Shutter (photography)

A shutter can also be used to allow pulses of light to pass outwards, as seen in a movie projector or a signal lamp.

Other mechanisms than the dilating aperture and the sliding curtains have been used; anything which exposes the film to light for a specified time will suffice.

The exposure time and the effective aperture of the lens must together be such as to allow the right amount of light to reach the film or sensor.

Special flashbulbs were designed which had a prolonged burn, illuminating the scene for the whole time taken by a focal plane shutter slit to move across the film.

The disc then spins to an open section that exposes the next frame of film while it is held by the registration pin.

Focal-plane shutters are usually implemented as a pair of light-tight cloth, metal, or plastic curtains.

At shutter speeds faster than the X-sync speed, the top curtain of the shutter travels across the focal plane, with the second curtain following behind, effectively moving a slit across the focal plane until each part of the film or sensor has been exposed for the correct time.

The effective exposure time can be much shorter than for central shutters, at the cost of some distortion of fast-moving subjects.

In the simplest version of Guillotine shutter a plate with an aperture slides across the lens opening.

When the shutter release lever is actuated, the spring causes the disk to quickly rotate once so that the hole passes the camera aperture and allows light through for a brief moment.

The blades slide over each other in a way which creates a circular aperture which enlarges as quickly as possible to uncover the whole lens, stays open for the required time, then closes in the same way.

Flash synchronization is easily achieved with a pair of contacts that close when the shutter is fully open.

Effectively the shutter acts as an additional aperture, and may cause an increased depth of field, undesirable if shallow focus is being used creatively.

The term diaphragm shutter has also been used to describe an optical stop with a slit, near the focal plane of a moving-film high-speed camera.

The early Compound shutter had a pneumatic mechanism, with a piston sliding against air resistance in a cylinder.

More accurate clockwork mechanisms then replaced the airbrake, and the German Compur,[3][6] and the later Synchro-Compur, became virtually the standard quality shutter.

The company Compur Monitor was still in business as of 2012[update], but made only gas detection systems.

Image sensors without a shaded full-frame double must use serialized data transfer of illuminated pixels called rolling shutter.

Dynamic range and noise performance are not compromised, because these sensors do not utilize a global shutter.

Lower-cost cameras and low-light or low-contrast situations will make the effect more pronounced and it is in these cases that AF lag is more noticed.

In these cases, the photographer can switch to manual focus to avoid the delay that is attributable to the AF function.