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الخطوة 4: التحكم في التعرض / تقنيات القياس .. معدات وتقنيات إضافية .. المرشد خطوة بخطوة للتصوير الفوتوغرافي
STEP 4 : EXPOSURE CONTROL / Metering techniques
Light meters measure the light so that the mid - tones of the subject are always accept- ably reproduced in the picture . ( The basic methods of taking light readings were intro- duced on pages 42-3 . ) But by using more advanced meters or methods of taking readings you can more closely control the tonal range in your pictures .
You may want to bring out detail in the highlights or shadows or limit the range of tones in your picture . With practice you can take your exposure readings and deter- mine which parts of the subject will repro- duce dark gray , mid - gray or light - gray .
For most subjects a built - in camera meter is convenient and quick to use . If you are using filters or other lens attachments that alter the light reaching the film , a through- the - lens meter automatically measures the reduced light . But a hand - held meter is more versatile for advanced exposure control . It enables you to take more specific measure- ments from the subject or fit attachments to control the exposure reading .
Instead of taking a reading from the re- flected light , by fitting a light - diffusing dome over the meter you can measure the light that illuminates the subject - an " incident " light reading . This ensures that maximum detail in the highlights is recorded on the film . Some hand - held meters are also avail- able or can be adapted , by using a spot reading attachment , to take distant read- ings from a very small part of the subject .
Advanced light reading equipment
Most hand meters have a small plastic dome or disk which fits over the light sensitive cell . This is used for incident light readings where the meter is pointed toward the light source instead of the subject . The plastic dome diffuses the light as it enters the cell and widens the meter's angle of view . On a selen- ium cell meter the dome clips over the cell . The much smaller cell on a CdS meter can be covered by a sliding diffusing attachment .
Some hand meters will accept a narrow angle , spot reading at- tachment . This has a viewfinder that you can aim the meter accur- ately to cover a selected part of the subject . A spot meter enables you to read from a very small area of a distant subject and so is very useful with long focus lenses .
Spot meters with a built - in view- ing screen are more sophisticated than the adaptors . You dial in the ASA film speed and shutter setting before viewing the subject through a viewfinder . The meter covers a 1 ° angle of view , which is shown on the viewfinder . The aperture number for the correct exposure of each area appears on a display when you pull the meter trigger .
Spot meter readings can be modi- fied by turning a dial so that the chosen area will be white on the print instead of mid - gray .
Taking readings for highlights
The two pictures , right , show the effect of measuring for highlights in exposure . In the top picture an overall reading was taken and the highlights are overexposed . In the bottom picture the reading was taken with an incident light reading attachment on meter . This ensured that highlight detail - very important here was not overexposed .
There are three ways of ensuring correctly exposed subject high- lights . You can use a spot meter to measure highlights only , and then modify the reading . This measures from the reflected light .
The other two methods a white card , and a meter fitted with a diffusing attachment use inci- dent light . When using a white card , hold it near the subject and take a reading about 6 ins ( 15 cm ) away from the card . Then increase the meter reading by eight times to reproduce highlight detail almost white , not gray .
With an incident light attach- ment , hold the meter near the sub- ject pointing toward the light source for highlight detail . The reading gives correct exposure .
STEP 4 : EXPOSURE CONTROL / Metering techniques
Light meters measure the light so that the mid - tones of the subject are always accept- ably reproduced in the picture . ( The basic methods of taking light readings were intro- duced on pages 42-3 . ) But by using more advanced meters or methods of taking readings you can more closely control the tonal range in your pictures .
You may want to bring out detail in the highlights or shadows or limit the range of tones in your picture . With practice you can take your exposure readings and deter- mine which parts of the subject will repro- duce dark gray , mid - gray or light - gray .
For most subjects a built - in camera meter is convenient and quick to use . If you are using filters or other lens attachments that alter the light reaching the film , a through- the - lens meter automatically measures the reduced light . But a hand - held meter is more versatile for advanced exposure control . It enables you to take more specific measure- ments from the subject or fit attachments to control the exposure reading .
Instead of taking a reading from the re- flected light , by fitting a light - diffusing dome over the meter you can measure the light that illuminates the subject - an " incident " light reading . This ensures that maximum detail in the highlights is recorded on the film . Some hand - held meters are also avail- able or can be adapted , by using a spot reading attachment , to take distant read- ings from a very small part of the subject .
Advanced light reading equipment
Most hand meters have a small plastic dome or disk which fits over the light sensitive cell . This is used for incident light readings where the meter is pointed toward the light source instead of the subject . The plastic dome diffuses the light as it enters the cell and widens the meter's angle of view . On a selen- ium cell meter the dome clips over the cell . The much smaller cell on a CdS meter can be covered by a sliding diffusing attachment .
Some hand meters will accept a narrow angle , spot reading at- tachment . This has a viewfinder that you can aim the meter accur- ately to cover a selected part of the subject . A spot meter enables you to read from a very small area of a distant subject and so is very useful with long focus lenses .
Spot meters with a built - in view- ing screen are more sophisticated than the adaptors . You dial in the ASA film speed and shutter setting before viewing the subject through a viewfinder . The meter covers a 1 ° angle of view , which is shown on the viewfinder . The aperture number for the correct exposure of each area appears on a display when you pull the meter trigger .
Spot meter readings can be modi- fied by turning a dial so that the chosen area will be white on the print instead of mid - gray .
Taking readings for highlights
The two pictures , right , show the effect of measuring for highlights in exposure . In the top picture an overall reading was taken and the highlights are overexposed . In the bottom picture the reading was taken with an incident light reading attachment on meter . This ensured that highlight detail - very important here was not overexposed .
There are three ways of ensuring correctly exposed subject high- lights . You can use a spot meter to measure highlights only , and then modify the reading . This measures from the reflected light .
The other two methods a white card , and a meter fitted with a diffusing attachment use inci- dent light . When using a white card , hold it near the subject and take a reading about 6 ins ( 15 cm ) away from the card . Then increase the meter reading by eight times to reproduce highlight detail almost white , not gray .
With an incident light attach- ment , hold the meter near the sub- ject pointing toward the light source for highlight detail . The reading gives correct exposure .
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