Depth of Field

Aperture describes an adjustable opening inside your camera lens that controls the amount of light striking the film. As the size of the aperture changes, the angle of light striking the film also changes. It is this angle change, much like eyeglasses change the angle of the light, that creates changes in depth of field.

Aperture is measured by F-Stop on your camera controls. F-Stop settings represent a ratio derived from the size of the lens opening and focal length. Aperture has historically been confusing for new photographers (and some established photographers) because of the apparent conflict in description. A small F-Stop is a large aperture opening and a large F-Stop is a small aperture opening. Because a smaller aperture limits the amount of light entering the lens, a large F-Stop also requires more light to properly expose an image.

A simpler way to remember the relationship between F-Stop/Aperture and Depth of Field is:
• Large F-Stop = Large Depth of Field = More Light Needed
  
• Small F-Stop = Small Depth of Field = Less Light Needed

This means that larger F-Stops, such as F11, will require slower shutter speeds and produce images with larger depths of field. Smaller F-Stops, such as F4, will allow faster shutter speeds and produce images with shallower depths of field.