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it will lead to the unification which is a most 
desirable feature and also it will lead to simpli- 
AUTOMATIC STEREO 
PHOTO ELECTRIC CELLS 
STEREO 
S PHOTOGRAPHS 
eC OF 
_—CONDENSER LENS 
SCANNING SPOT 
CONDENSER LENS = 7 
IMAGE_OF y 
SCANNING SPOT J OBJECTIVE LENS 
\ 
OBJECTIVE LENS —_— 
\ 
Y 
SCANNING SPOT 
COILS 
\ 
DEFLECTION = a 
/ 
OPTICAL AXES 
   
    
    
  
    
FLUORESCENT SCREEN 
"——CATHODE -RAY TUBE 
Figure 2. Dual Flying Spot Scanner 
moving spot of light, small enough to resolve the 
finest detail. Fluctuations in the light trans- 
mitted by image detail are detected by photo 
-electric cells. This method of examination is 
called flying-spot scanning and is a common 
television technique. 
Figure 2 illustrates flying-spot scanning 
applied to two photographic transparencies. The 
spot of light is produced by the electron beam of 
the cathode ray tube (C.R. T.) striking the fluores- 
cent screen on the end of the tube. The spot 
moves from its normal central position in re- 
sponse to voltages applied to external deflection 
coils. Separate deflection coils independently 
contro] the spot in perpendicular X and Y co- 
ordinate directions on the screen. Objective 
lenses project the scanning spot on to each photo- 
graph, and the density of image detail determines 
the amount of light reaching the photo-cells at 
any instant. As the spot scans the images, 
separate electrical signals are thereby generated 
for each image. 
Projection Plotters 
  
Up to the present time Stereomat has been 
applied only to projection-type plotters? Un- 
fortunately, the speed potential of Stereomat is 
only partially realized with projection plotters. 
Nevertheless, they have proven to be an economi- 
cal medium for experimeatation during develop- 
ment of the image comparison techniques and 
establishment of the internal logic. 
Projection plotters provide an optical 
arrangement similar to that of Figure 2. The 
C.R.T. replaces the viewing  platen of the 
plotter, and the photo-cells replace the illumin- 
ation lamps. 
For viewing the model, an "anaglyph" image 
is projected on to the face of the C.R.T. by the 
optical system illustrated in Figure 3. The 
dichroic mirror reflects red (or green) viewing 
light from the lamp but transmits blue scanning 
light from the C.R.T. Viewing light passes 
downward through the photographic transparency 
to form an image on the C.R.T. face; scanning 
light passes upwardinto the photo-cell. The blue 
filter further isolates the photo-cell from the 
viewing light. 
Unfortunately, the red-green spectacles 
worn by the operator do not suppress the ap- 
pearance of the blue scanning pattern complete- 
ly, and the residual pattern tends to interfere 
with viewing to some extent. For precise manual 
positioning, the scanning pattern can be elimin- 
ated by depressing a button on the carriage. The 
spot then assumes a position in the centre of 
ruuvrm, unuer chaurmanstip Os vir rieava, out no 
adequate record of the discussion is available 
for publication. 
  
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