Depth of Field:
Also known as the “Zone of Acceptable Sharpness”, the ‘Depth of Field’ is the distance across the part of the picture that is acceptably sharp to the eye. When a lens focuses on a subject it creates only one point of clarity in the image. There is a gradual fall-off of sharpness either side of that point. Within the sharp zone the image appears sharp to the eye. The edges of the ‘depth of field’ are defined by the point where the loss of sharpness becomes noticeable.
Factors in creating the Depth of Field
Depth of field is dependent on a number of factors. These are:
- The focal length of the photographic lens;
- The design of the photographic lens itself;
- Aperture size;;
- Digital image sensor format and size;
- The ‘Circle of Confusion‘
- Aperture size (F stop)
- The camera-to-subject distance.
The actual control of the depth of field for a particular lens is via the control of the aperture settings. A larger Aperture size (f-stop size) gives a shallow depth of field. A small aperture size gives a deep depth of field. The range of aperture sizes depend on the photographic lens design and the design of each of the lens elements in it.
Depth of Field useage
The use of sharp and blur areas in images goes beyond the technical into the aesthetic. A photog with control over the zone of sharpness in a picture has two advantages…
- The image sharp area helps direct the eye to the subject in focus.
- The quality of blur (bokeh) and degree of blur helps to obscure or reveal the details in the area outside of the sharp zone. This gives the viewer clues to the nature of the rest of the picture.
The control of areas of the image that are sharp, and the degree of blur in an image are important composition factors. As a result they are important to the overall aesthetic of the image too.
For images and ideas on Depth of Field see this Google search.
Can be confused with…
Depth of field is often confused with depth of focus. These ideas both relate to the same phenomenon. However, they are on either side of the lens. Depth of field is the of the sharpness range in the area beyond the lens. It is outside of the camera. The ‘Depth of Focus’ is the sharp zone of focus on the inside (imaging side) of the lens.
Depth of Focus
Circle of Confusion
Definition: Photographic lens