4 
The tuo measuring telescopes are rigidly connected to the cardans L' 
and U 1 at a distance _a; left and right, cross-slide systems guide 
them in the so-called mechanical picture planes. The distances between 
the mechanical picture planes and the cardans and can be ad 
justed to correspond to the principal distance of the taking camera. 
The dispositive planes are parallel to the mechanical picture planes. 
Each cross-slide system is rotatable around tuo axes to permit the 
introduction of relative and absolute orientation. 
The simplest approach to mounting the Stereomat on the B8 would have 
been to equip each of the two optical systems with a cathode ray tube, 
two dichroic mirrors, a condenser and a photocell. These additional 
elements, however, would have increased the weight of the scanning 
system, which must be moved by the spacerods, to an intolerable 
extent. In view of the intended dynamic operation it was anticipated 
that the instrument's measuring accuracy would suffer. Moreover, the 
synchronous movement of photocells and illumination on opposite sides 
of the diapositives would have presented design problems. 
Since a diapositive is considerably lighter than a Stereomat scanning 
system, it was logical to redesign the restitution cameras in such 
a way that the spacerods guide the diapositives, while the optical and 
electronic parts of the scanning system are stationary in the camera. 
Figure 2 shows the application of this principle in the B8-Stereomat. 
As far as the measuring accuracy of the instrument is concerned, 
moving the pictures is perhaps less advantageous than moving the 
optics, due to the greater sensitivity to rotations. However, in 
comparison with the inertia problems resulting from moveable optics, 
this is of little consequence. Moreover, it offers complete freedom 
in the design of the scanning system and in the choice of the required 
electronic components.