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Vertical banding ASI183C

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#1 MikeF1960

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Posted 22 May 2019 - 12:30 PM

I have a ZWO ASI183C pro cooled OSC.  Generally, I like this camera and for me anyway, there has been somewhat of a learning curve to navigate. I have made progress though.  

 

Anyway, I was doing some experimentation with this using an 8" f/4 Newt.  I am trying to improve star shape and color in my images so I thought I would try dropping the gain down to 0, which in the ASCOM software for this is a pre-set for highest dynamic range.  

 

In this experiment, I did 130 frames @30s each using gain of 0 with a sensor temperature of -15c.  I calibrated using 50 darks, 50 flats, and 500 bias frames. I processed this in DeepSkyStacker.

 

I was expecting a lot more noise than I get when I run at unity gain but this vertical banding took me completely by surprise.  I've never seen this before in any camera except a Nikon D700 that I've used in the past. 

 

The attached jpg has been reduced in size.  It is simply the TIFF opened in Pixinsight and autostretched and saved as a jpg.

 

Anybody have any insights into this?  I guess mainly, I want to determine if it may be a problem with the camera or just that this particular combination of exposure, gain, calibration, etc. is just not good with the ASI183C.

 

Thanks,

Mike

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#2 einarin

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Posted 22 May 2019 - 12:35 PM

https://www.cloudyni...-2#entry8237945

 

Edit: maybe you could try without bias as Jon suggests in that thread.


Edited by einarin, 22 May 2019 - 02:00 PM.

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#3 OldManSky

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Posted 22 May 2019 - 01:07 PM

It could be the banding Jon mentions in the article einarin linked to.  In that article, he mentions that banding is practically gone at gain 50+, and that gain 0 probably isn't a good idea.

But I also notice that your calibrated image still has amp glow on the left-hand side.

If you took matching darks, that shouldn't be there.  Amp glow on the 183 calibrates out nicely.

 

So what I'd suggest:  look at individual lights, darks, flats, and bias.  Stretch them aggressively.  See which (if any) has banding.  Make sure you're using matching exposure times/gains/offsets for your darks.

And let us know what you find.


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#4 MikeF1960

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Posted 23 May 2019 - 10:52 AM

Thank you OldManSky...

 

Yes, the amp glow is something I've figured out so that's not a problem.  Generally, I don't use bias frames with the 183 and the amp glow then is solved.

 

I did some dark flats last night to see if that would make any difference and it did not.  On the darks, bias and dark flats, I can see this banding.  It is not apparent on the flat frames nor on any individual light frame.

 

I also re-stacked everything in PI to see if it could possibly be a DSS thing but I ended up with similar results.

 

I'm thinking this is simply a situation where this -0- gain setting is not right for this camera.  I'll likely go back and conduct the same experiment using a gain in between unity and HDR to see if I can meet my objective of improving star color and shape.

 

I appreciate that you took the time to respond...

CS,

Mike



#5 einarin

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Posted 23 May 2019 - 11:12 AM

Was it with cmos cameras - not to use bias and not to scale dark frames ?

https://www.cloudyni...as-dark-frames/



#6 OldManSky

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Posted 23 May 2019 - 03:32 PM

Good luck, Mike.

I haven't seen any banding on lights or calibration frames with my mono version of the camera...but then, I haven't tried gain 0, either, so that is indeed the likeliest suspect!

Let us know if it goes away with a higher gain, ok?



#7 Jon Rista

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Posted 23 May 2019 - 04:06 PM

It could be the banding Jon mentions in the article einarin linked to.  In that article, he mentions that banding is practically gone at gain 50+, and that gain 0 probably isn't a good idea.

But I also notice that your calibrated image still has amp glow on the left-hand side.

If you took matching darks, that shouldn't be there.  Amp glow on the 183 calibrates out nicely.

 

So what I'd suggest:  look at individual lights, darks, flats, and bias.  Stretch them aggressively.  See which (if any) has banding.  Make sure you're using matching exposure times/gains/offsets for your darks.

And let us know what you find.

I have not encountered this kind of banding myself, to be honest. I have seen much finer banding, per-column, faint banding at lower gains, which is fairly normal with sensors that have per-column readout (and it usually disappears at higher gains). The problem shown in the OP seems to be an actual issue with the sensor readout...



#8 Jon Rista

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Posted 23 May 2019 - 04:15 PM

Does the vertical banding issue occur in individual subs?



#9 MikeF1960

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Posted 23 May 2019 - 05:25 PM

Hello Gentlemen,

 

I do not see the banding in individual subs.  But as you might imagine, part of my search for the root of the issue included stacking the data in a number of different ways to try to see if I can figure something out.  What I have found is that if I stack only the lights, I can see the banding and it is quite strong.

 

So I was wondering if perhaps my calibration frames were not adequately calibrating the banding out of the lights or if it was a peculiarity specific to this sensor and the -0- gain setting.  All of my calibration frames were carefully done and I did make sure everything matched with regard to exposure times, gain and temperature settings.

 

I do not have this issue at all when I do my work using unity (111) gain.  I was just sort of hoping that running certain types of imaging using a higher dynamic range gain setting might in result in better color and maybe better star shapes.  Using a f/4 instrument, I have the luxury of speed.

 

So I will try using a gain value of 53 as suggested and see what happens.  Otherwise, I think I am getting decent results with this camera using unity gain.  But we're always looking to improve, right?

 

 

Interestingly, when I had this problem with my Nikon D700 I investigated it on all the Nikon fora and what I gathered is that there are actually seams in the sensor that cause this, at least in that particular camera.  I don't know if that is actually true but a number of people mentioned that.

 

I am appreciative of all the folks that responded  to my questions.  I was sort of thinking it could be a common issue that would have a well-known solution.

 

So thank you Jon, OldManSky and Einarin for taking the time to consider my problem and your generosity in your responses!
 

CS,

Mike


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