326 THREE-DIMENSIONAL PHOTOGRAPHYIt would be far easier to initiate method (b), but if criticism
and future trouble are to be avoided, it is definitely advisable to
standardize upon method (a).
Introduction.-For some time, perhaps as much as a year or
more, it would be necessary to carry a small “box” in each issue
of a publication which would briefly explain how the ability to
see the three dimensions may be acquired. But if two or three
national publications were to make a practice of running a single
page of stereos in each issue, public demand would not permit
them to be abandoned after a year.
Learning.-General training would present difficulties. Elderly
people would have more difficulty than young ones. Because
ophthalmologists still differ as to the value of stereo, there would
be professional opinions, pro and con. Many people, feeling the
strain which accompanies the initial divorce between accommo-
dation and convergence, would be convinced that their eyes were
being injured. As a matter of interest, I had to change ophthal-
mologists not long ago because the one I had insisted that my
“lack” of normal co-action between accommodation and conver-
gence was pathological and insisted upon treatment to restore it.
I patiently told of the trouble I had taken to achieve it, and was
then told I had probably ruined my eyes! I went to another, and
considerably better qualified man and he laughed at the idea. He
told me that a number of his colleagues were bitterly opposed to
any form of stereo and even refused to use the professional instru-
ments based upon stereo principles. He agreed with modern stereo
researchers that stereo skill is valuable and well repays any slight
difficulty incident to acquiring it. He then pointed out that my
range of vergence was considerably greater than would be ex-
pected in a patient less than half my age, with presbyopia con-
siderably delayed.
Method.-There is perhaps no better method than that of using
the mask to start with. If the two eyes cannot converge upon a
common point, they will try to fuse the two similar images even
under unusual conditions of convergence. I have found the great-
est success in teaching stereo viewing by starting with small pic-
tures with eomm separation, and gradually substituting others of
increasing separation until 6omm was reached. This is the end
point, because there are many people who have less than 65mm