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الجمع بين فتحة العدسة وسرعة الغالق .. تقنية الكاميرا .. المرشد خطوة بخطوة للتصوير الفوتوغرافي
Combining aperture and shutter speed
We have been looking at the three most important camera controls : focus , aperture , and shutter . Focus has the most straight- forward function . It is used to give a sharp image of the key part of the picture - perhaps a building in a landscape , faces in a group , or the eyes in a close - up portrait . Lens aper- ture and shutter speed each affect the image in two distinct ways . First , they modify the amount of light which reaches the film - the aperture by altering its brightness , the shut- ter speed by controlling the time it is allowed to act . Second , they both have their own effect on the image . The aperture alters the depth of field , which is important when the subject includes elements at different dis- tances from the camera . The shutter speed affects the image when either the camera or subject is moving .
Shutter speed and aperture combinations For the film to record the image clearly it must receive the right amount of light , that is , it must not be overexposed or underexposed Under normal lighting conditions it matters little whether you use a fast shutter speed with a wide lens aperture or a slow shutter speed with a small lens aperture ; both give the film the same amount of light . ( A con- tainer can be filled with the same amount of water over a short period of time through a wide funnel , or over a long period through a narrow funnel . )
The diagram below shows the doubling and halving relationship of the aperture and shutter settings on the camera . This allows you to combine different settings , altering the effect on the image , but admit- ting exactly the same quantity of light . For example , your exposure meter or film in- struction leaflet may indicate that your sub- ject needs an exposure of 1/60 sec at f8 . Instead of using this exposure , you could set 1/500 sec at f2.8 , or 1/15 sec at f16 . Each combination will expose the film to the same quantity of light , but , as the pictures at the top of the opposite page show , they give very different images . The choice of settings on both controls can be used to suit the subject and the effect you want to create .
Selecting the exposure :
Sometimes the light level alone determines the exposure setting . It may be so low that you have to use a slow shutter speed and a wide aperture to get any image at all , letting as much light as possible through to the film . Or it may be so high that the fastest speed and smallest aperture are needed . But for a great deal of your photography you will find from your exposure meter or guide that you have a reasonably wide choice of different aperture and shutter speed com- binations . In the pages which follow we shall be looking at the way the correct ex- posure for various lighting conditions and subjects is measured .
Once you have determined the exposure , you can then decide how you will interpret your subject . Consider the ways depth of field can be used either to emphasize one chosen zone or to get everything in focus . When setting the shutter speed , remember to consider the effects of camera shake and the blur created by moving subjects .
How aperture and shutter speeds combine :
The combinations of aperture and shutter settings above show how exactly the same exposure can be given various ways . Provided that each change of f number is matched by a corresponding change of shutter speed , the film will receive the same amount of light . So if your light meter or film instructions ) suggests one of these combinations , you can change to any one of the others to alter the depth of field or the amount of blur . If you change one control without compensating with the other the overall exposure is altered . For example 1/30 sec at f8 gives the film twice as much light as 1/60 sec . 18 .
Not shown in this diagram is the range of very slow speeds , down to 1 sec , offered by many cameras , which combine with aperture settings in the same way .
The controls on the camera :
The location of the aperture and shutter controls shown on the camera above is typical .
Some cameras have the con- trols on s on adjacent rings . If you first set any combination to give the required exposure , the two rings , turned together , will keep the ex- posure constant by altering both the aperture and shutter speed in inverse proportion .
Exposure at 1/500 sec at f2.8 The picture above was taken using a very fast shutter speed and a wide lens aperture . Even the fastest movement ( ringed area ) has been " frozen " and the wide aperture has left much of the background ( boxed area ) unsharp .
Exposure at 1/60 sec at 18 The picture above had the same overall exposure as the one on the left , but used a slower shutter speed and a smaller aperture . The fastest movement ( ringed ) has blurred and the middle distance has become sharp .
Exposure at 1/15 sec at f16 Here the same overall exposure combined a very slow shutter speed and a small lens aperture . Nearly all movement has blurred , and the small aperture has made almost the whole scene sharp ( boxed area ) .
Exposure at 1/15 sec at f2.8 When your subject is very dimly lit , as shown above , you may have to combine a slow shutter speed with a wide lens aperture to give the film enough light . In this ex-ample you could give the same exposure by choosing sec at 18 , or 2 secs at f16 . provided you sup- port the camera steadily , prefer- ably on a tripod , and the subject remains absolutely still .
Reminders : camera controls
Focusing controls which part of the subject records sharply
Moving the lens brings parts of the subject at different distances from the camera in or out of focus . You can measure and set your subject distance or you can check the sharpness visually , by a focusing screen or rangefinder .
The extent of sharp detail is controlled by the aperture
The aperture controls image brightness ( through the amount of light it admits ) and the depth of field . The aperture ring is scaled in f numbers . The higher the f number the smaller the aperture and the greater the depth of field . Depth of field also increases if you use a shorter focal length lens ( see pp . 94-5 ) or increase subject distance .
Shutter speed affects the way movement records
The shutter controls the time the image is exposed to the film , and consequently , the amount of blur on the image . Blur varies accord- ing to camera movement , and the relative speed , direction , and distance of the subject .
The exposure is determined by the aperture and shutter speed
When taking a photograph you usually have a choice of combinations of aperture and shutter speeds . Provided they still give sufficient light to the film you can choose to have either wide or narrow depth of field , frozen or blurred movement .
Combining aperture and shutter speed
We have been looking at the three most important camera controls : focus , aperture , and shutter . Focus has the most straight- forward function . It is used to give a sharp image of the key part of the picture - perhaps a building in a landscape , faces in a group , or the eyes in a close - up portrait . Lens aper- ture and shutter speed each affect the image in two distinct ways . First , they modify the amount of light which reaches the film - the aperture by altering its brightness , the shut- ter speed by controlling the time it is allowed to act . Second , they both have their own effect on the image . The aperture alters the depth of field , which is important when the subject includes elements at different dis- tances from the camera . The shutter speed affects the image when either the camera or subject is moving .
Shutter speed and aperture combinations For the film to record the image clearly it must receive the right amount of light , that is , it must not be overexposed or underexposed Under normal lighting conditions it matters little whether you use a fast shutter speed with a wide lens aperture or a slow shutter speed with a small lens aperture ; both give the film the same amount of light . ( A con- tainer can be filled with the same amount of water over a short period of time through a wide funnel , or over a long period through a narrow funnel . )
The diagram below shows the doubling and halving relationship of the aperture and shutter settings on the camera . This allows you to combine different settings , altering the effect on the image , but admit- ting exactly the same quantity of light . For example , your exposure meter or film in- struction leaflet may indicate that your sub- ject needs an exposure of 1/60 sec at f8 . Instead of using this exposure , you could set 1/500 sec at f2.8 , or 1/15 sec at f16 . Each combination will expose the film to the same quantity of light , but , as the pictures at the top of the opposite page show , they give very different images . The choice of settings on both controls can be used to suit the subject and the effect you want to create .
Selecting the exposure :
Sometimes the light level alone determines the exposure setting . It may be so low that you have to use a slow shutter speed and a wide aperture to get any image at all , letting as much light as possible through to the film . Or it may be so high that the fastest speed and smallest aperture are needed . But for a great deal of your photography you will find from your exposure meter or guide that you have a reasonably wide choice of different aperture and shutter speed com- binations . In the pages which follow we shall be looking at the way the correct ex- posure for various lighting conditions and subjects is measured .
Once you have determined the exposure , you can then decide how you will interpret your subject . Consider the ways depth of field can be used either to emphasize one chosen zone or to get everything in focus . When setting the shutter speed , remember to consider the effects of camera shake and the blur created by moving subjects .
How aperture and shutter speeds combine :
The combinations of aperture and shutter settings above show how exactly the same exposure can be given various ways . Provided that each change of f number is matched by a corresponding change of shutter speed , the film will receive the same amount of light . So if your light meter or film instructions ) suggests one of these combinations , you can change to any one of the others to alter the depth of field or the amount of blur . If you change one control without compensating with the other the overall exposure is altered . For example 1/30 sec at f8 gives the film twice as much light as 1/60 sec . 18 .
Not shown in this diagram is the range of very slow speeds , down to 1 sec , offered by many cameras , which combine with aperture settings in the same way .
The controls on the camera :
The location of the aperture and shutter controls shown on the camera above is typical .
Some cameras have the con- trols on s on adjacent rings . If you first set any combination to give the required exposure , the two rings , turned together , will keep the ex- posure constant by altering both the aperture and shutter speed in inverse proportion .
Exposure at 1/500 sec at f2.8 The picture above was taken using a very fast shutter speed and a wide lens aperture . Even the fastest movement ( ringed area ) has been " frozen " and the wide aperture has left much of the background ( boxed area ) unsharp .
Exposure at 1/60 sec at 18 The picture above had the same overall exposure as the one on the left , but used a slower shutter speed and a smaller aperture . The fastest movement ( ringed ) has blurred and the middle distance has become sharp .
Exposure at 1/15 sec at f16 Here the same overall exposure combined a very slow shutter speed and a small lens aperture . Nearly all movement has blurred , and the small aperture has made almost the whole scene sharp ( boxed area ) .
Exposure at 1/15 sec at f2.8 When your subject is very dimly lit , as shown above , you may have to combine a slow shutter speed with a wide lens aperture to give the film enough light . In this ex-ample you could give the same exposure by choosing sec at 18 , or 2 secs at f16 . provided you sup- port the camera steadily , prefer- ably on a tripod , and the subject remains absolutely still .
Reminders : camera controls
Focusing controls which part of the subject records sharply
Moving the lens brings parts of the subject at different distances from the camera in or out of focus . You can measure and set your subject distance or you can check the sharpness visually , by a focusing screen or rangefinder .
The extent of sharp detail is controlled by the aperture
The aperture controls image brightness ( through the amount of light it admits ) and the depth of field . The aperture ring is scaled in f numbers . The higher the f number the smaller the aperture and the greater the depth of field . Depth of field also increases if you use a shorter focal length lens ( see pp . 94-5 ) or increase subject distance .
Shutter speed affects the way movement records
The shutter controls the time the image is exposed to the film , and consequently , the amount of blur on the image . Blur varies accord- ing to camera movement , and the relative speed , direction , and distance of the subject .
The exposure is determined by the aperture and shutter speed
When taking a photograph you usually have a choice of combinations of aperture and shutter speeds . Provided they still give sufficient light to the film you can choose to have either wide or narrow depth of field , frozen or blurred movement .
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