-2- 
unacceptably the mass to be moved by the space rods and consequently, 
caused a deterioration of the accuracy. To avoid this the Wild Company re 
designed the B-8 so that the plate carrier is moved by the space rods, and 
the optics, including the optical duplexer and the scanning system, remain sta 
tionary. By careful design they succeeded in keeping the loads on the space 
rods unchanged while retaining the required accuracy. 
Transport System 
For the automated version of the B-8 a new Z transport system was designed 
whereby the Z carriage is moved by a servo-motor driven léadscrew, which is 
electrically coupled to a Z position indicator having an accuracy of ± 15 microns. 
This Z transport system is carried on the space rod carriage and moved in the 
X and Y directions by a bar system coupled by steel tapes to the X and Y drive 
motors (Figure 1). The orthophoto carriage is driven by the same steel tapes 
and thus moves in synchronism with the space rod carriage, but on a separate 
table. The orthophoto carriage and supporting table are contained in a light 
proof box behind the B-8 (Figure 2). 
The orthophoto carriage mounts a cathode ray tube (CRT) facing upwards and 
a lens system to focus the CRT image on film held up by a vacuum plate. For 
daylight operation this film is inserted in the lightproof box using a special cas 
sette. 
Optical Duplexer 
Figure 3, a schematic of the optical duplexer, as suggested by Hobrough and 
adapted to the B-8, shows the blue CRT light passing through the half silvered 
mirror being focused by lens on the diapositive and intensity modulated by 
the density variations of this plate. This modulated light is collected by the lens 
L2» passed through the dichroic mirror and is thrown on the photo multiplier 
P where it is converted into an electric current. At the same time the yellow 
light from Q, reflected by and collected by illuminates the diapositive 
from below. Lens L^ passes the image of this illuminated field, reflected on its 
way by Mp to the measuring mark. Further lenses and prisms make viewing of 
this image possible by the operator. Although this system does not project the 
CRT light into the viewing system or the viewing light into the photo multiplier P, 
a certain amount of these lights is reflected and enters nevertheless. This inter 
fering light is removed by the use of appropriate yellow and blue filters. 
The center of the scan pattern on the CRT establishes the elevation datum for 
the Stereomat. It is important that this datum be identical to that seen by the 
operator using the measuring marks. The CRT's are mounted upon a slide system 
that is adjustable in the X and Y directions until this condition is achieved. 
Stereomat Operation 
The basic Stereomat circuitry has been described by Hobrough (1). This paper