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 
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