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عدادات الكاميرات .. تقنية الكاميرا .. المرشد خطوة بخطوة للتصوير الفوتوغرافي
Meters on cameras
Nowadays most cameras have their own built - in light meter , which can be either coupled or uncoupled . On an uncoupled meter you must first read the meter , then choose and set the shutter and aperture values . On coupled systems the read - out , usually in the camera viewfinder , responds directly to adjustments of the aperture and shutter controls and indicates when they are correctly combined .
The light - sensitive cell in a built - in metering system is either on the exterior or inside the main body of the camera . If it is on the exterior , the cell does not measure the light entering the lens ( that is , the light that acts on the film ) so it can be misleading . It only measures light coming from the gen- eral direction of the subject , and does not compensate when a filter or a different lens is attached .
These problems are overcome by a " through - the - lens " meter ( TTL ) , which ap- pears almost exclusively on single lens reflex cameras . Its light - sensitive cell , posi- tioned inside the camera , measures the light that passes through the lens , thereby taking into account the effect of lens aperture and any filters or close - up attach- ments you may fit to the camera . Through- the - lens meters are always coupled directly to the shutter and aperture controls , and some can set the controls automatically .
Meters on single lens reflex cameras :
Most built - in meters on single lens reflex cameras are through- the - lens types . They have the advantage of only measuring the light that forms the image . The light - sensitive cell can be in various positions . Often several cells are used on or around the pentaprism , where they receive a general view of the image on the focusing screen . The meter is powered by a small replaceable battery housed in the camera body . Exposure information is shown on a display on the focusing screen , either by a moving needle or colored indicator lights .
Viewfinder displays :
Three typical viewfinder displays for through - the - lens meters are shown left . The simplest , top . is a needle which is centered for the correct exposure by adjusting the aperture or shutter ( according to the model of camera ) . The center display includes the shutter set- ting and is centered by changing the lens aperture . A similar ar- rangement to this , but using light signals , is shown in the bottom viewfinder display .
Meter reading areas :
Through - the - lens meters measure light from the subject in various ways . Some view the whole pic- ture area , averaging out the light and dark areas , top right . This is fine if your picture has roughly equal amounts of light and dark areas .
A few through - the - lens meters give " spot " readings , center right - they read a small area of the picture , usually a central zone marked on the focusing screen . This enables you to read exposure for just one key area , such as a face , or to take more than one measurement from the light and dark areas which can then be averaged to get an overall reading . A spot reading allows you greatest control and accuracy but it is also easy to make a mistake , for instance measuring only the sky when your subject is mostly landscape .
Some meters use a " center- weighted " system , which measures most of the picture but gives prominence to the central area , bottom right . This works well provided the central area is rep- resentative of the whole scene .
Using a through - the - lens meter :
1. Set the ASA ( or DIN ) rating of your film in a window on the shutter dial or on the film speed dial on the camera body .
2. Set the control ( i.e. shutter or aperture ) most important for the picture , considering subject movement and depth of field .
3. Focus the image . Then , if you have a spot or center - weighted meter , point the camera so the meter reads the appropriate area of the subject .
4. Turn the aperture ring ( or alter the shutter speed ) until the indi- cator ( or lights ) in the viewfinder display shows that the correct exposure is set .
Priority metering :
Some single lens reflex cameras have priority automatic metering -you select either aperture or shutter speed and the meter automatically sets the other control .
Aperture priority :
If your camera has an " aperture priority system you always set the f number yourself and the cam- era sets the shutter speed auto- matically . This is particularly suit- able for subjects such as landscape . still life , or close - up work , see right and below , where careful control of the depth of field is important .
Shutter speed priority :
Some automatic meters have shut- ter speed priority- you choose the shutter speed and the meter sets the aperture . In bright conditions you will be likely to get a greater depth of field than when the light- ing is poor . Shutter priority systems are particularly suited to action photography , below , or where you want to create blur deliberately . such as shown right .
Usually priority automatic systems are options on cameras that also allow manual operation . On some cameras now you can choose either aperture priority or shutter priority automatic metering .
Meters on direct vision cameras :
Light meters on direct vision viewfinder cameras are either coupled to the exposure controls , or uncoupled . The uncoupled meter camera , right , is the simp- lest : first set the film speed on the calculator on top of the camera , shown right ; a needle moves along a scale on the calculator to give the reading . When your selected aperture or shutter speed is set against the reading , the calculator will show you the other setting to make for the correct exposure .
The cameras , below right , have coupled meters , which may be manually set . Manual cameras may have a " follow pointer " read- out , as shown far right . Automatic cameras may have priority metering , or may set the controls independently , without you having to do anything .
The two cameras shown near right have selenium cell meters which do not need batteries ; the third has a battery - operated CdS cell meter .
Follow pointer viewfinders :
Some manual coupled - meter cam- eras have a needle - and - pointer exposure guide in the viewfinder . The needle is fixed by setting either aperture or shutter ( depending on the camera ) ; the pointer is then moved by altering the second con- trol when they coincide , the correct exposure is set .
Meters on cameras
Nowadays most cameras have their own built - in light meter , which can be either coupled or uncoupled . On an uncoupled meter you must first read the meter , then choose and set the shutter and aperture values . On coupled systems the read - out , usually in the camera viewfinder , responds directly to adjustments of the aperture and shutter controls and indicates when they are correctly combined .
The light - sensitive cell in a built - in metering system is either on the exterior or inside the main body of the camera . If it is on the exterior , the cell does not measure the light entering the lens ( that is , the light that acts on the film ) so it can be misleading . It only measures light coming from the gen- eral direction of the subject , and does not compensate when a filter or a different lens is attached .
These problems are overcome by a " through - the - lens " meter ( TTL ) , which ap- pears almost exclusively on single lens reflex cameras . Its light - sensitive cell , posi- tioned inside the camera , measures the light that passes through the lens , thereby taking into account the effect of lens aperture and any filters or close - up attach- ments you may fit to the camera . Through- the - lens meters are always coupled directly to the shutter and aperture controls , and some can set the controls automatically .
Meters on single lens reflex cameras :
Most built - in meters on single lens reflex cameras are through- the - lens types . They have the advantage of only measuring the light that forms the image . The light - sensitive cell can be in various positions . Often several cells are used on or around the pentaprism , where they receive a general view of the image on the focusing screen . The meter is powered by a small replaceable battery housed in the camera body . Exposure information is shown on a display on the focusing screen , either by a moving needle or colored indicator lights .
Viewfinder displays :
Three typical viewfinder displays for through - the - lens meters are shown left . The simplest , top . is a needle which is centered for the correct exposure by adjusting the aperture or shutter ( according to the model of camera ) . The center display includes the shutter set- ting and is centered by changing the lens aperture . A similar ar- rangement to this , but using light signals , is shown in the bottom viewfinder display .
Meter reading areas :
Through - the - lens meters measure light from the subject in various ways . Some view the whole pic- ture area , averaging out the light and dark areas , top right . This is fine if your picture has roughly equal amounts of light and dark areas .
A few through - the - lens meters give " spot " readings , center right - they read a small area of the picture , usually a central zone marked on the focusing screen . This enables you to read exposure for just one key area , such as a face , or to take more than one measurement from the light and dark areas which can then be averaged to get an overall reading . A spot reading allows you greatest control and accuracy but it is also easy to make a mistake , for instance measuring only the sky when your subject is mostly landscape .
Some meters use a " center- weighted " system , which measures most of the picture but gives prominence to the central area , bottom right . This works well provided the central area is rep- resentative of the whole scene .
Using a through - the - lens meter :
1. Set the ASA ( or DIN ) rating of your film in a window on the shutter dial or on the film speed dial on the camera body .
2. Set the control ( i.e. shutter or aperture ) most important for the picture , considering subject movement and depth of field .
3. Focus the image . Then , if you have a spot or center - weighted meter , point the camera so the meter reads the appropriate area of the subject .
4. Turn the aperture ring ( or alter the shutter speed ) until the indi- cator ( or lights ) in the viewfinder display shows that the correct exposure is set .
Priority metering :
Some single lens reflex cameras have priority automatic metering -you select either aperture or shutter speed and the meter automatically sets the other control .
Aperture priority :
If your camera has an " aperture priority system you always set the f number yourself and the cam- era sets the shutter speed auto- matically . This is particularly suit- able for subjects such as landscape . still life , or close - up work , see right and below , where careful control of the depth of field is important .
Shutter speed priority :
Some automatic meters have shut- ter speed priority- you choose the shutter speed and the meter sets the aperture . In bright conditions you will be likely to get a greater depth of field than when the light- ing is poor . Shutter priority systems are particularly suited to action photography , below , or where you want to create blur deliberately . such as shown right .
Usually priority automatic systems are options on cameras that also allow manual operation . On some cameras now you can choose either aperture priority or shutter priority automatic metering .
Meters on direct vision cameras :
Light meters on direct vision viewfinder cameras are either coupled to the exposure controls , or uncoupled . The uncoupled meter camera , right , is the simp- lest : first set the film speed on the calculator on top of the camera , shown right ; a needle moves along a scale on the calculator to give the reading . When your selected aperture or shutter speed is set against the reading , the calculator will show you the other setting to make for the correct exposure .
The cameras , below right , have coupled meters , which may be manually set . Manual cameras may have a " follow pointer " read- out , as shown far right . Automatic cameras may have priority metering , or may set the controls independently , without you having to do anything .
The two cameras shown near right have selenium cell meters which do not need batteries ; the third has a battery - operated CdS cell meter .
Follow pointer viewfinders :
Some manual coupled - meter cam- eras have a needle - and - pointer exposure guide in the viewfinder . The needle is fixed by setting either aperture or shutter ( depending on the camera ) ; the pointer is then moved by altering the second con- trol when they coincide , the correct exposure is set .
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