posted Friday, 20 January 2012, 23:07 (+0800), by Martin
This is the ninth article in a
series on "understanding your camera"
that I am writing as I teach camera basics and camera operation to my children.
Let me start with a definition of "depth of field". Wikipedia defines "depth of field" as
A small depth of field is also referred to as "shallow focus", and a large depth of field is also known as "deep focus".
The term "depth of field" is often abbreviated as "DOF".
There are a number of factors that affect the depth of field in a photo.
The second photo shows a much larger depth-of-field due to a much smaller aperture.
Shallow depth of field will draw the viewer's eye to a specific part of the image, typically desired in portrait photography.
Conversely, deep depth of field ensures all components of the image are in focus, which is typically desired in landscape photography.
Understanding the factors that affect depth of field allow you to be aware of the impact of varying any of those factors, and thus have more control over the depth of field in your photos.
Because depth-of-field is one of the key aspects I like to control in my photography, most of my photos are taken with the mode set to aperture priority. This allows me to choose the aperture, rather than allowing the camera to select the aperture.
Definition
Let me start with a definition of "depth of field". Wikipedia defines "depth of field" as
"the distance between the nearest and farthest objects in a scene that appear acceptably sharp in an image".
If the entire image is sharp (ie, all in focus), it has a large depth of field.
If an image has the foreground sharp, while the background is blurred, it has a small depth of field.
A small depth of field is also referred to as "shallow focus", and a large depth of field is also known as "deep focus".
The term "depth of field" is often abbreviated as "DOF".
Factors Affecting Depth of Field
There are a number of factors that affect the depth of field in a photo.
- Distance between camera and subject
Shorter distance = less DOF; longer distance = more DOF.
The further the camera is away from the subject, the more DOF you will get.
This is one of the reasons macro photography is challenging. With very short distances between the camera and the subject, the depth of field tends to get very small. - Focal length
Longer focal length = less DOF; shorter focal length = more DOF.
Longer focal lengths mean less DOF, which is one of the reasons why longer length lenses can be great for portraiture photography. - Aperture
Larger aperture = less DOF; smaller aperture = more DOF.
Opening up the aperture reduces the DOF, while stopping down the aperture increases the DOF.
A "fast" lens with a larger maximum aperture (say, f/2.8 or larger) allows a smaller depth of field to be achieved than a kit lens with a maximum aperture of f/4. - Format size (ie, sensor size in a digital camera, film size in a film camera)
Larger sensor = less DOF; smaller sensor = more DOF.
Full-frame DLSR cameras provide smaller depth of field than a crop-sensor DSLR.
Point-and-shoot cameras, with their tiny sensors, typically struggle to provide a small depth of field. (This is due to the format size affecting the circle of confusion, but that is a complex topic that I will leave for a future post.)
The second photo shows a much larger depth-of-field due to a much smaller aperture.
very short depth-of-field due to lens being wide open at a large aperture of f/2.8
Canon EOS 50D, 24-70mm f/2.8L @70mm, 1/400 sec, f/2.8, ISO100
larger depth-of-field due to lens being stopped down to a small aperture of f/22
Canon EOS 50D, 24-70mm f/2.8L @70mm, 1/30 sec, f/22, ISO640
Why You Should Think About Depth of Field
Shallow depth of field will draw the viewer's eye to a specific part of the image, typically desired in portrait photography.
Conversely, deep depth of field ensures all components of the image are in focus, which is typically desired in landscape photography.
Understanding the factors that affect depth of field allow you to be aware of the impact of varying any of those factors, and thus have more control over the depth of field in your photos.
Because depth-of-field is one of the key aspects I like to control in my photography, most of my photos are taken with the mode set to aperture priority. This allows me to choose the aperture, rather than allowing the camera to select the aperture.
