PICTORIAL STEREOGRAPHY 153tions because no matter what adjustment is made, the focus of the
eye (accommodation) remains fixed upon some one plane, while
convergence must necessarily change constantly as one looks from
one object to another.
With objects not too near the camera, and particularly with a
projection screen at a distance coinciding with the normal near
point of vision, the separation is extremely slight and causes little
or no difficulty. But when an object is moved very near, necessitat-
ing a wide divergence between accommodation and convergence,
the strain of this unusual muscular activity is felt, and the specta-
tor complains of eye strain, pain, distortion or anything else he can
think of.
The compensations used are nothing more than concessions
made to these individuals who still have undeveloped stereo vi-
sion, who have not yet separated these bonded reactions. But the
experienced stereo worker who has completely broken bond and
in whom the two functions are wholly independent, can and does
see extreme closeup objects with the same ease he would look at
the original-and more important, he receives precisely the same
visual impression he would from looking at the original object.