114 THREE-DIMENSIONAL PHOTOGRAPHYFLASH TECHNIQUE.-under the usual conditions, the flash is the
specific illuminator of the principal subject. The exposure is de-
termined by using the usual guide number for distances of ten
feet and more. For nearer distances the aperture is a half stop
smaller than that called for. It has often been asked why you can
double the amount of light without overexposing; that is, when
you have daylight and then add the flash and give an expo-
sure which either one would require, why does not overexposure
result? There are several reasons. First, you are working outdoors,
where at night you would use a stop larger than the guide calls
for, so you are using the flash at what is really half strength.
Second, you use a flash because the subject or some part of it is
shaded and you wish to subdue the heavy contrast. Third, this
light intensity is present only near the camera and the greater
portion of the film area is lighted by daylight alone. Fourth, the
presence of a 100 percent increase in exposure is visible, but it does
not injure the film unless a base exposure much greater than
normal is used. In short, film latitude takes care of a lot of it.
With all of those factors involved, it is easy to see why the use
of “normal” flash aperture and time is not excessive.
The flash should, when possible, be extension flash, because the
centered flash can and will produce all of the undesirable results
which characterize it in night work; flat relief, pink eyes and all.
In outdoor flash, you are making a flash exposure with the day-
light acting as a base level of illumination.
SPECIFIC SUBJECTS.-NOW let us consider some of the types of
subject which were first mentioned.
Against the sun.-Flash is not used for contre jour effects, as
that requires a low level in the main figure to be contrasted with
the brilliant background. However, there are many occasions
when the desired angle is not such that the normal light is good;
often this angle is more or less against the sun, as when shooting
generally south at any hour. Flash will permit a fully exposed
subject under such conditions.
Spotty Eight.-If your model is posed in the shade of a tree, it is
probable that the light passing through the leaves will fall upon
the model as a spotty pattern of light and shade. This effectively
kills modeling and gives an appearance of exaggerated freckles.