So I tried my hand for the first time at star trail photography the other week. I screwed up enough of the settings that I wasn't particularly happy with the results, so given the rare opportunities that I have to do this kind of thing, I wanted to pick the brains of the more experienced photographers on here a bit... This was taken on a GX7 with the 7.5mm/f3.5 fisheye. This is about 25x exposures stacked, processed, and de-fished. They were taken at f3.5, ISO 640, and 60 seconds (longest I can do with the intervalometer). I converted to B&W and added grain because I was quite disappointed with the noise I was getting, even with a dark frame subtraction (there's a lot of seriously purple charge leakage around the edges of the frame before subtraction - I was shocked). You'll notice that there are some gaps...I screwed up the intervalometer settings so I had 30 second gaps in between the frames, so I tried to fix that with some radial blur. So my question is, what sort of methodology should I be using to get better results? 1) How much gap is necessary to leave in between intervals to ensure the files can be written? 1 second? 2? 3? (0 can't be set, so I assume it needs at least a little time to process/write the file). 2) Is f3.5 fast enough to use a lower ISO, or would I need a faster lens to do this kind of shooting? I was just having trouble picking up the stars, but I was previewing it on a screen, so maybe I would be able to pick it up when PP'ing the RAWs... 3) ISO 125 or ISO 200? Will there be a big difference between ISO 640 and base/low extended ISO for this kind of photography? 4) Best methodology for dark frame subtraction? Even if I have to deal with gaps, are the results better from the in-camera long-exposure NR than doing it manually with a dark frame? It's certainly more convenient... Thanks in advance for any help!