ZWO ASI183MM Pro Long exposure NB problem

[Star101]

I can image upto 2 minutes per sub and remove the amp glow using DARKS at the same 2 minute sub and same gain.

Last night I tried imaging NGC 1499 using Ha at 5 minute subs at 200 gain. I tried using DARKS and flats to remove the amp glow. I even redid the DARKS at 5 minutes and 200 Gain.  All same temperature, exposure and gain.

If I have to stick to 2 minute subs and below, so be it, although I do see others claiming 5+ minute exposures.

Suggestions please.

 

Historgram Stretch only 

[geordie85]

 I use a qhy183c and image using 300 second exposures and my darks completely eliminate the amp glow. 

How many darks did you use? Did you use darkflats too? When did you do your darks? Is it possible you had light leakage?

[Thalestris24]

Edit: As others have said - appears to be a calibration issue...

 

[vlaiv]

No, not external source to this (like star in outer field, or light intrusion in optical train), this is definitively amp glow, if you examine common pattern for ASI183 amp glow you will see that it matches perfectly:

Can you explain exact calibration process?

This sort of amp glow happens in two stages (from what I gathered over the internet, I have not had problem with ASI1600 although not pro version) - there is regular dark current amp glow - meaning that signal pattern builds over time due to temperature of sensor and surrounding electric circuitry. There is also additional part of amp glow that happens on some cmos sensors - readout amp glow - this one depends on speed of readout.

This is the reason for introduction of PRO versions of ASI cameras - they have on board RAM and fast readout happens from sensor to RAM and then slow readout over USB 2.0 can happen between camera RAM and computer.

If you can't remove all amp glow in long exposure images, please check

1) calibration process - it needs to be precise to remove all amp glow (using dark optimization can be problematic on CMOS sensors, as is use of bias frames)

2) Make absolutely sure that there is no temperature mismatch between lights and darks used

3) Although you mentioned yours is PRO version - what sort of download speed are you using (USB settings, USB 2.0 or 3.0, etc)?

[Thalestris24]

2 minutes ago, vlaiv said:

No, not external source to this (like star in outer field, or light intrusion in optical train), this is definitively amp glow, if you examine common pattern for ASI183 amp glow you will see that it matches perfectly:

Eeks! That's awful then. Apologies for my wrong assumption - should have kept my mouth shut....

[tooth_dr]

That’s shocking Amp Glow. 

[Adam J]

1 hour ago, Star101 said:

I can image upto 2 minutes per sub and remove the amp glow using DARKS at the same 2 minute sub and same gain.

Last night I tried imaging NGC 1499 using Ha at 5 minute subs at 200 gain. I tried using DARKS and flats to remove the amp glow. I even redid the DARKS at 5 minutes and 200 Gain.  All same temperature, exposure and gain.

If I have to stick to 2 minute subs and below, so be it, although I do see others claiming 5+ minute exposures.

Suggestions please.

 

I have see this a number of times and it usually boils down to what program you are using for calibration and what settings you are using.

I use APP and when these sensors came out they actually added a new feature called adaptive data pedistal to make them calibrate correctly.

Other stacking programs have not yet adapted.

I also suggest that if you are using pix insight then you must turn off dark frame scaling. Same goes for other programes with this feature. 

You need to calibrate your flats with dark flats if your not already.

Hope all that helps.

Adam

 

 

[Star101]

Thanks to everyone for such a quick response.

I will be honest. I am being lazy and use Pixinsight BatchPreprocessing as this usually works OK for me.

Having read all your questions, I went back to check all my steps. I found the answer  

I had reset my BatchPreprocessing window but left "OptimizeDarkFrames" checked!! I unchecked the box and ran again, see below. 
Thanks very much for all your input and helping me fix this. Much appreciated.

[vlaiv]

39 minutes ago, Star101 said:

I had reset my BatchPreprocessing window but left "OptimizeDarkFrames" checked!! I unchecked the box and ran again, see below. 

Yes, Dark optimization relies on bias being good - it tries to find good multiplier to compensate any difference in temperature - but it needs pure dark signal for that with bias removed. Bias is the one causing issues with CMOS cameras, so anything relying on bias removal is probably going to cause trouble.