Depth of Field
The depth of field defines the object distance over which the image is in focus.
Features of Depth of Field
- Smaller apertures (higher F numbers) give greater depth of field.
- Shorter focal lengths (smaller mm numbers) give greater depth of field.
- Greater subject distances give greater depth of field, unless a telephoto is being used.
Effects of Aperture and Focal Length on Depth of Field
- The lens aperture does more than control the amount of light—it also controls the depth of field.
- The more the lens is adjusted to a higher F number ("stopped down"), the greater the depth of field. The more the lens is adjusted to a lower F number (which is not called "stopped up"), the lower the depth of field.
- Changes in focal length also affect the depth of field.
- As focal length decreases (moves toward the wide angle direction), depth of field increases.
- As focal length increases (moves toward the telephoto direction), depth of field decreases.
- Since a wide-angle lens has a greater depth of field, it can give both a sharp foreground and a sharp background.
- At the same distance a telephoto lens will have less foreground and background in focus.