236 THREE-DIMENSIONAL PHOTOGRAPHY
curiosity as to where the huge glass was obtained. When well
done it is characterized by reality without conviction and when
poorly done there is no reaction. In stereo it is all so different.
You see the wineglass a couple of feet away with human fingers
grasping the stem, the distance is normal, the size is normal...
yet there sits the girl, maybe four inches high when standing, but
beyond any doubt a real, living human being! And you can do
it easily.
You will spoil some film, but the result is worth it.
You will need a mask box which has been described, and you
will mask out all but a portion of the field in the center laterally
and just above center vertically. Pose the model. It is advisable to
have the camera upon a tripod with tilt head.
Memorize the position of the model in the finder, or better yet
make a dummy camera with ground glass to mount on top the
stereo camera, using simple lenses of 35mm focal length, and out-
line the model’s position with a pencil in both frames. Remem-
ber that these exposures must be made separately and the parallax
must bring the model to the distance of the glass.
Now make the glass setup, align the glass and the model by
means of the memorized position or the dummy camera and ex-
pose for the glass. If you use the memory system you will be
lucky to get one good result from 20 shots, but with the dummy
camera you should get it within the first three or four.
Computation of parallax is easy, but failure often is a result of
failing to understand the importance of accuracy of measurement.
However, working by computation is, as we have said, untrust-
worthy and tedious. It is much better to work under visual
control.
The reverse of this method is just as practical and often easier
to accomplish, particularly when the alignment of the two images
does not have to be precise. Here suppose that the figure of a girl
is to be seen in a cloud of pipe smoke. This is all very good, but
the shape of the smoke changes constantly, so how are you to make
the two successive shots?
The shot of the smoker and his pipe is made in the usual way,
using any desired size from full head to full figure. It is advisable
to wait for a rather dense, large smoke cloud and to then shoot it