Three-Dimensional Photography - Principles of Stereoscopy

192 THREE-DIMENSIONAL PHOTOGRAPHY
A home model with 500 watt lamps, single speed blower and
f2.8 projection lenses is the one which will probably prove the
favorite, but for club and professional use the advanced model
with f2.3 lenses, double speed blower and equipped to handle 500,
750 or 1000 watt lamps will be preferred. The 1000 watt lamps
provide brilliant illumination for a screen 12 feet square or nine
times the area of the usual 50 inch screen. It might be added that
even with 500 watt lamps the projector has surprising brilliance.

OTHER FORMS OF PROJECTION

Although the use of polarized light to eliminate the unwanted

images, that is to make each visible only to its respective eye has

become the accepted modern method of stereo projection, there

are other means by which this may be accomplished.

If the projected images are not more than 21/4 inches wide, as in

table viewers, a simple mask such as that shown in Fig. 12-3 may

be used, in which the eyes EE’ see the two images SS’, the mask

preventing E from seeing S’ and vice versa. This mask is made

more efficient by giving it the box form shown in. 12-4, although

the principle remains the same.

S

S’

Fig. 12-5. Simple mask for crossed axes screen viewing.

For larger pictures, the two pictures are projected side-by-side

in reverse order and the eyes crossed when looking at them as

shown in Figures 12-5 and 12-6. In 12-6 the dotted line shows how,

by replacing the outer wall with its single aperture with one con-

taining two apertures the position of the crossing of the two paths

can be extended without making the box itself of ungainly length.