Air Dryer for the DSI
It always seems that when you solve one problem another one seems to crop up. Such is the case with my water cooled system for the DSI II Pro ( dsi_cooler.htm ). The cooler works great, to good, usually within minutes the chip gets all fogged up.
After investigating different desiccant systems I thought there has to be a better way. The problem with desiccant is that it always has to be replaced or recharged. And it can be rather expensive. The question was, what do I have to do and what do I already have in place.
What do I have to do? Defog (or defrost) the chip. What do I have? A cooler with ice water in it. So, I thought about how an automobile defrosts the windshield and took note that usually the air conditioner works at the same time to not only cool the air but also to take some of the moisture out of the air at the same time. This improves the efficiency. In seeing what happens when the cooler runs for a while, I noticed that the camera and cooler body got covered with heavy condensation very quickly. So I thought of an easy system to dry and circulate the air in and around the CCD chamber in the DSI II Pro. Why not defrost the chip with cool dry air. So here is how I do it, on the cheap!:
I thought of a canister that I can run air through that would be filled with a material that could cool and condensate the air as it was pumped through. Notice below.
This is a half gallon 'Ball' canning jar. Two holes are drilled into the top to accept a 'press fit' silicone aquarium air hose. The hose that is hooked up to the aquarium air pump goes down into the jar close to the bottom. The second air hose is inserted just below the lid and goes to the camera.
Now for the 'desiccant'. Seeing how my camera and cooler body would get just obliterated with moisture, I figured that anything that would get real cool and have a lot of surface area would extract moisture from the air. A supervisor at work who I discussed my problem mentioned a rather unique material. Aluminum pellets (look below for alternatives). They look like this:
These cooled in the jar do a very good job at cooling and condensing the moisture out of the air. So the setup with a aquarium air pump looks like this:
The jar is inserted in the cooler that is filled with ice before the imaging session. The air is pumped from the pump down through towards the bottom of the jar. From there it makes its way through the pellets, cooling and drying till it gets to the top and then out to the camera. I have used the jar after many consecutive nights even though water has collected at the bottom. When storing, I put the jar in the freezer so it is already chilled when it goes into the ice chest. When there is a break because of clouds I dump the pellets out to dry. Once dry, I put them back into the jar and then into the freezer so as to be ready for the next imaging runs.
A 3/16" hole was drilled in the back side of the camera body and it would except a standard aquarium air hose fitting that you get at the pet store with one of those 'air stones'. This feeds the back side of the DSI with the dry air. Getting it to the front of the chip is a different matter.
As it turns out the circuit board helped me out. The board is perforated on the sides of the chip. Note below:
What A break! So, air comes in the back and can go through the back of the board near the chip. Now all we have to do is let it escape by the chip and through into the CCD chamber.
The DSI comes with a full gasket that seals off around the front of the CCD chamber. What I did was get some gasket material of equal thickness and just make two halves for the top and the bottom. One might think that you can just eliminate this gasket but I believe it is necessary to ensure that the CCD chip presses firmly against the cold finger. But, this now allows dry air to purge onto the CCD from the sides.
I run this continuously. There is just a small stream of cold air. It has worked flawlessly over numerous times now. Since the whole backend of my setup gets chilled down close to 0 degrees C, when I take a filter out from my manual filter changer, it fogs up immediately. But as long as it stays in, it is nice and clear.
Alternative materials for desiccant.
The aluminum pellets are something that most people won't have access to. I am not really sure where to get them either. Anything that you can think of that could condensate moisture could work. Bee bee's, ball bearings, marbles etc. Something that does not rust would be preferable. Experiment and see what you can come up with.
Air pump: $9.00