The ER-55 equipment with universal table frame, shown in figure 3, 
illustrates a setup for a projection distance of 525 millimeters for use 
with vertical photography. These ER-55 projectors can readily be arranged 
for use with convergent photography, with provision for satisfying the 
Scheimpflug principle. This mode would then be equivalent to the arrange 
ment shown in figure 1. 
Super-wide-angle cameras have a shorter focal length than conventional 
wide-angle cameras and the projection distances of super-wide-angle plotters 
are also shorter. Thus the Balplex super-wide-angle projectors (see figure 6) 
have a projection distance of only 360 millimeters; this short projection 
distance is readily achieved with the universal frame. The Kelsh super- 
wide-angle projectors (see figure 7) have a projection distance of 440 
millimeters; although the projectors had to be extensively redesigned to 
accommodate super-wide-angle photography, no change was required in the 
universal frame. 
The Wild Heerbrugg super-wide-angle WH-6 plotter (see figure 8) is 
similar in principle to the super-wide-angle Balplex but differs somewhat 
in its parameters (see Table 1). The projector-and-support assembly of 
the WH-6 is so designed that it is compatible for use on the universal 
frame. 
TRACING TABLE 
Figure 9 shows an improved tracing table for use with double-projection 
plotters. The fingertip controls for light balance are shown on either side 
of the horseshoe base. A provision for a pantograph connection is located 
directly below the circular platen. An improved counter contains a graduated 
digit wheel, and a system of interchangeable gears provides direct reading 
in feet for a variety of plotting scales. This tracing table can be adapted 
for use with any of the projection systems listed in Table 1. 
9