ng 
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» film 
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Its; 
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- 597 = 
For the analytical determination of light fall - off, exact coordi- 
nates for particular grey values have to be known, related to the image 
center as origin. Consequently the reseau marks were used to guarantee 
uniform distribution of measurements. 
  
  
  
. . Abb. 
+ + + + + 1.3 1.4 
+ MR E rene 
© ho, r 1.1 
Socr d Ter a 
T T " T zz Fig.5: Configuration during point- 
wise measurement of grey values 
e Jd: ^ + de Distance A was controlled by the iris 
  
  
edge of the microdensitometer 
Fig. 5 illustrates the point configuration: per image 100 measurements 
had to be made (executed by ALVES /1/). For each f = 1 : 5,6 and 
f=1:8 14 images were evaluated; this finally makes 2800 values. 
e 
a - % . e : °% 
Po 9o. e 
te v" * eo 
1 to 
8 
T T T T T 
T T T T T T T T-—T T T T T Tou T T 
1 2 3.4 5 6 7 
9 10 11 12 13 14 15 15-17 16 19 20 21 22 23 24 25 
Image Center J 
Fig. 6: Distribution of densities at reseau marks within the LAMBERT- 
reflector full frame photography 
Fig. 6 shows a result for one image (f = 1 : 5,6). Every point corre- 
sponds to one measurement. The "nests" of 4 points around the reseau 
marks and the characteristic behavior of the grey level along the scan 
lines (1... 4, 5 ... 8 etc., see Fig. 4) can be detected clearly. For 
all measurements, grey wedge D 1247 was used, where 1 cm (z) corre- 
sponds to 0,1 D. All values were related to the brightest point in the 
image center. 
It is common to describe the light fall - off by a cosine function, 
admitting a radial and symetric behavior of the phenomenon (see SIEVERS 
/7/). This actually can be done here, yet with respect to a superim- 
posed linear light fall - off caused by the shadow from the ground. 
Approximative computation showed that 
3 
D. «f (1-cos a0) ; D. = A = 1) 
a a cos a 
D =f (1 - cos” o) $5, «s f( le 1) 
9 cos a 
and D -f(1-cos'a)