Re: Scopes dripping wet
- From: tony_flanders@xxxxxxxxx
- Date: 30 Dec 2005 06:31:46 -0800
Mango wrote:
> [Some observers] told me that in all observing sessions, they always
> end up with dripping ... scopes, meaning not just the lens are wet but
> also the tube because of the coldness. I wonder if you get your scopes
> wet everytime you watch.
Not every time, but except for those times that I just go out and look
half an hour at some small, discrete target or event, it's mighty rare
that the tube of my telescope *isn't* wet to the touch at the end of an
observing session -- or, at this time of year, covered with frost.
Any respectable scope is designed to handle this. I wouldn't
recommend leaving a scope out in the rain, but a little water
on the outside of the tube is nothing to worry about.
However, I rarely let my telescopes' objectives get wet, and when
I do, it's usually a sign that I've done something wrong. If you use
a refractor or a catadioptric, you really need to take positive steps
to avoid condensation on the objective unless you observe only
in ultra-dry conditions. For a refractor, a good long dew shield is
usually sufficient for a couple of hours, but catadioptrics typically
need electric heaters to keep the dew off. As a rule, Newtonian
reflectors are nearly immune to dew because the objective is
buried way back at the bottom of a long tube that acts as an
ultra-effective dew shield.
It's hard to imagine getting a refractor objective so wet that you
have to worry about water getting between the elements. You
would be unable to view through the scope long before that
happened.
- Tony Flanders
.
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