TRICK WORK 233The lines LA and RB are the parallactic rays which cross in
the center of the table T. The dotted lines LO and RO which
meet at 0 are the parallactic rays for the model.
If the two images are exposed separately, and if the model 0
can be placed in position X during the right exposure, then
moved in the direction of the arrow to position Y during the
exposure of the left film, it is obvious that the parallax of the
model will be identical with that of the table. As a consequence,
the model will appear in half natural size, in that spatial position
coinciding with the tabletop. If the vertical positions of the table-
top and the feet of the model are placed in correct alignment, the
finished stereogram will show a half size, living model standing
upon the tabletop. Such is the basic mechanism of space control.
Further than this there are only operational details to consider.
In the above figure (2), a similar problem is shown, but this
time the table is in the background, and the desired result is to
show a double sized giantess seated at the table. To increase the
effect and make it more definite, a second living model may be
seated at the opposite side of the table.
Here rays LT and RT are the parallactic rays for the chair
position beside the table T. There is no chair there, but the large
chair will appear there. LA and RB are the parallactic rays for
the model 0, who is seated midway between the camera and the
table. In making the first exposure, the model is moved to the
position X and for the second exposure to the position Y.
In the first figure the model moves to the left for the right
exposure and to the right for the left exposure. In the second ex-
ample, the model moves to the right for the right exposure and
to the left for the left exposure.
It might be argued that instead of moving the model in the
second example, which is somewhat difficult, it would serve the
same purpose to move the table according to the first example;
and the table is much easier to move than the model,