TRICK WORK 227Another shot of the same type was made of a cat walking along
a tree limb. As you know a cat usually starts down a tree trunk
head first and almost immediately swings about and backs down.
This tree limb was almost horizontal, but its smaller branches all
tended outwardly. The cat was walking upright along the limb.
Nothing but other limbs appeared in the field of view. The cam-
era tilt gave the limb a direction about ten degrees off vertical and
a position chosen which caused the smaller branches to tend up-
wardly. The result was a cat walking upon fully extended legs
down a tree trunk, an impossible thing to do because the position
would give no purchase for the claws.
This has been hardly more than a suggestion of the tricks which
can be done with the stereo camera, but it should be enough to
get you started and to free you from the bonds imposed upon the
use of the stereo camera by the conventional rules, Once you know
when you can violate the rules, you will find endless opportunities
to make shots which will combine full stereo realism with an ap-
parent disregard of physical laws like gravitation.
Most striking of all will be the tremendous effectiveness of the
stereograms as compared with the usual trick shot in planar
photography.
PARALLAX INvERsIoN.-There was a time when the photographer
who did not fully understand the effects of parallax, and of trans-
position, simply did not make stereograms. Today it seems that
more than half our stereographers have their slides mounted for
them, and are not even aware of the importance, or even the
existence of the step of transposition.
Perhaps that in itself would not be important, except for the
fact that those who are unfamiliar with transposition are not
familiar with the appearance of an untransposed slide. Several
times now we have received slides with letters requesting informa-
tion as to the cause of the’curious appearance exhibited. This
appearance is variously described as “fuzzy,” “blurred,” “double
exposure,” “eye-straining” and so on. In fact the slides examined
were all sharp, but the trouble with all of them was the absence
of transposition. In other words, the two unit images were
changed left for right and vice versa.
This has a direct bearing upon the subject of stereo vision it-
self, and there seems to be little doubt as to the value of the study