Hi all,
This past Tuesday evening I was doing some ccd imaging when I noticed
that a raw image seemed out of focus. I was unable to sharpen the
focus much, so I finally looked at the corrector on my C14. It was
badly "dew'ed" around the secondary mirror, only about 2" around the
edge remained clear. The dew'ed area was dense enough to be almost
opaque. I had a Kendricks heater running at 100% so I was a bit
surprised. I used a hairdryer to clear it up and was again surprised
to see that after 30 seconds or so it had not even started to clear.
Using a flashlight and my fingernail, I found the condensation was
inside of the corrector plate. It took several minutes of heat to
clear this up, at which time the scope needed to equilibrate to
ambient again.
The local weather in central Ohio has been very wet, over 85%RH, with
occasional dry periods when the humidity will drop to near 30%RH.
That night was unseasonably cool, about 35F.
My questions are: is this a common problem and, what should I do
about it? The OTA must "breath" of course, daily temperature swings
of 40F are not uncommon here. The observatory is ventalated so the
temperature inside probably does not exceed 10F over the outside
temp - therefore the scope changes through about 50F between day and
night. I can rig an air filter, fan, and dessicant chamber to blow
dry air in through the eyepiece port, but it seems it will just get
wet in there again. I bought the OTA from California and it is in
fine condition. There appear to be stiffeners inside which, if this
continues, I think might start to oxidize. Further, when the moisture
drys it leaves marks from the dust that adhered to it.
Thanks for your interest.
Regards,
Gary
