Some Dews and Dont's

Last night was another first for me, and this entry is to serve as a reminder of what NOT to do. Yesterday afternoon, we had a brief thunderstorm. Short, but some heavy rain for a few minutes; typical. The sky generally cleared up afterwards, so I decided to try an imaging session. OK, all set up. Time to run the flats for the night, and...

Bullseye!

That's what I got. What should it have looked like, you ask? (Thank you for asking.)

Normal Flat image

I'm not the brightest bulb in the box, but even I can tell something is not right.

After checking everything in the optical train I could think of, and finding nothing amiss, I was left with only the camera itself. I'm loath to remove it, once attached to the scope, just because it changes what the flats correct in the image; ie, a flat is useful for removing “dust donuts” from an image, but only if the camera is in the same orientation for both the flat and image. Removing the camera means wasting time re-shooting flats. But, detach it I did. And, if you paid attention to the title of this entry, you already know what I found...condensation in the camera.

I've been running the camera this morning to see if I can replicate the issue. After half an hour, no condensation. My worry was that the desiccant needed replacing, which is possible, but a pain. According to the instructions, it could need replacing after 3 years; I'm currently at 5 years with out a (known) need for replacement. So, I'm guessing the moral to this story is, don't try imaging after a thunderstorm when the humidity is still 100%. (So how do they do it in Florida?)