random "hot" pixels

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random "hot" pixels

Postby peter3 » Mon Jul 24, 2017 8:21 pm

I've just been testing an ASI1600 cooled camera. All seems to work well (running Maxim and ASCOM), except that I'm getting a large number of "hot" pixels that randomly pop up in each exposure. They do not repeat from one exposure to the next. I've tried the usual cable changes, port changes, computer changes, acquisition software changes, but they persist. They have a value of several hundred ADU above the surrounding pixels. They don't seem to depend upon temperature, but behave more like spikes in the read noise. They are most often in pairs, so the hot pixel filter in Maxim doesn't work well.

I would very much like to see a dark frame like the very smooth example on the ZWO website, but I'm not getting that. I've attached a small area to show what I see, it was done with the same settings as the ZWO sample dark frame, except at -15C instead of -25C. Putting the camera in a refrigerator to get down close to -25C didn't make much (if any) difference. Any ideas?

Peter
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cropped Image -001R.jpg
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Re: random "hot" pixels

Postby peter3 » Mon Jul 24, 2017 9:28 pm

Sorry, I gave some incorrect information for the attachment in my previous message. The gain was actually set for 1e-/adu, not the 5e-/adu of the ZWO site's sample dark.
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Re: random "hot" pixels

Postby einari » Tue Jul 25, 2017 5:29 am

So this is dark frame ? How long exposure ?
Have you tried taking real lights and then do calibration - how does the end result show up ?
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Re: random "hot" pixels

Postby peter3 » Tue Jul 25, 2017 3:48 pm

That one happens to be a 5 min dark. I'm still just doing camera diagnostics. This is my first CMOS camera, I'm used to CCDs that are much smoother noise wise, so I'm surprised to see these random "hot" pixels when the read noise is specified to be so low.

The bright pixels don't repeat from one frame to the next, so they wouldn't properly subtract out in a calibration. Their brightness is approximately the same for darks up to about 50 sec duration, then the more repeatable hot pixels from dark current start to show up (I'm at -10C detector temp).
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Re: random "hot" pixels

Postby Sam » Wed Jul 26, 2017 9:35 am

can you see them jumping when you run the camera in video mode
such like see from sharpcap
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Re: random "hot" pixels

Postby peter3 » Wed Jul 26, 2017 2:48 pm

Yes, I tried that software to see if it behaved any differently from running the camera under ASCOM.
Pretty much the same.
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Re: random "hot" pixels

Postby Wwilmoth69 » Mon Feb 12, 2018 10:36 am

I'm curious to the outcome of this as well. Had my camera for around 3 months now and all of a sudden I have alot of moving hot pixels as well. Calibrations does not remove these and they show up blue or red or green depending which stack they were in before a signing a color to them
I have the asi1600 mmc
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Re: random "hot" pixels

Postby peter3 » Mon Feb 12, 2018 3:46 pm

I haven't done any more experimenting. My present application has huge signal so it's not an issue. If there is a solution I would certainly like to know about it.
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Re: random "hot" pixels

Postby Wwilmoth69 » Mon Feb 12, 2018 6:22 pm

Not sure why calibra tion frames aren't removing these pixels

My images were smooth when I first got it but now the hot pixels move in each exposure each dark and show up after all calibration.

Not sure what has happened

https://drive.google.com/folderview?id= ... ePy4hbGyxk

Here's a folder with my latest target. Stars are wonky because I was only testing to see if a complete new set of calibration would correct it in final image but they just show up red blue green in final image
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Re: random "hot" pixels

Postby Sam » Tue Feb 20, 2018 2:20 am

sorry for later reply
we will check this problem when we back to work after holiday
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