© 
r=R/(B+G+R) (10) 
The overall intensity w is calculated by the following equation: 
2 1 
w- G^ d FR (11) 
3.3 Experimental Results 
The results for 22 aerial survey cameras are shown in Figure 12. Re- 
ferring to the data, we can classify the cameras into two groups ac- 
cording to the color of glare spots: more bluish than neutral and 
more reddish than neutral, where neutral is b = g = r = 0.333. It 
has been proved that, as we presumed, the difference in color, bluish 
or reddish, is dependent upon the color of the coating of the lenses: 
old cameras with purple colored coated lenses show bluish glare spots 
while recent cameras with amber-colored coated lenses show reddish 
giare spots. We found that the intensity of a spot is weaker with 
recent cameras than with old cameras. The reason for thís is now 
under investigation. 
4. Discussion 
The methods for measuring the exposure distríbution and the glare spot 
were established. However, the present measuring instruments need 
some improvements to achieve more accurate and precise measurements. 
The exposure distribution measurement is important and useful for 
evaluating the focal plane illuminance distribution of wide angle 
lenses and the improvement in the distribution by means of an A.V. 
filter. The detection of the change with time in focal plane illu- 
minance distribution, due to the deterioration of A.V. filter trans- 
mission and to the change in exposure time, are indispensable for the 
maintenance of the aerial survey camera. The glare spot is not con- 
Spicuous with modern camera lenses. However, the rear elements (near 
the film surface) in lens construction of the wide angle lens cone 
are thought to be the prime cause of the glare spot. Therefore, the 
glare spot will appear when very bright and uniform objects are photo- 
graphed. 
The relationship between the photometrically measured values and 
actual pictures needs to be investigated in order to establish the 
criteria for the evaluation of these measured values. 
This work was financially supported by the Geographical Survey insti- 
tute. 
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