In other words, the design of the plotting 
camera may be briefly described as a system 
with **eccentric disposition of camera Cardans K = Center of rotation 
^ C] 
  
  
  
  
and displacement of photos instead of optical of camera Pe 
systems", the c-axis acting as the primary axis: P — Perspective center S 
and the g-axis as the secondary axis. © 
It has been a frequent subject of discussion 
whether in such a system the optics should be 
displaced or the photographs. Both these 
solutions have been frequently used. There are 
even instruments which were originallydesigned 
for a movable optical system and later modified 
for displacement of the photographs. The most 
important argument in favor of photograph 
displacement is the avoidance of narrowly 
  
  
  
  
spaced intermediate images in the optical B : 
system and thus an improvement of image S E % 
quality. 
; : : Fig. 3 Planimat camera system 
The design using eccentric camera Cardans, 
on the other hand, is novel. The fact that the Cardan point K is located outside the perspective cen- 
ter P not only allows the use of an especially simple viewing optical system, but also results in a very 
rugged support of the camera which can be suspended from three points of the main instrument frame 
and need not be held in the perspective center by a complex mechanism. 
3. Construction of the Planimat 
Fig. 4 explains the design of the Planimat, while Fig. 5 is a general view of the instrument. Out- 
standing features are the integral tracing table IZ arranged within the sturdy frame of the instrument 
and the external tracing table EZ, which may be connected to the machine if desired. 
One striking detail of the ground-coordinate system is that the y-carriage is guided by the two 
spindles 5; and S,, preventing any rotation which might be introduced if a guide rail were employed 
on one side only. In spite of this, the spindles can be disengaged with the aid of the lever FH and the 
carriage moved free-handedly across the entire model for the purpose of relative orientation. The 
guide rails of the y-carriage are firmly supported by the robust casting of the basic frame. The x-rails 
are also especially rugged. This has been achieved by subdividing the rails of the x-carriage for the 
z and x-motions. 
À special feature of the z-carriage is that it is carried by four spindles jointly driven by a chain. 
This effectively avoids any tilting. 
With the exception of a single mirror which rotates together with the camera during w-movement, 
the viewing optical system is of the rigid type. The optical reversal systems do not contain any so- 
called half-angle controls. The spacing of the lens components in the image-forming beam is not 
varied during operation of the instrument. The photo-carriers are displaced in the y-direction in rela- 
tion to the image-plane reference point. 
Luminous marks of 40 um diameter (as referred to the image plane) are reflected into the light path 
as measuring marks. Their brightness can be controlled by the knobs H and thus adapted to a contrast 
level suitable for the kind of photographs to be plotted. The Dove prisms R are provided for compen- 
sating possible image rotation. 
The Cardan joints of the perspective center P are moved by the screw F for focal-length adjustment. 
The motion range proper is here 130 mm. In the lower range this permits focal lengths between 85 mm 
and 215 mm to be set, while the upper range covers focal lengths from 180 mm to 310 mm. Change- 
over from one range to another is achieved by shifting the Cardan bracket KT by 95 mm. At the center 
195