Small-Format Cameras, ContinuedFocal-planeshuttersFocal-plane shutters are essentially two light-proof cloth or thin metalcurtains in front of the film plane that move across the film in the samedirection. As the first curtain moves from one side to the other, the secondcurtain follows. The speed at which the curtains move is called shutterspeed. When a slow shutter speed is set, the second curtain waits a relativelylong time and the space between the first and second curtain is wide.Shutterspeed dials are located on the camera body and indicate time in fractions of asecond. Shutter, aperture, and mirror work together in a precise sequencethat repeats each time the shutter release trips. Most 35mm cameras havefocal-plane shutters. Focal-plane shutters simplify camera construction andmake interchangeable lenses smaller, lighter, and less expensive than leafshutters.Figure 7-12 shows a focal-plane shutter.Figure 7-12.—Focal-plane shutters.FrameindicatorThe frame indicator is a small window near the shutter-speed dial thatdisplays the number of pictures taken. Each time the back of the cameraopens, the number resets to “0.”Continued on next page7-19
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