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What Is Aperture?
Aperture means an opening. In photography, aperture refers to the hole in the middle of the camera lens which allows light to pass onto a digital camera’s image sensor or the film strip on a film camera. The aperture is made of a series of interlocking metal blades that open and close like an iris. Both aperture and shutter are the same mechanism—they both open and close when you click the shutter button. Shutter speed determines how long the aperture remains open.
You control the size of your camera’s aperture by twisting the ring around the lens to open the aperture wider or smaller. This affects how much light touches the sensor—a bigger aperture allows more light and a smaller aperture allows less light.
How Is Aperture Measured?
Aperture is expressed as a fraction, measured in f-stops. A low f-stop, or f-number, indicates a wider aperture, while a high f-stop narrower aperture. Just as ½ is a greater quantity than ¼, f/2 is wider than f/4. Both are wider than f/16.
There are many different lenses with different aperture ranges, but a basic camera lens will adjust to f-numbers within this range:
What Is an F-Stop?
F-numbers are the mathematical relationship between your camera’s focal length and the size of your aperture:
Focal Length / Diameter of Aperture = F-Stop
This means that aperture remains consistent across different cameras and focal lengths—the same f-stop will create the same exposure, no matter your camera’s focal length.
For example, say you have two cameras: one with a focal length of 90mm the other with a focal length of 60mm. An f/4 aperture setting on the 90mm lens creates an opening that is 22.5 mm (a quarter of the focal length), while that same aperture on the 60mm lens results in a 15mm wide opening (which is still a quarter of the focal length). Both cameras will produce the exact same image with the same depth of field and the same exposure, as long as the shutter speed and ISO remain consistent.
How to Adjust Aperture on Your Camera
You can manually set the aperture on your digital camera in one of two ways:
- Manual Mode: Written as “M” on most cameras on the top dial of camera, which takes your camera out of auto mode. In this mode, you also have control over shutter speed.
- Aperture priority mode: Written as “A” or “Av” on your camera. In this mode, your camera automatically adjusts the shutter speed according to the aperture you chose.
On some cameras, you select the aperture on the display screen. On other cameras, you select the aperture on the lens.
2 Advantages of Controlling Aperture Manually
Controlling the size of your camera’s aperture manually let you control two things: exposure and depth of field
Exposure: The amount of light coming into your camera. Controlling your aperture manually allows you to adjust exposure and image brightness beyond what the automatic settings on your camera will allow. If you are photographing when it is dark, you can select a lower f-stop—opening your aperture wider—ensuring your image isn’t underexposed (too dark). If you are photographing where there is a lot of light, you do the opposite—select a higher f-stop, which closes the aperture—to make sure your photo isn’t overexposed.
Depth of field: How much of your image will be in focus. Adjusting aperture also controls the depth of field which how much of your image will be in focus.
- A deep depth of field means that almost everything in your image will be in sharp focus, from things in the near foreground to things in the far background. Think of a basic phone camera, where everything in the image is sharp and in focus, even things that are far in the distance. Use a narrow aperture to achieve a deep depth of field when photographing wide vistas, like landscapes and city skylines, where you want everything to be in focus.
- A shallow depth of field means only the subject will be in focus and the rest of the image will be out of focus. For example, some phones have a portrait mode on their camera, which changes the depth of field so the foreground is in focus and the background is not. Use a large aperture to achieve a shallow depth of field when photographing a portrait against a busy background, so the person will be in focus and the background will be blurred to not distract the viewer.
How Are Shutter Speed and Aperture Related?
You may also adjust your aperture depending on your shutter speed.
- Compensate for a quick shutter speed: A quick shutter speed will avoid motion blur or capture quick movements clearly, but it does not let in much light. You can compensate for this decreased light by using a larger aperture (remember, a lower f-stop) to let in more light.
- Compensate for a slow shutter speed: A slow shutter speed lets in a lot of light and can be used to capture an image in low light without a flash or to blur the motion of a moving subject. You can compensate for this increased light by using a smaller aperture (higher f-stop) to ensure your image isn’t overexposed.
Learn how to master the elements of the exposure triangle with Jimmy Chin.