Depth of Field
Depth of field (DOF) is a term which refers to the areas of the photograph both in front and behind the main focus point which remain "sharp" (in focus). Depth of field is affected by the aperture, subject distance, focal length, and film or sensor format.
A larger aperture (smaller f-number, e.g. f/2) has a shallow depth of field. Anything behind or in front of the main focus point will appear blurred. A smaller aperture (larger f-number, e.g. f/11) has a greater depth of field. Objects within a certain range behind or in front of the main focus point will also appear sharp.
|This setup was used to produce the example below. A picture was taken of three postcards 0.7m apart using a 70mm telephoto lens which was focused on the first card.|
|As you can see, at a large aperture of f/2.4 only the first card is in focus, while at f/8 the middle card is sharp and the distant card is almost sharp. Click on the image for a larger version.|
Coming closer to the subject (reducing subject distance) will reduce depth of field, while moving away from the subject will increase depth of field.
Lenses with shorter focal lengths produce images with larger DOF. For instance, a 28mm lens at f/5.6 produces images with a greater depth of field than a 70mm lens at the same aperture.
Depth of Field Calculator
This depth of field calculator allows you to have a better understanding of the various factors that affect depth of field. For digital cameras, it is important to use the actual focal length and NOT the 35mm equivalent focal length determined by the focal length multiplier.
This article is written by Vincent Bockaert,
author of The 123 of digital imaging Interactive Learning Suite
Click here to visit 123di.com