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Dark streaks in stacked data

ZWO ASI6200MC Pro NGC5194 Artifacts Deep Sky Galaxy
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csummers avatar
csummers avatar
Still getting used to the ASI6200MC camera.  Among my first images if this stack of the whirlpool galaxy.  When I denoise this, the black streaks get enhanced causing dark splotches.  I'm wondering if strong dithering is the solution for this.  I don't see this in the individual images or the dark frames. This autostretched in PI 

Has anyone seen this before or know what is causing this?

Oskari Nikkinen avatar
Oskari Nikkinen avatar
Looks like walking noise, and almost bang on in the declination axis which means its most likely due to drift from any small polar alignment error.

Dithering will clean that up nicely and it will go away, although this night might be a bust if you spent long on it. If its not too long an integration yet spending a couple nights more while dithering will salvage this data too, as it will get rejected as outlier noise in stacking with the dithered subs.

By the way these new sensors are very clean so you probably dont need to dither too often. Something like a dither every 10 or so minutes will be more than enough, no need to dither after every frame.
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csummers avatar
csummers avatar
Thanks! That is the direction I needed.  Looks like it is most likely differential flexure as I'm guiding to about 1 pixel.  Off hand, my guess is the focusing block.  Searching on walking noise pointed me at good discussions on how to verify it and ways to track down the cause and minimize or eliminate it.
csummers avatar
csummers avatar
OK, so I integrated the stack with no calibration and the star trails match up with the walking noise: