Central shutter
From Free net encyclopedia
In photography, a central shutter is a type of camera shutter location.
Generally a central shutter 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.
Film-based cameras with a central shutter and interchangeable lenses often have a secondary shutter or darkslide that can be operated to prevent film exposure from occurring while the lens is removed. Without this, the current film frame could be exposed to light while changing lenses. Digital cameras do not suffer from this problem, even if they do use a shutter.
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 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 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.
- Generally much less quiet 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.
- 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.de:Zentralverschluss