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The range in which all objects in front of the camera lens appear to be in focus is called the depth of field. As discussed earlier, the image on televi¬sion is only two dimensional. Adding depth to the shot makes it more cred¬ible and aesthetically pleasing. It also lends reality to the frame.
The depth of field is dependent on (1) the focal length of the lenses (wide lenses provide greater depth of field), (2) the aperture (smaller openings provide greater depth of field), and (3) camera position (the greater the distance between the object and the camera, the greater the depth of field).
This means that the depth of field increases as the focal length decreases.
Conversely, the depth of field decreases as the focal length increases. When the depth of field is greater more number of objects appear to be in focus. When the depth of field is shallow, very few objects are in focus. Figures 2.6(a) and (b) give an idea of how images look when they are shot with shallow depth of field and greater depth of field.
When two characters or objects are lined up at different distances from the camera, it sometimes may be necessary to split the focus to keep both subjects in clear, sharp view. This is not done by focusing on a point midway between the two; rather, it is done by focusing on a point one-third the distance behind the front subject. In other words, focus will be sharp for an area one-third in front and two-thirds behind the point of focus.
Rack focus is where the focus shifts from one object to another within a single shot. Imagine two characters in a frame. The father is out of focus while the son, who is talking, is in focus. The moment the son stops speaking and the father begins, tJ.1e son goes out of focus and the father comes into focus. Follow focus o~:i:he other hand means changing the focus of the primary subject moving within a shot. Say we are shooting a person walking towards the camera in an MCU. Follow focus helps us retain the person in focus even as he is walking towards the camera.
Fig.2.6 Depth of field affects focus-(a) shallow depth yields fewer objects in focus, whereas (b) greater depth yields more objects in focus; also see Colour Plate 1
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