Three-Dimensional Photography - Principles of Stereoscopy

274 THREE-DIMENSIONAL PHOTOGRAPHY

made, but the initial calibration demands visual inspection in the

film aperture. There are “focusing prisms” and “focusing attach-

ments” available which will provide this and which are applicable

to most cameras.

In calibrating, remember that if the base of the reflector is not

parallel with the base of the camera, one image will be higher

than the other. If this happens do not conclude that your mirrors

are out of parallel. Just raise or lower one end of the reflector

base. That is, twist it with the lens axis as center of revolution.

Unless you are experienced in this kind of work, you should by

all means make your first attempts with a Stereotach, which may

be used without visual checking and calibrating, but you must

use extreme care to get the reflector base parallel with the cam-

era base.

FORMAT.-one serious objection to making stereo movies in this

way is the fact that the image is duplicated in the normal frame

which has proportions 3:4, and as a result the screen picture is a

very narrow, very tall image with the horizontal to vertical ratio

2:3.

The best solution we know of is that introduced by W. Wheeler

Jennings of Chicago, who widens the camera aperture from iomm

to 13 or iqmm, thus providing a single frame of 6.5 to 7mm wide

and 7.5 high, about the normal stereo format. Because the film

perforations come between frames, this change is possible. It might

Fig. 19-3. The variable base re- outer repeetors, while the solid
pector. The broken lines indi- lines indicate the “wide base”
cute the normal positions of the position.