Taking a quality photo requires an image that’s exposed correctly. For most users who shoot in automatic mode, the camera takes care of all the settings. But, as smart as digital cameras have become, they aren’t perfect. Elevating your picture-taking from good to great requires a general understanding of the three elements of exposure: aperture, shutter speed, and ISO.
High-end digital cameras can be scary to use, especially for users stepping up from a basic point-and-shoot. But once you know how a camera’s exposure settings work, a lot of that intimidation should be alleviated. When you have a basic understanding of aperture, shutter speed, and ISO – which are also the basics of photography, in general – you’re well on your way to mastering your digital camera’s advanced modes.
There’s a lot of technical mumbo-jumbo that goes into how a digital camera handles exposure, but we’ve simplified the process down to what matters to you.
Imagine a hole within the lens that opens and closes. The size of the opening is the aperture, and when you control the aperture you determine how large or small the hole is. The larger or smaller the hole, the more or less light is allowed in. Aperture is measured in f-stops, such as f/22 and f/4, but here’s the thing: The smaller the f-stop number, the larger the opening, and vice versa. So, when you are adjusting the settings, think of the opposite: If you want less light to enter (small aperture), go for a larger f-stop. How large your lens’ aperture can open will depend on your lens.
Aperture is mostly associated with an image’s depth of field (DOF), which, simply put, is how much of the photo is in focus. An image with a large DOF is in focus throughout, while a small (or “shallow”) DOF sees the focus concentrated on one particular focus point. When thinking about the f-stop, choose a smaller number (larger aperture to let in more light) to achieve a smaller DOF.
When would you want to control aperture? In close-up shots, like portrait or macro photography, you may want to blur out the background and concentrate the focus on the subject (small DOF), whether a person or flower, for example. In this scenario, you want a large aperture (small f-stop). For landscape photos, where you’d want everything in the image to be in focus (large DOF), you’d choose a small aperture (large f-stop).
As you’d guess from its name, the shutter speed determines how much time the camera is letting light in. Think of actual window shutters or blinds in your home, and how quickly or slowly you open and shut them: the longer you leave them open, the more light enters your room, naturally. Aperture and shutter speed work together: Whereas the aperture determines the amount of light that’s coming through the lens, the shutter is an actual screen that opens and closes to allow that amount of light to hit the sensor (“exposing the film”). When you control the speed – which is measured in fractions of a second (e.g. 1/30, 1/1000) – you are telling the camera how quickly or slowly to open and close the blinds. Unlike aperture measurements, shutter speed corresponds directly to time: the higher the number, the faster the speed.
Shutter speed plays a role in capturing motion, and determining how you want that motion to appear in your photo depends on your creative mood. Imagine a moving race car: Some may want a blurry effect (when it’s going around the track), while others may want to freeze that shot (when it’s crossing the finishing line). In the former example, you’ll want to try a slower shutter speed like 1/60, while the latter example would require a speed of 1/250 or more.
There are a few things to keep in mind. If you are using a very slow shutter speed, make sure your camera is stabilized on a tripod or non-moving surface to prevent camera shake; you want as little vibration as possible while the shutter is opened longer, because otherwise your image may look blurry. This is the case when it comes to the maximum focal length of your lens. An 18-35mm lens, for example, should avoid shutter speeds lower than 1/60 without some sort of stabilization.
ISO, or International Standards Organization, is a rating carried over from the film days (also known as film speed), but in digital cameras it means the same thing: sensitivity to light. When you hear someone describe a photo as being “too noisy” or having “too much noise,” you probably have the ISO to blame. To give you an example of light sensitivity, think of staring straight into the water while on a sunny beach or squinting at a clock in a semi-dark room. Now imagine your camera trying to capture images under those conditions – that’s how easy or hard the camera’s sensor has to work when capturing light.
In most normal shooting scenarios where conditions are well-lit, the ISO can be set low, usually around 100 to 400 (ISO is rated in the hundreds, e.g. 100, 200, 400, 800, etc.). A higher ISO allows you to enable faster shutter speeds and smaller apertures (larger opening). The sensor is working harder to expose the image. But a high ISO is where you get into trouble: this is when your images could look grainy (people who suffer from the eye disorder known as “visual snow” will be familiar with this “noise”). Many new cameras tout high ISO capabilities of 12,800 or more, but be wary of the results.
If a high ISO is problematic, when would you want to use it? If you plan to shoot in low-light situations – a house party, concert, restaurant, etc. – then you would need to increase the ISO. Advanced photographers prefer pushing up the ISO rather than using a flash to compensate for the lack of light. To minimize noise in your “dark” photos, set your camera on a tripod and, ideally, shoot mainly stationary subjects or objects. In all other, well-lit situations, however, it’s preferable to keep the ISO low.
Three components working hand-in-hand
As you’ve probably concluded, aperture, shutter speed, and ISO work together to properly expose an image. A change to one will impact the other two. For example, when you select a slower shutter speed, it affects the amount of light “exposing” the sensor because it’s opened longer; in this case, you would want to use a smaller aperture size to decrease the amount of light available, to compensate for the brightness.
But, today’s cameras include semi-automatic modes that help you figure out some of the settings. In the camera’s Aperture Priority semi-automatic mode (A or Av), the user is given control over aperture settings while the camera picks the appropriate shutter speed and ISO. Shutter Priority (S or Tv) works the same way.
Don’t freak out if this all seems overwhelming. Know that there’s no magic answer to understanding exposure, and even professional photographers constantly play with the settings until they get an image they are happy with. The key is to experiment and not be intimidated.
Key points to take away
- When it comes to the aperture setting, think of the opposite: a small f-stop number equals a large aperture setting, while the large f-stop number equals a small aperture setting.
- To blur the background of a portrait or a close-up (macro) image, choose a large aperture setting (small f-stop). To keep the entire image in-focus, choose a small aperture setting (large f-stop).
- To “freeze” a moving object, use a fast shutter speed. For a blurring effect, use a slower shutter speed.
- A tripod is handy when shooting images in very low shutter speed or when using a high ISO setting.
- When shooting in low light, avoid the highest ISO settings if you want to reduce the amount of noise in your photos.
- Changing one setting affects the other. If you are using a slow shutter speed, you may need to use a smaller aperture size to compensate.
- If you don’t mind handing over some control to the camera, choose Aperture Priority mode to only control depth of field or Shutter Priority mode for motion capture.
- There’s no wrong way to take a photo. Experiment with the settings until you get the shot you’re happy with.