The depth of field is a term used in cinema, but also in photography. This corresponds to the area of the image, whose elements are crisp, not fuzzy. It is also called zone of sharpness in the image or focal plane. More specifically, it is the distance between the first and the last net image.
The basics of depth of field
The depth of field depends on several criteria : the opening of the aperture, the focal length used, and finally the distance of the objects photographed or filmed. Thus, by reducing the aperture of the diaphragm or the focal length of the lens, we will be able to increase the depth of field, and therefore, the area of sharpness.
The depth-of-field permits in particular to give importance to a subject with respect to the other playing on the sharpness of different elements. If the depth of field is reduced, the main subject is highlighted, isolated, relative to other elements that are unclear. Conversely, if the depth of field is high, the subject is integrated with other elements of the image, who also have their importance. The blur effect on the 1st or 2nd plan is known in photography as bokeh.
The depth of field in cinema
Today, there is a uniformity of the use of the depth of field in cinema, particularly in the United States. Whether for hollywood blockbusters in 3D and independent cinema, the filmmakers american are more likely to offer plans with a depth of field very small, with a subject in sharp focus and the rest of the image blur. The use of digital cameras, slr camera for the filming of the short film also tends to generalize this type of image in the cinema.
However, it has not always been so. Great directors have used depth of field to strengthen the narrative of their film. The most symbolic is Orson Welles, who marked several generations of film fans and artists with his first film, Citizen Kane. During one sequence, he likes to change the depth of field to provide new information to the viewer. Similarly, the characters in the film are not consistently located in the foreground of the image, but may be indented, in the background, without being blurry.
Examples of the use of the depth-of-field – Preview of Citizen Kane
In this excerpt from Citizen Kane, we can see how Orson Welles uses depth of field to position, in space and narrativement, the character of Kane in relation to the other. Character at the center of all conversations, he is in withdrawal and is the final little participant, but a victim of the decisions of other people.
For an analysis of pus developed the use of depth of field in Citizen Kane and other films, you can also check out this analysis : depth of field
To go further
This video gives explanations of technical detail on the operation of the depth-of-field. It is a perfect complement to this article.