A shutter is a movable cover or screen that alternately prevents and permits the passage of some desirable (or undesirable) element.

A window shutter is something like a door for a window, usually made of a sturdy material and often louvered , whose original purpose was to protect windows or the interior of a building from extreme weather conditions. In many modern residential constructions, decorative shutters are attached to either side of windows strictly for visual appeal.

In pipe organs, a shutter prevents or allows air to pass through the pipes, producing the desired sounds.

In photography, a shutter is a device that administers the exposure by admitting light to the film for a specific period of time. Shutters are normally of two basic types:

• Central shutter
• Focal plane shutter

A timing mechanism is required to support the different shutter speeds. These were originally pure mechanical devices, but are now mostly replaced by electronic timers.

Cinematography uses a rotary disc shutter in movie cameras, a continuously spinning disc which conceals the image with a reflex mirror during the intermittent motion between frame exposure. The disc then spins to an open section that exposes the next frame of film while it is held by the registration pin .

In movie projection, the shutter admits light from the lamphouse to illuminate the film across to the projection screen. To avoid flicker, a double-bladed rotary disc shutter admits light 2 times each frame of film. There are also some models which are triple bladed, and thus do this and 3 times per frame (see Persistence of vision).

See also: shutter speed, camera, photographic lens