Dealing with dew

Ernie wrote:
Fall and winter in Vancouver are hard on this hobby, in more ways than
one. When it's not raining, I still have to deal with nights where the
humidity is constantly at 100%. Dew forms on everything, the eyepieces
and the finderscope especially.

Should I just be using this as a sign that it's time to go home, or
should I be using kleenex to wipe off the dew and keep going? I'd rather
not scratch the coating on the eyepieces, but I can't think of any way to
keep the dew away. The mirror isn't affected by the dew at all though, so
it's not like I'm doing anything nasty to the important optics.

No "kleenex" please.

If you don't want to invest the effort and time and money right now in a
full up dew fighter heater system, you can try a 12v hair dryer in the
interim to see if you really want to stay out on wet nights. Should be
available in an RV store - I got mine at a HW store - they are also
advertised specifically for astronomy with the usual 100% markup for
astro gear.

(Ernie) writes:

Fall and winter in Vancouver are hard on this hobby, in more ways than
one. When it's not raining, I still have to deal with nights where the
humidity is constantly at 100%. Dew forms on everything, the eyepieces
and the finderscope especially.

I found that a simple dew-shield made of cardboard keeps the
findescope clear of dew and, more relevant, frost. Try warming the
eyepices in your pocket for a while.

pej
--
Per Erik Jorde

lal_truckee wrote in message ...
Ernie wrote:
Fall and winter in Vancouver are hard on this hobby, in more ways than
one. When it's not raining, I still have to deal with nights where the
humidity is constantly at 100%. Dew forms on everything, the eyepieces
and the finderscope especially.

Should I just be using this as a sign that it's time to go home, or
should I be using kleenex to wipe off the dew and keep going? I'd rather
not scratch the coating on the eyepieces, but I can't think of any way to
keep the dew away. The mirror isn't affected by the dew at all though, so
it's not like I'm doing anything nasty to the important optics.

No "kleenex" please.

If you don't want to invest the effort and time and money right now in a
full up dew fighter heater system, you can try a 12v hair dryer in the
interim to see if you really want to stay out on wet nights. Should be
available in an RV store - I got mine at a HW store - they are also
advertised specifically for astronomy with the usual 100% markup for
astro gear.

Last Saturday night started out very dewy - I had to dry me secondary
three times in the first hour and a half, using a 12-volt hair dryer.
Then it dried out a bit, and I would occasinally have to dry off the
eye lens of an eyepiece. I usually do this shining a red light on it
while frantically fanning with the other hand. This usually works,
unless the dew is very heavy.

Often, condensation of the eye lens is caused by breath. Someone
posted recently (not necessarily here) they they were using swim
goggles with the faceplate removed to avoid this.

Clear skies,
Shneor Sherman

(Ernie) wrote in message ...

Fall and winter in Vancouver are hard on this hobby, in more ways than
one. When it's not raining, I still have to deal with nights where the
humidity is constantly at 100%. Dew forms on everything, the eyepieces
and the finderscope especially.

Sure, when I'm out for a long observing session in the country, it's
a rare night when I *don't* end up with dew all over everything. To
avoid dew on the finderscope, I just keep it capped when not in use.
Works like a charm; after all, how many minutes out of a multi-hour
session are you actually looking through the finderscope?

Mostly, though, I use my red-circle finder, where dew is a non-issue.
For all but the most critical work, I use the two-eye method, so it
doesn't matter at all if the finder is dewed. And if I really care,
I just wipe it off with a tissue -- no valuable optical surface to
destroy.

As for eyepieces, I *always* keep them in pockets when not in use.
In the winter, I usually wear three jackets (pile, down, and shell),
giving me 6 pockets to play with. In the summer, I use a fisherman's
vest, which has even more pockets.

More of a problem is when the secondary mirror dews up. I can and
do unfog it by holding the back with my hand to warm it up, but
that's time-consuming, and potentially uncomfortable and hazardous
in the winter. Obviously, a hair dryer is a better solution, but
that requires access to a power line, which I don't always have.

Once, my primary mirror fogged up. That's a sign of real trouble!

- Tony Flanders