What is aperture in photography?

(Image credit: Future)

What is aperture in photography? The term aperture refers to the opening of a lens' diaphragm – essentially a hole through which light passes to reach the camera. By changing your aperture, you can change and control how much light enters the camera sensor from your lens.

Key to understanding what is aperture in photography, you need to know that the size of the opening is calibrated in "stops" of light – also known as f-stops (more on f-stops here) and this numerical value also describes the ratio of a lens' focal length (the "f") to the diameter of the opening. 

Each successive stop is half as bright as its predecessor – which is a bit confusing, so a larger f-number actually means a smaller aperture. Thus f/2 is half as bright as f/1.4, f/2.8 is half as bright as f/2, and so on.

Aperture is one of the three fundamental pillars of the exposure triangle, (the other two being shutter speed and ISO), and it helps to be familiar with how these three elements come together to make up a correct exposure.

What is aperture in photography: the physical side

The concept of aperture can at first be tricky to grasp, but the physical side is simple!

An aperture itself (the opening) is formed by intersecting blades. Different lenses have a different number of blades, and these can move to make the opening larger or smaller depending on the f-stop that you select.

The aperture assembly is located in the barrel of the lens, between the lens elements. A motor opens and closes the aperture each time the shutter is fired. This matches the f-stop set by you on your camera, and the focal length used.

Here's our cheat sheet, previously formatted for Digital Camera Magazine. Download the image and save it to your phone's camera roll for quick reference (Image credit: Future)

What happens when you change the aperture?

Here's our second aperture cheat sheet (Image credit: Future)

Most lenses use a standard scale of f-stops to indicate the size of the aperture, although as we've already mentioned, each lens will have a determined aperture range depending on its design. For example, the best portrait lenses tend to have a wider maximum aperture, along with fast prime lenses.

There are two reasons why you'd want to change the aperture; to let in more or less light for your exposure, and to control the depth of field. A wider aperture will let in more light and give you a more shallow depth of field, while a narrow aperture lets in less light but means more of a scene will be in sharp focus.

The cheat sheet above explains when and why you would use narrow and wide apertures, either to let in more light to the sensor in low-light conditions or to use depth of field creatively to blur the background of your image.

Aperture explained at a glance

  • Aperture is calibrated in f-stops.
  • A smaller, narrower opening gives more depth of field. 
  • An aperture of f/22 is narrower than f/4.
  • Your maximum or widest aperture is determined by your lens.
  • The diameter of the aperture is focal length divided by the aperture value. So the diameter of an f/4 setting on a 100mm lens is 25mm (100mm divided by four). The diameter of an f/4 setting on a 28mm lens is 7mm (28mm divided by four).

Use the handy cheat sheet above to see this all for yourself. And make sure to keep us bookmarked for more great photography cheat sheets, along with all our general photography tips

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Lauren Scott
Managing Editor

Lauren is the Managing Editor of Digital Camera World, having previously served as Editor of Digital Photographer magazine, a practical-focused publication that inspires hobbyists and seasoned pros alike to take truly phenomenal shots and get the best results from their kit. 

An experienced photography journalist who has been covering the industry for over eight years, she has also served as technique editor for both PhotoPlus: The Canon MagazinePhotoPlus: The Canon Magazine and DCW's sister publication, Digital Camera Magazine

In addition to techniques and tutorials that enable you to achieve great results from your cameras, lenses, tripods and other photography equipment, Lauren can regularly be found interviewing some of the biggest names in the industry, sharing tips and guides on subjects like landscape and wildlife photography, and raising awareness for subjects such as mental health and women in photography.