>>4216842>>4216844The noise floor is actually lower at higher ISO, however, there is more shot noise, so IQ is worse. You wanna use the lowest ISO where read noise drops off when in low light, and base ISO everywhere else. This is assuming your camera is ISOless, which almost all are.
> The lowest ISO I can set is 640 if I want to keep DR400 so I usually set it to that if there's enough light around.The DR setting actually uses a lower iso than selected, 1 stop of 200 and 2 stops for 400, then the shadows and midtones are boosted 1 or 2 stops, respectively. This has the same effect as underexposing to not blow your highlights then boosting the shadows and midtones in post, which is something I do all the time. However, this setting also affects RAW files as well. You will get better results doing it yourself in post since the noise reduction in RAW editors is much more effective than in camera.
https://blog.kasson.com/gfx-100s/gfx-100s-dr-setting-affect-raw-files/ 