Shutter

The shutter of a camera or of the lens/shutter unit for a camera isolates the film in the camera from light until the shutter will be released. Depending on the shutter type releasing the shutter means to open it for a moment like a diaphragm, like a roller blind, or simply like a sliding door. A wind-up-mechanism or a litte electric servo delivers the shutter movement energy and controls the time of film enlightening.

Focal plane shutter

Focal plane shutter means that the shutter is located near the film plane. Most focal plane shutters are of the roller blind type, as light-tight roller blind over the rectangular window over the film plane, with a second roller blind closing the shutter window immediately when the other blind is opened or just opening. Fast shutter speeds are achieved by letting the light in through a narrow gap between the opening and the closing roller blind.

Leaf shutter

In some cameras the diaphragm of the leaf shutter and the diaphragm that defines the aperture for the exposure are identical. Then the opened shutter blades border a polygonal hole with the chosen aperture as diameter. Fast speeds can be achieved by limiting the aperture range for the fast speeds to small and that of the slow speeds to larger apertures. But in most cases there are two diaphragms behind a camera lens or between its optical elements. Then the shutter diaphragm has less but faster leaves which open a hole of maximal aperture size while the second diaphragm, the iris diaphragm, borders the selected aperture.

leaf shutter, blades not yet fully open

Compur leaf shutter mechanics

typical rotary shutter as already used in 19th century

guillotine shutter

Imagine a sliding door opening and shutting. Sometimes such simple shutter constructions are called guillotine shutters.

Rotary shutter

Cheap box cameras are often equipped with a simple rotary shutter. It consists of a release lever, a spring, a round tin slice with a whole and a rotation lock lever. When the release lever is used the spring causes the slice rotating once so that the hole in it passes the camera aperture. In this moment the light enters for an instant, except when the rotation locking lever was used before. Then the hole stays in front of the aperture hole until the shutter release lever is let loose.

Shutter drive and control systems

From the control aspect, there are these different kinds of shutter systems in classical cameras. Things are somewhat simplified things for brevity. Ignored here are the "iris" type leaf shutters found on fixed lens rangefinder cameras, and you can substitute mechanical leaf shutters for curtain shutter:

• Purely mechanical -- A spring is released mechanically from the shutter release button that drives the curtain, and the curtain speed is controlled mechanically.

• Mechanical hybrid -- A spring is released mechanically from the shutter release button that drives the curtain, and the curtain speed is controlled electronically.

• Electrical hybrid -- A spring is released electrically from the shutter release button, which is really a switch, and naturally the curtain speed is controlled electronically.

• Purely electrical -- Electromagnetics drive the curtain and is triggered by the shutter release button, which is a misnomer in this case as it is simply a switch for a horizontal motor.

Glossary Terms