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8 BOUSKY 
is no point, therefore, in setting the nominal exposure for the high 
altitude photograph at the same point on the D-log E curve as the 
nominal exposure for the low altitude photograph. Instead the exposure 
may be appreciably reduced as indicated. This leads to a seemingly 
paradoxical conclusion that a film having a sensitivity rating of 20 may 
be faster athigh altitude than a film with a rating of 100 at low altitude. 
Moreover, it may be desirable to record the high altitude photo- 
graph at a gamma somewhat greater than unity to enhance the recorded 
detail contrasts since the total range of density may be kept low 
enough to still effect fairly optimum interpretability. Both exposure 
and gamma are, therefore, separate factors of importance and are not 
necessarily interchangeable or equivalent in testing. 
The true appraisal of the ground detail size classes, the detail 
contrasts, and the scene illumination ranges are especially critical in 
view of the fact that future high altitude photography may, of neces- 
sity, be associated with smaller format sizes which imposes an addi- 
tional limitation on photographic performance. With these factors in 
mind, some of the methods used in evaluating photographic performance 
may now be reviewed. 
CAMERA TESTING 
In years past considerable difficulty was experienced by the 
military services in finding a basis for specifying performance quality 
of aerial cameras in a form suitable for acceptance testing. Manu- 
facturers and using agencies found it hard to agree on definitive numer- 
ical values to represent quality or performance. Even when they could 
agree, the criterion often could not be reproduced or test results 
repeated. 
Several years ago, through very commendable joint effort in the 
United States by the Air Force and industry, a standardized test method 
was evolved to serve as a basis for manufacture of aerial cameras. 
This was also extended to include lenses and films as well. 
This accepted standardized camera test method specified the 
photographic recording of a standardized three-column black and white 
target having a brightness ratio from white to black of 1000 to 1. The 
type of film and its development were also specified. The product of 
this test method is called resolution, and is expressed in lines per 
millimeter at the threshold, While resolution is not, strictly speak- 
ing, a true measure of photographic quality, it did represent the best 
single number that could be used in equipment evaluation.improvements 
Because the resolution test could be reproduced with reasonable 
accuracy, it soon came to be used as indicative of quality. This was 
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