4. Calibration of the Camera Lens by Least Squares Adjustment 
Usina the LAMBERT Reflector 
Photography of the LAMBERT reflector was taken during hazy sky, paying 
attention to the configuration described by Fig. 3. For the practical 
approach, KODAK - EKTACHROME 
COLOUR film was used, taking pic- 
tures with apertures of 1 : 5,6 
and 1 : 8. As tests had shown, film 
development by fully automatic 
procedures provided best results; 
Y i. e. no disturbing influence was 
b added by the film development. 
Manual tank development however 
means a real risk for the photo- 
Fig.3: Configuration for taking photos graphy (see ALVES /1/). The camera 
from the LAMBERT reflector (hazy sky) at 1 m distance from the reflector, 
did not affect the plate by shadows. 
  
  
This is in accordance with Fig. 4 which shows microdensitometer profiles 
at 4 different sections of the original image. The profiles run in a very 
smooth way (compared for instance with Fig. 2), which proves the excellent 
quality of the LAMBERT reflector. 
4 
mo 3 A 
Ree s Center eue a t 
T A + IS e 
Center of Illumination 
  
  
  
  
  
Fig. 4: Microdensitometer profiles along 4 different sections of full-frame 
reflector photography(scan direction from top to bottom) 
The peak is caused by the reseau mark and indicates the image center 
However, a slight difference of the "top" and the "bottom" branches is: 
obvious, caused by a shadow from the ground. This effect could be avoided 
by illuminating the reflector according to the principle of ULBRICHT's 
Sphere Photometer. Apart from the ground effect the profiles charac- 
terize nothing but the light fall - off by the camera lens. As there is 
a slight density displacement from the image center (indicated by the 
reseau mark's peak), the image itself can not correctly be taken for 
a mask in order to compensate for light fall - off in a pure analog mode. 
It is anyway more rigorous to execute the following steps analytically.