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التصوير الفوتوغرافي الحديث
تحديد الوضع الصحيح ..
معايرة مقياس التعرض ..
CALIBRATING THE EXPOSURE METER
Any photographer who takes his work seriously uses an exposure meter . The day of guessing exposure has long since passed . Nevertheless , every photographer should have a fairly good idea of what his exposure should be before he takes a meter reading . Even after a relatively short experience in the field of photography , you should have taken enough pictures under average lighting conditions so that you should be able to get along very nicely if something happens to your exposure meter . Nevertheless , there are some photographers who rely so slavishly on their meters that they give no thought at all to the readings they are getting other than to expose accordingly . If anything goes wrong with their meters , they are completely lost . A dropped or jarred meter may be thrown off calibration by two or three stops without their realizing it , and they can go on making wrong exposure after wrong exposure without realizing that their pictures may be worthless . For that reason , every photographer should make it his business to memorize the basic exposures required for most common conditions under which he works so that if his exposure meter shifts seriously out of calibration , he will spot it immediately .
If you suspect your meter is off calibration , it is easy enough to check it against another . For your comparison , try to get another which is either of the same make or the same general type so that it covers approximately the same angle of view . Take meter readings of typical subjects in which the illumination is fairly uniform over a much wider angle than the meter itself includes so that slight inaccuracies in the way you hold the meter will not affect its reading .
There may be times , however , when it is not possible to compare one meter against another . Under those circumstances , you can still determine the accuracy of your meter within one or , at the most 2 f / numbers . One of the following three tests will generally serve .
No. 1 Wait for a clear cloudless day and find a spot where you can get a clear view of the sky without interference from branches of trees , buildings , or other obstructions . Face due north point the exposure meter 45 ° upwards so that you take in nothing but blue sky , and take a reading The meter should indicate an exposure of about 1/125 second at f / 22 with a film speed of ASA 160. ( See Figure 19. ) .
Fig.19 ( Courtesy of W.T.Chester )
No. 2 Spread several sheets of ordinary newspaper on the ground in an open area so that the paper is in direct , bright sunlight . On a clear day the exposure reading taken off the paper should be about 1/500 second at f / 22 for a film speed of ASA 160. ( See Figure 20. )
No. 3 This test should be done indoors at night or in a room in which the shades can be drawn so as to reduce the level of illumination to the point where it will have very little effect on the meter . Set up a standard 100 - watt electric light bulb ( be sure the bulb is new and unused ) , and hold the exposure meter exactly 20 inches from the side of the bulb . You should get an exposure reading of about 1/125 second at f / 11 with a film speed of ASA 160. ( See Figure 21. )
NEWSPAPER ON SIDEWALK
Fig.20 ( Courtesy of W.T.Chester )
تحديد الوضع الصحيح ..
معايرة مقياس التعرض ..
CALIBRATING THE EXPOSURE METER
Any photographer who takes his work seriously uses an exposure meter . The day of guessing exposure has long since passed . Nevertheless , every photographer should have a fairly good idea of what his exposure should be before he takes a meter reading . Even after a relatively short experience in the field of photography , you should have taken enough pictures under average lighting conditions so that you should be able to get along very nicely if something happens to your exposure meter . Nevertheless , there are some photographers who rely so slavishly on their meters that they give no thought at all to the readings they are getting other than to expose accordingly . If anything goes wrong with their meters , they are completely lost . A dropped or jarred meter may be thrown off calibration by two or three stops without their realizing it , and they can go on making wrong exposure after wrong exposure without realizing that their pictures may be worthless . For that reason , every photographer should make it his business to memorize the basic exposures required for most common conditions under which he works so that if his exposure meter shifts seriously out of calibration , he will spot it immediately .
If you suspect your meter is off calibration , it is easy enough to check it against another . For your comparison , try to get another which is either of the same make or the same general type so that it covers approximately the same angle of view . Take meter readings of typical subjects in which the illumination is fairly uniform over a much wider angle than the meter itself includes so that slight inaccuracies in the way you hold the meter will not affect its reading .
There may be times , however , when it is not possible to compare one meter against another . Under those circumstances , you can still determine the accuracy of your meter within one or , at the most 2 f / numbers . One of the following three tests will generally serve .
No. 1 Wait for a clear cloudless day and find a spot where you can get a clear view of the sky without interference from branches of trees , buildings , or other obstructions . Face due north point the exposure meter 45 ° upwards so that you take in nothing but blue sky , and take a reading The meter should indicate an exposure of about 1/125 second at f / 22 with a film speed of ASA 160. ( See Figure 19. ) .
Fig.19 ( Courtesy of W.T.Chester )
No. 2 Spread several sheets of ordinary newspaper on the ground in an open area so that the paper is in direct , bright sunlight . On a clear day the exposure reading taken off the paper should be about 1/500 second at f / 22 for a film speed of ASA 160. ( See Figure 20. )
No. 3 This test should be done indoors at night or in a room in which the shades can be drawn so as to reduce the level of illumination to the point where it will have very little effect on the meter . Set up a standard 100 - watt electric light bulb ( be sure the bulb is new and unused ) , and hold the exposure meter exactly 20 inches from the side of the bulb . You should get an exposure reading of about 1/125 second at f / 11 with a film speed of ASA 160. ( See Figure 21. )
NEWSPAPER ON SIDEWALK
Fig.20 ( Courtesy of W.T.Chester )
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