Every thing works quite fine during your imaging sesion. It seems you’ll get some wonderful images that night. Suddenly, the guide star seems to fade away, and guiding fails. No clouds in the sky, so?
From the thousand things which can go wrong and spoil an image, I discovered one of these last night. My anti-dew system failed, and the dew quicky landed on my corrector lens. I wasn’t able to see this until it was too late in the night, as I simply didn’t get suspicios about this failure.
I was imaging the Cocoon Nebula, a fine object indeed. I was able to take my H-alpha, narrowband images (with 700-second subs), but my R, G and B images (at 500 seconds) got almost all of them spoiled. I could only use one sub per each channel! The result: a noise image. I have had to apply a quite aggressive noise reduction process, and this can be seen in the background.
On the other hand, it’s impressive how a narrowband image can work with not-so-good RGB ones. Taking into account the problems, I can be satisfied with the result. And with the lesson learnt!