Understanding The Exposure Triangle
Many things have changed in the photography world since digital technology emerged, but the central tenets have never changed. The most important steps in becoming a great photographer remain understanding ISO, shutter speed and aperture. But understanding the three isn’t always that easy, so in this article we’ll look at each aspect individually, before seeing how the three interact with each other. To start with, your camera will need to be on manual mode, so that all these functions can be altered.
ISO
ISO relates to film speed from the days of film cameras, and determines how sensitive the camera is to incoming light. ISO actually stands for International Standards Organisation and is sometimes called ASA (standing for American Standards Association). With ISO, the lower the number the more light you will need to achieve a good exposure. So, for example, ISO 100 is best suited to being used with studio lights or bright sunshine. The lower the number, the less ‘grain’ or, as it’s known in digital terminology, ‘noise’ the image will have.
When digital cameras first came on the scene, high ISOs were a complete no-no, as the deterioration from digital noise was so high. Edges of buildings could become blurry and pixels reproduced in the wrong colours. Modern DSLRs, particularly those designed for pro use, are far better able to cope with higher ISOs, which can be particularly useful if you’re shooting in dark and dingy situations. Most people still agree though that a lower ISO looks far nicer in a photo.
Shutter Speed
Shutter speed refers to how long the shutter in you camera is open for, and therefore how long it is letting light into the camera for. (If you have noticed by now, just about everything in photography has to do with light, and our control of it.) A typical shutter speed range on a DSLR will go from a fast shutter speed setting of around 1/4000th sec to 1/8000th sec, down to a very slow setting of 30 seconds or a B (Bulb) setting, where you can choose how long to leave the shutter open for. One thing to remember with shutter speed is that 1/60th sec is generally the slowest you can shoot with your camera hand-held. Any slower than this and you’ll need a tripod to control camera shake. So, what do we use different shutter speeds for? Here’s a handy guide to the general brackets:
1–30+ seconds: Night and lowlight photos, using a tripod
2-½ second: To create an ethereal look on flowing water
Landscape photos to add an enhanced depth of field
½-1/30th second: To add motion blur to the background of a scene
1/60th–1/100th second: Hand-held photos without a large telephoto
1/250th–1/500th second: Freezing sports / action shots
1/1000th–1/4000th or 1/8000th second: Freezing fast / up-close motion shots
Hand-held photos with a large telephoto
Remember that the faster your shutter speed is, the less light will be being let into your camera.
Aperture
Of all the settings on a camera, aperture is the one that tends to confuse the most. Unlike shutter speed and ISO, it has two distinct functions. Let’s look at the simplest to understand first of all – controlling depth of field. Depth of field really is the single most important thing to master in photography, as it is choosing the right depth of field that takes photos from snapshots to professional images. Put simply, depth of field is a range of distances around your subject (known as the focal plane) that are in acceptable sharpness. There’s no abrupt change from sharp to unsharp – depth of field occurs as a gradual transition. So, how do we tell whether our shot is going to have a small depth of field (very little behind the subject sharp), or a large depth of field (all of the photograph is sharp)?
Aperture, and therefore depth of field is controlled by f-stops. A small depth of field is represented by a small f number (e.g. f4), whereas a large depth of field is represented by a large f number (e.g. f22). A large depth of field is commonly used for landscape shots, where the whole image needs to be sharp, whereas you’ll see smaller depths of field used in portraiture, in order to isolate the subject from the background.
The camera’s f-stops also control the amount of light that passes through the iris of your lens. This is where things can get a little confusing, as a large aperture is actually represented by a small f number. So f2, for example, would be a large aperture as it lets a lot of light into the lens. Conversely, f22 is a small aperture, as the iris opening in the lens will be small and only letting a little light in. In the photography world, the common slang is ‘stopping down’ (making the aperture smaller) or ‘opening up’ (making the aperture larger).
The Exposure Triangle
The reason we refer to ISO, Shutter Speed and Aperture as the exposure triangle is that every time you change one setting, it affects the other two and so on and so forth in a constant triangle. How do you know where to start with the settings? Well, much of it will depend on the available light but a good starting point is to think what depth of field is needed for the shot that’s going to be taken. So, for example, if you’re taking a portrait you’re going to need an aperture of around f4-f5.6 for a nice head and shoulders shot with a blurred background. In addition, you’ll want a low ISO of around 100-200. This means that your aperture will be open and letting in a lot of light, meaning that you should be able to use a faster shutter speed of around 1/250th to balance out the light. Obviously, these settings may need to be adjusted depending on how much light is available.
If you’re shooting a landscape, you will need a large depth of field to make sure everything is sharp. So, a setting of f22 will achieve this, but won’t allow much light into the camera meaning that you’ll need a slower shutter speed. This is why many landscape photographers use a tripod, so as to allow for the large depth of field.
Obviously, there will be situations where you’ll need to set your shutter speed first (shooting action or at night for example) or your ISO (shooting in very lowlight in situations where you’re unable to use flash). But, by understanding the three sides of the triangle separately, you’ll be able to put the three together more successfully.
© Jo Plumridge