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Figure 1-28 Depth of Field

Photography (Basic) - Introduction to photography and other graphic techniques
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Figure 1-26.–Focusing for one object. I  M  A  G  E       P  O  I  N  T  S (  C  I  R  C  L  E O  F   C  O  N  F  U  S  I  O  N  ) Figure 1-27.–Image on film in front of and in back of the point of sharp focus. FOCUSING FOR ONE OBJECT.–Focusing is done essentially to obtain the proper distance between the lens and the film. When light rays come from a far object and pass through a lens, they form a sharp image close to the lens. When light rays come from a near object, they form an image farther away from the lens. This means that the lens must be focused on either the far or the near object, depending on which one the photographer  wants  to  have  in  sharp  focus.  When  a sharp image of the near object is desired, the lens should be focused by moving it farther away from the film. When you want a sharp image of the far object, move the lens closer to the film (fig. 1-26). CIRCLE  OF  CONFUSION.–A     picture     is basically  an  accumulation  of  many  points  that  are  exact images  of  points  composing  the  subject.  After  light strikes a subject, it is reflected from many points on the subject. A camera lens redirects these reflected rays into corresponding points on the film. Each of these points is reproduced by the lens as a circle. When the circle is smaller than l/100 inch, it appears as a sharp point to the eye. When the circle is larger than 1/100 inch, the eye sees it as a circle, and the image is blurred or out of focus. Each out-of-focus circle on the film is called a circle of confusion and can be visualized as the cross section of a cone of a light ray (fig. 1-27). l-23







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