TRICK WORK 223ground for the second shot must be large enough to fill the whole
film area. The actual size of course depends upon the distance
between camera and background, and this in turn determines the
size of the model.
In the first type of double exposure, the second model is
introduced into the scene, and the position is recorded automati-
cally. But in the separate exposure method, it must be remem-
bered that distance will be faithfully reproduced. For example if
the man is seated ten feet from the camera, and the second model
is also placed ten feet away, the figure will appear to be in the
smoke cloud. But if the second is only five feet away, then the
figure will be much larger than life size and will be suspended in
air between the observer and the smoke cloud. This is the easiest
and least effective way.
If the model is 20 feet from the camera, the size of the figure
will be in miniature, but it will be seen behind the smoke cloud,
and of course a very large black background will be required for
this purpose. The position in space can be controlled as explained
later in the chapter.
One way to eliminate the large background is to make use of
camera masks, but as there is no precision finder or ground glass
focusing available on the usual stereo camera, the arrangement
must be made by approximation. These masks are made of black
card or heavy black paper. An area is cut or torn from them to
leave an opening corresponding to the position of the model. If
the masks are situated about one inch before the lenses, the block-
ing will be effective and the nearer the mask to the lens, the
broader will be the vignette border. As the mask is moved away
from the lens the open area grows smaller, the edges become
sharper. Even when using distances of three to four inches the edges
will still be satisfactorily softened, If the mask is placed very near
the lens surface, almost in contact, there will be no masking, but
a variation in exposure can be seen. In short, any portion of a
lens theoretically covers the entire film, and practically the effect
is nearly enough the same to prevent effective masking so near
the lens.
A variation of the old motion picture mask box can easily be
made. This is a rectangular box with flaring sides. It may be
made two inches wide by six long, extending two inches from the