16 HISTORY OF PHOTOGRAMMETRY IN THE UNITED STATES
wide film giving 200 exposures. The film is
held flat in the focal plane by vacuum. Each
five-lens camera has a matched transform-
ing printer for restitution of the oblique
photos, which when matched to the ver-
tical and mounted, produce a composite
photograph in the form of a Maltese cross
with an over-all size of about 32 by 32
inches.
The Tandem T-3A Camera, Figure 2,
consists of two T-3A cameras in a tandem
mount, with one camera crabbed at an
angle of 45 degrees with respect to the
other. Thus, the four oblique pictures of
one T-3C camera fill the spaces between
the obliques of the other. This arrange-
ment gives a 9 lens composite picture (one
Fic. 2. Tandem T-3A Camera.
vertical was not used) with over-all dimen-
sions of about 32 inches.
T-3A photography was used for compila-
tion of topographic maps with vertical and
oblique multiplex equipment, for hastily
prepared composite photomaps, and for
radial line extensions of control.
Stereocomparagraph
The Stereocomparagraph, Figure 3,
is essentially a mirror stereoscope mounted
on a base with a parallax measuring device
or parallax bar, a drawing attachment,
and a parallel motion mechanism. The
parallax measuring device consists of two
marks or dots on glass discs which are
mounted on a base bar in such a manner
that they may be moved laterally. The
right hand mark is attached to a microm-
eter screw to change and measure the
spacing between the marks. This microm-
eter is graduated from 0 to 25 mm. and
Fic. 3. Stereocomparagraph.
may be read directly to 1/100 mm. It may
also be clamped at any reading as desired.
The right hand mark may also be ad-
justed through a small range in a direction
perpendicular to the micrometer screw.
The left hand mark is held in place by a
locating pin and may be adjusted in incre-
ments of 5 mm. through a range of 25 mm.
Nominal spacing between the marks is
150 mm.
The drawing attachment is a metal arm,
one end of which is attached to the base
of the instrument. There is a pencil chuck
in the other end of the arm, with provision
for raising the pencil lead from the map
sheet. The compilation is essentially a
tracing of the left hand photograph of the
stereoscopic pair.
The instrument may be attached to any
standard drafting machine or parallel mo-
tion device, to provide parallel movement
of the parallax bar at all times.
Normal-angle Multiplex
The normal-angle Multiplex was devel-
oped for use with photography of the T-3A
precision mapping camera and photog-
raphy with 8% inch focal length camera
with 7 by 9 inch format. The equipment
consists of both vertical and oblique pro-
jectors, reduction printers, supporting
frame, cast aluminum plotting table, a
tracing table and accessories. The projec-
tion distance to the plane of best definition
is 360 mm. The projectors have a principal
distance of 46.04 mm. and accommodate
46 by 54 mm. diapositives. Usable depth of
fiel
dist
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