Electrical modifications and construction of electrical accessories can
be dangerous. Do not attempt such activities unless you are qualified
to do them
safely, without injury to yourself or your property. Anyone
not qualified for these activities should secure the help of a
licensed electrician. It is always recommended to consult with the
appropriate manufacturer prior to modification of any equipment, as
this may void warranties and/or alter the
Eyepiece Dew Heaters
and eyepiece dew
will cost about $50-$70, depending on the model and electronics
options. I made mine from a pair of battery operated
hunting socks that I purchased from Cabela's
about $25 (below left photo). I used components from this sock
because it uses a
low amperage to eliminate the possibility of electrical shock.
Each sock contains a 10 cm strip of
coiled, high resistance wire (most likely nichrome wire,
but I'm unsure
about this) in each toe. The wires were easily removed
damaging the socks, and the socks were retained for cold starry nights.
The high resistance wire is packed in cloth tape and insulated on one
side (below right photo).
I set one of the two heating wires aside and did not remove it from the
cloth tape (this wire was used for the eyepiece dew
I carefully removed the other resistance wire from its cloth
packing (this wire was used for the Telrad dew heater). The below left
photo shows the resistance wire after removal of the cloth tape. The
below right photo shows the same wire after straightening, re-soldering
to the copper wire, and insulation of the soldered connections with
I cut a small piece of 3mm polycarbonate to
the same width as the Telrad window. I filed two grooves into the
polycarbonate and glued the wires into place (below left photo).
The below right photo shows how the heating element installs
the Telrad. The heating wires are bent upward, so they give direct
contact with the glass Telrad window. I will probably purchase a small
clamp to clamp the polycarbonate strip against the top of the Telrad
window. Total fabrication time was only 1-2 hours!
Following are a few additional photos that show the heating element
installed in the Telrad.
The eyepiece heater is much simpler. The resistance wire that was not
removed from the cloth tape is just wrapped around an eyepiece. The
below left photo shows a first test. I will insulate the side
facing away from the eyepiece, pack the resistance wire in a
waterproof-electrically insulated outer shell, and add some Velcro to
make attachment to
the eyepiece easier. Alternatively, this resistance wire could possibly
to make a secondary mirror heater. The below right photo shows the
and eyepiece dew heater system. Only about 1-2 hours fabrication time
and approximate cost $25.