DEFORMATION MEASUREMENTS 
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FIG. 2. The Zeiss’ stereocomparator. 
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The negatives are placed in the holders, which can be rotated around vertical axes by (11) 
     
   
and (19). The negatives are illuminated from beneath and can be viewed through the stereoscope 
(8) in which the measuring marks are located. Both negatives can simultaneously be translated 
under the stereoscope in the longitudinal (x'-) direction of the instrument by the wheel (1). The 
x'-coordinates of the left negative can be read on the scale (16). The stereoscope can be translated 
in the lateral (normally z'-) direction by the wheel (15), and the corresponding coordinates can be 
read on the scale (4) through the eyepiece (5). The right negative can be separately translated 
towards or from the left one by the parallax-screw (10), carrying the scale, on which the parallaxes 
can be read. By the screw (13) the right negative can be translated laterally. The setting of the 
wheels (1) and (15) and particularly the screw (10) is determined by the coincidence of the floating 
dot with the details of the three-dimensional model of the pictures, and is performed with high 
precision. The estimation of the scales (16) and (4) is 0,01 mm. and of the scale on (10) 0,001 mm 
For deformation measurements, the pictures are oriented in the stereocomparator according to 
  
  
  
  
  
  
  
  
  
   
  
    
figure 6 and the dz' are determined by the aid of (10). 
To use stereoscopic methods for the de- 
termination of the distances dz', one pic- 
ture is taken for each stage of deformation. 
If the respective pictures are taken with 
the same inner and outer orientation, the 
distances dz' will appear as parallaxes in 
relation to the images of the fiducial marks 
or the backing frame of the camera. For 
the stereoscopic measurement of the dis- 
tances dz', the pictures are placed in a 
stereoscopic instrument and oriented so 
that the distances dz’ appear as horizontal 
parallaxes. If the deformations are vertical 
in the object, the pictures will be turned 
90 degrees in their planes for the measure- 
ments. See Figure 6. The best instrument 
for the measurements is a stereocom- 
parator. See Figure 2, Of course instru- 
ments like the stereoplanigraph or auto- 
graphs can also be used. Also a mirror 
stereoscope and parallax bar can be used 
with good results although the work is 
rather inconvenient when compared with 
work with a stereocomparator. Because the 
deformations generally are very small, the 
optical distortion of the camera lens has 
practically no influence upon the position 
differences dz’. 
In order to assure the inner and outer 
orientation of the camera being constant 
from exposure to exposure, it is advisable 
to use a number of fixed balls outside the 
object. If parallaxes appear in such points, 
the inner or outer orientation has been 
changed. In such cases the parallaxes may 
be used to compute the required correc- 
tions. Of course, the fixed balls can also be 
used as a reference system.