Three-Dimensional Photography - Principles of Stereoscopy

APPENDIX C

FREE VISION FOR ILLUSTRATION

Although the subject of free vision has been explained in this
volume, we wish to present, at the risk of repetition, a resum6 of
practical free vision as it can be learned by anyone interested in
acquiring a new and fascinating visual skill.
The illustration of books and periodicals by three dimensional
photographs and drawings would enormously enhance the value
of an illustrative material. Now that color reproduction is com-
monplace, the use of color stereograms would approach the ideal.
In fact, the desirability of the process has been recognized for
years. The only fact which has been ignored is that a fully practi-
cal process has been available for years. One which demands no
more than three or four periods of ten to 15 minutes for its com-
plete mastery.
It is not necessary at this time to review the theory and methods
which already have been presented in this book. It will be re-
called that the process involves:

(1) Printing the normal stereogram by any of the conven-

tional processes of reproduction.

(a). Transposed stereograms

(b). Untransposed stereograms

Either (a) or (b) have a homologous separation not

exceeding 6omm.

The transposed stereograms are more difficult to see without

benefit of viewer. It would be more accurate to say that this

method is the more difficult to learn. Once mastered it is as easy

and natural as reading.

The use of untransposed stereograms (b) offers the easy method

so far as learning is concerned, but whereas (a) leads to a visual

relaxation which is restful, method (b) demands a greater-than-

normal degree of convergence and tends toward increasing a pres-

ently unpleasant national condition, namely, a tendency toward

“squint” (cross-eyes) which is already aggravated by our habits

of continued close vision.

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