Shutter (photography)

In photography, a shutter is a part of a camera that lets light in for just the right time. This light hits either photographic film or a photosensitive digital sensor, making a picture. Shutters can also send out quick flashes of light, like in a movie projector or a signal lamp.

The shutter opens for a little while and then closes, so the picture is captured correctly. How long it stays open can be changed for the perfect picture. Some cameras decide the time automatically, while others let you set it yourself using buttons or a dial on the camera. This helps you control how bright or blurry your picture will be.

Camera shutter

Camera shutters can be placed in different spots.

• Leaf shutters are often placed inside a lens group, or less commonly right behind the lens, or even more rarely in front of the lens, and block light where it is narrow.
• Focal-plane shutters are set near the focal plane and move to uncover the film or sensor.

Behind-the-lens shutters were used in some cameras with few lens options. Shutters in front of the lens, sometimes just a lens cap that is taken off and put back for long exposures, were used in the early days of photography. Many ways have been used; anything that lets light hit the film for a set time works.

The time a shutter stays open (exposure time, often called "shutter speed") is set by a timing tool. These were once pneumatic (Compound shutter) or clockwork, but since the late twentieth century are mostly electronic. Mechanical shutters usually had a Time setting, where the shutter opened when the button was pressed and stayed open until it was pressed again, Bulb where the shutter stayed open as long as the button was pressed (originally done by squeezing an actual rubber bulb), and Instant exposure, with settings from 30" to 1/4000" for the best leaf shutters, faster for focal-plane shutters, and more limited for basic types. The flip of exposure time in seconds is often used for marking shutter settings. For example, a marking of "250" means 1/250". This does not cause trouble in real use.

The exposure time and the effective aperture of the lens must together let the right amount of light reach the film or sensor. Also, the exposure time must be right to handle any movement of the subject. Usually it must be fast enough to "freeze" quick movement, unless a bit of motion blur is wanted, for example to show a feeling of movement.

Most shutters have a flash synchronization switch to start a flash, if linked. This was quite hard with mechanical shutters and flashbulbs which took time to get bright, focal-plane shutters making this even harder. Special flashbulbs were made which stayed lit longer, shining the scene for the whole time a focal plane shutter slit moved over the film. These issues were mostly solved for non-focal-plane shutters with the coming of electronic flash units which light almost right away and give a very quick flash.

When using a focal-plane shutter with a flash, if the shutter is set at its X-sync speed or slower the whole frame will be lit when the flash lights (otherwise only a part of the film will be lit). Some electronic flashes can give a longer light pulse that works with a focal-plane shutter set at much higher shutter speeds. The focal-plane shutter will still give focal-plane shutter changes to a fast-moving object.

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

Focal-plane shutter

Main article: Focal-plane shutter

A focal-plane shutter is placed just before the film, at the focal plane, and moves an opening over the film until the whole frame has been lit. Focal-plane shutters are usually made as a pair of light-tight cloth, metal, or plastic curtains. For shutter speeds slower than a certain point (known as the X-sync speed of the shutter), which depends on the camera, one curtain of the shutter opens, and the other closes after the right exposure time. At shutter speeds faster than the X-sync speed, the top curtain of the shutter moves over the focal plane, with the second curtain following behind, effectively moving a slit over the focal plane until each part of the film or sensor has been lit for the right time. The real exposure time can be much shorter than for central shutters, at the cost of some change of fast-moving subjects.

Focal plane shutters have the good point over central leaf shutters of letting the use of swap-in lenses without needing a separate shutter for each lens. (Leaf shutters behind the lens also let swapping the lens using a single shutter.)

They have some bad points as well:

• Change of fast-moving subjects: although no part of the film is lit for longer than the time set on the dial, one edge of the film is lit an important time after the other, so that a sideways moving shutter will, for example, stretch or shrink the picture of a car going in the same or the opposite way to the shutter movement.
• They are louder, which spoils quiet and nature photography.
• Their more complex working structure causes a shorter life than other shutter designs.
• If a focal-plane shutter camera is left with sunlight on the lens (and the mirror up for an SLR), it is possible to burn a hole in the closed curtain of a non-metal shutter.
• Camera shake from the hit of the larger curtains starting and stopping fast. Camera makers have learned to fix SLR mirror-hit by adding a mirror lock-up choice in some cameras. This takes the camera-shake from the big hitting mirror inside the camera, but does not stop camera-shake from the shutter itself. Mirror-lock-up brings another problem: with the mirror locked-up out of the way the seeing viewfinder cannot be used for focusing, framing, or exposure measuring. Digital SLR cameras with a live preview screen that shows the view from the main lighting sensor can avoid this problem, as the photographer may focus and frame using the live preview screen instead. This stops most camera shake from the focal-plane shutter in DSLRs, as instead of a first curtain an electronic shutter is used.

Simple leaf shutter

A simple leaf shutter is a type of camera shutter with a working part of one or more turning metal leaves which normally does not let light through the lens to the film, but which when started opens the shutter by moving the leaves to uncover the lens for the needed time to make a light, then shuts.

Simple leaf shutters have a single leaf, or two leaves, which turn so as to let light through to the lens when started. If two leaves are used they have curved edges to make a roughly round opening. They usually have only one shutter speed and are commonly found in basic cameras, including disposable cameras. Some have more than one speed.

Guillotine shutter

In the simplest version of Guillotine shutter a plate with an opening slides over the lens opening. Simple versions from the 1880s and 1890s were often called Drop shutters. They worked up and were usually worked by a rubber band, a spring or just gravity. Later they were set to work side to in hand cameras where they were spring worked with spring strength or pneumatic control.

Rotating shutter

Simple rotary shutter

Many low-cost box cameras had a shutter made of a round metal disk with a hole cut in it along with a spring-loaded start lever, with the solid disk stopping light from entering the camera. When the shutter start lever is used, the spring makes the disk turn fast once so that the hole goes past the camera opening and lets light through for a short time. Rotary shutters usually only had one fixed, rough shutter speed, although most cameras had a Time choice that would keep the shutter open when the release is used, allowing for longer lights.

Hemispheric

The shutter plate was made of a part of a ball fixed to turn behind the lens. It was a type of shutter found on the Photosphere and other cameras.

Diaphragm shutter

• Diaphragm or leaf shutters

One diaphragm shutter opening over another in an Akarex camera

Dial-set three-leaf _Compur_ shutter, partly open.

Entries in _Cassell's Cyclopedia of Photography_, 1911. The word _diaphragm shutter_ has since gone from common use.

A diaphragm or leaf shutter (as not the same as the simple leaf shutter above) is made of a number of thin blades which quickly uncover the camera opening to make the light. The blades move over each other in a way which makes a round opening which grows as fast as possible to uncover the whole lens, stays open for the needed time, then closes in the same way. The more blades, the more truly round the opening. Flash synchronization is simply done with a pair of contacts that close when the shutter is fully open.

Ideally the shutter opens right away, stays open as long as needed, and closes right away. This is mainly the case at slower speeds, but as speeds get close to their highest the shutter is far from fully open for a big part of the light time. Really the shutter works as an added opening, and may cause an increased depth of field, not wanted if shallow focus is being used on purpose. Or it may cause working darkening if the diaphragm is outside of the lens (like a focal plane shutter or apodization filter).

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

A few types and makers of leaf shutters became very well known. The early Compound shutter had a pneumatic working, with a piston moving against air force in a tube. They were quieter at slow speeds than clockwork, but possibly very wrong. More right clockwork workings then took the place of the airbrake, and the German Compur, and the later Synchro-Compur, became almost the standard good shutter. Later the Japanese Copal shutter was widely taken up in good tools. The German Prontor and Japanese Seikosha shutters were also widely used. Up and Down with Compur: The development and photo-historical meaning of leaf shutters, by Klaus-Eckard Riess, translated by Robert "The Professor" Stoddard gives a full history and working description of leaf shutters. The company Compur Monitor was still in work as of 2012^[update], but made only gas finding tools. Leaf shutters under the Compur, Copal, and Seiko names are no longer made.

Central shutter

A central shutter is not a type of shutter as such, but means the place of the shutter: it is usually a leaf shutter (or simple leaf shutter), and set inside the lens group where a quite small opening lets light cover the whole picture. Leaf shutters can also be set behind, but near, the lens, letting lens swapping. The other way to a central or behind-the-lens shutter is a focal-plane shutter.

Swap-in-lens cameras with a central shutter inside the lens body need each lens to have a shutter built into it. In use most cameras with swap-in lenses use a single focal plane shutter in the camera body for all lenses, while cameras with a fixed lens use a central shutter. Many middle-format and most big-format cameras, however, have swap-in lenses each fitted with a central shutter. A few swap-in-lens cameras have a behind-the-lens leaf shutter. Big-format press cameras often had a focal-plane shutter. Some had both a focal-plane shutter (for lens swapping) and a lens with central shutter (for flash matching); one shutter would be locked open.

Film cameras, but not digital cameras, with a central shutter and swap-in lenses often have a second shutter or darkslide to cover the film and let changing lens in the middle of a roll without clouding the film.

The main good points of central and behind-the-lens leaf shutters compared to a focal-plane shutter are:

• Flash matching is possible at all speeds because the shutter opens fully, unlike a focal-plane shutter moving a slit quite slowly over the film for a short real light.
• Small size is possible as the shutter is placed where the bunch of rays is narrow, either inside or just behind the lens.
• Many types have no link between the starting working and the film moving working, letting many lights (this can be a bad point, as many lights can be made by mistake if the photographer forgets to move the film).
• Usually much quieter.
• More right pictures in high speed panning—side focal plane shutters stretch or shrink the picture in such cases.
• Longer shutter life.

Some bad points of the central shutter are:

• For a swap-in lens group, each lens has to have a shutter built into it.
• All leaf shutter speeds are limited by the speed at which the leaves can move: usually 1/500th of a second for a high-works diaphragm shutter and 1/125th of a second for a simple leaf shutter.
• Some types may have no link between the starting working and the film moving working, letting wrong many lights a common problem, although this is a point of camera making rather than the shutter itself.

Electronic shutter

Digital image sensors (both CMOS and CCD image sensors) can be made to give a shutter same working by moving many pixel cell charges at one time to a matched shaded double called frame transfer shutter. If the whole-frame is moved at one time, it is a global shutter. Often the shaded cells can be read on their own, while the others are again taking light. Extremely fast shutter working is possible as there are no moving parts or any serialized data moves. Global shutter can also be used for videos as a change for rotary disc shutters.

Image sensors without a shaded whole-frame double must use serialized data moving of lit pixels called rolling shutter. A rolling shutter checks the picture in a line-by-line way, so that different lines are lit at different times, as in a mechanical focal-plane shutter, so that motion of either camera or object will cause right changes, such as slope or shake.

Today, most digital cameras use a mix of mechanical shutter and electronic shutter or mechanical shutter only. Mechanical shutter can let up to 1/16000 seconds (for example the Minolta Dynax/Maxxum/α-9 film camera had a highest of 1/12000, a record in its time, and the later digital Nikon D1 group could do 1/16000), while electronic shutter can let at least 1/32000 seconds, used for many superzoom cameras and now many Fujifilm APS-C cameras (X-Pro2, X-T1, X100T and others).

Stacked CMOS sensors bring together the image sensor itself with ADCs and digital memory in the same pack. The reading of these sensors is faster than old sensors, because the changed picture is moved into the digital memory in the sensor itself during reading and only after moved out of the sensor. This gives an electronic shutter which is as fast as a mechanical focal-plane shutter. Some cameras using stacked sensors, like the Nikon Z9, took away the mechanical shutter completely. Dynamic range and noise working are not made worse, because these sensors do not use a global shutter.

Shutter lag

Main article: Shutter lag

Shutter lag is the time between pressing the shutter button and the camera taking the picture. In older cameras, this delay was very small. But in many digital cameras, there can be a noticeable delay. This delay can be a problem when taking pictures of fast-moving subjects, like in sports or action scenes. Some cameras have a delay of about 1/50 of a second, while others can take longer to start taking the picture.

Often, the delay happens because the camera is trying to focus automatically. In low light or when the scene is not very clear, focusing can take longer, causing more delay. Using manual focus can help reduce this delay.

Shutter cycle

A shutter cycle is when a shutter opens, closes, and then gets ready to open again. Many digital cameras keep track of how many times the shutter has done this. They also store details like how fast the shutter opened and how big the opening was. You can see this information using special websites and apps that read the Exif data.

Projector shutter

In movie projection, a shutter lets light shine on the film being shown. To stop the screen from flickering, a shutter with two blades lets light through twice for each frame of film. This creates a steady look to our eyes. For slower film speeds like 16 frames per second (used in many silent films and Regular 8mm) and 18 frames per second (Super 8), a shutter with three blades is used instead.

Shutters can also control light pulses without any film, like in a signal lamp.