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Re: [APML] Home made Dew Shield?
>I was out on Friday attempting to capture some of the Perseids (well why
>not since they're here) and suffered from dew on the lens. I searched the
>web for hints on making dew shields but only came up with 'insultation'
>techniques and also one on hand-warmers...
Dew is never a problem at our Observatory. Over the years, I have made
numerous different optic heaters to keep dew from forming. What use is a
great night if your lenses have a coating of water on them?
You can try <http://www3.sympatico.ca/mark.kaye/dewheat.htm> for a
complete description on how to make a dew heating band. These tools are
extremely effective in keeping dew from starting to build up on objectives
of refractors or SCTs.
I do not have pictures on line of a heated dew cap. From my humble
opinion, one of the biggest problems encountered by SCT owners is the
corrector plate. It is bare faced to the sky, right there to collect stray
light and moisture (to say nothing of the occasional finger print).
Back in our SCT days, I made a simple dew shield from blue foamy camp
bed roll. I cut a piece to the circumference of the scope tube giving it
ever so slight a flare when it was rolled into a tube. I painted the
inside flat black and I mounted several one watt resistors that I wired in
parallel to give about twenty ohms total. These were mounted about five
centimetres up the roll so that the resistor was on the inside and I poked
the leads through to the outside so that they could be wired together. I
mounted the resistors so that they acted like a stop for the tube sliding
onto the end of the scope. This simple dew cap ended our moisture and
frost problems forever. It also noticeably helps with contrast in places
were stray light is a problem.
Clear skies!
MK
The Observatory by the Lake
http://www3.sympatico.ca/mark.kaye/
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