Sponsored By:

Subject: Re: LX200:Dew Prevention/Finder Mount
From: Brandon Jones
Reply To: mapug@shore.net
Date: Mon Jun 10 02:14:17 1996

> finder's objective? How should I heat the eyepiece(s) (35mm Panoptic to 12mm
> Nagler), resistors around the 2 inch Meade diagonal, around the eyepiece? Will
> the 1A Skylight filter I use for a dust seal on the end of the OTA also dew, if
> Thanks,
> Bruce Miller

I had problems with the 2 inch mirror diagonal dewing out in its
center.The other problem with this was the diagonal body,especially
if you grab it with unprotected hands when it is at a temperature of
-10 deg C .It is a big chunk of very cold metal.I cured this by
making my own heater using a piece of aluminium plate cut to
the size of the back of the diagonal.
The plate was one sixteenth of an inch thick.
The screws on the back of the diagonal are long
enough to fix the plate to the back and hold it down after drilling
four matching holes in the plate. Onto the plate
I glued two ceramic resistors of value 47 ohms and connected them in parallel
electrically to give 23.5 ohms.
Over the top of all this I fixed a small plastic box held into place by
one metal pillar fixed to the plate by a countersunk screw.
Into the side of this box I fitted a panel mounting 2.5mm power
connector as used on the rest of the LX200 power cord connector
this was connected to the ends of the resistors.This gives about
six watts on 12 volts and appears to work ok in my climate.
My corrector plate heater is 3 metres of 22swg nichrome
wire wrapped around and glued to the base of the dew shield.
again connected with a similar connector.This for a 12inch
gives a max of 18 watts and two switched lower power levels
of 9 and 12 watts approx.Even though this would be difficult
to power in a portable application it has cured all of my
dewing problems in a fixed site permanently mounted
set up.

Brandon S.Jones