MOUNTING, TRANSPOSITION AND SPACING 87from the camera. The less the homologous separation, the nearer
the object.
If a mask be prepared with two openings whose corresponding
sides (that is, the two left sides, or the two right sides) are sepa-
rated by a distance of, let us say, imm less than the homologous
distance of the nearest object in the foreground, and if this mask
is laid over the stereogram, the stereoscopic appearance of the
mask will be that of an opening or “window” nearer the observer
than the nearest object. In short, the appearance will be that of
looking out through a window at the scene.
Obviously if the prints are trimmed exactly to match this mask
and are mounted upon a black or dark card, the general effect
will be the same. The mount will form a window nearer the eyes
than the scene itself. This is known as “window trimming.” Many
stereogaphers consider it essential. However, the mere fact that
Fig. 5-11. The Window (C). The window is in the plane of the petals
of the flower.
striking effects are often obtained by deliberately throwing the
window back into the mid-distance is sufficient proof that conven-
tional window trimming is nothing more nor less than a personal
preference of the individual. (Figs. 5-9, 5-10, 5-11, 5-12, 5-13, 5-14,
and 5-15.) (Note that the separations of the flower images are the
same in all seven slides.)
To produce the window effect it is necessary that the images be
so trimmed that they appear to be farther away than the frame
produced by the edges of the prints. The “frame” must conform