Central shutter

In photography, a central shutter is a type of camera shutter, so called because it is situated between the lens and the focal plane. In many cases it is contained within the lens body itself, at the convergent image point.

For this reason, many cameras with a central shutter and interchangeable lenses require that each lens for that camera has a shutter built into it. Note that this would also require the lenses to be changed in complete darkness, or have a secondary shutter or darkslide that can be operated to prevent film exposure from occurring.

The most basic type of central shutter is the metal leaf shutter, but the diaphragm shutter is used on many professional systems where the central shutter is located within the lens body.

The main advantages of the central shutter are:

• Relatively simple construction is possible.
• Less expensive to produce than a focal plane shutter.
• Flash synchronization is possible at all speeds because the shutter opens fully.
• Small size is achieved by placing the shutter at the focal convergent point either inside the lens or inside the camera body.
• Many versions have no connection between the cocking mechanism and the film advance mechanism, making multiple exposures possible.

Some disadvantages of the central shutter are:

• Each lens in an interchangeable system has to have a shutter built into it.
• Shutter speeds are limited to how fast the shutter can be made to move; normally 1/500th of a second for a diaphragm shutter and 1/125th of a second for a leaf shutter.
• Some versions may have no connection between the cocking mechanism and the film advance mechanism, making accidental multiple exposures a common problem.
• On medium format and small format systems a separate viewfinder, rangefinder, or twin lens reflex system has to be provided for focusing and composition.