224 THREE-DIMENSIONAL PHOTOGRAPHYcamera. The masks are cut from pieces of 2x6 black paper. If
the paper is laid out in two squares with centers 70mm apart, the
corresponding areas may be cut with little trouble. But if for any
reason these masks are to be used with a background which shows
any detail, that is, a background not solidly black, the relative
positions of the apertures must be cut to place the aperture where
you want it.
With the black background the mask has no spatial position,
and the same care is not necessary. Inaccuracies will result in a
certain stereo discrepancy at the edges of the space where only one
image appears, but these may be disregarded. No one will see
them unless atention is directed to the error.
Such masks make it possible to reproduce distant figures in
miniature without the use of an impossibly large background.
Another method is to have the model and black background in
one room, the camera in another and to shoot through a doorway,
using the non-illuminated room in which the camera stands, as an
extension of the black background.
DuPLIcATIoN.-This is still another variation of double expo-
sure. The mask box will be needed, or a special lens cap mask.
It is necessary that the masks be carefully adjusted, something
which can be done when the camera is empty, placing a strip
of matte celluloid in the film track and using it as a ground
glass. If the mask segment is too large there will be a double
exposed strip down the center, that is a light strip which spoils
the effect. If the segments are too narrow there will be an un-
exposed strip in the center which is even worse. The straight side
of the mask opening must be cut so that the dividing line comes
exactly at the film center. Once this has been determined the
masks may be used at any future time with full assurance. If the
mask box is used, the matte celluloid is used to mark the central
dividing line on the edges of the mask box.
Set the two masks at the same side, left, for example. Pose your
model at that side of the normal film area, in some pose suggest-
ing a companion. An old favorite is to have the model seated as
though playing bridge. Make the exposure. Then place the masks
to cover the opposite side of the lenses and pose your model again
on that side of the table. Make the exposure. If the masks are