QHYCCD

Concentric ring due to frosting?

Concentric ring due to frosting?
« on: March 29, 2011, 11:10:12 PM »
Hello All,

I posted this topic on another forum:

http://www.cloudynights.com/ubbthreads/showflat.php/Cat/0/Number/4483434/

In short, I have a REALLY weird vignetting issue with a QHY-8L, that is imposing a "donut" in everything, including flats (which are then anything but flat -- see the images in the post above).

Post # 4 in the thread suggests that the TEC cooler may be causing frosting in the camera, and that I have a dessicant issue.

Could this be possible?  If so, how would one go about solving this issue?

Thanks for any feedback you can offer.

Jeff W
Reading, PA

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Re: Concentric ring due to frosting?
« Reply #1 on: March 29, 2011, 11:23:14 PM »
Hello,

     Please check if it is the ice problem. And check if it is on front of the optic glass window or it is on front of the CCD sensor. If it is on front of the CCD sensor  please use the dessicant tube to solve this problem.In software release board you can find QHY8L 's user manual and do it as it said.
     If it is on front of the optic windows. Please consider using the heater.

     
Best regards,
Qiu Hongyun

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Re: Concentric ring due to frosting?
« Reply #2 on: March 30, 2011, 01:56:55 AM »
Hi Jeff,

It looks to be as a moisture issue.
Looks like the CCD needs to be cleaned first.
Once you get moisture on the CCD, you need to clean it. Because it leave a thin residue on the surface, and will always show up on every power up.
So remove the cap of the camera, and use acetone and a soft cloth (Not Cotton swabs, etc), and gently wipe of the residue.
Then in front of a heater or hot air dryer, reseal the camera by placing the cap on tightly.

You shouldnt have any more issues.
The only other place to look for is the front of the glass filter/seal. This can be cleared by reducing the temp down by 5 deg C and recheking every 5 minutes to see if its cleared.

Theo

Re: Concentric ring due to frosting?
« Reply #3 on: March 30, 2011, 02:28:55 PM »
Hi Jeff,

It looks to be as a moisture issue.
Looks like the CCD needs to be cleaned first.
Once you get moisture on the CCD, you need to clean it. Because it leave a thin residue on the surface, and will always show up on every power up.
So remove the cap of the camera, and use acetone and a soft cloth (Not Cotton swabs, etc), and gently wipe of the residue.
Then in front of a heater or hot air dryer, reseal the camera by placing the cap on tightly.

You shouldnt have any more issues.
The only other place to look for is the front of the glass filter/seal. This can be cleared by reducing the temp down by 5 deg C and recheking every 5 minutes to see if its cleared.

Theo

OK, gentlemen, I *think* I have figured out what happened.... but will want your advice before trying to correct it.

Reading page 12 of the manual, I see:

Quote
Don’t put the glass window of the CCD upside down. Cold air will focus on the optic windows if it is upside down. It will cause lower temperature of optic windows.

Unfortunately, this has been my "standard procedure" during setup.  I would use eyepieces to align on stars, then attach the QHY to polar align via software, then switch back to an eyepiece to re-align on stars once polarly aligned, then reattach the QHY to image.   During the times the eyepiece and star diagonal were attached, I would stand the QHY up vertically, glass-down (to keep the glass from being exposed to dust) -- there is no lens cap that fits over a SCT connector.  I was also driving the cooler to its extreme once imaging began.

I *really* don't want to open the internal chamber and expose the CCD sensor to air (much less have to clean it) unless I have to.  Given the above, is it likely that my contamination is on the CCD sensor?  Or do I just (hopefully) have an issue on the OUTSIDE glass, which I'm much more comfortable cleaning?

On to heating.... I've looked at the M42->M42 heater you produce, and it comes with bare wire leads.  What should they be connected to?   Could I accomplish the same goal with a dew band connected to my controller, wrapped around the glass end of the camera?   That would allow me to control the temperature via the hub...



Thanks for steering me in the right direction....

Jeff W
Reading, PA

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Re: Concentric ring due to frosting?
« Reply #4 on: March 30, 2011, 04:42:53 PM »
A simple test on a table will determine if you need to clean the CCD sensor.
Its realyy very easy to clean it. Takes less than 3 minutes to do, and most of that time is scratching your backside !.
All you need to remember is to seal the camera over warm/hot dry air, like a heater or blow dryer (On Hot).
You can check with your local provider/dealer about the heaters, but the ones i supply, are already terminated with the DC2.1mm plug and i also supply a Spliter DC cable to power it up from your existing power supply. So you wouldnt need to cut or solder anything.

But all you would really need to do is just to reduce the temp a little anyway, and that should fix your issues.

Theo

Re: Concentric ring due to frosting?
« Reply #5 on: March 30, 2011, 05:12:27 PM »
Hi Theo,

I'll do a tabletop test later to find out, but now I'm suspecting the sensor itself is dirty/moist.

I've been leaving the camera attached to the scope for extended periods (weeks), without sealing it in with a desiccant.  I fear I've learned a steep lesson in putting it back in it's sealed, desiccant-containing box between sessions.

From what I've read today, that's a no no.  Many days to next clear skies, though, so I'll have time to dry it out.

I'll keep you posted....

Jeff

Re: Concentric ring due to frosting?
« Reply #6 on: March 30, 2011, 10:39:52 PM »
Hi Theo,

I'll do a tabletop test later to find out, but now I'm suspecting the sensor itself is dirty/moist.


That's affirm.   http://www.flickr.com/photos/41622748@N05/5575529277/lightbox/

If you look closely, you can see tiny beads of water forming just below the sensor, between the large yellow dots.  Similar condensation has begun on the top side of the chip, and I'm sure it will progress across the chip, perhaps moreso if it were cold and outside.

The above was taken indoors with the camera at -21C, in a room that was 22C ambient, after only 20 minutes of cooling.

Now, the $1,000 question is.... will using the desiccant tube be enough to dry it out to the point where this won't happen again?   Or will I have to crack it open and clean the sensor?

Jeff
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Re: Concentric ring due to frosting?
« Reply #7 on: March 30, 2011, 11:29:49 PM »
Hello,

       The QHY8L is designed to allow user open the CCD chamber to clean it. You need connct with the desicant tube then screw off the front part.  And clean it  You can prepare some silicon gel (should be unused new gel)
and installl into the dessicant tube following the user manual.

       After take the front part off .Please clean the dust and add some vaseline on the screw of the front part. This will keep the airproof after you rescrew on it.


Best regards,
Qiu Hongyun

Re: Concentric ring due to frosting?
« Reply #8 on: March 31, 2011, 12:28:29 PM »
Hello,

       The QHY8L is designed to allow user open the CCD chamber to clean it. You need connct with the desicant tube then screw off the front part.  And clean it  You can prepare some silicon gel (should be unused new gel)
and installl into the dessicant tube following the user manual.

       After take the front part off .Please clean the dust and add some vaseline on the screw of the front part. This will keep the airproof after you rescrew on it.


Best regards,

OK, cleaning is done.  I hope I didn't screw anything up!  It's now resealed with Vaseline, connected to the desiccant tube, which contains fresh silica gel beads, and is back in its airtight case with more desiccant paper.   Time will tell whether this resolves the issue.

However, while cleaning it, I noticed a rather large defect on the glass cover -- not on the sensor, but on the part that screws off.   I was unable to remove it with anything -- not even acetone.   What would I need to do to have a new "hood" shipped out, if it even needs to be?   When screwed on, the defect is over a spot *just* outside the rectangle of the sensor, on the long edge.  I couldn't get a good enough macro photo to actually show the flaw, but I've put an arrow onto a photo to show you where it is:

http://www.flickr.com/photos/41622748@N05/5577533322/lightbox/

Jeff

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Re: Concentric ring due to frosting?
« Reply #9 on: April 01, 2011, 12:22:01 AM »
If you need a macro to spot it, its not an issue, also if its out of the CCD path, its of no concern.

As long as the spots on the glass dont get too large, small spots, like dust, etc, wont cause much grief.

Theo

Re: Concentric ring due to frosting?
« Reply #10 on: April 01, 2011, 12:56:42 AM »
If you need a macro to spot it, its not an issue, also if its out of the CCD path, its of no concern.

As long as the spots on the glass dont get too large, small spots, like dust, etc, wont cause much grief.

Theo

This isn't dust.  It's a chip or flaw in the glass.  I estimate it is equivalent to at least a couple dozen of pixels wide.... and a re-examination shows it is just WITHIN the rectangle of the the sensor when tightened down.   It's just that my iPhone wasn't good enough to photograph it to show you here, nor was my digicam (15 MP, not a DSLR).  It's brutally obvious to the naked eye, though.  I suspect it it what is causing the "horseshoe" in the upper left of this:

http://www.flickr.com/photos/41622748@N05/5572625701/

Jeff

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Re: Concentric ring due to frosting?
« Reply #11 on: April 01, 2011, 04:33:31 AM »
No, the horse show looks like a piece of fibre. Because its thin and nearly in focus, it is more likely on the CCD itself. If it where further away, it would be just a shadow, like dust looking like donuts.

You can recheck now that you have cleaned the CCD.
If there is a shadow after the clean, then you have confirmed an issue.
But as i said, the CCD looked like it needed a clean.

Theo.