Cycles : Cámara : Profundidad de campo [ Blender ]
One of the effects that bring more realism to an image synthesis is obtained by focusing an object or region located at a distance of cámara.Simula the human eye to focus attention on a particular object, finding other objects more or less blurred.
In photography this effect is known to focus / blur and depth of field of the image, being the result of two factors, aperture and shutter speed.
Rendering made with “Cycles” Blender allows you to define the field profundid very easily. Will select in the scene the camera and go into the menu for your configuration by clicking its icon.