Chroma Noise

[Grierson]

Apologies as I am not really a beginner but I'm not sure where else to ask the question. Perhaps Mods can move the post.

The image below is a heavily cropped single 600sec sub of IC5146 which I took to test out the Off Axis Guiding of my new Edge HD 8". To the right of the centre of the image is a patch of what appears to be rough chroma 'noise?'. I wonder if anyone can tell me what the likely cause could be. My poor PixInsight processing skills or a hardware issue? The camera is a ZWO294 cooled to -20 degrees. I should add that no such issue appears on all my shorter duration subs to date. Any comment would be welcome. Thanks - John

 

Edited September 26, 2020 by Grierson

[Adam J]

54 minutes ago, Grierson said:

Apologies as I am not really a beginner but I'm not sure where else to ask the question. Perhaps Mods can move the post.

The image below is a heavily cropped single 600sec sub of IC5146 which I took to test out the Off Axis Guiding of my new Edge HD 8". To the right of the centre of the image is a patch of what appears to be rough chroma 'noise?'. I wonder if anyone can tell me what the likely cause could be. My poor PixInsight processing skills or a hardware issue? The camera is a ZWO294 cooled to -20 degrees. I should add that no such issue appears on all my shorter duration subs to date. Any comment would be welcome. Thanks - John

 

I think the camera thread would be the place. Never seen anything like that before, is it on every single frame of just the stacked image?

Edited September 26, 2020 by Adam J

[Grierson]

Yes, thanks Adam, that was my dilemma. Camera or Software? 
This is a single unstacked image. I did take nine subs and they all exhibit the same issue. - John

[Adam J]

9 minutes ago, Grierson said:

Yes, thanks Adam, that was my dilemma. Camera or Software? 
This is a single unstacked image. I did take nine subs and they all exhibit the same issue. - John

any chance that there was any condensation built up in the sensor at the time?

[Grierson]

34 minutes ago, Adam J said:

any chance that there was any condensation built up in the sensor at the time?

Yes I suppose that is possible. I had no reason to check at the time.

[andrew s]

What do, bias and dark frames look like? Are they clean or do they show any problems? 

Regards Andrew 

[Waldemar]

Looks like some condensation to me as well. There are also a lot of dust bunnies in that image and some really dark spots, so it even could be an build up of small partikels due to condensation earlier on.

[Grierson]

Thanks for the replies. Sorry for the delay in responding. I do not take bias frames Andrew. Received wisdom seems to suggest they are not needed with a cmos camera. My darks look ‘normal’ but they were taken earlier in the day at -20deg. I will now take a look at the condensation issue. John