When two flash units of equal intensity and at equal
distance from a subject illuminate the same area, the
exposure for one unit should be determined and then the
exposure should be halved because twice the intensity
of light is reflected from the subject.
Flash pictures can be made without the camera
shutter and flash being synchronized, using a technique
called open flash. In the open-flash method, the camera
shutter is set at T or B, the shutter is opened, the flash
unit fired, and the shutter closed. The open-flash
technique is sometimes used when the level of light over
a large scene is very low or at night. This method of flash
photography allows the photographing of large scenes
that ordinarily are quite difficult to illuminate with
artificial light. The photographer can walk into a scene
with the flash unit and illuminate sections of the scene
or the entire scene. Any number of flashes can be used
during the exposure while the shutter remains open. A
silhouette of your body can be recorded if your body
gets between the flash and the camera.
To arrive at the exposure for an open-flash picture
using a manual flash, determine your flash-to-subject
distance and f/stop. Keep the distance equal to the
objects being illuminated when using manual flash; for
example, when the f/stop for the scene is f/5.6 based on
a flash-to-subject distance of 10-feet, every flash within
the scene should be 10 feet from that section of the scene
being illuminated, When an automatic flash is used, the
flash automatically shuts off when the proper amount of
light is reflected from the subject, providing the object
is within its distance range. When you are using a
manual flash, the exposure for open flash is determined
as previously discussed. This is true unless two or more
flash units with equal intensities are used at equal
distances, or two or more flashes from the same unit at
the same distance are used to illuminate the subject.
Interesting multiple exposures can be made with
only one or two electronic flash units. Multiple exposure
pictures, besides being artistic and interesting, are often
used to study subject motion and position. This can be
accomplished by the following procedures:
1. Darken the room and position your subject
against a black background.
2. Allow enough background area for the number
of different exposures you intend to make. When you
are using a ground glass camera, mark off on the glass,
with grease pencil, the areas where the subject should
be for each different exposure. If not using a ground
glass camera, make a pencil sketch to help you position
the subject.
3. Set up the electronic flash lights so the minimum
amount of illumination falls on the background itself.
4. Turn off all room lights and make your first
exposure. Then, without advancing the film, move your
subject to the next position for the second exposure.
Repeat this procedure for each image you want to record
on the film.
Action of any kind, no matter how slight, can add
interest to most pictures. Each type of action requires a
different camera technique, but because of the short
duration of light from electronic flash, it is ideal for
recording any action ranging from a fleeting expression
to a sports triumph. Most electronic flash units have a
maximum flash duration (the length of time the light is
on) of about 1/800th second, and a minimum flash
duration as short as 1/20000th second, thus you can
"freeze" almost any action with the flash.
Indoors, where there is little existing light, you have
no problem because the electronic flash itself stops the
action; however, outdoors in daylight, you may
encounter ghost images. Ghost images can occur when
existing light and a slow shutter speed are used in
conjunction with electronic flash. A ghost image appears
as a blur when one image is recorded by the existing
light and a second sharp image by the electronic flash.
Flash photography, outdoors at night, can produce
very underexposed photographs if not taken properly.
Outdoors, flash does not carry very far; therefore, it can
be difficult to light objects from a distance; however,
this limited coverage also gives you great control.
Indoors, part of the output of a flash unit is reflected
from the ceiling and walls back to the subject. Rarely do
you find such reflective surfaces outside, so some light
is lost. To compensate for the light lost, you must open
up your aperture when photographing objects at any
distance. Because so much light is absorbed in these
large areas, it may not be uncommon to open up your
aperture two or three f/stops. Tests should be conducted
before shooting in large, indoor areas, such as
gymnasiums and hangar bays or outdoors at night, to

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