Lesson 3/Learning Event 7
Learning Event 7
CALCULATE DAYLIGHT EXPOSURE
1. A system of calculating outdoor daylight exposure without the aid of a
photoelectric exposure meter (light meter) is necessary for determining a
proper exposure for the various daylight condition, subject reflectance,
lighting direction, and film sensitivity.
The f/16 rule, an established
practice in the Army and among many professional photographers, has been
proven to be an accurate approach for the calculation of daylight exposure.
Many photographers use this rather than using their light meters. There are
three good reasons why photographers do not rely on the automatic built-in
exposure meters in their cameras. First, the photographer wants to control
the exposure for a desired effect instead of the camera controlling it.
Second, exposure meters can't think; it does not know what the
photographer's intentions are for, in the finished photograph.
Third,
exposure meters are mechanical and subject to failure.
They can be
inconsistent, consistently wrong, or fail all together.
Knowledge and
practice of the f/16 rule will enable you to spot when the exposure meter is
lying.
This could mean the difference between the success of failure of
your assignment.
2. The f/16 rule is based on the basic exposure norms and the ISO.
The
basic exposure norms are: bright sun, front lighting, and average subjects
which are all based on f/16. Hence the term "BASIC EXPOSURE." To complete
the rule, set the shutter speed to match, or nearly match, the film's ISO
speed rating, for example, ISO 125 and 100 set the shutter speed at 1/125,
for ISO 50 and ISO 64, set the shutter speed at 1/60.
a. The procedure then is to change the basic exposure (f/16 for each
daylight condition as follows:
Bright sun on light sand or snow; f/22
Bright sun (no change); f/16
Hazy sun, soft shadows; f/11
Cloudy bright, no shadows; f/8
Heavy overcast; f/5.6
Open shade; f/5.6
b. And correct for subject brightness:
Light (bright) subjects, stop down one stop.
Average subjects (no change).
Dark subjects, open one stop.
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