Dumb question: with the first example (twilight), wouldn't raising the exposure in post be functionally equivalent and have the same amount of noise? You are taking the same signal and boosting it to a desired gain, whether in camera or in post. right?

Honestly had to research a bit before answering your question, and there is debate on this. I am adamant on staying below 200 or maybe 400-600 on every picture though :D My best pictures are all on super low ISO because that's what makes them "creamy" and sharp (and I dig that).

Often when I take a high ISO (relative) I find myself also adding an extra layer of edit ("remove noise") which I think just hurts the image. Adjusting exposure alone I feel does less damage.

I really don't find adding exposure on post (when RAW) damages as much as adding ISO and adding noise.

ISO is really just boosting a sensor sensitivity to light which I feel is not optimal and adds it's own set of artifacts. I would always prefer to add more exposure and me being the one adding the artifacts and playing with the edits, rather than the camera.

But then again, I just shoot for hobby and not a PRO! You can check out some of my pics at @franciscojgo

Not necessarily. It first begins by depending on what your settings are (ISO, aperture, shutter speed). With all settings neutral, if I add an extra stop of light, i’m going to get more blown out exposure from letting more light in (f/4 -> f/2.8 — this will open the lens wider, therefore letting more light hit the sensor) but no additional grain since my ISO may be set at my bodies base of 100-200 ISO for shooting outdoors.

Now if i’m shooting indoors and my glass doesn’t have a decent f-stop that shoots in lowlight, i can leave my aperture down and raise my ISO to maybe 1200, but when you do this, that is when you’ll get grainy pictures because you’re moving away from the cameras sensor base ISO that it’s calibrated for.

But if you want to adjust everything in post processing, you’ll need to shoot RAW because JPEG do not hold enough data that’ll allow you to adjust it accurately.

Increasing the ISO adjusts the gain earlier in the signal chain where less noise/error has entered. So the snr will be better vs adding gain at the end.