DSLR Cooling - Condensation Prevention

[glend (Glen)]

Condensation is an issue for cooled DSLRs; it doesn't matter if it's in a cooler box or has a cold finger, internal condensation and/or filter fogging can happen. Management through measuring humidity, watching dew point, desiccant plugs/bags, filter heaters, has been the normal approach.

Here is a workable solution that I have found for stopping condensation inside a cold finger cooled Canon 450D, and it should work for cooler boxes as well. It involves replacing any air carrying moisture with an inert gas (Argon in this case). Argon is a gas used in welding as a shield gas to prevent oxygen from reaching the weld spot. Argon is heavier than air, and will displace air. Argon will not carry moisture.

The photos below show the simplicity of this solution. All that's required is a disposable Argon bottle ($38 from Bunnings), a disposabe gas bottle regulator to control the flow, and a length of cheap hose to deliver the gas into the camera (or cooler box).

On my Canon 450D, I have drilled a small hole in the side panel near the USB connector (the space behind this hole is vacant to the centre of the camera and provides a good pathway for the gas). With the camera positioned as per the photo, the tube is inserted into this hole and the regulator turned on just enough to get the gas to flow - you don't want to blast it out. If you can feel the gas against your finger then that's good enough. As Argon is heavier than air it flows like a liquid (that you can't see) so holding the camera in that position will keep the Argon inside and not let it flow out. You need a way for the displaced air to get out of the camera so a vent is required, in most cases with a cold finger there will be some open space around the connector board and this will be ok. The actual free airpace inside the camera is pertty small so it doesn't take long to fill it with Argon. Remove the hose and tape over the fill hole and the vent space with duct tape. You can tape over the battery compartment door as well. Don't worry too much about the camera panel seams, the Argon will fill the internal space for hours and if it does flow out it will be trying to get out the downward side (gravity remember) because it is a heavier gas.

Lastly, turn the camera on its back and remove the T-thread adaptor, coma corrector, flattener etc and fill the front of the camera with Argon as per the photo. Put the adaptor/corrector back on the camera. This will prevent any fogging of the inside glass of the corrector/flattener/filter that you may have on the outside of the shutter curtain. That's it. You could store your camera/cooler inside a large ziplock bag and it should be fine for days.

The camera should be condensation free (internally) for a night of imaging with the cooling running. I can't guarantee it but in my testing it has worked for hours of imaging below dew point, been left overnight and when I opened the camera back the next day there was no evidence of internal condensation. I can't say how long it will be good for but I am aiming to refill the camera with Argon before each imaging run.

Just a final word of caution concerning using Argon in this way. As Argon is heavier that air, it is important that you don't breath it into your lungs (especially those idiots who think they will change their voice trying that) , it will settle in the bottom of your lungs and is hard to get out. There is an old story about welders being held up by their feet to drain argon out of their lungs. In daily use for this purpose it poses no threat, if left open the gas will just flow onto the ground.

I will have an update on this solution, and gas bottle longevity, after my next trip to the dark site. So far so good.

[ZeroID (Brent)]

A cunning plan, a plan so cunning you could fill it with Argon and it would never freeze.

Clever to say the least. Given me a few ideas. I'll have to go see if our Bunnings has argon available, I confess I have never even looked for it previously.
I'd fill the bottom of the focusser tube on the Lunt when I am chilling the ZWO. Better than using warm air across the window.

[rcheshire (Rowland)]

Sensational! Time to work on sealing the camera. Argon has been an obstacle because of leakage, and basically, I didn't trust it to be reliable for the application, thinking sealed CCDs. The simplest way is as you say, to seal all of the camera, as much as possible - thinking a shrink wrap bag? Access to all the buttons and the on off switch with a bit of a push.

[glend (Glen)]

A quick search on ebay uncovered a number of SLR dry bag options like this:

http://www.ebay.com.au/itm/DSLR-SLR-...-/321146596462

It would need to be modified but they are out there and pretty cheap.

Even cheaper would be a simple food grade ziplock bag modified for the purpose.

[sharpiel]

Cold fingers now look much more sustainably viable. Good thinking there...