The exposure triangle is one of the backbones of filmmaking and photography. Here’s everything you need to know about it.
The exposure triangle consists of three elements: ISO, aperture, and shutter speed, which all influence exposure. In this case, exposure describes the amount of light that the film or sensor in a camera is exposed to. This amount is measured in so-called “stops of light”. If you increase exposure by one stop, you double the amount of light that falls onto your film/sensor. If you decrease it, on the other hand, you halve the amount of light.
As ISO, aperture, and shutter speed, work interdependently, you will always have to balance them out. If you increase one of them, you will have to decrease the other ones. This can be a tedious process to learn, and even absolute professionals often take their time to find the appropriate setting.
ISO describes the sensitivity to light of the film. It’s important to note, that the ISO used to be fixed, and still is today, if you’re shooting on film, that is, since film always has a set ISO value. Nowadays you can change the ISO of your digital camera. While a sensor’s sensitivity cannot actually be changed, ISO controls the gain that is applied to the signal after the photo has been taken, although simply put, it has the same effect as it does on film. A film or sensor that is more sensitive to light, will need less light to create an image.
The higher the ISO, the brighter your image will be, which allows you to shoot in situations with poor light, but turning your ISO up is always a compromise, since it distorts your image with noise. How high you can really go with the ISO depends on the size of your sensor. The bigger it is, the higher you can go, without losing too much quality.
While most photographers and filmmakers will avoid a high ISO like a plague, some use it as a stylistic element. Jim Jarmusch’s break-through film Stranger Than Paradise was shot on 16mm film and later blown up to 32mm, which gives it a lot of noise, compared to other films. Whether this decision was a purely artistic one or whether it was made out of financial necessity is irrelevant today, because not only does the noise underline the mood of the film, it also set a benchmark for later Indie films like Kevin Smith’s Clerks or Darren Aronofsky’s Pi.
Aperture describes the amount of light the lens lets in. The lower the aperture value, the wider open the lens is, the more light reaches the film/sensor. Furthermore, the aperture is decisive for the depth of field (to which extent an image is in focus): The higher the aperture value, the tighter the opening in the lens, the more concentrated the light, the more depth of field.
Depth of field dictates how much information you share with your viewers – the deeper it is, the more is in focus, ergo visible. Gregg Toland, director of photography, was one of the first in his field to use deep depth of field. He worked on legendary films, such as John Ford’s Grapes of Wrath and Orson Welles‘ Citizen Kane, which is popularly regarded as the best film ever made. Much of the praise for Citizen Kane goes to Gregg Toland’s revolutionary style. While in the 1930s most directors of photography shot in a shallow depth of field, to emphasize on the most important part of the shot, Toland would have the audience decide what is relevant, by putting everything into focus.
Shutter speed dictates how much time it is for light to hit the film/sensor. The slower it is, the brighter the image will be. Keep in mind to put your camera on a tripod or hold it very steadily (rather go with the tripod), when you decide to shoot with slow shutter speed since the light will be hitting the sensor/film for a relatively long time and pick up any movement as a blur. I would advise keeping your shutter speed high if you are shooting sports, action, or anything with a lot going on.
On the other hand, of course, you could use the blurry effect, created by movement, as a stylistic element, because it can make for some great images. For his film Chungking Express, Wong Kar Wai shot a police chase with very slow shutter speed, which made for an amazing shot in an amazing film. Quentin Tarantino was “blown away” when he first saw it and he even decided to bring it out on VHS in the United States, with an introduction and post-film discussion by himself (check out the video below).
Now go out there and practice endlessly until you can get the right aperture setting in your sleep! In case your camera’s battery is dead at the moment, you can try out different combinations of shutter speed, ISO, and aperture, and their effects on this cool little website: http://www.exposuretool.com/