Three Ways to Regulate Light

ISO

In traditional (film) photography ISO was the indication of how sensitive a film was to light. It was measured in numbers (you’ve probably seen them on films – 100, 200, 400, 800 etc). The lower the number the lower the sensitivity of the film and the finer the grain in the shots you’re taking. In Digital Photography ISO measures the sensitivity of the image sensor. The same principles apply as in film photography – the lower the number the less sensitive your camera is to light and the finer the grain. Higher numbers mean your sensor becomes more sensitive to light which allows you to use your camera in darker situations. The cost of doing so is more grain (although cameras are improving all the time and today many are able to use high ISO settings and still get very useable images). An example of a situation you might want to choose a higher ISO would be photographing an indoor sporting event where the light is low and your subject is moving fast.

Shutter Speed

Shutter speed is the length of time your camera shutter is open, exposing light onto the camera sensor. Essentially, it’s how long your camera spends taking a photo. This has a few important effects in how your images will appear. When you use a long shutter speed, you end up exposing your sensor for a significant period of time. The first big effect of shutter speed is motion blur. If your shutter speed is long, moving subjects in your photo will appear blurred along the direction of motion. This effect is used quite often in advertisements of cars and motorbikes, where a sense of speed and motion is communicated to the viewer by intentionally blurring the moving wheels. Slow shutter speeds are also used to photograph the Milky Way or other objects at night, or in dim environments with a tripod. Landscape photographers may intentionally use long shutter speeds to create a sense of motion on rivers and waterfalls, while keeping everything else completely sharp.

Aperture

Aperture is a hole within a lens, through which light travels into the camera body. It is an easy concept to understand if you just think about how your eyes work. As you move between bright and dark environments, the iris in your eyes either expands or shrinks, controlling the size of your pupil. In photography, the “pupil” of your lens is called your aperture. You can shrink or enlarge the size of the aperture to allow more or less light to reach your camera sensor. Aperture has several effects on your photographs. One of the most important is the brightness, or exposure, of your images. As aperture changes in size, it alters the overall amount of light that reaches your camera sensor – and therefore the brightness of your image. A large aperture (a wide opening) will pass a lot of light, resulting in a brighter photograph. A small aperture does just the opposite, making a photo darker.