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Where has all this noise come from?

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#1 BlakPhoenix

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Posted 29 September 2020 - 12:13 AM

Hi all, I've been out of imaging for a few months but am getting back on the train now. I am following all the same techniques I have used in the past, but I am now getting crazy noise all over my images. I have no idea where this is coming from or what to do to remove it / prevent it in my future imaging sessions.

 

Below is an integration of 4 hours of the Large Magellanic Cloud on a RedCat51 & ASI294MC Pro combo. I took darks, flats, flat darks (or is it dark flats?). Images were taken at 45 seconds, 120 gain & -10C.

 

I have attached a full image so you can get an understanding of what the whole picture looks like, as well as a 100% crop of part of the image so you can see the exact pattern. At first I thought it was fixed pattern noise, so I upped by dithering to every 2nd frame but this hasn't fixed the issue. What else could it be? I'm also aware there is a spot in the middle of the image, I believe this may be a moisture issue from cooling too fast? I believe they are separate issues though as only some frames have the spot in them.

Attached Thumbnails

  • integration1.jpg
  • integration2.jpg


#2 maxsid

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Posted 29 September 2020 - 01:52 AM

Walking noise because of no dithering?


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#3 PirateMike

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Posted 29 September 2020 - 04:03 AM

Walking noise because of no dithering?

That would be my guess.

 

Miguel   8-)

 

.



#4 BlakPhoenix

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Posted 29 September 2020 - 05:42 AM

Walking noise because of no dithering?

I thought it could be that at first, but the set up dithered every 2 images. The dithering was at a scale of 1, and set to a random direction up to 5px (with a pixel scale of 2:1 with guider to main camera).


Edited by BlakPhoenix, 29 September 2020 - 05:44 AM.


#5 Ron (Lubbock)

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Posted 29 September 2020 - 07:51 AM

I once had a sudden noise problem like this one with my old Atik camera.  It turned out there was a small piece of grass stuck inside the end of the USB connector.  Perhaps try replacing your USB cable?



#6 Lead_Weight

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Posted 29 September 2020 - 12:07 PM

It actually looks more like dew to me. With walking noise, you get streaks a pixel or two wide from the fixed pattern noise. This doesn't look like that. Looks like dew.


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#7 cmooney91

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Posted 29 September 2020 - 12:12 PM

I had a similar effect (not as bad) with my 294 after I read up and tried matched Dark-Flats (I do EAA live stacking). For a while I manually dithered to counteract it. It needed  >50px moves for the size/pitch of the splotchy pattern, maybe your dither distance wasn't far enough to break the pattern?

 

The last time I was out it was bad enough that I started toubleshooting and disabled flats and it went away. I then took plain normal flats with no bias or flat darks (4s, low gain, dim panel) and the images looked much better.

 

That is one of the benefits of live stacking, you can discover and resolve calibration issues before its too late. 


Edited by cmooney91, 29 September 2020 - 12:18 PM.

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#8 BlakPhoenix

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Posted 30 September 2020 - 05:51 AM

It actually looks more like dew to me. With walking noise, you get streaks a pixel or two wide from the fixed pattern noise. This doesn't look like that. Looks like dew.

Thanks Andrew, I feel that it could be dew too. I think that's what the dark cirelce in the centre is from as well, it's not on all the subs though. I may have to try and test and see if dew is forming inside the camera body when it's cooled so cold.



#9 PirateMike

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Posted 30 September 2020 - 06:20 AM

If it not dew and it's not a walking pattern, then maybe it's this with dew and/or walking pattern.

 

https://www.youtube....hFuETrQ_spYV51r

 

The big circle does say something. Watch all three.

 

 

 

Miguel   8-)



#10 BlakPhoenix

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Posted 30 September 2020 - 06:24 AM

It actually looks more like dew to me. With walking noise, you get streaks a pixel or two wide from the fixed pattern noise. This doesn't look like that. Looks like dew.

I have confirmed that dew is forming on the sensor when it is cooled. There is one large spot in the middle of the sensor (which I believe caused the purple haze in teh top image, however the could also be more in finer spots causing the other noise.


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#11 BlakPhoenix

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Posted 30 September 2020 - 06:47 AM

If it not dew and it's not a walking pattern, then maybe it's this with dew and/or walking pattern.

 

https://www.youtube....hFuETrQ_spYV51r

 

The big circle does say something. Watch all three.

 

 

 

Miguel   8-)

Thanks Miguel, I will watch that series and see what I can learn from it. :)



#12 sharkmelley

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Posted 30 September 2020 - 02:57 PM

I have confirmed that dew is forming on the sensor when it is cooled. There is one large spot in the middle of the sensor (which I believe caused the purple haze in teh top image, however the could also be more in finer spots causing the other noise.

That would explain the issue I found in your ASI294MC Pro Dark Current thread.

 

Mark



#13 BlakPhoenix

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Posted 30 September 2020 - 05:09 PM

That would explain the issue I found in your ASI294MC Pro Dark Current thread.

 

Mark

Hey Mark, yes I agree that's the exact spot that the dew was forming, and can be seen here with the blue circle much more pronounced than what you mentioned in that thread. You have a great eye for these details!

 

Next step, to fix the dew! I have contacted the retailer to see if this falls under warranty or not (don't want to open the camera housing in case of voiding warranty issues). If it's not covered by warranty then I'll work through the desiccant tablet resetting/replacing steps to see how I go.




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