5 
Figure 2 Geometric Scheme cf B8 Modified for Stereomat 
The construction of the optical and electronic scanning elements, 
which are symmetrical in the left and right cameras, is shown 
schematically in Figure 3. The flying spot, which moves on the 
tube face in a random pattern around a center of gravity in the 
optical axis, passes through the half-silvered prism £ and is 
sharply imaged by the lens onto the diapositive. Depending on 
the density of the image details just scanned, the condenser lens 
below the diapositive throws more or less light on the photocell. 
The current which results rises or falls according to whether 
the flying spot passes from a dark to a light part of the diapositive, 
or vice versa. 
At the same time, the field of view is illuminated from below via the 
dichroic mirror £ and the condenser lens. The objective passes an image 
of the illuminated field through the half-silvered prism £ onto the 
measuring mark £.