Aperture is one of the essential concepts of photography that can greatly affect the look and feel of your images. It refers to the size of the opening in the lens that allows light to enter the camera. This opening can be widened or narrowed to allow more or less light through to the sensor.
The closest analogy is the human eye. In the eye, the amount of light allowed in is controlled by the pupil. In bright light, the pupil narrows. In dark environments the pupil widens significantly. Likewise, by adjusting the aperture, you can control the amount of light that enters the camera, as well as the depth of field of the image. More on this below.
The pupil in your eye is the easiest analogy to a camera's aperture.
Aperture is measured in f-stops, which are represented by a series of numbers. f-1, f-2.4, f-16, etc. The lower the f-stop number, the larger the aperture opening and the more light enters the camera. Conversely, the higher the f-stop number, the smaller the aperture opening and the less light enters the camera. Think 'low f-stop' = 'wide pupil', 'high f-stop' = 'narrow pupil'.
Closeup of f-stop markings on a camera lens denoting aperture
How Does Aperture Affect Depth of Field?
Aperture also affects the depth of field of the image, which refers to the range of distances in the image that appear sharp. A larger aperture (lower f-stop number) produces a shallower depth of field, meaning that only a small portion of the image will be in sharp focus, while the rest of the image will be blurry. This effect is often used in portrait photography, where the subject is in sharp focus while the background is blurred, creating a sense of separation between the subject and the background.
Conversely, a smaller aperture (higher f-stop number) produces a deeper depth of field, meaning that a larger portion of the image will be in sharp focus. This is often used in landscape photography, where the photographer wants to capture as much detail as possible in both the foreground and background.
Balancing Aperture with Light
Choosing the right aperture for a given situation requires balancing the need for light with the desired depth of field. In low-light situations, a larger aperture (lower f-stop number) may be necessary to allow enough light into the camera, even if it results in a shallower depth of field. In brighter conditions, a smaller aperture (higher f-stop number) can be used to achieve a deeper depth of field. Many photographers practicing astrophotography use low f-stop apertures to let a greater amount of light pass to the sensor from dark night skies. This lets them capture a more sharp image with a faster shutter speed than they would have to with a narrower (higher f-stop) aperture.
Aperture and Image Quality
In addition to affecting exposure and depth of field, aperture can also affect the quality of the image. Generally, lenses perform best when the aperture is stopped down a few stops from its maximum opening, which can result in sharper and more detailed images.
Conclusion
Aperture is an essential concept in photography that affects the amount of light that enters the camera, the depth of field of the image, and the quality of the image. Understanding how to use aperture effectively can help you create well-exposed images with the desired depth of field and visual impact.