Shutter (camera)
As a closure , also shutter in which is photo and video technology a light-tight, mechanically movable element referred to, which at a camera in the optical path before the image plane is located. During the exposure time , this element is opened for the duration of the preset shutter speed , in which the light coming from the lens hits the image plane. After exposure the shutter closes and protects until the next recording, the photosensitive layer of the recording material or to the digital image sensor from unwanted exposure to light.
Film cameras have a rotating shutter or a so-called sliding shutter that moves back and forth. Models with a slide lock are the Pathé-Baby, the Pathé Moto, several Beaulieu constructions or the Pentacon-AK 8 / Pentaka 8.
Closure techniques
There are mainly two locking techniques used:
- the central lock for large and medium format cameras as well as compact and viewfinder cameras .
- the focal plane shutter , in 35mm cameras with interchangeable lenses and medium format cameras.
Central locking
Compact, medium-format and large-format cameras usually have a central shutter with resilient, curved blades that open radially for the duration of the exposure. The central shutter, like the focal plane shutter, can be located in the camera housing or inside the lens between the front and rear lens groups .
Focal plane shutter
The focal plane shutter is located in the camera immediately prior to the film plane (engl. Focal plane shutter ) in the housing. For exposure purposes, a double curtain or its slot with a variable width quickly passes in front of the film. The width of the slot determines the exposure time. The longer the exposure time, the wider the slit.
If, as with SLR cameras , the slot or central lock is in the housing, one lock is sufficient for all interchangeable lenses . Lens replacement is simplified without an additional film cover.
Some single-lens medium format SLR cameras, whose lenses work with a central shutter, also have an (additional) focal plane shutter. However, this is not used for exposure, but only as an aid or auxiliary shutter that protects the film from incident light when focusing or when changing lenses.
Other closure techniques
With large-format cameras, spherical shell, roller and louvre locks are also used, with cameras used in astrometry and satellite geodesy, the rotary lock . The latter breaks down the trail of rapidly moving celestial bodies into short, easily measurable pieces. The guillotine lock still exists as a construction for simple cameras, located between the slit and central lock.
A rotating rotor shutter was used on the Olympus Pen FT half-format reflex camera . This simple and very fast type of shutter was or is, in simplified form, also common in older box and roll film cameras and in general and more complex in film cameras.
For the advantages and disadvantages of the individual locking techniques, see the corresponding article.
Very short exposure times can also be achieved by means of stroboscopic flashes or prism shutters, similar to the technology used in some film cameras.
As in the times of the early photographers, very long shutter speeds can also be achieved with manual handling of the cap (lens cover). The combination of manual shutter cover and automatic shutter with a long time also makes sense for some motifs.
The control of long shutter speeds with remote release or cable release can be found under the designation B (ulb) or B (alg), named after an earlier release mechanism, or T (ime) or Z (eit), in contrast to the M (oment) release for the regular exposure time.
The shutter remains open as long as the shutter release button is pressed. With other, often identically named designs, it only closes with a second release or with renewed cocking of the lock.
In addition to astro and night photography, long shutter speeds can also be found, together with simple shutter slides, in experimental pinhole cameras .
Shutter control
Mechanically controlled shutter speeds are usually up to 1/1000 of a second with focal plane shutters, and up to 1/500 second with central shutters . The shortest purely mechanical shutter speed is 1/4000 second ( Nikon FM2 ). Longer shutter speeds in the low seconds range can be found in older cameras, controlled by a self-timer type of clockwork.
In this context, a distinction is made between self-tensioning shutters, which are tensioned by film transport or pressure on the shutter release, and shutters that have to be tensioned by hand before the respective exposure.
With an electronic shutter control by electromagnets and control electronics , modern 35mm cameras achieve the shortest shutter speeds of 1 / 12,000 s ( Minolta Dynax 9xi and Dynax 9 ) and system cameras ( Olympus OM-D E-M1 Mark II ) even of 1/32000 s, but also automatically controlled ones Times of up to 30 seconds and longer can be achieved electronically with an electrically controlled shutter.
Longer and extremely long exposure times that exceed the performance of the actual shutter can be achieved with the "B" or "T" settings. With "B" the shutter remains open as long as the shutter release is pressed, with "T" the first press of the shutter release opens the shutter, the next press closes it. In the "B" setting, the exposure control can be taken over by an external timer; alternatively, a lens cover can be removed and put back on for very long exposure times in order to avoid blurring when the shutter is released .
Others
In the early days of photography, exposure times of several minutes, but at least several seconds, were required. The cameras of the time therefore did not require any mechanized shutters that only opened for a precisely defined moment. Instead, the photographer simply removed the lens cap and put it back on at the end of the exposure time.
With old and also with many modern cameras with automatic or semi-automatic exposure control, the shutter speeds can be selected manually. Fully automatic machines that do not allow manual setting of the shutter speed are not considered professional , as they prevent the photographer from consciously influencing the image effect through different exposure times.
The automatic exposure control of such program shutters enables quick photography, but the sometimes necessary checking and correction of the values is not possible or only possible indirectly.
The sometimes annoying long delay between the shutter release and the shutter opening, usually caused by AF (autofocus) or digital processes, is almost completely eliminated with manual presetting.
Some very simple cameras also only have a single exposure time and possibly also only a single f-number , a principle that has been used in amateur photography since the introduction of roll film .
See also
Web links
- Locks of historical cameras and a large overview of German central locks
- Camera shutter in the Olympus Wiki
- Detailed specialist article on various closures with excellent images
- Comparison of mechanical locks versus digital locks
Individual evidence
- ↑ Wolfgang Baier: Source representations for the history of photography. 2nd edition, Schirmer / Mosel, Munich 1980, ISBN 3-921375-60-6 , p. 318
