@gadolf I did some reading for exposure advise. I had tried the night before with a very long but dim lens (600mm equiv, but only f6. 7), and all my stars and the comet had blur from sky movement and the shots were either much too dim (approaching -2.0 EV) or had a lot of high ISO noise. Here’s an example:
The advise I read was that unless you have a star tracker, stick to medium telephoto or moderate wide angle, use the 500 rule to set the shutter speed, use the widest aperture possible (manual focus on a star or the comet), and then dial in exposure with ISO. So that’s what I did the next night. In the main shot in the OP, I’m using a 100mm equiv. f1.7 lens, so the longest allowable shutter speed was 5 seconds, which allowed for a shot at base ISO (200) at about -0.7 EV. This gave a nice exposure of both the sky and palms with sharp stars and comet, however, I needed a shorter shutter speed because there was some wind and the palm trees were moving too much for 5 seconds. So I boosted the ISO to 640, which let me get down to a 2 second shutter speed at the same EV. It took a couple of tries to get an interval with low wind so that the trees would not be blurry, but eventually that worked. Even higher ISO (1200) allowed for much faster shutter speed, but too much noise in the sky, so the ISO 640 shot was the one I eventually went with. All together, I only had about 15 minutes to get the shot, so could not play around too much with various exposures. For my scene and camera (Olympus OMD EM1ii) -0.7 EV seemed to work and allowed a lot of leeway for shadows and highlights in post. For ETTR I think I would have had to boost the ISO too high for the needed shutter speed.