The exposure triangle may sound like a geometry term, but it actually refers to three central features of exposure: aperture, shutter speed, and ISO. And for many people learning photography, the relationship between them can be confusing.
In photography, you have to balance the three sides of the exposure triangle to achieve a specific result. When you adjust one, you need to accommodate at least one of the others. To create a photo that is properly exposed, though, you need to get the three elements working together.
Along with affecting exposure, they determine the overall appearance of an image. So, understanding the exposure triangle is necessary for both technique and composition.
Aperture is how open or closed the lens’ iris is—this is the hole in the lens that lets in light. An F-stop is a number on your camera that tells how open or closed the aperture is.
- The wider the aperture (or lower f-number), the more light that reaches the sensor.
- A narrow aperture (or higher f-number) lets less light reach the sensor.
When you adjust the aperture, the depth of field changes, and it affects how much of the shot is in focus. The smaller apertures (higher f-stops), give a greater depth of field and allow more of a scene to be in focus—like in landscapes. Wider apertures (lower f-stops) create a narrow depth of field. This helps when you want to isolate your subjects, like in a portrait. It can make the background blur and keep the focus on the subject.
Shutter speed is a measurement of how long the shutter stays open. So, it refers to the length of time the sensor is exposed to light. It is measured in seconds. Faster shutter speeds allow the sensor to collect light for less time, resulting in a lower exposure. Slower shutter speeds will enable the sensor to collect light for longer, resulting in a higher exposure. So, if you want to double the amount of light, you would need to double the length of the exposure.
Using a higher shutter speed allows you to maintain sharpness, especially in the case that the subject or camera is moving. When the shutter is open longer, the camera is recording the elements in the frame. So if one of them moves, it could result in blurriness. On the other side, a long shutter speed can create visually stunning effects—like with the blurring current in a river, for instance.
Think about ISO as the sensitivity of the digital sensor. The ISO number shows how quickly a camera sensor absorbs light:
- Higher ISO values mean the sensor doesn’t need to get as much light to make the right exposure. So, you can use a faster shutter speed. This is great for times with little light but can result in less detail.
- Lower ISO values mean the sensor has to get more light to make the exposure. It is recommended for clearer images with more detail.
When taking photos indoors (or when there is less light), you have to increase your ISO if you don’t want to sacrifice shutter speed. Otherwise, If you go down in shutter speed (to let in more light), your images will become blurry. It’s better to have a grainy image that shows a well-defined subject than a blurry one.
ISO, aperture, and shutter speed: working together
Using the in-camera light meter will help you balance all three of these essential elements. You can see the light meter through the viewfinder or on the back of the camera. It will let you know precisely how much light is entering your camera. If you have lots of lines to the positive, you have too much light. And vice versa. A good exposure typically falls somewhere around the middle.
Understanding the basics of shutter speed, aperture, and ISO—and how they work together— will help you get the results you want.