John Hayes:
Now I'm really puzzled. The camera has worked just fine for the last two nights. If it weren't for the fact that the problem went away on the first night after we swapped cables, I would conclude that the camera window had frosted over. This camera might be old enough to require a new desiccant pellet and if the humidity were sufficiently high, frost could have formed. I don't know. I didn't mention that when I was first having the problem, I slewed over to the moon and took a few images, which were sharp enough to rule out frost. If it keeps working, I'm ok with that but this problem will be in the back of my mind going forward. Weird.
John
The camera has no desiccant pellets inside of the chamber, just the desiccant tube you thread into the side of the camera body. If that isn't installed, I would get it installed. If it is instated, I would have the local team dump and fill the tube.
First, don't open the seal to the drier tube port unless you definitively establish that fogging is the issue! And John's response seems to indicate that it is not.
I have a QHY camera that works the same way and did not interpret the use instructions of this drying tube to be a permanent installation. First of all, my camera has never required that I dry it in the 3 years I have used it, and I live in the Pacific Northwest. Very much unlike my ZWO camera! Maybe I got lucky and the QHY is just better sealed than the ZWO. Maybe my QHY camera is also a rare such example. Installing the drier tube requires the breaking of a seal to remove the plug and then creating a new seal with the drier tube. Should be straight forward, but if fogging really is not the issue, the last thing I would do is break any seal on a camera that is dry, even a seal that is meant to be accessed. Working at high elevation in Chile, in one of the driest locations on the planet, I would not be looking at this issue as a problem, except as you (John) have quickly and simply done. The other thing is that just because these cameras can be cooled to 40-50 degrees below ambient, it just seems foolish to push the limit as seems to be so commonly done. I suppose its just cool to be "cool"! The most important issue is camera temperature stability. Maybe the holiest of astrophotographers just cannot get by without subs that are done at -40C, never mind that darks, etc. and software take care of these issues superbly.
I could see leaving the drier tube installed if I had a remote observatory and I had a fogging problem and there was no one around to bump and bend the damn thing sticking out in a prime location for damage. Also, if your camera's seal is not great and actually needs a drying tube to be permanently attached, then it is likely the small amount of dessicant it holds will not last for very long and you will need to go and replace it. Also, most dessicants which have a decent capacity also are rather poor at dropping RH in the chamber to very low levels. Drierite, calcium sulfate, on the other hand is able to dry to very low partial pressure, but suffers from low capacity. It is also a dust generator, and I would never use it in such an installation without including a fine filter between the dessicant and the camera chamber.
