Misting and condensation on the optical window
Category: Astronomy Equipment
Posted by: Tom How
The weather finally decided the clear a couple of nights back- clear skies and no moon! Whatever next? Unfortunately it was very cold and a school night, so not perfect for revisiting astronomy for the first time in months.
Most of the kit actually worked, but the extreme low temps - around minus 6C, gave some problems with the camera. The Artemis camera doesn't have setpoint cooling, it just cools as much as it can below ambient. Of course, ambient was rather chilly, and the extreme cooling was causing condensation to form on the outside of the optical window in front of the camera - making imaging impossible.
My single dew heater was busy trying to keep the SLR lens dry, so I had nothing to attach to the camera to help warm it up - in the end I had to give up - annoying, but we'll cope.
Today I've made a 5 watt resistor band which I have taped around the camera to give a small amount of warmth to that area of the camera body. This should just be enough to warm the optical window and prevent dew forming on the optical window of the camera.
Dew on the optical window is particular bad for Ha narrowband imaging, as water absorbs at those vital longer wavelengths.
I'm going to test this now - hopefully things will stay dry.
The molecular seive drying agent inside the camera has worked very well - even after 6 weeks in the damp shed, the camera didn't have any moisture or dew or ice forming on the CCD sensor.
Most of the kit actually worked, but the extreme low temps - around minus 6C, gave some problems with the camera. The Artemis camera doesn't have setpoint cooling, it just cools as much as it can below ambient. Of course, ambient was rather chilly, and the extreme cooling was causing condensation to form on the outside of the optical window in front of the camera - making imaging impossible.
My single dew heater was busy trying to keep the SLR lens dry, so I had nothing to attach to the camera to help warm it up - in the end I had to give up - annoying, but we'll cope.
Today I've made a 5 watt resistor band which I have taped around the camera to give a small amount of warmth to that area of the camera body. This should just be enough to warm the optical window and prevent dew forming on the optical window of the camera.
Dew on the optical window is particular bad for Ha narrowband imaging, as water absorbs at those vital longer wavelengths.
I'm going to test this now - hopefully things will stay dry.
The molecular seive drying agent inside the camera has worked very well - even after 6 weeks in the damp shed, the camera didn't have any moisture or dew or ice forming on the CCD sensor.
