Understanding Depth of Field

Depth of Field (DOF)

Depth of Field is the amount of distance between the nearest and farthest objects that appear in acceptably sharp focus in a photograph. One can think of DOF like drawing for the first time. When you first begin to draw your images are usually flat looking, for example drawing a triangle. The triangle is flat, and once you get better at drawing you learn how to make it 3-Dimensional... followed by being able to draw a pyramid with an appearance of a town/mountains/people in the background. 

This photo shows good DOF by having the first person in focus followed by other people/objects in the back, adding depth and significance to the picture.

The picture above is one way to represent how DOF can be played with a landscape photo. Many times DOF is strongly shown during a portrait/headshot photo. Many people want to have that "background blurriness" effect called Bokeh. The way Bokeh is achieved is by having a high F-stop number and as most photographer say, "wide open". When somebody is talking about shooting wide open they are referring to shooting with their Aperture low in number, allowing a lot of light to come in. These low numbers are usually F/2.8, but can get down to F/1.4 or lower.

The more open your lens is, the more DOF you're going to have.
-F/1.4-F/4 = A lot of light in, focus on 1 thing, a lot of DOF
-F/5-F/12 = Less light in, many things in focus, less DOF
-F/12-F/22 = Little light in, everything in focus (mostly), little DOF

This photo was taken with prime 50mm at F/2.0. Shooting so wide open allowed for a lot of light to come in and allowed for me to focus on just the one subject (the little girl). 

If I were to have shot this photo above with the same shutter speed but with at F/16 then you would have seen her and bushes/flowers in the background ALL in focus and clear. But having the option to shoot at F/2 I was able to have good DOF and Bokeh.

Below is an example of BAD DOF

This photo* is an example of bad DOF. Everything is sharp, there appears to be no background other than the clouds, and it looks flat (not 3-Dimensional). 

*http://www.flickr.com/photos/24203918@N00/146599451/