration. If the flats would have worked, the dust spots would be gone as well as the light gradient. As such, the actual processing didn't went according to plan.


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(@skanker)
Main Sequence Star Customer
Joined: 6 months ago
Posts: 26
December 19, 2018 09:47  

I used the DSLR-tuorial by Mabula... Maybe i ve made a mistake during the workflow!? 

CS Gernot

This post was modified 3 months ago by skanker

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(@vincent-mod)
Black Hole Moderator
Joined: 2 years ago
Posts: 272
December 19, 2018 23:16  

Maybe or the calibration data you have isn't good enough, it's possible. The image below shows gradients and dust still present, which should've been corrected by the calibration frames (and remaining gradients from light pollution can be corrected in the Tools menu). You can always send me a few flats, darks, bias and lights to see if I can tell if something is wrong there.

Screenshot 2018 12 20 at 11.10.55

This post was modified 3 months ago by Vincent Groenewold - Moderator

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(@skanker)
Main Sequence Star Customer
Joined: 6 months ago
Posts: 26
December 20, 2018 18:27  

At first thank you for your support Vincent 🙂

I've uploaded the masters and a flat to the drive folder. Maybe you can check out the files and judge them!

Additional info:

-The gradient in the stack is moonlight. 

-The reason why the flats can't correct the dustpoints is maybe that I've created them the morning after the shooting session ( the lens was moved).  I hope this is english and you understand what I mean haha 🙂

 

CS Gernot

 

This post was modified 3 months ago by skanker

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(@vincent-mod)
Black Hole Moderator
Joined: 2 years ago
Posts: 272
December 20, 2018 21:13  

Yes I get it. 😉 I'm not sure what you mean with the drive-folder though, do you have a link to it you can share with me? You can send it to vincent@astropixelprocessor.com


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(@skanker)
Main Sequence Star Customer
Joined: 6 months ago
Posts: 26
December 20, 2018 21:22  

I meant the Google Drive - link in the first posting 🙂 Klick on the link and you will find the added data!

https://drive.google.com/drive/folders/1lejQi18FL-0NlBh55dOCepqeS4uF0gM4?usp=sharing

Cheers Gernot 

This post was modified 3 months ago by skanker

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(@vincent-mod)
Black Hole Moderator
Joined: 2 years ago
Posts: 272
December 21, 2018 00:06  

Ahhh, sorry. 🙂 Will check it out thanks.


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(@vincent-mod)
Black Hole Moderator
Joined: 2 years ago
Posts: 272
December 22, 2018 21:42  

So I don't see a lot of things wrong, but the flats might be. A good way to get those right is to have a very even illumination (e.g. with a flat-panel) en going for exposures close to a second. Sequence Generator Pro has a nice calibration wizard for that (using the DLSR built-in histogram to check isn't the best way, but if you do, aim for a peak at around 80% of that range). I also wonder if you changed the focus when taking the flats? It's vital not to change that as it also might be the dust is now out of focus.

Further, take more data, also for the darks and bias. For darks I go for at least 60 or so, but I made a few at 150 (that's a lot yes, but statistically a nice target, I just let the dslr shoot in a dark box outside when it's cloudy). Bias is easy as it's fast, so 100 is a nice target. If that's too much for you, you can get away with around 50 for both. For the lights, also more data will help reducing noise. Noise will always be there ofcourse, I just take it for what it is as I'm more interested to bring forward very weak details instead of wanting an almost black background (which does require good calibration as your dust spots will pop up a lot then). The moon light pollution can be corrected using the Light Pollution tool in the tools tab (9).

This post was modified 3 months ago by Vincent Groenewold - Moderator

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(@skanker)
Main Sequence Star Customer
Joined: 6 months ago
Posts: 26
December 23, 2018 11:41  

Thanks for checking the files! Next time I will make more calibration pictures. I'm also worried about the flats... I produce them with the "white t-shirt"-method because a flat-box is so expensive. Maybe that's not accurate enough!?

screenshot

This is a 250% view of the stack... I thought after stacking nearly 50 pics the noise would be reduced more. I think the color mottle is extreme !?

Is that normal ?

CS Gernot 

This post was modified 3 months ago 2 times by skanker

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(@whixson)
Red Giant Customer
Joined: 6 months ago
Posts: 85
December 24, 2018 07:51  

You might want to try dithering between frames to reduce the mottling. Tony Hallas has a good video on YouTube about DSLR astroimaging that goes over this and other techniques. 


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(@astrogee)
White Dwarf Customer
Joined: 8 months ago
Posts: 20
December 24, 2018 17:08  
Posted by: Vincent Groenewold - Moderator

So could you post the 2 end results next to each other as pictures? It's very likely a difference in stretching for background versus signal (and the processes between the two are very different).

So looking at the stack in APP, I can see there is no correction made during calibration. If the flats would have worked, the dust spots would be gone as well as the light gradient. As such, the actual processing didn't went according to plan.

Hi Vincent, How do you know there is no correction made? Are you looking at the filename? The fits header? I would like to be able to confirm this without a doubt because I need to take flats untethered to get the correct exposure with high ISO. I need to verify that the flats (which have different size from the lights) are in fact used in the flow. Thanks.

PS: Here is an example filename from my last stack: St-med-3605.0s-NR-x_1.0_LZ3-NS-full-eq-add-sc_BWMV_nor-AAD-RL-noMBB

This post was modified 3 months ago by astrogee

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(@skanker)
Main Sequence Star Customer
Joined: 6 months ago
Posts: 26
December 25, 2018 13:15  

At first merry christmas to all of you 🙂

@ Whixson

I think dithering isn't possible with my equipment...

As Vicent said, the key is the use of more darks and more bias!

Does somebody know if color mottle will increase with higher iso settings?

CS Gernot 

 


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(@vincent-mod)
Black Hole Moderator
Joined: 2 years ago
Posts: 272
January 2, 2019 22:29  

I just looked at the end result and still saw dust in the frame, which indicates the flats were either wrong or not used during processing. It looks like there was a problem with the flats themselves.


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(@skanker)
Main Sequence Star Customer
Joined: 6 months ago
Posts: 26
January 7, 2019 12:39  

Thx for your help Vincent! I think the flats were the problem...

In my later project of NGC 7000 everything worked fine 🙂

https://www.astropixelprocessor.com/community/gallery/ngc-7000-lrgb/#post-4860

CS Gernot


(@vincent-mod)
Black Hole Moderator
Joined: 2 years ago
Posts: 272
January 9, 2019 02:40  

Ahh awesome!


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(@mabula-admin)
Quasar Admin
Joined: 2 years ago
Posts: 2056
January 9, 2019 22:48  

Dear Gernot @skanker @vincent-mod,

I have read the enitre thread, do you think this still needs a clarification regarding the amount of noise after stacking 50 frames?

If so,then you will need to provide all light frames and the masters on the Google Drive, so I can make the integration myself and give you feedback. Right now, I only see the Masters on Google Drive, right?

I will be able to tell if you masters are okay or not, and whether noise reduction from stacking is working well or less well for some reason 😉

Cheers,

Mabula

Main developer of Astro Pixel Processor and owner of Aries Productions


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(@skanker)
Main Sequence Star Customer
Joined: 6 months ago
Posts: 26
January 10, 2019 07:45  

Hello Mabula!

There is no need for this... thank you 🙂

Cheers

Gernot


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(@mabula-admin)
Quasar Admin
Joined: 2 years ago
Posts: 2056
January 17, 2019 18:37  

Excellent, thanks Gernot @skanker 😉

Main developer of Astro Pixel Processor and owner of Aries Productions


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