Depth of field
Changing the aperture size affects depth of field
•A smaller aperture increases the range in which the object is approximately in focus
depth_of_field At f/32, the background is distracting. At f/5.6, the flowers are isolated from the background.
f / 32
f / 5.6
Flower images from Wikipedia   http://en.wikipedia.org/wiki/Depth_of_field