Half my processed i...
 
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Half my processed image looks different to the other half - ASI6200MC Full-Frame Cam  

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(@itarchitectkev)
Red Giant Customer
Joined: 2 years ago
Posts: 68
February 7, 2020 14:29  

Hi,

I have a strange issue that I can't seem to track down. 
I am using an ASI6200MC Pro Full Frame camera. On processing images last night  (Ha-Oiii Color) I noticed exactly (it appears to be exactly half) of my image is processed differently than the other. I can see a delineation line. The attached pic is obviously reduced andsuper brightened to try and show the problem more clearly.

OrionASI6200MCFOVTest 8x10Mins TSAPO65Q LENHANCE 2020 02 06 Edit 2

I have
- 10 min subs as 16-Bit Flats
- Flats 22K ADU + DarkFlats
- Master Bias
- Darks
- BPM


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(@vincent-mod)
Quasar Admin
Joined: 3 years ago
Posts: 1416
February 7, 2020 14:42  

So just a number of questions to get to understand it a bit better; is this a mosaic or just a large FOV? How do you create your bias frames and could you show me the master-bias? Are you using LNC?

 


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(@itarchitectkev)
Red Giant Customer
Joined: 2 years ago
Posts: 68
February 7, 2020 14:51  

This is a full 9756x6388 FITS.

Bias was shortest exposure - I went for 0.002 seconds. Master Bias is 122Mb in size. Where can I upload?


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(@vincent-mod)
Quasar Admin
Joined: 3 years ago
Posts: 1416
February 7, 2020 14:54  

Right, so maybe just an screenshot of the masterbias? I just need to see the quality of it as some sensors also have problems with using the shortest exposure for a bias, which is especially an issue with CMOS sensors. As your sensor is a relatively new one, I'd advice to make the bias frames at about 0.1 seconds as a minimum or use dark-flats.

Flats I'd also advice at around 32000 ADU.

This post was modified 2 months ago 2 times by Vincent Groenewold - Moderator

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(@itarchitectkev)
Red Giant Customer
Joined: 2 years ago
Posts: 68
February 7, 2020 15:07  

Here's a screenshot. Looks ok?

MasterBiasASI6200MC

 


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(@vincent-mod)
Quasar Admin
Joined: 3 years ago
Posts: 1416
February 7, 2020 15:13  

Could you stretch it a bit more? Difficult to say. I would advice though to try another processing with your darkflats being the only bias. Selecting LNC with 3 iterations and checking again.


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(@itarchitectkev)
Red Giant Customer
Joined: 2 years ago
Posts: 68
February 7, 2020 15:44  

As soon as you said about the Bias I'm giving the process another go and it didn't make a difference.

I've tried 16K, 22K, 26K and 32K ADU Flats (and associated DarkFlats) as only had this camera for 48 hours so still trying to work out what is really required so no changes.

Given this is appears to be a 50% split, are dimensions of the FITS a factor? Whilst I've had mosaics processed in APP before, is this a 4k limit somewhere, given 4096 is around about half of the 9k wide resolution of this?


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(@vincent-mod)
Quasar Admin
Joined: 3 years ago
Posts: 1416
February 7, 2020 16:20  

There are no real limits to that no, so it wasn't clear to me but this is indeed a mosaic? If so, you did have MBB on as well set to about the % of overlap?


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(@itarchitectkev)
Red Giant Customer
Joined: 2 years ago
Posts: 68
February 7, 2020 16:49  

Not a mosaic - a full-frame sensor FITS.


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(@vincent-mod)
Quasar Admin
Joined: 3 years ago
Posts: 1416
February 7, 2020 17:01  

Ok, thanks. It's rather difficult to tell without the raw data, is a zipped light sub very big still? Maybe I can have a look at some raw frames.


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(@itarchitectkev)
Red Giant Customer
Joined: 2 years ago
Posts: 68
February 8, 2020 14:02  

I'm going to just put this on hold for now as it could very well be the data captured - though I can't see it clearly at all in my individual subs. I just processed another target from the same night, further away from the bright moon, and it appears to be fine. Same optics/setup/length of exposure, etc. So for now I'll re-test on a moonless night if the stars align in a couple of weeks!


(@vincent-mod)
Quasar Admin
Joined: 3 years ago
Posts: 1416
February 8, 2020 14:30  

Ah right, some residual gradient in the background maybe. Light pollution correction doesn't help this at all? I always advice to really stretch the image in the preview window, over-saturate the backgound as well and then slowly start with 5 boxes around the image, then add some more when it seems the gradient model looks ok (which you can check with "show corrected image" button). This might show a light source (the moon) somewhere on the side of the image. Which then would be a good correction model. I'm always looking for the background to become nice and even.

Screenshot 2020 02 08 at 13.29.17


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