There are many combinations of aperture, shutter speed, and ISO that will correctly expose an image. With all those combinations, which one is the right one? If you leave your camera in full program mode, your camera will pick a combination for you. However, letting your camera have complete control is not why you bought an expensive DSLR or mirrorless camera! Learning how to adjust the settings and modes on your camera before you click the shutter will give you the upper hand. You will end up capturing images creatively, rather than by chance. Read on to find out how aperture, shutter speed, and ISO affect the look and feel of a photograph and how to choose the best camera settings to take creative control of your images.
In my last article on the Exposure Triangle, I talked about what aperture, shutter speed, and ISO are and how they work together. Before I talk about how to choose a creative exposure, let’s discuss how aperture, shutter speed, and ISO visually affect the look of an image. For more technical information on aperture, shutter speed, and ISO, take a look at Nasim’s excellent “Beginner’s Guide” articles on the site.
Out of the three exposure variables, aperture is the one that controls the depth of field in an image. That is, how much of the scene in front of, and behind what you focused on is acceptably sharp. The wider the aperture, the narrower the depth of field and the less of the scene that is in focus. A narrow depth of field works well to isolate a subject. Portrait photographers often use this technique to separate their subject from a busy background.
In these first two images, I was able to isolate the main subjects using a wide aperture (relative to the focal length of the lens). Notice how the backgrounds are completely blurred out.
In these next three images, I used selective focus to draw your eye to the subject while still leaving some details in the backgrounds. This helps to give a sense of context to the images.
A narrow aperture will give you a much greater depth of field. Landscape photographers often use a small aperture to create images that are in focus from foreground to background.
Here are some examples. Notice how objects in the foreground are sharp as well as objects in the distance.