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Old 18-02-2011, 11:57 PM
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[1ponders] (Paul)
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Solving SBIG frosting issues

I've had an ST-7 for a number of years now and I've avoided using it because of frosting issues. No matter how many times I charged the desiccant plug as soon as I started to go below 0 deg the chip would frost up (funnily enough not the guide chip) and it would take a long time to sublimate off. Consequently I hardly ever used it for the purpose it was bought for, variable star measurements.

I had thought of trying to dehumidify the chamber before putting the plug in but I couldn't think of a simple way to do it. Well I had a bright idea the other day (well for me that is), what if I were to put the camera in a plastic bag with zip lock, along with a closet camel and seal the bag over night. I could then charge the plug in the oven, wrap it in plastic to keep it dry over night and the next day crack the plastic bag and slip my hand inside and screw in the plug.

The plastic bag I used was one of those vacuum storage bags. I didn't vacuum it because i figured that if i did, when I cracked the bag humid air would enter and defeat the purpose. So I just squeezed most of the air out to reduce the volume, sealed and left it over night with camera and camel inside.

After putting the plug in I switched on the camera and turned up full cooling to quickly reach -8 deg. Not a sign of frosting. I am one happy chappy I'm still to check it after a day or so but if you are having the same issue this solution seems to work a treat.
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Old 19-02-2011, 02:25 AM
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Octane (Humayun)
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Excellent!

Thanks for the heads up, Paul.

I haven't experienced this issue, as yet, but, then again, I've only used my camera for six nights to produce one image!

H
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Old 19-02-2011, 05:23 AM
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When I first got my sbig I thought I had the same problem. I baked the dessicant, placed it back in the camera, and still had frosting issues. What I found is that The dessicant had to be back in the camera for about a day before the frosting stopped.

Nice tip with the closet camel.

Brett
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Old 19-02-2011, 07:11 AM
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[1ponders] (Paul)
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Cheers Humayan. I hope you dont. But I believe that the problem was mostly solved with later cameras.

I originally checked the yahoo SBIG group and here Bert and that was the info I got as well, "should be fine in a day or two". But even after a week there was no difference, the camera would frost up.

Part of the initial problem was the large rubber ring under the front plate wasn't seated in its groove properly and part of the ring was protruding into the chamber so air could get in and out. So that every time I chilled the camera it would suck fresh air in as the internal volume of air would decrease due to reduced temp. I was sent some new rings and it didn't fix the problem. I'm really hoping this is a permanent fix.
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Old 19-02-2011, 07:38 AM
Doomsayer
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The Particle Wave Tech rechargeable dessicant plugs for ST cameras work well - provided you get a good seal to the chamber. The SBIG ones can only take so much baking if they are subject to repeated moisture. So far my STL camera has only required one baking session - PWT don't seem to make them for STL cameras though.
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Old 19-02-2011, 07:49 AM
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[1ponders] (Paul)
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Quote:
subject to repeated moisture
that was one of the frustrating thing about it, the camera was always stored in its pelican case with gel packs. If this doesn't work then the only thing I can think of is that the chamber itself (apart from the plug seal and the face plate seal) wasn't sealed properly during manufacture
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Old 19-02-2011, 08:08 AM
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JohnG (John)
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I always run the camera at 0.00c for about an hour or so prior to lowering the temp, I find that stops any frosting, works quite well on the ST2000XM which I found was prone to a frost buildup.

Cheers
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Old 19-02-2011, 08:14 AM
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[1ponders] (Paul)
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If it happens again John I'll give that a shot. thanks

Hopefully though I've solved it.
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Old 19-02-2011, 02:01 PM
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I would suggest a better method, and its what i do when ever i crack open a CCD chamber seal.

Grab a large plastic Zip lock back, large enough to be able to manipulate the parts from the outside.

Next place the camera with the chamber open (CCD Exposed), and any other parts needed to seal the camera inside the bag also.
Then Remove as much air as possible by Sqeezing out all the air.
Next, go visit a Panel beater (Car Crash repairers) or someone that has a Mig Welder, give them 5 or 10 bucks, and get them to fill the bag with Argon (Used with Mig welders). To do this, open up the bag slightly, just enough to get the nozzle inside the bag, then get him to fill the bag up, and allow it to overflow (Bag expands to max) for a few seconds. To help remove the little air left inside, sqeeze the bag a few times to push out the air/argon mix already inside.
Then make sure to only fill it to 1/3 and no more, then reseal it by zipping it tight again.
The reason for only 1/3 filled, is so you can grab/handle the bits inside the bag to reseal your camera.
Once its all sealed up, thats it. Your camera is now Argon charged, and will help heaps.
Its not just the Sbigs that have this common issue. So there is quite a bit of info out there about remedies..
But my method is the best way to gas fill your camera.

Theo
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Old 19-02-2011, 02:31 PM
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[1ponders] (Paul)
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Thanks for that Theo. If this doesn't work, or next time I have to charge my plug I'll certainly give that one a go.
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Old 19-02-2011, 02:55 PM
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bert (Brett)
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That is very interesting with the argon.

I have a mig Welder (btw tig welders use argon as well) and there are different types of argon. A cheaper version welds only mild steel and another is used to weld mild steel and aluminium. I wonder if it ok to use both argon gasses?

I might give it a go next recharge. Atm I get one year out of a rebaked dessicant plug.

Brett
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Old 19-02-2011, 03:02 PM
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[1ponders] (Paul)
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I have a sneaky suspicion that maybe my chamber isn't properly sealed. There is no way i would get a year out of a plug.
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Old 19-02-2011, 03:20 PM
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Do you put the dummy plug in the hole when whist you are baking the dessicant?
If the camera is open to air for a reasonable time then water is absorbed into the printed circuit boards and it takes a couple of dessicant recharges to get it dry.
If you are using the dummy plug and there is still a problem with moisture there is almost certainly a leak.
You then take the front off the camera and reposition the O ring seal. After this you recharge the dessicant a couple of times and it should remain dry.
My ST9E lives in the open and never goes back in its pelican case. I make it go straight to -20 from ambient and only need to recharge it about annually.
My ST10XME is even better and I have only ever recharged it once since owning it.
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Old 19-02-2011, 03:25 PM
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multiweb (Marc)
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With my QHY8 I use a sealed pelican box. On one side I have the camera open and on the other compartment I place the dessicant heatbox still warm. I think the difference in temp helps in sucking any remaining bit of moisture out of the camera body. I do that religiously after each imaging session.
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Old 19-02-2011, 03:48 PM
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Hi Terry, yes I do use the dummy plug when baking normally. I'm hoping this technique of leaving it sealed in the bag with the plug chamber open and with the closet camel in there will take care of any remaining moisture in the chamber and circuit boards. I'll leave it in the bag with the camel for a few days to make sure.

I've had the cover off a number of times over the past few days. There have been shadows and marks on images that could only have come from the chip itself. I've cleaned the chip and I've also smeared the large O ring with a very light smear of supa-lube to help seal the chamber.

I've also noticed at the bottom of the desiccant plug chamber there is some sort of white soft sealant (?) around the the junction of the walls and base of the plug chamber. I've re-smeared this sealant around the junctions to make sure they're well covered.

Thanks for the idea Marc. With the problems we've had with humidity lately I'm going to build a sealed cupboard to keep optics and cameras in the keep closet camels in there and change them regularly. Heating it may even be an option. Its not just cameras that are suffering atm. Even though its always sealed with something in the focuser, my WO 72 has fungus starting on the inside of the lens. Its not been very good weather anywhere lately for astronomy gear.
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Old 19-02-2011, 07:31 PM
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There is suppose to be an O ring under the dessicant. Is it present?
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Old 19-02-2011, 07:35 PM
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Quote:
Originally Posted by bert View Post
That is very interesting with the argon.

I have a mig Welder (btw tig welders use argon as well) and there are different types of argon. A cheaper version welds only mild steel and another is used to weld mild steel and aluminium. I wonder if it ok to use both argon gasses?

I might give it a go next recharge. Atm I get one year out of a rebaked dessicant plug.

Brett
Any (non explosive) dry gas will work.
My old home made CCD leaked and I use to fill it with N2 using liquid nitrogen that I had a ready source of at the time. It kept it very dry.
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Old 19-02-2011, 08:17 PM
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I used my QHY9 for the first 12 months with no sealing faceplate. I'd religously put the filterwheel and camera into separate ziplock bags with dessicant after each imaging session, then reassemble quickly before us. I've also been superstitious with bringing the camera to -1deg for at least 15-20mins before setting to -25. All this has worked well for me.

Went straight to -25 the other night and had a bit of frosting
QHY9 is pretty good with heater circuit around the main chip mind you.

I must try the argon one day though. Makes sense. Plenty at the lab, just have to figure out a way to get access to the plumbed lines.
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Old 19-02-2011, 09:15 PM
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[1ponders] (Paul)
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Quote:
Originally Posted by Terry B View Post
There is suppose to be an O ring under the dessicant. Is it present?
Yes Terry the O ring that goes over the nose of the desiccant plug is there
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Old 20-02-2011, 06:44 AM
Dennis
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Originally Posted by [1ponders] View Post
>snip
Thanks for the idea Marc. With the problems we've had with humidity lately I'm going to build a sealed cupboard to keep optics and cameras in the keep closet camels in there and change them regularly. Heating it may even be an option. Its not just cameras that are suffering atm. Even though its always sealed with something in the focuser, my WO 72 has fungus starting on the inside of the lens. Its not been very good weather anywhere lately for astronomy gear.
Hi Paul

Ouch re the WO fungus, that is most unwelcome news indeed and I feel your pain!

I relocated all my optical stuff into the spare room and use a dehumidifier throughout our humid summer months to keep the room at around 60-65% which if I use my camera and astronomy gear on a regular basis, seems to keep the fungus at bay.

I recently started keeping my EM200 in the room as I noticed fungus appearing on the reticule of the Polar Alignment Scope.

The water container in the dehumidifier has a capacity of 12 litres and during the worst days of the season, it can almost fill up in a couple of days.

Good luck – it is a battle worth fighting given the cost of our gear.

Cheers

Dennis

EDIT: Here is a link to a dehumidifier similar to the one we have:
http://www.delonghi.com.au/products/...sp?Model=CFO8E

Last edited by Dennis; 20-02-2011 at 06:52 AM. Reason: Added link to humidifier
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