After an unexpectedly long session where I came within maybe 20 metres of a Kārearea (NZ Falcon), I realised my exposure compensation was set to -2EV. I couldn’t believe it.
The images were salvageable, but not to the quality I wanted.
The reason I was at -2EV was from a few nights before — seeing what I could get of the moon handheld at 600mm (the answer: nothing that was usable), but what a silly thing NOT TO CHECK the setting a few days later.