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What's causing this uniform artifact ?

CMOS Collimation DSO EAA Optics Reflector
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#1 GaryShaw

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Posted 12 May 2021 - 12:27 PM

Hi:

Last night we finally had a clear-ish late evening sky - SQM 18.79.  I noticed M63, an old friend, was well positioned  so I moved in for some time with it.

 

Skies seemed clear but it was windy - 10-15 mph and gusty I estimate. I was running flats and darks and messed with the histo to the best of my ability but I could not remove the noise(?) pattern you see in this cropped image. I've begun using a TG 365 cover on the mount/scope and noticed the collimate knobs had loosened - probably from friction with the cover as I remove and replace it. Doesn't seem like a collimation thing but I plan to re-collimate and tighten all the adjusters so there's more tension holding them where I leave them. Unfortunately they protrude from the back end of the carbon fiber tube of the TS scope - talking with TS about that.

 

Anyway, please click to enlarge and have a look. Share any ideas you have on what causes this.

Many thanks!

Gary

 

 

M63 Sunflower Galaxy: ASI 294 MC, 71 frames/ 8 sec/ 300 gain/ 203mm F4 Newtonian

 

M63Sunflower_Stack_71frames_568s_WithDisplayStretch 2.jpg

 

 



#2 Dynan

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Posted 12 May 2021 - 12:46 PM

Are you dithering? Looks like it could be walking noise.



#3 GaryShaw

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Posted 12 May 2021 - 12:59 PM

Hi 

No dithering. I’m just observing live with a camera ….EAA

What causes walking noise?

thank you 

 

Gary



#4 SanjeevJoshi

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Posted 12 May 2021 - 01:19 PM

Any chance you had upper atmosphere thin clouds? reminds me of how some of my images look when observing thru thin clouds.   Seems like a clear enough night but thats because the set up can punch thru clouds, although the view quality suffers on details a bit for objects other than stars.  What was the FHWM level roughly in Sharpcap?

 

Assuming proper process for flats and darks, the only other question would be about the flat.

 

How does the exposure and gain you used for the flat compare with the exposure and gain you used for the EAA in Sharpcap?


Edited by SanjeevJoshi, 12 May 2021 - 01:34 PM.


#5 Dynan

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Posted 12 May 2021 - 01:56 PM

Fixed pattern noise in a sensor repeatedly appearing in the (nearly) same spot causes the pattern similar to what you're seeing. It MAY be the cause. Dithering removes this by moving the exposure on the sensor by a small amount, either every frame, or every nth frame.


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#6 Rickster

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Posted 12 May 2021 - 03:24 PM

Looks atmospheric to me.  I take it that you have never seen this before? 



#7 GaryShaw

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Posted 12 May 2021 - 03:47 PM

Looks atmospheric to me.  I take it that you have never seen this before? 

Rick, I’ve seen a variety of speckled, splotchy patterns in images but never really categorized them to recognize similar instances later on … guess I should do that once I have knowledge of what the causes and cures are for various patterns. 
thank you

Gary



#8 bips3453

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Posted 12 May 2021 - 04:28 PM

That is the inter-galactic cosmic web! ;-) 



#9 Rickster

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Posted 12 May 2021 - 09:54 PM

Rick, I’ve seen a variety of speckled, splotchy patterns in images but never really categorized them to recognize similar instances later on … guess I should do that once I have knowledge of what the causes and cures are for various patterns. 
thank you

Gary

I am the same way.  I know I have seen that pattern on numerous occasions, but I have not kept track of what I thought caused it at the time.




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