16 
OPTICAL AND SENSITOMETRIC DEVELOPMENTS 
than 15 microns. And 15 microns radial distortion for those who have not 
tried to measure it, can be an elusive quantity. Work is continually being done 
on better methods of measuring distortion. The photographic method, with the 
lens mounted in the mapping camera, is still favored in spite of some attractive 
features about the goniometer meth 
od. Search is also being made for an 
even better lens to replace the Plani- 
gon. The WILD (AVIOGON) lens 
has not yet been tested by the Lab 
oratory. 
The activities of the USAF in the 
field of sensitometric materials will 
be briefly described. Figure 13 shows 
three curves which are useful in the 
.sensitometric studies. Curve A is the 
standard H&D curve. Curve B is 
the gradient curve, or a plot of the 
first derivative of Curve .<4. Curve Cis Fig. The small 1 stop calibrator, 
the resolving power curve. It is only 
natural that there be interest in high resolution, contrast rendition, and high 
emulsion speed, particularly for night photography. The speed of the ma 
terial is represented by the positions of these curves with respect to the log 
E axis; the further to the left, the faster the material. Usually there is interest 
in an image brightness range of about 1:10, as represented by the solid line 
on the log E axis. The position of this line indicates the exposure where one 
would expect to obtain the best results. In practice it is found, however, that 
the exposure is much further down on the toe of the H&D curve, particularly in 
night photography. 
These and other sensitometric aspects of aerial photography are due 
for much more study. There is par 
ticular interest in increasing film 
speed for night photography. The 
most promising results to date have 
been achieved with hydrazine com 
pounds where true increases of ex 
posure index have been attained that 
exceed a factor of 3 with high speed 
materials. 
The resolving power camera used 
in the laboratory in studying photo 
graphic film is shown in Figure 14. 
It is actually a special sensitometer 
of the intensity scale type which pro 
jects a reduced picture of a resolving 
power target through a miscroscope 
lens on to the film, and varies the ex 
posure in graded steps. It is largely 
automatic, requiring only that the 
operator move a modulating filter 
slide and press a button which posi 
tions and holds the film and controls 
exposure. 
Fig. 11. A new Air Force night lens—24 inch 
f/3.5 for 9 inch by 18 inch coverage.