Camera Shutter Types

Depending on
the timing mechanism
used, shutters are divided
into electronic or mechanical type

The shutter is
complicated mechanism acting like a window shade allowing light to
pass
for a determined period of time, for the purpose of exposing to light
the digital image sensor to capture a scene. It is placed either behind
the camera
lens or is built into the middle of the lens, next to the aperture

The time for which a shutter
remains open (exposure time) is determined by a timing mechanism and
depending on the mechanism used there are two main camera shutters
types:

• Electronic
  Camera Shutter Type

• Mechanical
  Camera Shutter Type which have moving parts and come in two
  kinds – Leaf
  and Focal Plane Camera Shutter Types.

Electronic Shutters

Electronic shutters
simply turn
the sensor on and off to capture the exposure. The image builds up as
light
is captured by the sensor.

Because these camera shutter types do not have
moving parts, they are less expensive and can be found in the cheapest
cameras, but ironically also in the most expensive. They can be
exceptionally accurate when designed with precision.

Mechanical Shutters

A leaf shutter
is a type of camera shutter consisting of a mechanism with one or more
pivoting metal leaves which normally does not allow light
through the
lens onto the film or digital
image sensor, but which
when triggered
opens the shutter by moving the leaves to uncover the lens for the
required time to make an exposure,
then shuts.

This shutter, often called an iris
or diaphragm shutter, mimics the action of the iris in your
eye that
opens wider in dimmer light and closes down in bright light.

The larger the number of blades,
the more accurately circular is the aperture. An odd number of blades
are usually used: 3, 5, or more.

The other type of mechanical
shutter is the focal plane shutter and is found in
all digital SLRs. It travels in front of the digital
image sensor, just
above the plane of sharp focus hence its name and works by opening one
curtain to begin an exposure
and closing another curtain to end it.

The front curtain opens first,
moving across the plane of the sensor until it is fully open. Then,
after the sensor has been left exposed for the desired amount of time,
the rear curtain begins to follow it, gradually covering the sensor
until it is completely concealed.

For slower shutter speeds,
the first curtain opens from (usually) right to left, and there is a
point at which the entire image sensor is exposed to light.
After the
required time with the shutter open, the second curtain closes the
aperture
in the same direction. The fastest shutter speed at which this
happens is called the flash sync speed.

This process is demonstrated in
the below diagram where the black rectangle represents the frame
aperture through which the exposure is made, the first shutter curtain
is shown in red and the second shutter curtain shown in green is on the
right side:

Faster shutter speeds
are achieved by the second curtain closing before the first one has
fully opened. This results in a vertical slit that travels horizontally
across the film or digital image sensor as demonstrated in the below
diagram:

On newer cameras the
curtains run
vertically. This makes them faster than older shutters that
ran
horizontally because they have less distance to cross (24mm as opposed
to 36mm). This faster speed makes it possible to have a
faster flash
sync shutter speed. Using this technique, modern SLR cameras are
capable of shutter speeds of up to 1/8000 of a second.