On last week’s roll of film, I did a little testing.
Film can handle overexposure much better than underexposure. (Which is the opposite of digital–with digital, it’s easier to blow the highlights.) Each roll of film is rated, according to the box, at some specific ISO. But it’s common for many photographers to set the ISO of their cameras lower than the box rating in order to slightly overexpose the film and get nicer negatives. Fuji NPH is box-rated at ISO 400, but I set it at ISO 200 for these first two rolls. Also my reading online tells me that with expired film, it’s common for the speed to be sacrificed, meaning it’s not uncommon to need to shoot at a lower ISO than the box says. Since I have a bunch more rolls of the same film, I wanted to test it to see what ISO I really want to be shooting at. I shot it at each of six different ISOs, adjusting the shutter speed accordingly so the meter told me I had correct exposure.
Based on these results, I decided to rate it at ISO 100 this week, because I like how that frame came out the best.