|stereo variant of Ball Bearing Shutter, image by inkyfingerz|
A leaf shutter is a shutter found on some cameras, using a small number of identical overlapping metal blades, called leaves, to open and close in order to expose a photograph. It is usually placed near the iris within the camera lens. The leaves are arranged in a circular pattern, suitably pivoted near the housing periphery, and made to move in a rapid oscillating fashion such that they together uncover the common central area for a predetermined period of time, enabling a picture to be taken. The shutter mechanism is governed by a clockwork mechanism and powered by a strong spring tensioned by setting the shutter before each exposure. The delay between opening and closing the blades determines the exposure time which usually may be adjustable within a limited range for the photographer to choose from. The shutter may be equipped with a delay action which, when set and released, triggers the shutter after a short period of time, in the region of 10 seconds. A threaded socket may also be present for attaching a cable release for the photographer’s convenience.
|old shutter of a Contaflex, image by bomobob|
The leaf shutter allows synchronising flash at every available shutter speed, because the whole picture area is exposed simultaneously, which is not always the case using the focal plane shutter.
Most leaf shutters for folding cameras have two thread mounts for the the lenses, one in the front side and one in the back. The reason is that most of these shutters have a built-in iris diaphragm. The lenses for these cameras are two-part lenses, each part delivered in an own lens barrel with thread. The reason is that the lenses work best when the diaphragm is placed between certain elements of the lens. This construction allowed also the concept of convertible lenses. Leaf shutters can be found on all types of cameras including early folding cameras, large format view/plate cameras, rangefinder & viewfinder cameras, some SLRs and medium format cameras.
The manufacture of leaf shutters is highly specialized, and usually not made by the camera makers them selves. Common types of shutters are the German Compur and Prontor, and the Japanese Copal, Citizen and Seikosha.
Depending on the way the shutter is arranged with respect to the lens, it is referred to as "between-lens" or "behind the lens" shutter.
- Leaf shutters can synchronise a flash at any available shutter speed.
- They are generally more compact and less noisy than focal plane shutters.
- They do not distort the image of moving objects.
- Leaf shutters are typically not capable of shutter speeds as high as modern focal plane shutters
- Cameras using leaf shutters must either have a shutter in each lens, like the Hasselblad 500, or have the shutter in the camera body, which limits the range of possible focal lengths and the maximum aperture, like the Paxette.
- This is particularly true when elecronic flashes connected to the X sync socket are concerned. Flashbulbs of different types, with different time to peak, various flash duration and connected to different sync sockets (e.g. X, M or F) have certain limitations in this aspect - for example S-class flashbulbs can be used at shutter speed not shorter than 1/20 s.