I decided to make an internal dew heater on my DSI II Pro imager.
My DSI has a
homemade peltier cooling permanently attached.
It is also permanently fixed to my
homebrewed filterwheel.
Any dew heater added in the past has taken ages to be effective when
wrapped around the nosepiece (external) Even with Alfoil and
decent wattage thrown at the problem. Far too much metal is
heatsinking away the effectiveness.
So I decided to test a few ways to incorporate something internally to
what is my favourite camera.
I made two formers to hold resistors of various values in a circle, as close
as possible to the front window of the CCD. (PIC 1)
Firstly I tried an aluminium former, the idea being to wrap the risistors
on the outside of it in a shallow rebate and Araldite them in.
Conductive heat transfer was very minimal. Most of the heat was lost
by transferring straight to the backing mount of the filter-wheel and
then to the DSI casing metal and nosepiece.
So I tried a nylon former, the idea being to place the resistors INSIDE the
former and to radiate any heating effect directly into the CCD/ nosepiece
chamber (the chamber is sealed by the Baader filter in the end of
the nosepiece).
This worked extremely well. On a recent night with the CCD at 3.5C and
dewpoint at 11C , dew instantly formed on the chip.
When the resistors were switched on to my PWM 12v the dew was gone
in about 10 mins.
I then wound the PWM back to almost minimum to see if the dew started to reform.
No dew in 2 hours. This tells me i could probably feed in
6v to the PWM occasionally.
Steve