resolution of the negative. Inspection of air negatives 
will quite frequently show that even where the general 
quality looks good, shadow detail is underexposed, and 
highlight detail too black to print. Optimum quality- 
negatives with maximum information content are the 
exception rather than the rule, and this situation must 
remain, so long as measurement of subject brightness 
range forms no part in the art of taking air photographs. 
To rectify this state of affairs, one requires an 
instrument for the measurement of maximum and minimum 
subject brightnesses, and to use a continuous film 
processor, or spiral tank developer in order to control 
development gamma more accurately than is possible with 
spool tanks. It will be shown later that if these two 
facilities can be made available, tables could be 
prepared for use with the brightness range meter to 
determine: 
1. Whether or not the brightness range was long 
enough to permit acceptable quality photo 
graphy. 
2. The appropriate development gamma for 
accommodation of the measured brightness 
range. 
3. The best type of film to use for the subject. 
4- The exposure to be given. 
By this means it should be possible to secure optimum 
quality negatives on the basis of rational measures 
with guessing procedures quite ruled out. 
A Maximum and Minimum Brigntness Meter 
Maximum and minimum brightnesses most frequently 
occur in detail that is quite small. For example, in 
the shadow of a tree, and the roof of a building, or 
small patch of sunbaked earth. The beam from a photo 
meter to measure these must therefore be very narrow, 
otherwise maximums and minimums will be lost in integ 
ration. Such a narrow beam photometer can be fixed 
in an aircraft so that the forward scanning of the 
scene is by the aircraft’s forward motion. To effect 
lateral scanning the beam could be refracted backwards 
and forwards laterally by means of a rotating glass. 
Only maximum and minimum readings are required, so the 
photometer should record on the basis of a maximum/ 
minimum thermometer. Direct reflections of the sun in 
water or glass surfaces would need to be screened out, 
and this could be accomplished by virtue of their 
extreme brightnesses which would be much in excess of 
anything else in the scene. It would also be necessary 
to build in a correction to allow for the fall-off in