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Cause of ASI1600MM Banding?

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#1 rhart426

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Posted 06 May 2021 - 11:16 AM

Hello all,

 

I'm having an issue with horizontal and vertical banding with this camera:

 

O3_Superstretch.jpg

 

This is with an ASI1600MM, using the ZWO 36mm/7mm bandpass O3 filter, super-stretched in PixInsight.  The data is from several nights and has been calibrated in PixInsight.  The gain/offset used for all data is 200/50.  The exposure time and temperature varied by session, which was accounted for in calibration.  The data from the Ha and S2 filters was acquired, calibrated, and stacked using the same procedure used for O3 and exhibits no banding, so I've ruled out the acquisition process.  I tried stacking the subframes from each session separately, both calibrated and uncalibrated, and the banding is still present in each case, ruling out bad calibrations or sessions.  I dither every 3 frames via PHD2, so FPN shouldn't be an issue either.  Exposure times varied from 1.5m to 3.5m.  There is no banding present in the flat frames used to calibrate each session.  For reference, this is the Ha filter (it's had a little more processing done):

 

Ha_Superstretch.jpg

 

Any ideas on what could be causing this?  I've read that it can be an issue at low gains and/or when not dithering enough, but those causes aren't present here.



#2 Der_Pit

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Posted 06 May 2021 - 04:27 PM

I haven't seen vertical banding with my 1600.  I do get horizontal banding with gain 0, so mostly used 76, although (for me) it usually gets invisible when processing enough frames.

No idea on the reason for it, quite sure something of the electronics though.  Could be fluctuations in the reference voltage of the ADC.  But again, I'm only guessing....



#3 happylimpet

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Posted 06 May 2021 - 05:11 PM

I got banding on my 1600 using lower gains (from doing flats at lower gain, stupidly), so i too used gain 200 for everything, and never saw it again.

 

Aside from that Ive no suggestions Im afraid.



#4 tloebl

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Posted 06 May 2021 - 06:13 PM

what sort of different results would I see and need to know about using gain of 200 vs unity 139 with the 1600?



#5 dswtan

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Posted 06 May 2021 - 06:25 PM

From other threads on this, you might try bumping up the offset first, rather than the gain. Lower offsets seem to have been reported causing this (e.g. 20). Personally I have never seen bands on my 1600 at unity gain, offset 40, 0C, 60-sec.



#6 rhart426

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Posted 07 May 2021 - 12:30 PM

Thanks all for the replies!

 

I performed some further tests to attempt to track down the culprit, but came up empty again.  I was able to remove most of it with the CanonBanding script and thus salvage the data, but I'm still mystified as to what caused it.  I went back and checked the data I have for another target using the same settings and filter and there's zero banding.  If I figure it out I'll post here for posterity.



#7 Der_Pit

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Posted 07 May 2021 - 04:38 PM

From other threads on this, you might try bumping up the offset first, rather than the gain. Lower offsets seem to have been reported causing this (e.g. 20). Personally I have never seen bands on my 1600 at unity gain, offset 40, 0C, 60-sec.

At least on my side I cannot confirm that.  I use an offset of 10, no banding with either 139 or 76.  Only at 0.

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