Central shutter
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In photography, a central shutter is a camera shutter normally located within the lens assembly where a relatively small opening allows light to cover the entire image. The term is also used for shutters behind, but near to, the lens. The alternative to a central shutter is a focal-plane shutter.
Interchangeable lens cameras with a central shutter within the lens body require that each lens has a shutter built into it. In practice most cameras with interchangeable lenses use a single focal plane shutter in the camera body for all lenses, while cameras with a fixed lens use a cheaper central shutter.
Film cameras, but not digital cameras, with a central shutter and interchangeable lenses often have a secondary shutter or darkslide to cover the film and allow changing lens in mid-roll without fogging the film.
Central shutters usually use either the simple the simple leaf mechanism or the superior diaphragm mechanism.
The main advantages of the central shutter compared to a focal-plane 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 where the bundle of rays is smaller, 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.
- Generally much quieter operation because of fewer and less bulky moving parts
- More realistic photographs in high speed follow-through—lateral focal plane shutters compress or elongate the image in such cases.
Some disadvantages of the central shutter are:
- For an interchangeable lens system, each lens has to have a shutter built into it.
- Leaf shutter speeds are limited by the speed at which the leaves can move: normally 1/500th of a second for a diaphragm shutter and 1/125th of a second for a simple leaf shutter.
- Some versions may have no connection between the cocking mechanism and the film advance mechanism, making accidental multiple exposures a common problem, although this is a feature of camera manufacture rather then the shutter itself.
