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المصراع .. تقنية الكاميرا .. المرشد خطوة بخطوة للتصوير الفوتوغرافي
Shutter
The shutter not only controls the exact moment when the film is exposed to light but also the duration of the exposure i.e. the amount of light that is admitted . We can use the same analogy as we did for the aperture . The length of time the shutter remains open controls the quantity of light that reaches the film in the same way that the quantity of water admitted to a container is controlled by the length of time it flows . Doubling the time the water flows will double the quantity in the container and , equally , doubling the time that the shutter remains open doubles the amount of light admitted to the film .
Some shutters , generally those on direct vision viewfinder cameras , fit within or just behind the lens body and use a set of blades which rapidly open or shut . These are called diaphragm , or leaf shutters . The other principal type of shutter the focal plane shutter is found on most single lens reflex cameras and consists of two separate blinds positioned just in front of the film .
Shutter speeds vary little between cam- eras - usually the longest time the shutter will automatically remain open for is 1 sec , the briefest exposure may be 1/250 sec , although many single lens reflex cameras have shutters with 1/500 or 1/1000 sec settings . As well as exposure , shutter speed controls how subject movement records ( see below and pp . 34-5 ) .
Shutter speed settings :
Shutter speeds , like f numbers , decrease in a regular sequence each shutter speed setting is half the previous exposure time . This shared doubling and halving se- quence is particularly important when combining aperture and shutter settings ( see pp . 36-7 ) .
Set the shutter to B ( " Bulb " ) and it will remain open for as long as you hold down the shutter re- lease button .
Bladed and focal plane shutters :
Bladed shutters are fitted to direct vision viewfinder cameras and those cameras where the viewing system is such that light need not pass through the lens until exposure . The mech- anism is inside the lens body .
On a single lens reflex camera , with through the lens viewing , the shutter is posi- tioned in the camera body , just in front of the film ( at the focal plane ) . This means that you can change lenses at any time without exposing the film .
Focal plane shutters have two blinds , which pass in succession in front of the film to give the exposure . The shutter speed dial alters the gap between them - the nar- rowest gap giving the shortest exposure time .
Using the shutter speed control :
The positioning and appearance of the shutter speed dial vary according to the two types of shutter . Most focal plane shutters have a setting dial on the top of the camera body . The numbers represent fractions of a second " 250 " is 1/250 sec . Most bladed shutter ( direct vision viewfinder ) cameras have a similarly num- bered ring around the lens body , near the aperture control .
In both cases the shutter mech- anism is tensioned when you wind on the film ready for the next exposure , and fired by pressing the shutter release on the top or front of the camera body . ( Simple cameras either have a one - speed shutter , or offer two or three speeds , marked not in times , but , say , in weather symbols . )
Shutter speed and movement :
Shutter speed makes a consider- able difference to the way moving subjects record in your pictures The three pictures above show the same scene taken at , from left to right , 1/15 sec , 1/60 sec , and 1/250 sec . At the lowest shutter speed 1/15 sec - subject move- ment has recorded blurred , imply- ing action , but with a loss of detail The faster times - 1/60 sec , cen- ter , and 1/250 sec , right pro- gressively eliminate the blur , re- vealing detail , but reducing the sense of movement .
At speeds less than 1/60 sec it is easy to blur the entire image accidentally because you are hold- ing the camera unsteadily . If you want to avoid camera shake and most subject movement blur , keep to speeds of 1/125 sec and shorter . You can prevent shake at lower speeds by supporting the camera securely , preferably on a tripod ( see p . 34 )
Shutter
The shutter not only controls the exact moment when the film is exposed to light but also the duration of the exposure i.e. the amount of light that is admitted . We can use the same analogy as we did for the aperture . The length of time the shutter remains open controls the quantity of light that reaches the film in the same way that the quantity of water admitted to a container is controlled by the length of time it flows . Doubling the time the water flows will double the quantity in the container and , equally , doubling the time that the shutter remains open doubles the amount of light admitted to the film .
Some shutters , generally those on direct vision viewfinder cameras , fit within or just behind the lens body and use a set of blades which rapidly open or shut . These are called diaphragm , or leaf shutters . The other principal type of shutter the focal plane shutter is found on most single lens reflex cameras and consists of two separate blinds positioned just in front of the film .
Shutter speeds vary little between cam- eras - usually the longest time the shutter will automatically remain open for is 1 sec , the briefest exposure may be 1/250 sec , although many single lens reflex cameras have shutters with 1/500 or 1/1000 sec settings . As well as exposure , shutter speed controls how subject movement records ( see below and pp . 34-5 ) .
Shutter speed settings :
Shutter speeds , like f numbers , decrease in a regular sequence each shutter speed setting is half the previous exposure time . This shared doubling and halving se- quence is particularly important when combining aperture and shutter settings ( see pp . 36-7 ) .
Set the shutter to B ( " Bulb " ) and it will remain open for as long as you hold down the shutter re- lease button .
Bladed and focal plane shutters :
Bladed shutters are fitted to direct vision viewfinder cameras and those cameras where the viewing system is such that light need not pass through the lens until exposure . The mech- anism is inside the lens body .
On a single lens reflex camera , with through the lens viewing , the shutter is posi- tioned in the camera body , just in front of the film ( at the focal plane ) . This means that you can change lenses at any time without exposing the film .
Focal plane shutters have two blinds , which pass in succession in front of the film to give the exposure . The shutter speed dial alters the gap between them - the nar- rowest gap giving the shortest exposure time .
Using the shutter speed control :
The positioning and appearance of the shutter speed dial vary according to the two types of shutter . Most focal plane shutters have a setting dial on the top of the camera body . The numbers represent fractions of a second " 250 " is 1/250 sec . Most bladed shutter ( direct vision viewfinder ) cameras have a similarly num- bered ring around the lens body , near the aperture control .
In both cases the shutter mech- anism is tensioned when you wind on the film ready for the next exposure , and fired by pressing the shutter release on the top or front of the camera body . ( Simple cameras either have a one - speed shutter , or offer two or three speeds , marked not in times , but , say , in weather symbols . )
Shutter speed and movement :
Shutter speed makes a consider- able difference to the way moving subjects record in your pictures The three pictures above show the same scene taken at , from left to right , 1/15 sec , 1/60 sec , and 1/250 sec . At the lowest shutter speed 1/15 sec - subject move- ment has recorded blurred , imply- ing action , but with a loss of detail The faster times - 1/60 sec , cen- ter , and 1/250 sec , right pro- gressively eliminate the blur , re- vealing detail , but reducing the sense of movement .
At speeds less than 1/60 sec it is easy to blur the entire image accidentally because you are hold- ing the camera unsteadily . If you want to avoid camera shake and most subject movement blur , keep to speeds of 1/125 sec and shorter . You can prevent shake at lower speeds by supporting the camera securely , preferably on a tripod ( see p . 34 )
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