17Concepts in PhotographyAperture value and the depth of fieldYou can blur or sharpen the background of a photo by changing the sizeof the aperture. A large aperture gives your photos a shallow depth offield (DOF). Objects immediately in front of or behind your subject willbe blurred, while the subject will be in focus. A small aperture gives yourphotos a deep depth of field. Objects far in front or far behind your subjectand your subject will be in focus.A photo with a deep DOF A photo with a shallow DOFThe aperture housing contains several blades. These blades move together andcontrol the amount of light passing through the center of the aperture. Thenumber of blades also affects the shape of light when shooting night scenes. Ifan aperture has an even number of blades, light divides into an equal numberof sections. If the number of blades is odd, the number of sections is double thenumber of blades.For example, an aperture with 8 blades divides light into 8 sections and anaperture with 7 blades into 14 sections.7 blades 8 blades
