Quote Originally Posted by Alan
So, higher ISO is a trade off between lower noise in the shadows, but higher noise in the highlights? Or, is it the other way around?

In the context of fixed exposure (i.e. in Manual mode), it's a trade off between noise and highlight clipping.


For example, take a low light scene with these settings:


1/250, f/8, ISO 100 = 7 stops of highlight headroom (very hard to clip highlights), but lots of noise


1/250, f/8, ISO 1600 = 3 stops of highlight headroom (4 stops are clipped compared to ISO 100), but less noise.