Three-Dimensional Photography - Principles of Stereoscopy

22 THREE-DIMENSIONAL PHOTOGRAPHY
miniature cameras, black and white or color. Loading and opera-
tion are similar to other 35mm cameras.
The lenses are 40mm focal length, f3.5 aperture, coated. In
tests made in the Stereo Guild laboratories, definition was found
to be excellent yielding a good, crisp image. Focus is controlled
by coupled rangefinder. The control is a vertical disc set at the
top-rear of the camera. This dial has an engraved depth-of-field
scale for all apertures down to f16.
The shutter is the usual French guillotine type, giving perma-
nent, positive synchronization and with automatic speeds from
one second to 1/25o with Time and Bulb. The lenses and shut-
ter are mounted upon a movable lens board of the conventional
type which moves with the focusing operation.
The rangefinder and finder are located in the top plate of the
camera. The release is at the top-right-front'of the body, and the
button is threaded for cable release. Just at the left of the lens
board are the two contact sockets for the internal flash synchro-
nizer.
So much is more or less conventional, but there are some novel
features.
The picture width is 30mm, although the height is the 24mm
normal to 35mm film. This format is directly related to two other
novel features. This width is considerably greater than the 22.5
and 24 of our domestic cameras. The choice, however, is a mat-
ter of personal preference.
This picture width makes it impossible to use the original inter-
locked sequence, so there is only one odd picture between pairs,
so the sequences is: 1-2-1-2 3-4-3-45-6-5-6"7-8-7-8* and so
on. It will be seen that the film may be cut at any point marked
without interrupting a pair. This type of sequence makes
necessary a film advance which is long-short-long-short and so on,
that is the actual film winding knob is turned about 1/4 revolution
to wind the film, and the next film has to be wound 5/4 revolution
and so on.
The fundamental reason for the picture width is the fact that
this camera serves for both single and stereo exposures. By turn-
ing a small knob on top of the camera, one film aperture is ob-
scured and the film transport altered to a single frame advance.