ISO determines the film’s sensitivity to light.
The *correct speed you should shoot the film at is written on the side of the film canister, or on the film packaging. The higher the ISO, the more sensitive the film is to light [better for dark/night photography], a high ISO also produces increased grain.
The lower the ISO, the less sensitive to light [better for sunrise/sunset and day photography], however a low ISO produces less grain, so sharper photos.
*You can over or under expose film for different results by setting it higher or lower than the speed shown on the film.
The ISO setting helps ensure that your image is properly exposed.
Your camera will either read the film speed automatically [via DX coding] or you’ll have to set it manually. If it’s manual, make sure to set it to your chosen film speed before shooting.
With expired film, results can vary, for vintage/ experimental photos, shoot it at the speed on the film. If you’re looking for results as close to the original examples of the film, we recomend to over-expose 1 stop every decade. i.e ISO 400, Expired in 2010, shoot at ISO 200.
So what film is right for me?
There is no ‘correct’ ISO for your photography, as there are many aspects you can take in to account [the weather, the lens, the camera, expired film, using a tripod/flash etc] but as a general rule of thumb here's a list that should help you choose.
- Low speed - ISO 100 and under, are easily used outdoors on sunny days.
- Medium speed - ISO 125-320, work well outdoors on sunny and semi-overcast days and indoors with flash.
- High speed - ISO 400-800, work well on overcast days, indoor and dim light.
- Super High speed - ISO 800-6400, excels in night photography and existing-light photography such as night sports matches and stage shows.
Remember, the higher the number, the more grain in your photos.