Preparations for photography 
  
Prior to each series of photographs a revision of the Sinar camera took place in a labora- 
tory. The parallelism of image plane and lens panel and also the position of the fiducial marks were 
checked and, if necessary, adjusted. Following that the camera was sharply focussed with ground 
glass and magnifier to a screened plane placed at a distance of 2,8 m ; then it was fixed on its tube 
and braced, This was done to prevent a change of the interior orientation during transport of the 
camera from the laboratory to the camera station, 
At the site the model had to be prepared too, It stood at the IL in a mechanical measuring 
instrument in which it had been constructed, Since it was impossible to photograph the model in 
this location it had to be transported to a prepared place on the floor, To maintain the spatial posi- 
tion of the model the four corners of the model frame were leveled and later on adjusted in the 
same position on the floor, The camera position was such that the camera could be fixed to a gal- 
lows or s special rack and operated from a scaffold. 
When the model was leveled on the floor the control points were screwed into the frame. 
Because of the short sighting distances of about 2 to 5 m needles pressed into the plastic material 
of the rods served as targets for the theodolite observations, 
As mentioned before, the tops of masts had to be fitted with an auxiliary device, It con- 
sisted of a rod of known length which was posed and fixed on the point that its tip defined the sys- 
tem point, At the other end of the rod a milled cross defined the longitudinal axis and served as a 
target, Normal to the axis was a quadratic collar with four targets, If it was possible to measure 
at least two targets of the collar and the target in the axis the coordinates of the wanted system 
point could be computed, 
  
This picture shows the arrangement of model, rack and camera, Auxiliary device to determine top an foundation points of masts. 
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