Am I imagining this? It seems that certain somewhat older film stocks have a grain characteristic whereby if well exposed, the negative seems relatively fine grained, but where less exposed (such as in shadows) the grain is much more pronounced. I shot some Fuji NPS 160 (35mm) and it seems to have this issue, where Portra 160 does not. It's kind of frustrating, because different parts of a single image may have different graininess.
The mystery to me is --- what is the innovation that seems to cause this to be less of a problem with more recent films?
Yes you are right. Color neg gets less grainy when exposed more. You may get very good results by setting the camera meter to overexpose 1 or even 2 stops all the time.
The newer films include new technologies such as 2-electron sensitization, dye layering etc. to make smaller grain at higher speed.
The aging of the film also affects the shadow grain greatly. So, those old films may have had considerably less grain when they were fresh.
The simplest answer is that larger grains are faster and in film there is a range of grain sizes. So the shadows will have the greatest effect on only those faster grains, hence more visible grain.
This is also why reversal processed films have much finer grain. The larger grains are used in the initial exposure and unfortunately we usually fix away the finest; but in reversal processing the final image is composed of only the crème de la crème .
Interesting...so I wasn't imagining it!
I have a 1,000ft roll of Fuji Reala 500D that manifests this, although it's quite universally grainy. (It's ECN-2 movie stock which I can process). Maybe it's lost some speed - it must be quite old, although there doesn't seem to be much color shift (very little correction needed upon scanning, at least). I think my predecessor stored it well. Maybe I will try it at different speed settings and see if that significantly changes the grain aspects.
Also, with the Fuji NPS 160, I should probably try that at 125ASA or even 100 -- the grain overall was quite good, except in the shadows.