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What's Causing This Banding

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25 replies to this topic

#1 matt_astro_tx

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Posted 16 September 2021 - 10:45 AM

Shot the horsehead this morning.  Getting weird stuff.  What's not working right?  The flats?  Help.

 

AT60ED @ 287mm w/ 0.8x ATRF

ASI183MC Pro w/ UVIR Cut

 

30" x 150 lights

10 darks

10 flats

10 bias

 

Processed in Siril for Mac.  Big stretch in MS Photos to show the banding.

 

Horsehead (2)

 



#2 ChiTownXring

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Posted 16 September 2021 - 11:11 AM

Quick guess... Condensation on the sensor? Does it show up on all frames lights and calibration?


Edited by ChiTownXring, 16 September 2021 - 11:12 AM.


#3 ngc7319_20

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Posted 16 September 2021 - 11:27 AM

Random thoughts:  Was the camera fully cooled when you started imaging, or was it still cooling down? 

 

Check whether banding is only in lights or flats / darks / bias also.  Dithering would help the lights, but not the calibration frames.

 

If you google the camera name and "banding" there is a lot of stuff.

 

There is some suggestion that banding results from gain < 54.  Try a different gain.

https://www.cloudyni...nd-temperature/

https://www.cloudyni...anding-asi183c/


Edited by ngc7319_20, 16 September 2021 - 11:28 AM.


#4 OldManSky

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Posted 16 September 2021 - 11:40 AM

What does a highly-stretched flat look like?

'Cause if I had to guess, my guess would be patterns on whatever you put over the front of the scope to do flats...



#5 matt_astro_tx

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Posted 16 September 2021 - 02:11 PM

Thanks all.  Here are responses.

 

I shoot at gain 0.  So it's possible I'm getting some weird stuff from that.  I like gain 0 because it maximizes the modest well depth of the 183.  Paul - what gain did you used to shoot your 183 at?

 

I used a white kirkland brand t shirt stretched over the front of the scope to shoot my flats.  Turned on the blindingly bright overhead LED lights in my kitchen and aimed the scope at a blank patch of wall.  Using the ASIAir to shoot flats it auto-calculates exposure to get you the 50% histogram.

 

The camera was cooled and stable at -10C for all exposures and calibration frames.

 

I'll go back and check my lights and flats this weekend to see if it shows up on either of them.  Thinking Paul's right and it might be bad flats.


Edited by matt_astro_tx, 16 September 2021 - 02:12 PM.

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#6 OldManSky

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Posted 16 September 2021 - 07:34 PM

Matt,

I shoot my 183 ( it’s actually on my new Esprit 100 right now!) usually At gain 111 for NB and gain 50 for LRGB. 0 gain should be fine, but read noise there was a bit high for me, despite the larger well depth.

 

Let us know about the flats!



#7 matt_astro_tx

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Posted 17 September 2021 - 09:31 AM

Well here's my stacked flat FIT if anyone wants to take a look at it.

 

Admittedly I just started taking flats, so I'm not sure how well I'm doing on those.

 

I was going to upload the whole dataset but it's 7.2GB.  I can if anyone is interested in downloading a file that big.



#8 OldManSky

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Posted 17 September 2021 - 09:37 AM

Hey Matt, I downloaded the stacked flat.  Have to do some actual work, but will look at it later :)



#9 OrionSword

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Posted 17 September 2021 - 09:52 AM

What was the exposure time for your Flats?  Also try re-calibrating the lights without Bias for now.


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#10 matt_astro_tx

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Posted 17 September 2021 - 10:20 AM

What was the exposure time for your Flats?  Also try re-calibrating the lights without Bias for now.

Looks like the exposure time was 3.8s.

 

I'm running a script with flats and bias omitted for now to see if the problem goes away.  Don't have time to manually process everything to omit just the bias today...


Edited by matt_astro_tx, 17 September 2021 - 10:24 AM.


#11 matt_astro_tx

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Posted 17 September 2021 - 01:56 PM

Ok, so here are multiple process runs with different calibration applied to try and narrow it down.

 

This one is from the original post, fully calibrated, with darks, flats, and bias applied:

Horsehead (2)

 

This one only has the darks applied (no flats or bias):

result No flat Or bias Sm

 

And this one has no calibration applied (lights only):

result No Dbf Sm

 

It looks to me like the banding is there in my uncalibrated lights!  What do you guys think?  And what would be the cause of that!?



#12 ks__observer

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Posted 17 September 2021 - 02:06 PM

If you stretch the uncalibrated light the banding seems to be there.

My guess is you need to dither more.

gallery_263201_9741_3154476.png



#13 matt_astro_tx

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Posted 17 September 2021 - 02:18 PM

If you stretch the uncalibrated light the banding seems to be there.

My guess is you need to dither more.

Unfortunately with my setup I can't dither.



#14 ks__observer

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Posted 17 September 2021 - 02:21 PM

Unfortunately with my setup I can't dither.

What kind of mount are you using?



#15 matt_astro_tx

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Posted 18 September 2021 - 11:18 AM

A star adventurer 2i.  I know, I know...  undecided.gif



#16 matt_astro_tx

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Posted 18 September 2021 - 11:29 AM

I reran it with DFB's but this time with background extraction on each frame.  Looks like it made the noise even worse.  Like it raised the noise floor of the whole image, which only accentuates the banding.  Again, just experimenting until I we can reach a conclusion.

 

result Bg extract Sm

Edited by matt_astro_tx, 18 September 2021 - 11:30 AM.


#17 ks__observer

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Posted 18 September 2021 - 01:24 PM

You can dither one direction with SA:

https://www.cloudyni...tar-adventurer/

 

There was also a recent thread that showed that if you purposely go out of polar alignment a tiny bit (i forget which direction), that the drift will act as a nice dither.


Edited by ks__observer, 18 September 2021 - 01:24 PM.

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#18 matt_astro_tx

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Posted 18 September 2021 - 04:22 PM

Thanks.  Yes, I could do dithering with my SA2i but I'm not controlling my exposures from the mount.  I am using the ASIAir to control and have an ASI183MC Pro camera.  My understanding is that the SA2i can only control exposures and dithering with a DSLR and a bulb/shutter cable.

 

I'm not sure whether I can dither while using the ASIAir because the Air is not compatible with the SA2i as a mount.  While I have the SA2i plugged into a USB port on the Air to provide it with power, it does not communicate with it... (does not show up in the ASIAir software).

 

I'll start a new thread to see if anyone has been able to do it.


Edited by matt_astro_tx, 18 September 2021 - 04:22 PM.


#19 ks__observer

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Posted 18 September 2021 - 04:29 PM

You can always try to manually dither: Move the camera a touch every 15 or 20 minutes.



#20 matt_astro_tx

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Posted 18 September 2021 - 04:43 PM

Never thought of that.  However, I don't stay up with my rig all night.  I get on target, setup an imaging run, and go to bed!


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#21 matt_astro_tx

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Posted 20 September 2021 - 07:52 AM

Anyone have any ideas?  I intend to get more time on target this week, but as I pointed out in post #11 it looks like the banding is present in my lights.  That's very concerning.  Hoping to get some ideas for a solution before I shoot again.  There's clear skies all week...



#22 acommonsoul

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Posted 20 September 2021 - 08:47 AM

I used to get that problem when I was using my DSLR on my Sky Guider Pro. The only way I was able to get rid of it was with a lot of post processing. I used the Astroflat plugin for PS and Affinity a lot. Once I upgraded my mount and started dithering, those banding problems went away.



#23 matt_astro_tx

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Posted 20 September 2021 - 09:23 AM

Ok.  Thanks for the tip.  Welcome any other feedback.



#24 klaussius

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Posted 20 September 2021 - 10:03 AM

Flats should calibrate that out. Check your flats and make sure that banding pattern is also in them, and that you're calibrating your flats with proper bias/flat darks.

 

It's possible that it won't calibrate the banding out perfectly, and it's possible that what you're seeing is the leftover banding from imperfect calibration. Dither would help with that, but if you can't/won't dither, you could reduce the banding by running a canon debanding script, which basically takes care of this very same problem.



#25 jdupton

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Posted 20 September 2021 - 10:06 AM

Matt,

 

   I looked at you uploaded integrated Flat frame and it looks good with no real issues in the image. However, I note from the FITs header that the exposure was claimed to be 37.58 seconds long and the temperature for the Flat frames was 20.5°C -- at ambient. Those will not cause any major issue but should probably have been taken under temperature conditions more closely matching you Lights and Darks. If the long exposure time is correct and this is a stack of multiple Flat frames, that might be why no banding is seen in the Flat (in addition, of course, to the much greater signal brightness).

 

   I also looked at some the samples you uploaded to your Gallery. They appear to show both horizontal and vertical banding. Have you inspected the Light frames individually to see whether the banding moves around or is it always in the exact same spot frame to frame? That can give a clue to the origin.

 

   Have you considered that this might be a hardware issue? Banding such as seen in the Lights can be caused by noise in your electrical cabling and connections. It could be un-cancelled common-mode noise in the USB transfer or could be conducted noise on the power line to the camera. (Power line noise is more common for such banding. USB noise will usually only be seen on the USB power signal lines.) Both of these sources can be helped with the use of external ferrite cores clamped onto the USB and power cables to the camera. These are available on Amazon and might be available in the Dallas area at electronics retailers. They are easy to attach as an experiment and will generally have no side effects on your equipment. Just clamp one each onto the USB and power feeds near the camera.

 

   Whether or not this is electrical in nature, can you tell us more bout your setup? What power source do you use? How is the camera attached via USB? Does it go through a USB Hub? How long are the cables? Do either the power or USB cables pass near a source of EM radiation like a WiFi antenna?

 

 

John




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