136 THREE-DIMENSIONAL PHOTOGRAPHYactually increase the stereo relief. They only make more apparent
the relief which exists, just as when we look down a wooded glade
we obtain a sense of greater distance than when we look out over
the ocean or across a vast plain. The enhancement of effect is no
more and no less than is given to actual direct vision under similar
conditions. This is true of all the psychological devices.
CONTOUR INTERFERENcE.-In selecting the point of view, any
objects which are located partly in front of other objects more
distant will enhance the stereo depth. The comparison of the
glade and the open plain applies here as well. The effectiveness is
increased just as it is for direct vision.
One need not fear for the confusion which exists in the planar
photograph-those accidental mergers which tie up objects in the
foreground to those in the background. The classic example of
having a tree growing out of the head of the subject need not be
feared in stereo, for the tree will appear in its correct position far
behind the subject, and the two will interfere no more than if a
similar distance divided them laterally.
SIZE DIMINUTIoN.-This will be seen in any composition in
which the two preceding factors have been given place. It is as
automatic as perspective, provided there are objects included
which serve to bring out the factor.
In this connection it may be remarked that the surprising and
frequently ridiculous size relationships seen so often in planar
photography are never encountered in stereo. For example, take
the photograph so often made for reasons of comedy in which a
man is stretched out upon a park bench or the like, and photo-
graphed with his feet a yard or so from the lens and his head
eight or nine feet away. The feet appear to be about two feet
long. When the same thing is made in stereo, the man appears to
be proportioned with complete normality and appears in the
position he actually occupied.
The same thing is true of the perspective of tall buildings. The
stereo camera may safely be tipped upward to include the top of
any skyscraper. When the picture is viewed, all sense of falling
backward is lost and you seem to be looking upward in the most
natural manner. In viewing such stereograms, the realism is en-
hanced by holding the stereoscope so the head will be tipped at
an angle similar to that necessary to view the original scene.