Filters

Photography (Basic) - Introduction to photography and other graphic techniques
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Figure 13-1.–Basic components of a motion-picture camera. Figure 13-2.–Rotary shutter. shock and prevent the film from breaking (fig. 13-1). The shutter in most motion-picture cameras is a focal plane type and is called a rotary disk shutter. A rotary disk shutter is a disk that has a segment cut out, causing the shutter to have a light and dark cycle as it rotates. Exposure is made when the cutout segment of the shutter passes in front of the film. The film is advanced during the dark cycle (fig. 13-2). A motion-picture camera is used to photograph action in a rapid succession of still pictures on a long strip of film. Each picture area on a motion-picture film is called a frame, and the speed that the camera is operated is called frames per second (fps). The standard operating speed for 16mm cameras is 24 fps. When the camera operating speed and the rate of projection are the same, the action looks normal; therefore, the standard projection speed is also 24 fps. However, it is possible, and sometimes desirable, to make motion pictures at a slower or faster rate than 24 fps. You may do this to either slow down or speed up the action on the screen. To portray a subject in slow motion, you operate the camera at a speed faster than the standard 24 fps, but keep the projector at the standard speed. To portray a subject in fast motion, you operate the camera at a speed slower than 24 fps, and the film is projected at 24 fps. All changes to the portrayal of normal subject motion should be done by adjusting the camera speed, not the movie projector. Camera speeds in the thousands of frames per second are used in scientific and experimental research to measure and observe such things as the fall of liquids, the speed of objects in flight, and the bursting characteristics of objects. When films shot at very fast fps rates are projected at 24 fps, the illusion of subject motion on the screen is slowed down considerably. At these speeds the viewer can study details of the subject matter and obtain research data. Motion-picture cameras are classified according to the size (width) of the film they use. The most common motion-picture film sizes are as follows: 8mm, super 8, 16mm, and 35mm. In the Navy today, motion-picture film has almost been completely replaced with video film; however, Hollywood productions still use motion-picture film as large as 70mm. Lenses used in motion pictures are basically the same as lenses for still photography; therefore, the information on optics presented in chapter 1 also applies to motion-picture camera lenses. The standard or normal focal length lens for a 16mm camera is 1 inch (25mm). Longer or shorter focal length lenses should be considered as long focal length (telephoto) or wide-angle lenses, respectively, depending on what size film is used. A long focal length lens for 16mm film is 38mm or longer. A wide-angle focal length lens for this camera is 13mm-17mm. Table 13-1 illustrates some typical camera and lens combinations. FILTERS With one exception, the use of filters for motion pictures is the same as for still photography. The effects that filters produce on motion-picture film emulsions are the same as the effects they produce on still photographic film emulsions. The one exception is the use of a polarizing filter. Camera panning should be avoided because variable darkening of the image results. The information on filters presented in chapter 3 applies to motion-picture photography as well as still photography. 13-2

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