Factors that affect Depth of Field:
- f-number: Increasing f-number (reducing aperture diameter) increases DOF (foreground & background are all in focus). Decreasing f-number (increasing aperture diameter) decreases DOF (soft/blurred backgrounds).
- Focal length of the lens: The smaller the focal length number of the lens, the greater the DOF.
- Distance: The greater the distance of the subject from the camera, the greater the DOF.
A shallow DOF is ideal for photos where you want to call attention to your subject and not be distracted by the background, for example, portraits. A large DOF is ideal for landscape photos where you want everything in focus.