Depth of field
- The distance between the nearest and the furthest objects that give an image judged to be in focus in a camera.
What is depth of field?
Depth of field in both amateur/professional photography and videography is simply the distance between the nearest object and furthest object within an image which is deemed to be in focus or ‘sharp’.
A large depth of field has objects in the foreground and background in focus, and is often called deep focus. A small depth of field has a small focal plane where the acceptable distance of focus is shallow, this is often called shallow focus. This difference can be seen in the graphics below:
How to Adjust Depth of Field
As a photographer, being able to control the depth of field in an image is one of the primary creative tools at your disposal. Adjusting the depth of field changes how viewers of your image will identify either a single key object or view objects from near to far.
The depth of field is primarily adjusted using the aperture control of your camera/lens. The larger the aperture opening in the lens the shallower the focal plane is and hence the narrower the depth of field is. For portraits it is advisable to have a shallow depth of field to throw your background out of focus and keep your main subject (your person) key to the image. For landscapes it is advisable to have a wide depth of field, aiming to make as much of the image in focus – from a foreground object which should lead the viewer into the image to the horizon.
Near:Far Focal Ratio
The depth of field beyond your focal plane is always larger than the depth of field in front of your focal plane. This depends on the distance you are focusing on, but typically there will be more in focus behind your subject in focus than in front.
Hyperfocal Depth of Field
The hyperfocal distance is the nearest focusing distance where the depth of field extends to infinity past your focal plane. If you focus your camera at the hyperfocal distance, you will get the largest possible focal range for your given settings.
In practice you may often use this technique when taking landscape images, we do here at Photography 101 – and when out in the field a good rule of thumb is to focus on an object which is 1/3 into your image from you. With a suitably high f/number you should then get an image which is sharp throughout - with maximum depth of field.