Depth is the perception of three-dimensional space created through composition and camera placement.
Technical Details
Depth of field is calculated using the formula: DoF = 2Nc(f/F)², where N is the aperture number, c is the circle of confusion (0.025mm for 35mm film), f is the focus distance, and F is the focal length. For a 50mm lens with an aperture of f/2.8 and a focus distance of 3m, the depth of field is approximately 60cm. Wide-angle lenses from 14mm produce 3-5 times greater depth of field than telephoto lenses over 100mm with the same settings. Split diopters allow for different focus ranges within a single image without changing the aperture.
History & Development
In 1941, Orson Welles established the deep focus technique in "Citizen Kane" with Gregg Toland, who, using an aperture of f/8-f/11 and a 28mm wide-angle lens, achieved consistent sharpness from 0.5m to infinity for the first time. Jean Renoir had already experimented with depth staging through object movement between image planes in "La Règle du jeu" in 1939. Starting in 1959, the Nouvelle Vague deliberately reduced depth of field to a range of 10-30cm by using longer focal lengths and wide apertures.
Practical Application in Film
In "Barry Lyndon" (1975), Stanley Kubrick used NASA-developed f/0.7 Zeiss lenses for extremely shallow depth of field in candlelight scenes. Sergio Leone systematically composed three image planes in his Westerns: extreme close-ups in the foreground, the action space in the midground, and the landscape in the background. Modern blockbusters like "Mad Max: Fury Road" use depth staging for orientation in action sequences – sharp foreground for protagonists, blurred background for a sense of speed.
Comparison & Alternatives
Depth of field differs from bokeh by having a measurable spatial component rather than a purely aesthetic quality of blur. Rack focus shifts focus planes temporally, while split focus renders multiple planes sharp simultaneously. CGI-based post-focus technologies like Lytro allow for subsequent focus adjustment but do not achieve the optical quality of practical depth of field. Focus pulling remains the standard for feature films, while autofocus is increasing in documentaries.