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  #1  
Old 14-02-2018, 06:26 AM
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gvanhau (Geert)
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CCD Aging, Is this normal?

Hello

I own a Atik CCD 383L bought new in 2012 (KAF 8300 CCD).

At present time I noticed an increased difficuty to process my pictures. Every time I had to collect more and more pictures in order to get a more or less dencent image.

So I decided to compare som pictures from the begining of the CCD's live with recent pictures.

Bias are more or less the same, but what a bad surpise.... when I compared darks.

I attached a image comprising the following:
At top, original dark, calibrated dark an bias at 2013.
At bottom recent dark, recent calibrated dark an recent bias.

Sorry but the image was taken from screen using my cell pone.

Is this normal? is it a deffect of my camera? what do you think?

Regards

Geert
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  #2  
Old 14-02-2018, 09:02 AM
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troypiggo (Troy)
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I haven't done as detailed a comparison as you, but my QSI583ws (same sensor as you) has developed a column defect over time - one column, about third the height of frame. Not an issue, with dithering and image integration it disappears.

Not quite the same issue as you with noise getting worse over time. Does your camera get heavy use?
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  #3  
Old 14-02-2018, 10:16 AM
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Quote:
Originally Posted by troypiggo View Post
I haven't done as detailed a comparison as you, but my QSI583ws (same sensor as you) has developed a column defect over time - one column, about third the height of frame. Not an issue, with dithering and image integration it disappears.

Not quite the same issue as you with noise getting worse over time. Does your camera get heavy use?
Well, I use my camera almost every clear night.
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  #4  
Old 14-02-2018, 10:32 AM
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RickS (Rick)
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Hi Geert,

I have noticed a lot more column defects in KAF-16803 cameras as they age but not much change in bias or dark noise.

Rather than try to judge from screen stretched images I'd suggest you use the DarkBiasNoiseEstimator script to do a numerical before and after comparison.

Cheers,
Rick.
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  #5  
Old 14-02-2018, 11:14 AM
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multiweb (Marc)
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Same here. My 10yr old QHY8 has more hot pixels, so does my aging lodestar. My 6yr old QHY9 has a couple of bad columns developing. Nothing major that cannot be calibrated out or dithered. Just gotta be aware of it.
I'm getting a few hot pixels myself. I wish I could go through a calibration. Maybe dithering will come with old age.
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  #6  
Old 14-02-2018, 12:54 PM
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Quote:
Originally Posted by RickS View Post
Hi Geert,

I have noticed a lot more column defects in KAF-16803 cameras as they age but not much change in bias or dark noise.

Rather than try to judge from screen stretched images I'd suggest you use the DarkBiasNoiseEstimator script to do a numerical before and after comparison.

Cheers,
Rick.
I run this scritp and got these results.

I can see that bias has almost not changed, but dark...
Note that darks are 1800 sec exposures

Geert
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  #7  
Old 14-02-2018, 12:57 PM
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Quote:
Originally Posted by multiweb View Post
Same here. My 10yr old QHY8 has more hot pixels, so does my aging lodestar. My 6yr old QHY9 has a couple of bad columns developing. Nothing major that cannot be calibrated out or dithered. Just gotta be aware of it.
I'm getting a few hot pixels myself. I wish I could go through a calibration. Maybe dithering will come with old age.
I think many of us have some hot piexels
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  #8  
Old 14-02-2018, 02:23 PM
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Quote:
Originally Posted by gvanhau View Post
I run this scritp and got these results.

I can see that bias has almost not changed, but dark...
Note that darks are 1800 sec exposures
The read noise is about where you'd expect at 10 to 11e- (gain is probably somewhere between 0.4 and 0.45) but the noise in the new dark is much worse. If long subs consistently show that behaviour then that would certainly explain why you need more subs now.

The degradation of individual pixels over time due to cosmic rays is well known but I wasn't aware of aging affecting dark current/noise that badly. I wonder if the sensor isn't getting cooled correctly now?

Cheers,
Rick.
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  #9  
Old 14-02-2018, 08:16 PM
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The additional noise could be coming from the support electronics around the CCD that's getting old, e.g. the A to D converter or any shift registers / amplifiers.
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  #10  
Old 14-02-2018, 09:03 PM
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Quote:
Originally Posted by billdan View Post
The additional noise could be coming from the support electronics around the CCD that's getting old, e.g. the A to D converter or any shift registers / amplifiers.
Hi Bill,

I'd expect an issue with the readout circuitry to affect the bias frames as well as darks?

Cheers,
Rick.
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  #11  
Old 14-02-2018, 09:51 PM
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Yes that's true Rick, except they are 30-min darks so the readout circuitry has been heating up for a while, compared to a quick bias readout.
As well as the increased noise the offset is also much larger than the bias reading.

Anyway trying to remote diagnose an issue is useless without an oscilloscope and another good camera sitting next to the faulty one.

Cheers
Bill
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  #12  
Old 14-02-2018, 10:16 PM
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Quote:
Originally Posted by billdan View Post
As well as the increased noise the offset is also much larger than the bias reading.
Hence my hypothesis that the sensor is warmer causing more dark current and thus more dark current noise. The numbers match very well. The additional noise is almost exactly what you'd expect if the extra offset was due to dark current.

Quote:
Originally Posted by billdan View Post
Anyway trying to remote diagnose an issue is useless without an oscilloscope and another good camera sitting next to the faulty one.
We're dancing on the edge of that dichotomy between HW and SW engineers and I only get paid for that in my day job so I'll shut up now

Cheers,
Rick.
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  #13  
Old 14-02-2018, 10:30 PM
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Are both images at the same temperature?
My thought - maybe the cooling isn't working so well now.
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  #14  
Old 14-02-2018, 10:49 PM
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Quote:
Originally Posted by RickS View Post
The read noise is about where you'd expect at 10 to 11e- (gain is probably somewhere between 0.4 and 0.45) but the noise in the new dark is much worse. If long subs consistently show that behaviour then that would certainly explain why you need more subs now.

The degradation of individual pixels over time due to cosmic rays is well known but I wasn't aware of aging affecting dark current/noise that badly. I wonder if the sensor isn't getting cooled correctly now?

Cheers,
Rick.
Hello
I tried different things; I tested de cam wo cooling; and the ressult was much worse.
I also suspected on the power supply (regulated 13.2V) so I went over to batteries, and result was also worse because this cam from the beginning showed more hot pixels when voltage was under 12.5V and its still the same.

I also disconnected every thing else connected to the scope and to the pc....that did not do any change...

Geert
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  #15  
Old 14-02-2018, 10:56 PM
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Quote:
Originally Posted by kens View Post
Are both images at the same temperature?
My thought - maybe the cooling isn't working so well now.
Hello Ken
Both images were taken at -20C. using Maxim DL.
That was also my first suspect, but turning cooling off produces much more hot pixels.
However it could be that the contact between the cooler and the chip is not so good anymore? Next time I will open the cam and check this.

Geert
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  #16  
Old 14-02-2018, 11:00 PM
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Quote:
Originally Posted by billdan View Post
Yes that's true Rick, except they are 30-min darks so the readout circuitry has been heating up for a while, compared to a quick bias readout.
As well as the increased noise the offset is also much larger than the bias reading.

Anyway trying to remote diagnose an issue is useless without an oscilloscope and another good camera sitting next to the faulty one.

Cheers
Bill
Hello Bill
That is a good point.
I have an oscilloscope and other measuring stuff, but I'm lacking the good camera to compare.

Geert
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  #17  
Old 14-02-2018, 11:33 PM
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Hi Geert,

You could try and cool down the support electronics with a can of freeze just before the 30 minute readout happens. If it improves the noise you know where the problem lies.

There is also corrosion to consider as well, my 3 yr old QHY12 had to be sent back to China for repair because the printed circuit board tracks were corroded and I was getting severe horizontal banding across each image.

Cheers
Bill
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  #18  
Old 15-02-2018, 11:23 PM
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Another direction to consider

Could be that some aspect of the electronics in your camera has degraded ?
A capacitor leaked or dried out or degraded, a dry joint fractured, some corrosion, bad connection on a connector or IC socket or maybe a faulty component - could be from thermal variation or shock.

Stray interference, poor voltage regulation, poor bus timing or floating levels, transients that shouldnt be there or other forms of signal detection problems - 1001 possibilities really that might be potential causes of extra noise or degraded signal.

Could even be related to the USB cables or related external electronics and external electrical noise interference.

I'd consider asking the manufacturer about it and getting their opinion and maybe getting it serviced.

CCD electronics are actually tuned circuits to some degree.
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  #19  
Old 17-02-2018, 12:19 AM
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To exclude one or more of the possible reasons mentioned so far you could do this simple test: Take a dark at 50% and 25% exp time and estimate whether the dark signal is also 50% and 25%. If so, there probably is a constant dark current (at constant temperature).
If not, there may be a temperature rise (dark current grows faster with time) or an electronic defect (dark current is already high in the beginning).
Of course, there may be more than one reason, but thats not very likely.

Erwin
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  #20  
Old 18-02-2018, 03:12 PM
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Quote:
Originally Posted by rally View Post

I'd consider asking the manufacturer about it and getting their opinion and maybe getting it serviced.

CCD electronics are actually tuned circuits to some degree.
Spot on.

The circuits traces will corrode over time and change their resistance values and the CCD can be affected by high energy cosmic rays (permanent hot pixels )

This is one of the reasons I run a dehumidifier in my observatory every night to help mittigate any corrosion.
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