7 
rectified for actuating the meter relay. The servomotor (15) then 
turns spindle (17) in the correct sense until the coil of the servo 
transformer is again at the central position in relation to the 
cone, viz. until the signal voltage has sunk to zero. The negative 
carriage has thereby been adjusted to the correct height. 
The curve inversor of this control system is computed for a nominal 
focal length f of 150 mm, but the focal length of each lens is 
taken into consideration in the length of the arm CA of the elbow 
lever. 
Since sharp autofocusing on the photographic emulsion must also be 
provided for copying frames and thick emulsion backs, the curve is 
adjustable in height. The adjusting screw and scale are at the 
back of the instrument. Distances of up to 30 mm between the emulsion 
and the surface of the projection table can be corrected for. 
The projection table rests on a double cradle. A sturdly bar is 
fixed below the table center and perpendicular to its surface, 
passing through a sleeve in an x-y cross slide which is driven 
by the two handwheels and which tilts both the rod and the table 
(see Fig.7). The tangents of these 
through 
tilt angles are proportional to the number of spindle rotations 
driving the cross slide, and can therefore be transmitted by 
appropriate gearing directly from the spindles to the tangent 
counters. 
In order to maintain sharpness of focus when the projection table 
is tilted, the Scheimpflug condition must be fulfilled: this re 
quires that negative plane, central plane of the lens and projection 
plane all intersect in one line. The transformation of the table 
turning the handwheels) into the 
corresponding negative tilts CK ^ and OC^ is taken care of in the 
E4 by a simulator. This reconstructs in a simple manner the re 
lationships given by the Scheimpflug condition: 
tan OC 
and tan OC 
x 
\J 
y 
\J