select a wider aperture to control depth of field, start by
setting your main flash at one-half or one-fourth power
and adjust your fill flash appropriately.
Adjusting lighting ratios by flash-to-subject-
distance is another method to control lighting ratios. An
easy way to calculate footage for a 3:1 ratio with two
lights of equal intensity is to think of the full f/stops (2,
2.8, 4, 5.6, 8, 11, 16, 22, etc.) as distances in feet. Place
the main light at the desired distance closest to one of
the "f/stops," and place the fill light at the distance
indicated by the next larger number; that is, 5.6 feet and
8 feet or 16 feet and 22 feet, and so on.
Another easy method to control the lighting ratios
using an automatic electronic flash is to use the flash
unit in the automatic mode. When set in the automatic
mode, the flash-to-subject distance is not supercritical,
and there is some leeway as long as the flash units are
within their operating range.
To obtain a 2:1 lighting ratio, you simply have both
flash units set at the same automatic setting and at
approximately the same distance from the subject. For
a 3:1 lighting ratio, use the same automatic setting and
approximately the same flash-to-subject distances, but
set the fill flash at twice the film speed as the film being
used (main flash setting). For a 5:1 or even higher
lighting ratio, use the same automatic setting and
approximately the same flash-to-subject distance and
set the fill flash at four times more than that of the main
flash, and so on.
Any lighting ratio can be obtained when using an
automatic flash unit. By controlling the power output
intensity, adjusting the film speed setting, changing the
main and fill flash distances, or a combination of the
three, you can manipulate the lighting ratio easily to any
ratio. As with any stage of photography, practice and
testing with your camera and flash combinations in
various situations produces the best results.
SYNCHRO-SUNLIGHT
Bright sunlight, used as the only means of
illumination for an exposure, can produce deep
objectional shadows on a subject. When a flash unit is
used as a fill-in source of illumination, it reduces these
shadows and is known as synchro-sunlight photography.
Improperly handled, the synchro-sunlight
technique can produce an effect that makes the
photograph appear as if taken at night with a single flash.
This effect occurs when the flash illumination is more
intense than the sunlight.
The first step for proper exposure with synchro-
sunlight is to calculate the correct exposure for daylight,
and set the shutter speed and f/stop as though a flash is
not being used; however, keep in mind when using a
focal-plane shutter, the shutter speed must be
synchronized with the electronic flash unit. Avoid using
a fast film in bright sunlight when using a camera
equipped with a focal-plane shutter. In this case, you are
limited only to your aperture to control the exposure of
the film, because your shutter speed is nonadjustable. A
leaf shutter has an advantage over a focal-plane shutter.
When a leaf shutter is used, it provides more control over
depth of field since the shutter synchronizes at all shutter
speeds.
When you are using an automatic flash, the same
principles apply for synchro-sun that were explained in
the section for lighting ratio. The sun is used as the main
light, and your camera settings are determined directly
from your light meter. The easiest method is to set the
film speed (ISO) on your flash unit to twice the film
speed being used for a 3:1 lighting ratio and four times
the film speed being used for a 5:1 ratio. A fraction of
the manual power output can also be used to achieve the
desired lighting ratio.
Remember to compensate your exposure by
opening up two f/stops for a backlit subject and one
f/stop for a subject that is sidelighted when taking your
light meter reading from a distance. For color
photography, you should normally use a 2:1 or 3:1
lighting ratio. For black-and-white photography, a ratio
of 3:1 to 5:1 is acceptable.
MULTIPLE-FLASH UNITS
Multiple flash is the use of two or more flash units
fired in synchronization with the camera shutter. The
flash units can be auxiliary flash units, connected to the
camera by extension cords, or they can be slave flash
units. Slave units usually have self-contained power
sources and are fired with a photoelectric cell when light
from a master flash unit strikes the cell of the slave unit.
With multiple flash, exposure calculations are based
on the distance between the subject and the flash unit
that produces the most intense illumination to the
subject; therefore, you can have numerous auxiliary
flash units or slaves for a scene and only calculate your
exposure from the mainlight source. All other flash units
should be equidistant or at a greater distance from the
subject as compared to the flash unit on which the
exposure is based.
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