#1  
Old 14-02-2018, 05:26 AM
gvanhau's Avatar
gvanhau (Geert)
Registered User

gvanhau is offline
 
Join Date: Feb 2014
Location: Santiago, Chile
Posts: 203
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
Attached Thumbnails
Click for full-size image (IMG-20180103-WA0002.jpg)
105.3 KB82 views
Reply With Quote
  #2  
Old 14-02-2018, 08:02 AM
troypiggo's Avatar
troypiggo (Troy)
Bust Duster

troypiggo is offline
 
Join Date: Nov 2008
Location: Brisbane, Australia
Posts: 4,846
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?
Reply With Quote
  #3  
Old 14-02-2018, 09:16 AM
gvanhau's Avatar
gvanhau (Geert)
Registered User

gvanhau is offline
 
Join Date: Feb 2014
Location: Santiago, Chile
Posts: 203
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.
Reply With Quote
  #4  
Old 14-02-2018, 09:32 AM
RickS's Avatar
RickS (Rick)
PI cult recruiter

RickS is offline
 
Join Date: Apr 2010
Location: Brisbane
Posts: 10,584
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.
Reply With Quote
  #5  
Old 14-02-2018, 10:14 AM
multiweb's Avatar
multiweb (Marc)
ze frogginator

multiweb is offline
 
Join Date: Oct 2007
Location: Sydney
Posts: 22,060
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.
Reply With Quote
  #6  
Old 14-02-2018, 11:54 AM
gvanhau's Avatar
gvanhau (Geert)
Registered User

gvanhau is offline
 
Join Date: Feb 2014
Location: Santiago, Chile
Posts: 203
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
Attached Thumbnails
Click for full-size image (DarkBiasNoiseEstimator.PNG)
70.4 KB51 views
Reply With Quote
  #7  
Old 14-02-2018, 11:57 AM
gvanhau's Avatar
gvanhau (Geert)
Registered User

gvanhau is offline
 
Join Date: Feb 2014
Location: Santiago, Chile
Posts: 203
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
Reply With Quote
  #8  
Old 14-02-2018, 01:23 PM
RickS's Avatar
RickS (Rick)
PI cult recruiter

RickS is offline
 
Join Date: Apr 2010
Location: Brisbane
Posts: 10,584
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.
Reply With Quote
  #9  
Old 14-02-2018, 07:16 PM
billdan's Avatar
billdan (Bill)
Registered User

billdan is offline
 
Join Date: Mar 2012
Location: Narangba, SE QLD
Posts: 1,551
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.
Reply With Quote
  #10  
Old 14-02-2018, 08:03 PM
RickS's Avatar
RickS (Rick)
PI cult recruiter

RickS is offline
 
Join Date: Apr 2010
Location: Brisbane
Posts: 10,584
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.
Reply With Quote
  #11  
Old 14-02-2018, 08:51 PM
billdan's Avatar
billdan (Bill)
Registered User

billdan is offline
 
Join Date: Mar 2012
Location: Narangba, SE QLD
Posts: 1,551
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
Reply With Quote
  #12  
Old 14-02-2018, 09:16 PM
RickS's Avatar
RickS (Rick)
PI cult recruiter

RickS is offline
 
Join Date: Apr 2010
Location: Brisbane
Posts: 10,584
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.
Reply With Quote
  #13  
Old 14-02-2018, 09:30 PM
kens (Ken)
Registered User

kens is offline
 
Join Date: Oct 2014
Location: Melbourne, Australia
Posts: 314
Are both images at the same temperature?
My thought - maybe the cooling isn't working so well now.
Reply With Quote
  #14  
Old 14-02-2018, 09:49 PM
gvanhau's Avatar
gvanhau (Geert)
Registered User

gvanhau is offline
 
Join Date: Feb 2014
Location: Santiago, Chile
Posts: 203
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
Reply With Quote
  #15  
Old 14-02-2018, 09:56 PM
gvanhau's Avatar
gvanhau (Geert)
Registered User

gvanhau is offline
 
Join Date: Feb 2014
Location: Santiago, Chile
Posts: 203
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 -20°C. 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
Reply With Quote
  #16  
Old 14-02-2018, 10:00 PM
gvanhau's Avatar
gvanhau (Geert)
Registered User

gvanhau is offline
 
Join Date: Feb 2014
Location: Santiago, Chile
Posts: 203
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
Reply With Quote
  #17  
Old 14-02-2018, 10:33 PM
billdan's Avatar
billdan (Bill)
Registered User

billdan is offline
 
Join Date: Mar 2012
Location: Narangba, SE QLD
Posts: 1,551
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
Attached Thumbnails
Click for full-size image (CRC Freeze.jpg)
23.2 KB22 views
Reply With Quote
  #18  
Old 15-02-2018, 10:23 PM
rally
Registered User

rally is offline
 
Join Date: Sep 2007
Location: Australia
Posts: 896
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.
Reply With Quote
  #19  
Old 16-02-2018, 11:19 PM
ErwinL (Erwin)
Registered User

ErwinL is offline
 
Join Date: Jul 2017
Location: Germany
Posts: 16
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
Reply With Quote
  #20  
Old 18-02-2018, 02:12 PM
Peter Ward's Avatar
Peter Ward
Galaxy hitchhiking guide

Peter Ward is offline
 
Join Date: Dec 2007
Location: The Shire
Posts: 8,090
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.
Reply With Quote
Reply

Bookmarks

Thread Tools
Rate This Thread
Rate This Thread:

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off

Forum Jump


All times are GMT +10. The time is now 08:47 AM.

Powered by vBulletin Version 3.8.7 | Copyright ©2000 - 2024, Jelsoft Enterprises Ltd.
Advertisement
Bintel
Advertisement
Testar
Advertisement