My astronomy project:
Sensor dryer stains

Contents:

1. Dryer stains
2. Sealing the chamber and desiccant
3. Three nights outdoor tests
4. During work

Note:
I take no responsibility or liability for what are written here, you use the information on your own risk!

1: Dryer stains

You may also have noticed that you get these dryer stains on your camera sensor, especially if you have a DSLR camera. It's not dust, dust are more often banana shaped and easy to blow away. After I had cleaned the camera sensor from these dryer stains it only last for one night. After I take the camera indoors again it start to collect new dryer stains when it heat up to indoors temperature. About 10 new stains for each night. Is there a way to avoid these stains ?

Camera sensor:

This is how it could look like, new dryer stains came visible with old flat calibration files. Of course I can take new flats every night, but even better if I don't get these dryer stains in the first place.

I will try two of these three different approach to fix this moisture problem:

1. Close the chamber between the lens and the camera, then put in some desiccant in that space.
2. The opposite way, open the chamber to get better ventilation, maybe a fan too
3. Set some overpressure in the chamber with dry nitrogen gas

Desiccant:

Desiccant is used where you want to absorb moisture, in this case the space between the camera and the lens. These desiccant bags are of silica gel type, the most common. The space between the camera and lens are not perfectly sealed from the environment but to some degree. I have no idea if this will work but it's relatively easy to do a test.

Note: "Do Not Eat"

More to read about desiccant:

• https://en.wikipedia.org/ wiki/ Desiccant (Wikipedia)

If the silica gel are of reuse type. They can be dried by heat, at 60^o C for six hours, or at 120^o C for 2 hours. Higher temperature destroy the silica gel. Some say it can be dried it in the sunshine a dry day. Other use the microwave oven at medium power for five minutes, maybe the microwave oven should not be used for cooking after this. Read the instructions of your desiccant carefully.

This is said about silica gel and absorption:
"Silica gel can absorb upwards of 40% of its weight in water vapor at 100% humidity, and can reduce relative humidity (RH) in a closed container down to below 40% at any temperature in its range, until it is saturated." Ted Pella

The silica gel bags above weights 10 gram each.