CHAPTER 2STEREOSCOPIC CAMERASwo OR THREE YEARS AGO any discussion of stereoscopic cam-
T eras necessarily included a number of obsolete models simply
because there were so very few current models available, and
among these only one of modern type. Today the situation is
wholly different. The cameras follow the modern trend of stereo-
scopic technique, namely, the use of 35mm, natural color film.
Of course there are hundreds of larger cameras in use, hundreds
which make black-and-white prints as a rule. ObGously any cam-
era can be used for color, but in practise the 35mm camera is
largely devoted to color work; larger sizes to monochrome.
Nothing new has yet been introduced without meeting a host
of objections, a few justifiable, but most of them made simply
because the product is new. The miniature camera had a difficult
time for years, but that precedent did little to win favor for the
35mm stereo camera, although the latter involves far less actual
change of existing conditions than did the former.
In stereo, the vital viewing factor is visual angle-the angle
from the center of pupil to the extreme corners of the positive
image. It is obvious that if a smaller picture is viewed nearer the
eyes, the same angle is filled; and assuming, as we may, that the
image structure (grain and the like) is such that the image defi-
nition is retained, there is no limit to the smallness of the image
which is satisfactory. The sole limitation is image breakdown.
This is more than being merely satisfactory. If the viewers are
masked so that only the lenses show, there is nothing to indicate
size. Under such conditions, spectators who have volunteered
for the experiment repeatedly state a 3x6 inch or 6xi3cm trans-
parency to be the smallest of a group which includes both 35mm
and 16mm films. Size per se offers no advantages, no disadvan-
tages in stereo. Naturally the one who uses some particular size
will rise in arms to defend his favorite. That is always true in
photography, but disinterested experimenters have demonstrated
the impossibility of distinguishing among sizes by viewing the
images in normal viewers. The apparent size depends upon the
sole factor of visual angle.
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