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Author Topic: Need to clean motes on CCD sensor  (Read 2155 times)

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Offline konstantinos

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Need to clean motes on CCD sensor
« on: 10:18:55, 20 May, 2016 »
Hello
 
I would like your expert opinion with a problem I have with my SBIG ST2000XM astronomical camera.
The camera has the CCD chip Kodak KAI-2020M +
 
My problem is that the CCD sensor is full of motes.
I have tried many times with a blower and a small brush to clean it but the motes still remain.
After blowing and using the brush I have noticed the motes change position but they still remain on the CCD sensor.
I am not sure if they are caused by dust or humidity on the sensor.
 
I send you an image I took with my camera to see the motes.
 
Could you recommend the best way to get rid of these motes?

I am asking this question because this is what I have done
 
Open the camera for the first time. Open the CCD sensor chamber. Use a blower to remove any dust from the surface.
Close the sensor chamber. Put back the filter wheel. Camera ready. Take a flat frame. The frame looks very good all clean.
 
Then after some time without opening the camera again, I noticed these motes on my flat frames. Could these motes be caused by the humidity entering the CCD sensor the first time?
And for some reason the desicant has not absorbed the humidity or they are dust motes indeed which remain due to static electricity and have entered the sensor I don't know from where..?

For your reference this is what SBIG recommends
https://www.sbig.com/site/assets/files/18147/cleaning_20ccds1.pdf
 
Thank you

Offline Roger B

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Re: Need to clean motes on CCD sensor
« Reply #1 on: 10:41:33, 20 May, 2016 »
First thing I'd say is DO NOT USE a compressed air can,  These things spit fluid.  Also I wouldn't use isopropyl alcohol neat on a CCD it approx. 98% pure alcohol,  I've seen this strip the silvering off a mirror before.   

If you do open the ccd chamber to clean the CCD itself, I'd then put it somewhere dry like a airing cupboard afterwards in a sealed container to make sure no moisture is present.   

I can't really recommend on cleaning a CCD surface itself as I have screwed one up before.  All I's say is does the manufacture  do a "service" if they do then to be safe send it back for cleaning.

Rog
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Offline chris.bailey

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Re: Need to clean motes on CCD sensor
« Reply #2 on: 10:49:39, 20 May, 2016 »
They look too big to me to be on the sensor or its cover slip. I would think most likely they will be on the chamber glass. Dust on the sensor tends to be very small irregular shaped and very dark specks covering a few pixel sites.

It is virtually impossible to get rid of every last speck of dust outside of a clean room environment and static build up on the glass surfaces is a magnet. There is nothing in the image above that flat calibration frames won't get rid of.

Chris
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Offline ngwillym

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Re: Need to clean motes on CCD sensor
« Reply #3 on: 14:28:14, 21 May, 2016 »
This can help to figure out exactly where the dust is:
http://www.ccdware.com/resources/dust.cfm
Neil G
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Offline konstantinos

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Re: Need to clean motes on CCD sensor
« Reply #4 on: 07:01:21, 24 May, 2016 »
Hi

I have good news this time!

I continued my experiments to clean the camera.
This time I used these glasses wipes from Lidl (cost 1,11 Euro)
https://www.pentaxuser.com/images/comment_pictures/20982/20982_1423777878.jpg
and a mobile phone monitor tissue.

Use a W5 glasses wipe first and wipe gently on the surface then immediately use a mobile phone monitor tissue to absorb the moisture.
I did this on the CCD sensor surface and on the chamber glass window.

Then I took flat frames with the camera connected to the FLAT BOX only and bingo!!! The flats look very good now the dirt has almost gone.
But as you can see there a few motes just a few. These dust motes are not on the CCD sensor surface but on the the chamber glass window. It's easy to see this because they are big in size, not black in color and they are not focused.

See the camera flats here: https://www.dropbox.com/s/sq5gdb48i54elds/FLATS_camera.zip?dl=0

After that I connected the camera to my two telescopes one each time and took a flat frame.
Both telescopes show the same dust motes and in same position.

Vixen ED81s flat: https://www.dropbox.com/s/07h79ic9zmetzhj/FLAT-LUM-telescope-VixenEd81s.jpg?dl=0
Vixen VC200L flat: https://www.dropbox.com/s/dg9my8slmc7mabm/FLAT-LUM-telescope-VC200L.jpg?dl=0

My experiment proves that there are some dust motes on the the chamber glass window.
It seems difficult to remove them due to the fact that static electricity attracts them like a magnet.

I will need to repeat the cleaning process only to the chamber glass window.

Hopefully my problem will be completely or almost solved after that :)

Offline Einari

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Re: Need to clean motes on CCD sensor
« Reply #5 on: 08:16:26, 24 May, 2016 »
Eventually there will be dust motes again so have to do it again - or like Chris said " There is nothing in the image above that flat calibration frames won't get rid of".
So taking/using flats is the easier solution to get rid of them.
Tapio

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Offline konstantinos

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Re: Need to clean motes on CCD sensor
« Reply #6 on: 08:05:05, 25 May, 2016 »
Hi

My assumption was wrong. The dust motes were not in the chamber glass window but on the surface of the CCD sensor.

I tried to clean again the CCD sensor and now almost all the dust motes are gone as you can see in the attached flat frame.

The flat frame was captured with the camera attached to my telescope Vixen ED81s.

Here's the latest flat frame: https://www.dropbox.com/s/e8cu002pybqkvmr/new-flat.jpg?dl=0

You can compare it with the old flat frame with this setup:  https://www.dropbox.com/s/07h79ic9zmetzhj/FLAT-LUM-telescope-VixenEd81s.jpg?dl=0
But unfortunately the sensor is scratched now in the top left corner you can see the black line.

I would like to ask you if this is a big problem or this scratch can be removed after calibration of my light frames with the master FLAT frame.

Thank you

Offline Einari

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Re: Need to clean motes on CCD sensor
« Reply #7 on: 08:25:54, 25 May, 2016 »
That's not necessary a scratch - might be a hair also.
Tapio

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Offline konstantinos

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Re: Need to clean motes on CCD sensor
« Reply #8 on: 09:01:50, 25 May, 2016 »
I will check the ADU value in the defect. I guess if it reads 0 then it must be a scratch on the CCD sensor.

Offline chris.bailey

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Re: Need to clean motes on CCD sensor
« Reply #9 on: 09:19:52, 25 May, 2016 »
To start I would not have used either of those products to clean a CCD of mine! 1 Euro lidl spectacle wipes to clean an expensive CCD camera!

I had a water mark on the corner of my 383L from condensation and had no option but to clean it. I used individually sealed sensor swabs and Eclipse fluid. Each swab was only used for one wipe over the surface and then discarded. I suspect some of the diagonal marks you are seeing now are fluid residuals.

I am with Tapio, I suspect that to be a hair or a fibre from one of those cleaning cloths. It is quite dark so using flats may not fully correct for it. If you do have another go at cleaning it, do yourself a favour and spend 20 Euros on some safer cleaning products.
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Offline ChrisLX200

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Re: Need to clean motes on CCD sensor
« Reply #10 on: 11:41:48, 25 May, 2016 »
Yes it looks like a fibre, and it's not sitting flat on the face of the sensor (they rarely do) but probably one end is just stuck to it.

When I had this job I used a photographic puffer brush attached to a length of silicon tube, the other end of the tube I poked into a vacuum cleaner hose. That provided constant suction - but I kept the vacuum cleaner itself as far away as possible from the working area (acutally, outside the room with a partially closed door!). Gently brushing the sensor releases the particles and the air sucked everything out of the way. Brushing alone without the suction tends to merely re-distribute them, and static makes them immediately re-attach someplace else. Wiping isn't much better (with dry dust motes). Using wet cleaner is the last resort - only where you have a definite stain (from condensation etc.,) and is a seriously tricky job. These dust motes are dry though and should be removed by suction once released, so try that method first.

ChrisH
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Offline Nomis Elfactem

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Re: Need to clean motes on CCD sensor
« Reply #11 on: 13:51:43, 25 May, 2016 »
Yeap, that's almost certainly a hair and has come from the cloths you're using.

As Chris says, get something like Baaders optical fluid and use that.  Then before reassembling it use a rocket bower or the like to blow anything that's left away.

Good luck
S.
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Offline konstantinos

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Re: Need to clean motes on CCD sensor
« Reply #12 on: 20:49:50, 25 May, 2016 »
Hi

I have measured the ADU value inside the area of the streak and as you can see it's about 31,000 ADU

This proves is not a scratch on the CCD sensor. Maybe the streak is a kind of salted substance on the surface of the CCD sensor.

This could explain why it always remain still despite the methods I have used to clean it (cotton swabs, microfiber tissue, blower).

If this is the case what is the most effective method to remove salted substances from the CCD sensor?

And here's the original flat FIT as requested: https://www.dropbox.com/s/tcezzncsz9ihlzs/streak.fit?dl=0

Thank you

Offline konstantinos

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Re: Need to clean motes on CCD sensor
« Reply #13 on: 06:30:42, 27 May, 2016 »
Hi

Time now for more professional cleaning solutions. Hopefully the streak on the CCD sensor will be gone.

Otherwise I will have to live with it.

Offline Einari

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Re: Need to clean motes on CCD sensor
« Reply #14 on: 10:24:24, 27 May, 2016 »
You have to live with dust motes as they will be back eventually.
Tapio

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