Three-Dimensional Photography - Principles of Stereoscopy

STEREO MOVIES 273

wide latitude of detail design permissible. The actual require-

ments are few and simple.

1. The outer mirrors must be adjustable through about ten
   degrees, swinging upon a vertical axis.


2. This movement must not affect the precision of the vertical
   plane (the reflecting plane) of the mirrors. In short, a sturdy pivot
   must be provided which is exactly perpendicular to the base of
   the framework.


3. The outer mirrors should move laterally so that the base may
   be varied between two and one-fifth and six inches or a movement
   of one and three-fourths inches for each mirror. This is to con-
   trol parallax, especially when telephoto lenses of moderate focus
   are used. This motion must be along a rigid base so that the ver-
   tical planes of the mirrors will not lose parallelism.
   The inner mirrors should have as sharp an apex as possible, but
   it is not at all necessary that it be an “invisible line” joint. One
   amateur made use of a right angle prism with the sides surface
   silvered (aluminum vaporized). This is a sensible solution and
   one not too expensive.
   However, it is imperative that some means be provided by
   which the image as formed in the film plane can be subjected to
   visual examination. The equipment can be calibrated when once

Fig. 19-2. Adjustable reflector.
By pivoting, the rear edges of
the outer mirrors may be swung
as shown by the broken lines,

thus making it possible to place

the two stereo images in any de-

sired relationship upon the film.

Compare with Fig. 19-1.