In photography, Depth of Field (DOF) is essentially the Depth of Focus. It’s the distance between the nearest and farthest objects in the scene that appear acceptably sharp in the image. A shallow DOF tends to focus your attention on the primary subject of the image while effectively hiding from view the less important objects in the foreground or background. Alternatively, a large or deep DOF keeps most or all of the image in focus, allowing the viewer to see all objects in the frame.
Shallow vs. Deep DOF; Which to Choose?
Depending on your camera, you may have no choice. Inexpensive cameras typically take all photos with a deep DOF, and the images usually have all the objects in the scene in focus.
Shallow DOF photos are typically used in portrait or artistic photography, while deep DOF photos are typically used in applications such as landscape photography, where the scene requires everything in the frame to be in focus.
To achieve shallow DOF, you need either a lens with a small f-stop, a telephoto zoom, or a macro lens. A small f-stop lens (e.g. f/1.8 vs. f/5.6) has a large aperture, or opening, which focuses light more acutely on the optical sensor, causing objects in the foreground and background to be out of focus. You might be asking, “Why does a larger aperture cause a shallow depth of field? I won’t bore everyone with the details, but if you’re interested here’s a good forum conversation with a drawing that does a good job of explaining the physics.
Equipment I Use
Camera: Canon EOS Rebel T2i ($600 approx.)
Lens: Canon Prime 50mm f1.8 ($150 approx.)