Learn the Terms > Aperture and Depth of Field

Aperture and Depth of Field

How adjusting your plane of focus can drastically change your photos

Every time you take a photograph, the lens of your camera opens to let in light. The aperture setting determines how much or how little your lens opens when you take a photograph.

Aperture Priority

Many digital cameras can be set to aperture priority mode. In this mode, you set the aperture and the camera automatically selects the shutter speed so that the photograph has the right exposure.

Why Aperture Really Matters

When your lens is open very wide, the background is typically out of focus. Wide-open aperture is good for portrait photographs, when you don't want the background to interfere with your subject.

When your lens is only open a small amount, everything from the foreground to the background is in focus. This aperture is used for landscape photographs, so that all of the scenery in the photo is in focus.

The Aperture / Depth of Field Relationship

When you focus your camera on an object in space, you are also focusing on everything else around the object that is the same distance away from the camera. This can also be described as focusing on a PLANE, rather than a point.

The following illustrations will introduce you to two important concepts: plane of focus and depth of field.

Illustration One

plane of focus illustration

Illustration Two

plane of focus illustration

Illustration Three

Notice that in the two previous illustrations the plane of focus is very thin — it does not have any depth. This is an artificial illustration to demonstrate the plane of focus.

In reality, when you focus on an object in space, there is also an area in front of and behind the object that is also in focus. This area of focus is called the depth of field.

plane of focus illustration

To take better photographs with your camera, you need to be able to manually control the depth of field.

Find out how...