EXAMPLE: You are photographing a document with a
camera that has a 5-inch lens and the bellows are
extended 7 inches. Your light meter indicated an
exposure of 1/30 second at f/4. The new exposure time
is determined as follows:
To adjust the aperture, use the following formula:
EXAMPLE: A 4-inch lens is extended to 4 inches
beyond one focal length. The original camera settings
are 5 seconds at f/11. Using the above formula, the
problem is solved as follows:
f/16 RULE
You should use a light meter for most of the
photographs that you take in the fleet. These light meters
are either built into the camera or are separate hand-held
models; however, there may be times when your light
meter does not operate properly, or you do not have time
to use it in order to "grab" an awesome shot. The f/16
rule of exposure allows you to determine basic camera
exposure settings for both black-and-white and color
photography without the aid of electronic devices.
The f/16 rule states: The basic exposure for an
average subject in bright frontal sunlight is
f/16 at:
film speed
Therefore, to calculate the BASIC exposure for
bright, sunny conditions, set f/16 on the camera lens and
use the IS0 speed of the film for the shutter speed; for
example, when you use IS0 125 film, set the shutter
speed at 1/125 second and the lens aperture at f/16. For
IS0 64 film, set the shutter speed at 1/60 second and the
lens aperture at f/16, and so on. When the camera does
not have a shutter speed corresponding to the IS0 of the
film, use the shutter speed that is closest to the IS0 of
the film.
The f/16 rule is based on the correct exposure for an
average subject under bright, sunny conditions. If the
sun goes behind a cloud, however, then the lighting on
the subject is decreased and you must change the basic
exposure. The aperture settings for different daylight
intensities are as follows:
Bright sun on light sand or snow-f/22
Bright sun-f/16
Cloudy bright-f/11
Heavy overcast or open shade-f/5.6
For each of these different daylight intensity
situations, you begin with the ISO speed to determine
the shutter speed, set the aperture to f/16, and open up
or stop down the aperture for the lighting conditions.
After calculating the exposure, you can change the
setting to any equivalent exposure; for example, if you
determine the required exposure to be 1/500 second at
f/5.6 but you wish to use a small aperture for greater
depth of field, you can change the setting to 1/60 second
at f/16.
Remember, the f/16 rule provides you with a basic
exposure for front-lighted subjects only. When the
subjects are side-lighted or back-lighted, you must
double or quadruple the exposure, respectively.
Because many cameras are fully automatic, you
may wonder why you need to know basic exposure.
There are three good reasons for knowing and
understanding the basic principles of exposure. First,
you want to control the depth of field and stop action
instead of the camera controlling it. Second, a light
meter cannot think All a light meter does is respond to
the light it receives. You must know when to override
the camera; for example, when the subject is side-
lighted or back-lighted. Third, meters are mechanical
and can fail. They can be inconsistent, consistently
wrong, or fail altogether. When you can workout in your
head, roughly what the camera exposures should be, you
will know when the camera or light meter is wrong.
Knowing when a light meter is giving incorrect readings
could make the difference between success or failure of
an important photographic assignment.
The correct use of a light meter greatly increases the
accuracy in determining your camera exposure. You
should also understand that the incorrect use of a light
meter can result in consistently unacceptable results. To
assure consistently acceptable exposures, you must
become thoroughly proficient with the correct operation
of a light meter.

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