Depth of Field

The depth of field (DOF) is the distance in front of and beyond the point of focus that appears acceptably sharp in an image.

A large depth of field means that a large percentage of the field of view is in focus, from objects close to the lens often to infinity. You can control the depth of field by focal length, iris diameter and distance of the camera to the subject.

The smaller focal length and iris opening or a long distance between the camera and the subject, the greater the depth of field. In other words, the larger the f-number the greater is the depth of field.

The small depth of field is most apparent at night when the lens is fully open and the depth of field is at its minimum so objects that were in focus during the day may now be out of focus.

Depth of field may be important, for instance, in monitoring a parking lot, where there may be a need to identify license plates of cars at 20, 30 and 50 meters (60, 90 and 150 feet) away.