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Sensor Damage? - Help Request

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#1 JP50515

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Posted 22 August 2019 - 09:57 AM

Hey Guys,

I've got a situation I've been trying to resolve for some time now. An artifact suddenly appeared in my darks that has been making it very difficult to process data. 


Below are three super stretched images to accentuate the issue. Notice that it only appears in the dark frame and the data stack, but not the light frame or flat. 

The issue is the diagonal line on the bottom left side of the frame. It registers into the final stacked data and is present in every dark frame across multiple temperature settings and attempts to build a library. 
 

Scope cap is on, telescope and camera covered and closed in a dark shed. It always shows up exactly the same. 

 

If anyone has any idea what's going on here it would be super helpful, as I've been trying to figure this out for over a month at this point with no luck.

 

Thanks!

Single Dark Frame:

Dark_Demo.jpg

 

Single Flat Frame (unstretched) :

 

Oiii_-_Flat.jpg

Single Light Frame:

Stretched_Oiii_Light.jpg

Stacked Oiii Data:
 

Stretched_OIII_Stack.jpg
 


Edited by JP50515, 22 August 2019 - 09:59 AM.


#2 JP50515

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Posted 23 August 2019 - 10:47 AM

Hey Guys,

Just bumping this to see if anyone might have any ideas? I'm getting a bit desperate at this point, (this is my second attempt to ask here about it with no response). I have tried on my own for a couple months now to diagnose it without any luck. 

If anyone has any ideas at all as to what could be causing it, I'd be extremely grateful. 


Edited by JP50515, 23 August 2019 - 10:48 AM.


#3 Aaron_tragle

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Posted 23 August 2019 - 11:25 AM

This is a long shot, but I hope it helps atleast as a temporary solution. It sorta reminds me of a dead column, but dead columns show up in lights. Do you dither by a chance? I am thinking if you dithered enough that that line could be averaged out in the stack as a temporary solution until you get this fixed.


Edited by Aaron_tragle, 23 August 2019 - 11:26 AM.


#4 Aaron_tragle

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Posted 23 August 2019 - 11:26 AM

I would contact ZWO and send them a dark frame just to see what they have to say if you haven't already.


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#5 jdupton

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Posted 23 August 2019 - 11:31 AM

JP50515,

 

   The symptoms are very strange. My bet is no one else has seen something like this before. I sure haven't seen it in a sensor. The symptoms are confusing in that you have only seen it is the Dark Frames rather than in all frames. How closely have you really looked? Do you have PixInsight? Maybe a close look at the light frame using pixel by pixel samples would show a slight change in the values at the discontinuity.

 

   You say this happened suddenly and had never seen it before. Were there any changes to your normal procedures around that same time? Did you notice anything odd about the hardware around the time of the appearance of the artifact?

 

   Is there a time component to the severity of the defect? In other words, if you were to power up the camera and take a dark, then power down the camera for a minute, power it on again and wait for one or two hours and then take a second Dark Frame, are there any differences between the frames? You might want to try running that test and uploading the two Dark Frames for others to examine. For that matter, if you can upload one Dark Frame, one Flat Frame, and one Light Frame, I would take a look at them for you.

 

   I have only a wild, wild, wild guess at what might cause an artifact like what you show. Many years ago (about 40), I was tasked in my job to find the root cause for a prevalent memory DRAM failure. The problem was such that tests run shortly after power on would always pass. However, if the system were allowed to remain powered on for 24 hours, some memory storage locations would fail to be able to reliably store a bit of information.

 

   Working with the silicon foundry making the DRAM chips, we discovered the cause to be a domain boundary problem in the silicon the chip is built upon. Charge migration in the bulk substrate caused charge to pile up at the boundary between two crystalline domains within the silicon. This bulk charge build-up in turn caused the transistors nearer the surface of the chip to change characteristics -- they did not operate as they should. If power to the chip was removed, the bulk substrate was able to drain the stacked up charges and when powered back on, the chip would work perfectly again for a period of time before once again becoming unreliable and failing.

 

   As I said, this is a really wild guess as what might cause what you are seeing in the sensor. It must be something new since if the bulk silicon wafer the sensor was built upon had the above problem, it would have always shown it unless maybe you have changed you normal procedures and now run the camera for very long periods of time before doing your Dark Frames. However, there might also be a very remote chance that the sensor has sustained damage to the substrate. Theoretically, this could be caused by extreme thermal shock although that very rarely happens because of the thermal mass of the chip and especially the carrier it mounted on. If a small crack has occurred in the substrate then it is possible that charge build-up at the resulting boundary might cause an effect such as you have shown. If the symptom turns out to be a (partial) crack in the substrate, then you might expect the artifact to get worse as time goes on and the crack propagates to the surface where it will affect the electronic structure of the sensor itself.

 

   This is all very thin on evidence but it might be possible to test for a time-related symptom that could help pin down whether this is a sensor failure.

 

 

John


Edited by jdupton, 23 August 2019 - 11:37 AM.

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#6 WadeH237

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Posted 23 August 2019 - 11:43 AM

I am 99% sure that it's showing up in all of your frames.  You don't see it in the single flat and single light because it's a really dim artifact and it's lost in the noise.

 

You see it in the stacked OIII image because your calibration is off.  If you look, you can see that all of the bright areas in your dark frame are over corrected in stacked image.  The amp glows on the right, and the two glows on the left side of the dark frame are plainly visible as dark areas in the stacked image.  The thinness of the line in the single dark frame is widened in the stacked image because you registered all of the lights in the stack.

 

So first off, you should look at your calibration method.  The first thing to do is to make sure that if you are using PixInsight that you uncheck the "Optimize" option in the dark calibration.  That one thing may make it disappear.  The next thing to check is whether or not you are double subtracting the bias.  The best way to calibrate an ASI1600 is to ensure that the light frames and dark frames are taken with identical exposure times, gain, offset and temperature.  Then, when you do the calibration, do not do bias calibration.  Just do dark calibration with (uncalibrated) dark frames.  Note that I've omitted flat frames from the description.  For them, just calibrate the flats themselves with either bias or dark-flats before you use them.  When the calibration is done correctly, that stacked OIII image will have even illumination all the way to the edges and into the corners (except for where the registration edges are, but they will be perfectly straight and parallel to the sides of the frame).  My guess is, that your line will be gone, too.

 

Another option is to just mark all the pixels in the line with a bad pixel map.  If you are dithering, this is pretty much guaranteed to work.

 

Finally, all of the above is just to help with many kinds of defects, normal and otherwise.  It will certainly address your specific camera - but I don't think that what you are seeing is normal.  It's definitely worth contacting ZWO to see what they have to say.


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#7 JP50515

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Posted 23 August 2019 - 12:40 PM

Thank you guys. 

To answer a few questions:

1. Yes - Dithering is being used

2. The only change to gear would be the addition of a focal reducer. However, the issue persists with the camera off the train as well so I know it's camera related. 
 

I will try some of these different time based tests but so far it's just there all the time in the darks. If it were there in the flats + lights, would it not show up in the master flat + stacked lights (without darks) as well? (it doesn't, I've checked) 

 

 

I am 99% sure that it's showing up in all of your frames.  You don't see it in the single flat and single light because it's a really dim artifact and it's lost in the noise.

 

You see it in the stacked OIII image because your calibration is off.  If you look, you can see that all of the bright areas in your dark frame are over corrected in stacked image.  The amp glows on the right, and the two glows on the left side of the dark frame are plainly visible as dark areas in the stacked image.  The thinness of the line in the single dark frame is widened in the stacked image because you registered all of the lights in the stack.

 

So first off, you should look at your calibration method.  The first thing to do is to make sure that if you are using PixInsight that you uncheck the "Optimize" option in the dark calibration.  That one thing may make it disappear.  The next thing to check is whether or not you are double subtracting the bias.  The best way to calibrate an ASI1600 is to ensure that the light frames and dark frames are taken with identical exposure times, gain, offset and temperature.  Then, when you do the calibration, do not do bias calibration.  Just do dark calibration with (uncalibrated) dark frames.  Note that I've omitted flat frames from the description.  For them, just calibrate the flats themselves with either bias or dark-flats before you use them.  When the calibration is done correctly, that stacked OIII image will have even illumination all the way to the edges and into the corners (except for where the registration edges are, but they will be perfectly straight and parallel to the sides of the frame).  My guess is, that your line will be gone, too.

 

Another option is to just mark all the pixels in the line with a bad pixel map.  If you are dithering, this is pretty much guaranteed to work.

 

Finally, all of the above is just to help with many kinds of defects, normal and otherwise.  It will certainly address your specific camera - but I don't think that what you are seeing is normal.  It's definitely worth contacting ZWO to see what they have to say.

I do not have PI, but instead use APP for calibration and stacking. Up until recently it has seemingly done a great job for me with this, however now is really struggling to provide good stacks. I have not changed my method at all...which is a bit odd. Software doesn't typically start performing differently so I'm inclined to believe it's a "junk in - junk out" situation, but if you have any familiarity with APP I'd love some advice on properly calibrating within that software. I definitely do not feel I am getting the best results possible in that sense. 


Edited by JP50515, 23 August 2019 - 12:40 PM.


#8 OrionSword

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Posted 23 August 2019 - 12:47 PM

I have seen multiple striations and clouding in some Truesense 8300 sensors but they were there at first light and the sensor had to be replaced.  Flats show up sensor defects pretty well.  The diagonal pattern reminded me of a striation but in my case there were several.

Haven't seen them in CMOS sensors as yet.


Edited by OrionSword, 23 August 2019 - 12:48 PM.


#9 Anhydrite

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Posted 24 August 2019 - 10:44 AM

Could it be a small hair or spiderweb landed on the sensor?  Did you try to clean the sensor?

Definitely talk with the manufacturer.




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