If your exposure gives you the image that you wanted, and people respond to it the way that you wanted, it was correct.

Gordon Willis was famously known as "The Prince of Darkness" among cinematographers. Willis also famously hated the nickname. He would often retort, "It's not dark. It's proper exposure."

The thing is, in my twenty-some years of working with cameras in both motion and stills, I've noticed a stark divide in how people interpret the idea of "proper" or "correct" exposure. Photographers seem to regard correct exposure as something that's technically objective and measurable. Cinematographers seem to regard it more subjectively - it's proper for what you're trying to accomplish.

I should make it clear that this isn't a clean division. A lot of people in the film industry have gone the full "Shoot it clean and do it in post route." which I hate. Some photographers do a lot to play with their negatives to get what they want; but, I think I can count the ones of whom I'm aware on one hand.

An obvious factor is that photographers are trying to make one, single image that people will want to pay for regardless of context whereas cinematographers need to conform the images to work with a story that's being told over the course of several minutes or hours. A film like Man on Fire can have some really cool moving images made on cross processed reversal film running through hand cranked cameras; but, a lot of the individual pictures, if extracted from that shot, wouldn't look very good.

That said, I think that photographers would do well for themselves to look at some of the stuff that cinematographers do with exposure. Every shot of Sam Raimi's Spider-Man films was intentionally overexposed by one stop. Every shot in American Gangster was underexposed by a stop and pull processed an additional stop. LaLa Land was all overexposed by a stop and pull-processed.

The changes to the images may be subtle; but, our craft is all about subtlety. We're supposed to notice the little things and make things work so well for the viewer that they don't have to think about it.

Sometimes, what's best for an image is to fuck it up a bit. I don't think I'll ever have the balls to do what Gordon Willis or Harris Savides did in terms of underexposed negatives. The closest that I've come was a horror short that I shot several years ago which I shot on a low-contrast, 400ISO Fuji stock and underexposed by 2/3rds of a stop to have printed up. Even then, I was sweating through most of the production. Still, I have found myself thinking about exposure as another tool, and another decision to make in the creation of images rather than anything that's technically measurable.