تويت
التصوير الفوتوغرافي الحديث
تحديد الوضع الصحيح ..
جداول التعرض وكيفية استخدامها ..
EXPOSURE TABLES
Now that we understand the four factors that determine exposure , we can set up an exposure table that will give us the correct exposure for any given set of conditions . Table I is such an exposure table .
TABLE I
EXPOSURE TABLE FOR GENERAL PURPOSE FILM - ASA 125 to 160
The exposures given in Table I are safe , average exposures . You will usually find it possible to give half these exposures and still get usable negatives .
HOW TO USE THE EXPOSURE TABLE
Suppose you want to photograph a landscape with some detail in the foreground - the sky is slightly overcast so that only a faint shadow is thrown by the sun - and you are using black - and - white film , having an ASA speed of 160 . Refer to the exposure table ; the top row first to determine the type of subject , and the left hand column to determine the condition of the sun . An average landscape with some foreground detail is an average subject , and a sun that barely casts a shadow is a hazy sun . This gives us an exposure of 1/125 second at f / 8 .
Now let us take another example : an open beach scene in bright sunlight on a June day . According to our exposure table , this requires an exposure of 1/250 second at f / 16 .
The ASA system of indicating film speeds is a proportional system . This means that if the ASA rating of one film is twice that of another , the first film has twice the speed and , therefore , requires one - half the exposure . Referring to our table again , if you use a film having an ASA rating of 320 , the exposures would be exactly half those given in Table I. To arrive at these corrected exposures , you would either close down the lens one stop or use the next higher shutter speed .
Similarly , if you used a slow fine grain film with an ASA rating of 80 , you would use the next wider lens opening or cut the shutter speed in half .
تحديد الوضع الصحيح ..
جداول التعرض وكيفية استخدامها ..
EXPOSURE TABLES
Now that we understand the four factors that determine exposure , we can set up an exposure table that will give us the correct exposure for any given set of conditions . Table I is such an exposure table .
TABLE I
EXPOSURE TABLE FOR GENERAL PURPOSE FILM - ASA 125 to 160
The exposures given in Table I are safe , average exposures . You will usually find it possible to give half these exposures and still get usable negatives .
HOW TO USE THE EXPOSURE TABLE
Suppose you want to photograph a landscape with some detail in the foreground - the sky is slightly overcast so that only a faint shadow is thrown by the sun - and you are using black - and - white film , having an ASA speed of 160 . Refer to the exposure table ; the top row first to determine the type of subject , and the left hand column to determine the condition of the sun . An average landscape with some foreground detail is an average subject , and a sun that barely casts a shadow is a hazy sun . This gives us an exposure of 1/125 second at f / 8 .
Now let us take another example : an open beach scene in bright sunlight on a June day . According to our exposure table , this requires an exposure of 1/250 second at f / 16 .
The ASA system of indicating film speeds is a proportional system . This means that if the ASA rating of one film is twice that of another , the first film has twice the speed and , therefore , requires one - half the exposure . Referring to our table again , if you use a film having an ASA rating of 320 , the exposures would be exactly half those given in Table I. To arrive at these corrected exposures , you would either close down the lens one stop or use the next higher shutter speed .
Similarly , if you used a slow fine grain film with an ASA rating of 80 , you would use the next wider lens opening or cut the shutter speed in half .
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