PHOTOGRAMMETRIC ENGINEERING 17 
The dimensional stability and 
brittleness test apparatus is shown 
in figure 15. The air in the plastic 
chamber can be maintained constant 
at any relative humidity in the range 
from 5 to 95%. Humidity amplitude 
is measured with a pin gauge placed 
in this chamber (Figure 17). With 
this apparatus process shrinkage is 
also measured by comparison meas 
urements before and after processing. 
Furthermore, brittleness tests can be 
made in this chamber by placing in 
it the vise, as illustrated in Figure 16, 
which closes on conditioned loops of 
film. The film is placed in the jaws 
of the vise by means of a magnetic probe. The film loops are held together 
with paper staples. The jaws of the vise are closed by means of a small electric 
motor. The separation of the jaws, in thousandths of an inch at the point where 
the film breaks, is a measure of the film’s brittleness. 
Tests have recently been made of 
a new film base, developed by Du 
Pont, which has remarkable brittle 
ness characteristics even at low tem 
perature and low relative humidity. 
It is related chemically to the fiber 
Dacron. It also has very good dimen 
sional stability, although to date 
tests made on a laboratory scale show 
that the samples tested are not quite 
good enough for mapping photogra 
phy; much better results are expected 
soon from the pilot plant. In its pres 
ent form, however, it has great pos 
sibilities as a film base for reconnaissance photography. 
In connection with this discussion of the physical characteristics of film, the 
new Eastman Kodak prehardened aerial film should be mentioned. This new 
film, soon to become standard, can be safely processed at temperatures up to 95 
degrees F, and probably even higher. 
This material will be of value in 
meeting requirements for rapid proc 
essing, when suitable processing ma 
chines can be built. But of more im 
mediate interest is its drying rate, 
which is approximately 75% greater 
than for regular Aero Super XX. 
There is also interest in photo 
sensitive processes that are not, 
strictly speaking, photographic, being 
different from the conventional silver- 
halide process. Figure 18 is a repro 
duction of a sample photograph 
Fig. 13. Curves used in sensitometric studies. 
Fig. 12. The Planigon or Cartogon lens.