Three-Dimensional Photography - Principles of Stereoscopy

74 THREE-DIMENSIONAL PHOTOGRAPHY

Fig. 4-17. Viewing stereo-

Fig. 4-16. Cameras with gram made with cameras

convergent axes. with convergent axes.

grams under all conditions and of all types of subject.

the stereogram viewed orthostereoscopically does actually so re-
create the original scene that all of the major visual phenomena
experienced in viewing the original are also experienced in view-
ing the stereogram.
Referring again to Fig. 4-1, as the eyes converge upon A both
eyes are equally converged to a marked degree. Shifting vision to
B, the convergence is less, and both axes incline to the left. Pass-
ing to C the convergence is still less, and the dual inclination is
to the right. In looking at D while the inclination is still to the
right, both the inclination anaconvergence are less than for C.
Viewing a distant object, the axes are parallel, that is, there is zero
convergence and zero inclination.
If the stereogram is mounted so that the centers of the unit
images are not spaced to the correct degree of separation, then
when looking at some object in the far distance the eyes will either
converge and assume the position of looking at a relatively nearby
object, or they will diverge, a condition wholly foreign to normal
eyesight and usually painful, if not impossible.
Thus the stereographer has the responsibility of seeing that his
stereograms are mounted with the correct separation, as deter-
mined for the stereoscope he uses.

STEREO-RE-CREATION.-It is now possible to understand why