What is Aperture? Introduction Lesson

In our course on understanding the exposure triangle, we talked about the importance of light in photography and about controlling how much light gets exposed to the digital sensor in your camera to produce an image. You learned how ISO, along with the aperture setting and the shutter speed control how much light enters the camera to make you image. These three pillars work together to control lightness or darkness of a photograph. Today we’re going to talk specifically about aperture.

Introduction to Aperture

Aperture is the opening in the lens through which light passes to the camera and is measured in f-stops (or stops) usually ranging from 1.2 to 32. Inside the camera lens is a mechanical iris diaphragm that controls the amount of light transmitted to the imaging sensor in the camera. The diaphragm stops the passage of light, except for light that passing through the opening (or the aperture). It’s a lot like the shades on a window control the light.

Charles Bryant created a great video clip that will teach you the basic principles of aperture.

Understanding Aperture in Photography

We love this quirky 36 second video from Canon Australia that briefly describes aperture.

Aperture plays two important roles in photography. First, it limits the amount of light that passes through the lens so you get a properly exposed image. When you change the f-stop value, you change the opening of the iris. The lower the f-stop, the larger the opening (just the opposite of what you might expect).

Second, it controls the depth of field (which is the range in an image that is in focus). Another way to explain Depth of Field is the area of sharpness in front of and behind the subject you’re focused on.

Moving from one f-stop to the next (up or down) doubles or cuts in half the amount of light passing through the lens. A smaller f-stop number like 2.8 means a larger opening of the iris. When you change the aperture from a 2.8 to f4, its called stopping down.

Lenses have a range of apertures and lenses do not have all apertures available. When we say a lens is a 2.8 lens, that means the lowest aperture available is 2.8. In the diagram above you can see f-stops of; 1.4, 2, 2.8, 4, 5.6, 8, 11, 16, 32.

Changing the aperture is usually a setting inside your camera.

The Basics of Aperture (Video)

This entertaining 6 minute video on The Basics of Aperture by Larry Becker at B&H Photo goes into a little more detail on the mechanics of aperture.

Measuring Aperture

Aperture is measured in f stops. The larger the number under the f, the smaller the hole (aperture) and the less light that comes in.

How Aperture Affects Depth of Field

A wide open aperture results in a shallow depth of field whereas a smaller aperture results in a great depth of field. If you want to know why this is see our lesson on the physics of depth of field. If you’re interested in knowing what the “f” is about in all the aperture settings see our lesson on “aperture f number“.

Aperture Photography Course from Udemy

Master the Aperture Mode on your Digital SLR Camera

If you want to learn more about aperture, take a look at our article on adjusting aperture for extra information.