Exposure is one of the fundamental concepts in photography, and understanding it is crucial for producing well-composed images. In simple terms, exposure refers to the amount of light that reaches the camera's sensor or film. When we take a photo, we want the camera to capture just the right amount of light to produce a well-balanced image.
To achieve this, there are three main variables we can adjust: aperture, shutter speed, and ISO. These three elements work together like a photographic love-triangle to control the amount of light that enters the camera and, ultimately, the exposure of the image.
Adjusting exposure is like a triangle, with the 3 points being aperture, shutter speed, and ISO.
Aperture
The aperture is the opening in the lens that allows light to enter the camera. It is measured in f-stops, with a lower number representing a larger opening and a higher number representing a smaller opening. A larger aperture (smaller f-stop number) allows more light into the camera, while a smaller aperture (higher f-stop number) allows less light in.
Aperture also affects the depth of field, which refers to the range of distances in the image that appear sharp. A larger aperture (smaller f-stop number) produces a shallower depth of field, while a smaller aperture (higher f-stop number) produces a deeper depth of field. For a more in-depth explanation, read our article on aperture here.
Controlling your camera's aperture will allow you to adjust how much light is making it to the sensor and affecting your exposure.
Shutter Speed
The shutter speed refers to the amount of time that the camera's shutter remains open to allow light to reach the sensor. It is measured in seconds or fractions of a second, such as 1/60, 1/125, or 1/500. A faster shutter speed (e.g., 1/500) allows less light in and produces a sharper image of moving objects, while a slower shutter speed (e.g., 1/60) allows more light in and can create a sense of motion blur.
The longer you have a shutter open, the longer light has to expose your image to the sensor or film. Keeping in mind the effects of motion blur, adjusting your shutter speed is another way of controlling how much light your film or sensor takes in. Our article on shutter speed gives a more thorough explanation.
A dark night sky is captured by a slower shutter speed. You might even capture a couple of shooting stars with the accompanying motion blur.
ISO
ISO refers to the sensitivity of the camera's sensor to light. It is measured in numbers, such as 100, 200, 400, 800, and so on. A higher ISO number makes the sensor more sensitive to light, allowing for a faster shutter speed or smaller aperture, but it can also introduce noise or grain into the image. When cameras relied exclusively on film, this was a choice a photographer/videographer would make when they purchased the roll. In the age of digital sensors, this is a choice that most are able to make on-location when they are shooting but understanding your camera's ISO range and native ISO beforehand can help you compose your shots more effectively. With a higher ISO and more light sensitivity, you can use a higher shutter speed or higher aperture.
A roll of film with its ISO level (200) indicating how sensitive it is to light. High ISO = more light sensitive. Low ISO (100-200-400, e.g.) = less light sensitive.
Conclusion
The three elements of exposure work together, and adjusting one affects the others. For example, if you increase the aperture (lower f-stop number = more light), you'll need to use a faster shutter speed (less light) or lower ISO (less light sensitivity) to maintain the same exposure level. Similarly, if you increase the shutter speed (less light), you'll need to use a larger aperture (more light entering the camera) or higher ISO (more light sensitivity) to maintain the same exposure level.
In addition to these three variables, paying close attention to your lighting (natural or otherwise) plays a huge impact into how easy/difficult it is to get exposure right.
Many cameras also have exposure compensation settings that allow you to adjust the overall brightness of the image using software within the camera. You can use this setting to make the image brighter or darker than what the camera's metering system suggests. If all else fails, you can adjust exposure in post-production. See our article on dynamic range to better understand how a camera's sensor technology and codec can be used to correct exposure after the fact.
Understanding exposure is essential for taking great photos, and experimenting with aperture, shutter speed, and ISO can help you achieve the look you're going for in your images. With practice, you'll learn how to balance these variables to produce well-exposed images in a variety of lighting situations.