Depth of Field

One of the most imortant photographic concepts to grasp is depth of field. This term refers to the range of distance that appears acceptably sharp within an image.

Importance. Mastering depth of field in photography gives the photography control over how the viewer sees his picture. Using this technique forces the viewer to focus on a particular aspect of the shot due to its full clarity, making it stand out amongst the other objects in the frame.

Method. The objects placed in an image do not abruptly change from sharp to unsharp within the composition of the photograph. Instead, the change occurs as a gradual transition. Everything immediately in front or back of the focusing distance begins to lose sharpness, even if this is not perceived by our eyes or by the resolution of the camera. The term "circle of confusion" is used to define how much a point needs to be blurred in order to be perceived as unsharp. When the circle of confusion becomes perceptible to the eyes of the viewer, this region of the photo is said to be outside the depth of field and therefore no longer "acceptably sharp." As seen in Figure 1, an object relatively close to the main point of interest in the frame will still appear relatively sharp because the camera cannot easily differentiate the two as a result of their proximity. However, objects that are far away from t he main point of interest will appear unsharp due to the camera's inability to focus on two objects separated by such a great distance. In essence, the farther away an object is from the main point of interest, the less sharp it will appear.