Fig. 6. The folded collimator which is
mounted in the pit.
OPTICAL AND SENSITOMETRIC DEVELOPMENTS
to be equally useful, and that the
Commission’s work in this direction
will be continued.
Figure 8 is a histogram of a group
of 36 inch f/8 lenses. High contrast,
slow, fine grain, spectroscopic plates
were used on these tests and the Area
Weighted Average Resolution was
determined for each. As a quality
control technique, Bell & Howell
plotted the number of lenses having
approximately the same AWAR
against the AWAR for each month’s
production. This figure represents a
summation of the data. Through use
of such data can be prepared truly
meaningful production specifications.
The specifications merely require
that a certain percentage shall have
resolutions better than a specified
quality level. Another percentage is
allowed to fall to another quality
level, and finally all must be better
than the minimum quality level.
Later on there may be available a system of measuring lens performance
that does not involve the much-discussed and controversial problems of photo
graphic evaluation. Perhaps an electronic photometric method of lens evalua
tion will be evolved that will elim
inate the inconsistencies of reading
targets visually, and that will handle
satisfactorily such problems as type
of target, contrast of target, type
of sensitized material, and processing
techniques. The Bureau of Stand
ards, Boston University, the Uni
versity of Rochester, and Eastman
Kodak Company, to mention only
a few, are working closely with the
Air Force on this problem.
Figure 9 portrays the large T-
stop calibrator. It can accommodate
lenses up to 100 inches EFL and has
proved to be of considerable value
in evaluating night lenses and meas
uring image illumination.
The small T-stop calibrator is
shown in Figure 10. It utilizes the
collimator type of system as com
pared to the extended source method
of the previous picture. Both meth-
Fig. 7. Plate holder carriage and 0( ^ s are included in MIL-STD-150,
control panel. and have been approved by the
