SHUTTER

A movable cover for an opening. In photography, that opening is the lens - more specifically, the aperture. The shutter blocks the passage of light traveling through the lens to the film when it is closed, and allows light to reach the film when it is open. Shutters are composed of blades, a curtain, a plate or another movable cover. They control the amount of time that light is allowed to pass through the opening to reach the film.

Shutter and shutter speed

The shutter keeps light out of the camera except during an exposure, when it opens to let light strike the image sensor. The length of time the shutter is open affects both the exposure of the image and how motion is portrayed in it.

The shutter controls the duration of an exposure. The camera's shutter speed is a measurement of how long its shutter remains open as the picture is taken. The slower the shutter speed, the longer the exposure time. When the shutter speed is set to 1/125 or simply 125, this means that the shutter will be open for exactly 1/125th of one second. The shutter speed and aperture together control the total amount of light reaching the sensor.

Shutter speed is measured in seconds. A typical shutter speed for photographs taken in sunlight is 1/125th of a second. In addition to its effect on exposure, shutter speed changes the way movement appears in the picture. Very short shutter speeds are used to freeze fast-moving subjects, for example at sporting events. Very long shutter speeds are used to intentionally blur a moving subject for artistic effect.

Shutter is a mechanism which controls the duration of light passing the lens unit for correct exposure. In other words it is the timings.

In non- SLR camera they are marked on a ring in the lens barrel.

In SLR camera they are marked on the dial in the body or the LCD (liquid crystal display).

They are referred as shutter speed.

Shutter speed settings

There are a series of settings that have traditionally been used. These shutter speed settings are arranged in a sequence so that each setting lets in half as much light as the next slowest setting and twice as much as the next fastest. The traditional shutter speeds (listed from the fastest to the slowest speeds) include

1/1000, 1/500, 1/250, 1/125, 1/60, 1/30, 1/15, 1/8, 1/4, 1/2, and 1 second.

Although speeds faster than 1 second are fractions of a second most cameras display them without the numerator. For example, 1/2 second is displayed as 2.

Types of shutters

Principal present-day shutters are the leaf shutter and the focal-plane shutter.

a. The leaf shutter

The leaf, or diaphragm, shutter consists of a series of blades or leaves fitted inside or just behind the lens. The shutter opens by swinging the leaves simultaneously outward to uncover the lens opening. The leaves stay open for a fixed time – the exposure – and closes again. A combination of electromagnets or electromagnets and springs drives the mechanism, while an electronic circuit—often coupled with a light metering system—or an adjustable escapement in mechanical shutters controls the open time. This is typically between one second and ¹/₅₀₀ second.

b. Focal-plane shutter:

The focal-plane shutter consists of two light-tight fabric blinds or a combination of metal blinds moving in succession across the film immediately in front of the image plane. The first blind uncovers the film and the second blind covers it up again, the two blinds forming a traveling slit the width of which determines the exposure time: the narrower the slit, the shorter the time. The actual travel time is fairly constant for all exposure times. A mechanism or electromagnet and control circuit triggers the release of the second blind. Focal-plane shutters are usually adjustable for exposure times between one second (or longer) and ¹/_1,000 to ¹/_4,000 second.

The shutter and exposure

Slower shutter speeds let more light strike the image sensor making an image lighter. Faster shutter speeds let less strike it and make the image darker.

The shutter and motion

In addition to controlling exposure, the shutter speed is the most important control you have over how motion is captured in a photograph. Understanding shutter speeds is vital if you want to anticipate if a moving subject will appear in your image sharp or blurred. The longer the shutter is open, the more a moving subject will be blurred in the picture Also, the longer it's open the more likely you are to cause blur by moving the camera slightly.