(3) Although peacetime applications of comparative photography techniques
are numerous, their major application comes in combat, where the primary purpose
of such photographs is to show tactical changes in enemy positions, strengths and
weaknesses.
b. Comparative photography techniques.
(1) Before-and-after-action.
The simplest of the comparative techniques
requires only that the photographer get coverage of an enemy sector or
emplacement both before and after friendly forces have attacked it.
Such
pictures will show graphically the extent of damage to the enemy and whether the
attack has "softened" the enemy enough to permit the advance of friendly troops.
The same techniques have, of course, innumerable other applications such as
before-and-after medical or dental photography, before-and-after construction
photography, etc.
(2) Time-lapse.
Although all comparative photography must by definition
require two or more prints for comparison, possessing dissimilarities usually
obtained by shooting the photos at different times, there is a special class of
comparative photographs known as "time-lapse" photos.
Although this term is
commonly used for such things as "speeding up the action" on cinematography
(i.e., the opening of a flower), the Army uses the term to identify two or more
photos, taken at intervals of days or months, which depict changes in enemy
positions or strengths resulting from "buildups" or "withdrawals." Often the unit
photographer is assigned to take these photos on a regular basis so that a day-
to-day check is kept on enemy fortifications. Such comparative photos will often
reveal whether the enemy is massing for an attack or preparing for defense, and
foreknowledge of enemy intentions is invaluable to friendly forces.
(3) Flash recording photography.
A field commander is often faced with
the problem of where to direct his firepower in order to make it most effective
and a comparative photography technique called flash recording is made to order
for his purposes.
Basically the technique merely makes use of "muzzle flash",
the instantaneous burst of light which occurs when a weapon is fired at night,
recording these "flashes" photographically.
There are, however, various
procedures for performing the technique. Among them are:
(a) Night exposure. Exposure of the film is begun at dusk, when there
is sufficient light to allow a fairly short exposure and yet enough darkness to
enable the flashes to stand out against a dark background.
Polaroid film has
proven itself ideal for such work, not only because of the rapidity of processing
but also because of its extremely high emulsion speeds.
(b) Daylight and night exposure.
In this method, a partial exposure
is given the film during the daylight hours, with the camera mounted on a
tripod.
The film is then given a second exposure at night, usually a
time exposure, to record the muzzle flashes.
This technique has the advantage
of
giving a
record
of both the
flashes and
a
good image of
the
terrain unobtainable with a night exposure technique alone (fig 1-8).
Its
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