to give the operator a three-dimensional 
view of the terrain. 
The projectors are nominally distortion 
free and compensation for the distortion 
inherent in the metrogon lens is effected in 
the reduction printer (Figure 5.) The re- 
duction ratio in the reduction printer is 
adjustable to accommodate photography 
with focal lengths varying from 150 to 156 
mm. Printers have also been developed 
experimentally. for 3 inch, 5.2 inch, and 12 
inch focal length metrogon lens photog- 
raphy. Illumination in the reduction 
printer is provided by a bank of 37 in- 
candescent lamps, each of which is individ- 
ually controlled by an off-on switch to 
facilitate preparation of uniform density 
diapositives from negatives of non-uniform 
density. 
The single supporting frame is designed 
to support 9 projectors when mounted on 
the cast aluminum plotting table, provid- 
ing means for bridging control, the double 
frame is made up of two single frames 
with center adapter providing for mount- 
ing 18 projectors for control bridging. 
The wide-angle Multiplex equipment is 
the standard photogrammetric equipment 
of the U. S. Army Corps of Engineers for 
the compilation of topographic maps from 
aerial photography. 
The oblique wide angle Multiplex pro- 
jectors (Figure 6) are designed for com- 
pilation with 60 degree oblique trimetro- 
  
18 HISTORY OF PHOTOGRAMMETRY IN THE UNITED STATES 
  
FrG. 7. Horizontal Projecting Photo- 
grammetric Rectifier. 
gon photographs. These have the same 
principal distance as the vertical projec- 
tors and thus use diapositive plates pre- 
pared in the standard projection printer. 
The objective lens is canted with respect to 
the principal axis of the projector so that 
the plane of optimum focus is horizontal. 
Optimum plotting scale with the oblique 
projector is approximately twice the iso- 
line of the 60 degree oblique photographs. 
F1G. 6. Oblique Wide-Angle Multiplex Projectors. 
  
  
    
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
   
   
   
    
   
   
   
    
   
   
     
     
  
  
  
  
  
  
  
  
  
  
   
  
   
   
  
   
  
  
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