Depth of field // Features

Definition
depth of field is the distance between the nearest and farthest objects in a scene that appear acceptably sharp in an image.

How to alter depth of field
by changing your aperture, you can alternate between having a large or small depth of field. So this means you can change your aperture to a large depth of field if you want the background of your image in focus, or a small depth of field if you want to focus on a specific object in the image and have the background be out of focus.

Large depth of field

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As you can see here all the image is in focus, so you can see the objects that are in the very background of the image; therefore this is a large depth of field.

Small depth of field

Sourced from http://www.photoweeklyonline.com/wp-content/uploads/2011/07/Shallow_DOF.jpg

 

Sourced from https://posterjackcanada.files.wordpress.com/2012/03/shallow-depth-of-field.jpg

As you can see here only the subject of the image is in focus while the back ground of the image is out of focus so the viewers attention is on the subject, therefore this is a small depth of field.