Which component controls the length of time that light is permitted to pass through the lens?

• A. Shutter
• B. Diaphragm
• C. Filter
• D. Viewfinder

Answer: (A)

Exposure time—the duration light is allowed to reach the sensor or film—is controlled by the shutter. When the shutter opens, light passes through the lens for a set amount of time; when it closes, the exposure ends. A longer shutter duration lets in more light, brightening the image and potentially creating motion blur, while a shorter duration lets in less light, darkening the image and freezing motion. The diaphragm (aperture) changes the size of the lens opening to regulate light per unit time and affects depth of field, but not how long light is allowed through. A filter changes the light’s color or intensity before it reaches the sensor, without changing exposure time. The viewfinder simply shows a preview of the scene and does not control exposure. So, the shutter is the component that controls the length of time light passes through the lens.