I was out only briefly with the 20". The mirror was well cooled having fans running on it since 5:30pm. I still had the bar shaped aberration. For some reason I thought to turn off the fans to see the effect. At first I turned off the boundary layer fans, no change. Then I turned off the rear fan, and bingo! clean star images. The effect was immediate. I turned the rear fan back on and watched as the bar reformed.
I am very puzzled about this, since I had not made any change to the fan. It could be the rear light baffle I added is causing a weird air current -- but the boundary layer fan should take care of that, and anyway the aberration is there whether those fans are on or off. In any case, I will remount the rear fan and see whether that solves the problem, with the baffle on. Otherwise it's off with the baffle.
Nothing interesting to note other than there was a very bright ISS pass travelling west to south east, which faded post meridian as it finally entered earth's shadow. It's staying light very late now, so observing time is limited.
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