64 THREE-DIMENSIONAL PHOTOGRAPHY
when the two eyes view the objects A, B, C and D, as well as an
object at infinity. It is well to note that although we speak of an
“object,” we actually refer to some prominent point in the visible
surface of that body. Thus the significant ray path is, in each in-
stance, truly represented by a single straight line from the eye
(or lens) to that point in the object. As we have already seen,
orthostereoscopic results will not be achieved unless these signifi-
cant ray paths are duplicated when viewing the positive stereo-
gram.
Figure 4-2 shows the same field as it is photogaphed by two
lenses LL and LR. In both figures CC marks the position of the
Cyclopean Center, or the position of synthesized stereoscopic
vision.
If the negatives fp-fp are rotated vertically and horizontally
about the common center of the lenses, fp-fp will coincide with
p-p of Fig. 4-1. The focal plane of the camera becomes the picture
plane of the positive, with an inversion of image.
Figure 4-3 is the same as Fig. 4-2 except that the lenses have a
focal length which is one-third less than normal (considering the
conditions of Fig. 4-2 as normal). The direction of all ray paths
remains the same but fp-fp is now necessarily nearer the lenses,
making the images smaller throughout. If viewed with lenses of
similarly short focal length, it is obvious that the relationship be-
tween Fig. 4-1 and Fig. 4-2 would also exist between Fig. 4-3 and
any such condition. Therefore we pass directly to the viewing of
this smaller image in the normal stereoscope, as illustrated in
Fig. 4-4. The points of intersection remain fixed because they are
a part of the physical silver image. When this pair of images is
placed in the normal picture plane the results are as shown. The
points at which the rays terminate indicate the images as actually
seen; the points with no connecting rays show the true positions
of the objects where they should be seen orthostereoscopically.
The difference indicates the degree and kind of distortion (object
D is omitted on account of space limitations).
In each instance the object is seen at a greater distance than
normal, and all dimensions in the line of the visual axis (depth)
are increased. Objects appear elongated in depth and far distant.
To make these distortions clearer, we shall supplement the