The working principle of the Orthoprojector (Fig. 2) is obvious. The system of spatial coordinates 
is subdivided into the x, y-motion of the exposure slit A and the z-motion of the projection system C. 
This projection system is made up entirely of original components of the C 8 Stereoplanigraph, viz. 
Fig. 2 GZ 1 Orthoprojector. The cabinet on the right houses the scanning and control elements required for 
operation by the "storage technique”. 
a) plotting camera including plotting lens and aspheric correction plate, 
b) spot-light follower illumination 
c) Bauersfeld auxiliary lens system. 
The inclusion of an auxiliary lens system in the design of the instrument satisfies the demand for 
truly sharp imagery in the entire range of magnification, 
large lens aperture for short exposure times with low-efficiency lamps. 
In addition, the separation of plotting instrument and projector as well as the use of purely optical 
methods make it possible to employ both standard black-and-white material and color photography. 
In operation, the exposure slit A of the Orthoprojector travels in meander strips across the pro 
jection surface (Fig. 3). Its traveling speed in y-direction is uniform, but variable with the aid of 
pairs of change gears, x-steps are of equal size in one plot, but variable by appropriate means. 
The exposure is made without any overlap between strips. Consequently, the size of the selected 
x-step must correspond very exactly to the width of the slit in x-direction. 
Usual strip widths are about 4 mm, if the maximum enlargement of projection of approx. 4 X is 
used. The width of the slit in y-direction depends on the speed of the emulsion, the illumination 
system and the selected traveling speed of the slit in y-direction. The following values, which are 
frequently used for practical work, may serve as an approximate basis for general con sidérations : 
156 
BuL 3/1964