A pretty good rule of thumb is that you lose one stop of dynamic range with every doubling of iso.I learned something new today. I didn't know that higher ISO settings reduced the dynamic range. Seems like that is something I should have found out a long time ago......better late than never.
I would never underexpose on purpose (although there was an article about Steve McCurry using that for some effect). If at all possible, I tend to favor ETTR (without blowing our highlights) so there is as much data as possible to work with. But, when you cannot achieve a correct exposure with the sensor at base ISO, there are two options I was referring to in my post above.Given the D750's sensor is supposed to be highly ISO invariant, I tend to raise ISO as a last resort. And, in theory, you should be better off shooting a slightly underexposed raw image when light challenged, and then adjusting the exposure in post processing as this should give you back a bit of dynamic range.
your 1st sentence sounds like a contradiction ?
for me never ever underexpose on purpose, I used to do it for high school football but soon discovered what was waiting in the shadows under the helmets.
I had the same issue when shooting college football night games with my D300 years ago. I fought for every stop of light I could get, and still came up short on a number of shots. And you are correct, the shadows often were not pretty. And if you really want to see dark shadows, try roller derby!I used to do it for high school football but soon discovered what was waiting in the shadows under the helmets.
This illustrates that very well: https://photographylife.com/news/shutter-speed-aperture-iso-system-videoSo many great responses, I'll just add this: always use the lowest iso possible for your shooting conditions.