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طاولات التعريض وأجهزة القياس المحمولة باليد .. تقنية الكاميرا .. المرشد خطوة بخطوة للتصوير الفوتوغرافي
Exposure tables and hand - held meters
Once you have selected a film you must find out what exposure is necessary for the par- ticular subject and lighting conditions . After determining this , you can alter the aperture and shutter speed settings ( preserving the combined exposure ) to obtain the depth of field and blur you want .
If you have a simple camera , the easiest way of deciding the exposure to give is to use the symbols marked on the camera or follow the instructions packed with the film . The advice shown , right , will give you reasonable results for typical outdoor sub- jects , under five different daylight condi- But as soon as you tackle a different sort of subject , work inside or under artificial lighting , or use a different film speed , the guide fails . This is where an exposure meter . either a hand - held model or one built into the camera , is essential ( see pp . 40-1 ) .
Meters have a light - sensitive surface or " cell " to measure accurately the actual illumination reflected from the subject under all sorts of conditions . A separate hand - held meter has the advantage of serving all cameras and , unlike meters that are built into the camera , enables you to check exposure quickly without having to use your camera . This is particularly useful when you have the camera on a tripod with a carefully set viewpoint , because you are free to take close - up readings without dis- turbing the camera position .
Exposure tables and symbols :
The table above shows exposure information that is included with film . It lists the apertures needed for a 125 ASA film , when using a 1/125 sec shutter speed , under various conditions .
From top to bottom , the sym- bols describe direct , bright sun- light ; partly obscured sun ; shaded light and a bright sky ; hazy overall cloud ; and overcast con- ditions . If you wanted to use a dif- ferent shutter speed , the aperture settings would have to be corres- pondingly increased or reduced for each lighting condition .
The hand - held light meter :
Most hand - held meters have a light - sensitive cell , a needle and light - reading scale , and a calcu- lator to convert the reading into f numbers and shutter speeds .
The meter shown below has a selenium cell , which generates its own electricity from light and so does not need a battery . Some hand ( and all through - the - lens ) meters use a smaller , photo- resistant cell , which is more sensi-tive but needs a battery . With selenium cell meters under poor lighting , the hinged baffle at the back of the meter should be down to allow the needle to read over one scale . Under bright light the baffle should be up , covering the light - sensitive cell - the needle then reads over a different , higher scale . When using a hand - held meter be careful not to obstruct the light- sensitive cell .
Using a hand - held meter :
1. Set the ASA ( or DIN ) rating . of your film in the appropriate window on the calculator dial of your meter .
2. Point the light - sensitive cell on the rear of the meter toward the subject , and press the needle release switch to get a reading on the scale .
3. Find this reading on the cal- culator dial and move the pointer on the aperture setting scale to meet it .
4. The correct exposure is now given by any of the aperture and shutter speeds shown adjacent to each other , such as 1/150 sec at f16 , above .
Exposure tables and hand - held meters
Once you have selected a film you must find out what exposure is necessary for the par- ticular subject and lighting conditions . After determining this , you can alter the aperture and shutter speed settings ( preserving the combined exposure ) to obtain the depth of field and blur you want .
If you have a simple camera , the easiest way of deciding the exposure to give is to use the symbols marked on the camera or follow the instructions packed with the film . The advice shown , right , will give you reasonable results for typical outdoor sub- jects , under five different daylight condi- But as soon as you tackle a different sort of subject , work inside or under artificial lighting , or use a different film speed , the guide fails . This is where an exposure meter . either a hand - held model or one built into the camera , is essential ( see pp . 40-1 ) .
Meters have a light - sensitive surface or " cell " to measure accurately the actual illumination reflected from the subject under all sorts of conditions . A separate hand - held meter has the advantage of serving all cameras and , unlike meters that are built into the camera , enables you to check exposure quickly without having to use your camera . This is particularly useful when you have the camera on a tripod with a carefully set viewpoint , because you are free to take close - up readings without dis- turbing the camera position .
Exposure tables and symbols :
The table above shows exposure information that is included with film . It lists the apertures needed for a 125 ASA film , when using a 1/125 sec shutter speed , under various conditions .
From top to bottom , the sym- bols describe direct , bright sun- light ; partly obscured sun ; shaded light and a bright sky ; hazy overall cloud ; and overcast con- ditions . If you wanted to use a dif- ferent shutter speed , the aperture settings would have to be corres- pondingly increased or reduced for each lighting condition .
The hand - held light meter :
Most hand - held meters have a light - sensitive cell , a needle and light - reading scale , and a calcu- lator to convert the reading into f numbers and shutter speeds .
The meter shown below has a selenium cell , which generates its own electricity from light and so does not need a battery . Some hand ( and all through - the - lens ) meters use a smaller , photo- resistant cell , which is more sensi-tive but needs a battery . With selenium cell meters under poor lighting , the hinged baffle at the back of the meter should be down to allow the needle to read over one scale . Under bright light the baffle should be up , covering the light - sensitive cell - the needle then reads over a different , higher scale . When using a hand - held meter be careful not to obstruct the light- sensitive cell .
Using a hand - held meter :
1. Set the ASA ( or DIN ) rating . of your film in the appropriate window on the calculator dial of your meter .
2. Point the light - sensitive cell on the rear of the meter toward the subject , and press the needle release switch to get a reading on the scale .
3. Find this reading on the cal- culator dial and move the pointer on the aperture setting scale to meet it .
4. The correct exposure is now given by any of the aperture and shutter speeds shown adjacent to each other , such as 1/150 sec at f16 , above .
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