Understanding Aperture and Depth of Field
Here is a quick tutorial about Aperture and Depth of Field and how to use them for specific effects.
The aperture itself is the opening in the diaphragm that controls the amount of light passing through the lens and onto the film or sensor. The size of the aperture is referred to as the f-stop and it relates directly to the depth of field, which is the distance between the nearest and farthest parts of a scene that appear in focus, or the focal length divided by the diameter of the aperture.
Click here to view the tutorial