Re: An unlikely pairing.... and condensation problems!
- From: W. H. Greer <sendnomail@xxxxxxxx>
- Date: Sun, 04 Feb 2007 13:19:11 -0700
On Sat, 03 Feb 2007 00:19:09 GMT, "Steve & Lizzie"
<steveandlizzie@xxxxxxxxxxxxxxxx> wrote:
Now that I've come back down to earth, it's time for me to beg your advice
again. I found tonight that my scope got really wet with condensation. My
EP's were constantly steaming up - this I managed by gentle wiping with a
lens cloth. But I also found that my secondary mirror steamed up quite a
bit! I'm sure its bad practice but the only way round this was to use the
cloth again very carefully on the mirror! Is this just something that I have
to learn to live with or is there another way round it?
Ben provided a good reply. Nevertheless, I'll provide a bit of
reinforcement, etc.
One of the best (and most expensive) solutions for the eyepiece
problem is to provide gentle heat around the eyepiece. A dew removal
(heater) system is an effective, but costly solution.
A far more cost effective approach would be to wave your hand over the
eyepiece. The air flow should eventually clear the eyepiece. This
approach is less effective than the first one; but it costs nothing!
Of at least equal importance are preventive measures: Take great care
of how you exhale and the direction in which your exhaled breath goes.
You want to avoid breathing on your optics. Your breath will most
likely be warmer than the surrounding air and have a much greater
concentration of moisture. The moisture in your breath will instantly
condense on your cold optical surfaces -- if you allow it to reach
those surfaces.
Wiping the eyepiece isn't too terribly bad assuming the eyepiece and
the cloth are completely free from abrasive particles; but it's still
a risky operation. I prefer the wave of the hand approach (or in
extreme situations a dew heater). Eyepieces cost money to replace;
and money is not always easily acquired.
Next on the agenda is your mirror: Telescope mirrors are
first-surface mirrors. They're *far* more susceptible to sleeks, etc.
than your typical bathroom mirror. You should *never* wipe dew or
frost from a telescope mirror. Damage is practically guaranteed to
occur!
If airflow fails to clear the mirror in the field, then your only
reasonable option is to end your observations with that telescope! I
would cover such a mirror prior to bringing it inside. After it has
warmed sufficiently (this can take half a day or so depending on
temperature differentials) I would uncover it and allow any lingering
moisture to *completely* evaporate prior to re-covering it until the
next observing session.
A tube extension, as suggested by Ben, is an effective preventive
measure against dewed telescope mirrors. In addition, be careful with
your breath. Don't allow it to enter your telescope tube!
Personally, I *far* prefer preventive measures over dealing with wet
optical surfaces and the inevitable water spots that will follow.
One final piece of advice: NEVER clean your telescope mirrors until
you've thoroughly researched the topic and know exactly what you're
doing! My own telescope optics get cleaned less frequently than once
a year. In same cases it's been far less frequently! I prefer to
take preventive measures that minimize the risk of getting the optics
dirty.
--
Bill
Celestial Journeys
http://cejour.blogspot.com
.
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