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Small shadow spot moves through frames, starts over each night. What the heck?

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#1 stream41

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Posted 23 June 2022 - 09:22 PM

Stacked a ton of data from the last month, and I noticed a big shadowy line across one portion of the image. Pic here:

 

https://www.dropbox....ation2.jpg?dl=0

 

If you Blink through my subs, you can see the spot move "across" that line as the night goes by. It repeats the next night, and starts and ends in the same places. So that's why it made that line across the image. Kinda like an animation flip book, where it moves a little each page and creates the illusion of movement. Did the same thing across at least 5 or 6 nights of imaging, over the course of a month. I feel like I'm not explaining it very well, so here's a video of the spot moving in Blink, through the course of one night's imaging, then back to the start.

 

https://www.dropbox..../blink.mov?dl=0

 

(You'll probably have to download this .mov file - it plays at extremely low quality when you stream it from Dropbox)

 

Same mount location each night, etc. It's in the raw subs, calibrated, and registered subs. Is this some kind of reflection caused by a dust mote or something on the front element? I'm completely puzzled by why it moves across the frame as the night goes by. So obviously flats didn't take care of it, since it moves in each frame. Oh, and this happens in all my LRGB filters.


Edited by stream41, 23 June 2022 - 10:56 PM.


#2 james7ca

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Posted 23 June 2022 - 10:12 PM

Does your guiding drift during the night? If so once you register your images any fixed location on the sensor (dust or defect) will appear to move by that same amount and direction. This is one of the major reasons why people get pattern walking noise in their images, their guiding is drifting due to differential flexure between the guide scope and the main imaging rig.

 

That said, properly executed flats should take care of any dust in your optical path. Have you taken new flats since you started seeing this problem?


Edited by james7ca, 23 June 2022 - 10:17 PM.


#3 D_talley

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Posted 23 June 2022 - 10:18 PM

Looks more like a spider moving across a web somewhere in your optical train.  Take a peek to be sure. 



#4 stream41

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Posted 23 June 2022 - 10:53 PM

Does your guiding drift during the night? If so once you register your images any fixed location on the sensor (dust or defect) will appear to move by that same amount and direction. This is one of the major reasons why people get pattern walking noise in their images, their guiding is drifting due to differential flexure between the guide scope and the main imaging rig.

 

That said, properly executed flats should take care of any dust in your optical path. Have you taken new flats since you started seeing this problem?

I don't think I did a very good job of explaining what's going on.

 

The spot itself is visible in all my subs - raw, calibrated, and registered. But the spot moves a little with each sequential sub that was taken. When I start imaging the next night, the spot moves back to where it started, and moves across again as the night goes by. So when I take flats, it's only accounting for where the spot is at that time. Hence it doesn't erase that "line" that was created by the spot moving across the subs.

 

The only thing I can think of that would "move" across the frame like that is some kind of reflection as the scope moved.



#5 stream41

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Posted 23 June 2022 - 10:54 PM

Looks more like a spider moving across a web somewhere in your optical train.  Take a peek to be sure. 

That was my first thought - some kind of bug or something. But this happened several times over the course of a month, and the "path" that the spot took was the same each time. Obviously a bug wouldn't do that!


Edited by stream41, 23 June 2022 - 10:54 PM.


#6 Ryou

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Posted 24 June 2022 - 12:24 AM

The only thing I can think of that would "move" across the frame like that is some kind of reflection as the scope moved.

Easy way to test that reflection... Are you imaging the same target each night or staying in the same general sky vicinity? If so maybe try something in a different quadrant and of course look for any stray light rays hitting your scope.

 

Besides that when did this start and did you change anything between before and now?



#7 stream41

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Posted 24 June 2022 - 12:39 AM

Easy way to test that reflection... Are you imaging the same target each night or staying in the same general sky vicinity? If so maybe try something in a different quadrant and of course look for any stray light rays hitting your scope.

 

Besides that when did this start and did you change anything between before and now?

Yes, was hitting M81 for a month, so same part of the sky. There's also a bright street lamp across the street that would have been throwing all kinds of crap at my scope, which was aimed in that general direction. So that's what has me thinking it's some kind of dust reflection that moved as the angle of the scope to the street lamp slowly moved through the night.

 

And this is a new setup (the Esprit 120 / 183MM Pro combo), and M81 is my first target. So unfortunately there is no "before" for this rig.



#8 Ryou

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Posted 24 June 2022 - 01:14 AM

Yes, was hitting M81 for a month, so same part of the sky. There's also a bright street lamp across the street that would have been throwing all kinds of crap at my scope, which was aimed in that general direction. So that's what has me thinking it's some kind of dust reflection that moved as the angle of the scope to the street lamp slowly moved through the night.

 

And this is a new setup (the Esprit 120 / 183MM Pro combo), and M81 is my first target. So unfortunately there is no "before" for this rig.

If it's a consistent pattern/move every time and recurs then I'd definitely lean towards that. Again easy enough to test by just moving your scope or pointing at a different target. If it goes away then there is your culprit for sure



#9 james7ca

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Posted 24 June 2022 - 02:24 AM

It might be a drop of water (condensation) that is running across the camera's sensor window. That might start in the same spot each night is the source is unchanged. Seems a little unlikely to happen night after night in the same spot but I guess it's not impossible.

 

Also, what is causing those small black artifacts (two closely spaced black spots) on the right side of the image? They look almost exactly the same and there are (as I recall) five of them all in different locations.



#10 Der_Pit

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Posted 24 June 2022 - 06:23 AM

Hmm, one idea could be a dust mote on a filter that is illuminated by scattered light (reflection), casting a shadow.  With tracking, the location where the reflection comes from does move, and so would the shadow.

I'd check filters and camera front window for dirt.  Could even be almost invisible remains from an (oily?) drop.

Dirt on the entrance window (pupil) you cannot see, and on the sensor movement can only be explained by moving particles/drops, but as james7ca already said, that is highly improbable....



#11 stream41

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Posted 24 June 2022 - 09:04 AM

It might be a drop of water (condensation) that is running across the camera's sensor window. That might start in the same spot each night is the source is unchanged. Seems a little unlikely to happen night after night in the same spot but I guess it's not impossible.

 

Also, what is causing those small black artifacts (two closely spaced black spots) on the right side of the image? They look almost exactly the same and there are (as I recall) five of them all in different locations.

Those popped up in my master flats, but just for the luminance filter. Not sure what caused them - I'll have to redo those flats for sure. But this shadow "line" thing is present in all of my filters, except it's a bit fainter in the Ha filter and one of the LRGB filters - I think the blue one? Sorry I'm not at home right now to check.




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