2010-09-14 (2010B-0030): 9 hrs used Comment: Good night, clear, low wind, 1-2" seeing, some cirrus. Dewar window may need cleaning. Looked at V and WIYN 34 filter flats, and both had what appeared to be moisture stain patterns. Since they both had identical patterns, it had to be in the window or somewhere near the detector, not in the filters themselves. When telescope slewed, PI heard the counterweights clunking as if they were not tightened down.