Winn L. Rosch Hardware Bible, Sixth Edition

Shutters

The role of the shutter in a camera is to limit the amount of light getting in. Certainly too much light will overexpose film and overwhelm image sensors, but constraining the quantity of light isn't the only function of the shutter. After all, reducing the aperture will similarly prevent overexposure. The shutter controls exposure by its duration, the period during which light is allowed into the camera. Images often change over time—people blink, horses gallop, racecars race, grass grows, and paint peels. By limiting the time during which light is gathered, the shutter can capture a small slice of the image during which movement is minimal, even invisible. A fast shutter can simply stop motion—more correctly, stop the blurring effects ...