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REPORT OF COMMISSION VII 57 
shutter, this camera has a permanently open slit over which the film travels 
continuously at a speed proportional to and synchronized with the speed of the 
airplane. An undistorted, perfectly sharp, continuous image is recorded at 
speeds of upwards of 1,000 miles an hour. The “Sonne” camera has also been 
produced as a twin-lens type for stereo photography, where the desired stereo 
base is achieved through setting the lenses at a greater distance apart on oppo- 
site sides of the slit. The continuous strip-stereo camera operates best when pho- 
tographing from a fast jet photographic reconnaissance aircraft, from 300 to 
1,500 feet, or about 90 to 450 meters above the ground. But sometimes it may 
pay to fly at tree-top height to avoid radar detection and anti-aircraft fire. 
The importance of the continuous strip camera can hardly be overrated, 
and in the Korean War it has been of immense value to the UN Forces when 
gathering material for military intelligence. 
Either flash bombs or flash units are used to illuminate the target area for 
night photographic reconnaissance. The former are dropped from both greater 
and lower altitudes, and are ignited by timers, or, electrically, by radio. On the 
other hand, the latter are securely hung up, for instance, in the plane’s bomb- 
rack in order to give flashes from low and medium altitudes. Both kinds are made 
in various sizes, suitable for different operative purposes. Several very fine re- 
sults of such photography have been published on different occasions in recent 
years. Who does not remember with admiration the sharp and very detailed 
night stereo photos which, in the early summer of 1949, were taken over Ho- 
boken, N. J., by U. S. Air Force reconnaissance aircraft with small, but, under 
the circumstances, highly effective flash cartridges of 50,000,000 candle-power. 
Statements about new, improved types of flash-bombs and cartidges have also 
been published, as well as the special constructions of "dust bomb" type which 
scatter clouds of flash powder with tremendous illumination effect. 
Finally, I should also briefly mention the development of the last few years 
in the field of aerial films. First of all, as regards panchromatic film types, in- 
creased general high speed in certain cases, and in others increased red sensitiza- 
tion in particular, has been aimed at. Increased panchromatic high speed is of 
special importance in night photo reconnaissance with flash bombs and flashes; 
increased red sensitization is again desirable in all photo reconnaissance in day- 
light, but, above all, at great heights and distances. Good results have been 
achieved without any subordination of finer grains. The tendency of development 
points to still more speed, yet finer grains and lower shrinking coefficient in the 
film base. 
Infrared films of the conventional type are generally most sensitized to 
blue-violet and infrared. The infrared effect is obtained with a filter which 
absorbs most of the visible spectrum, in any case up to deeper red. The latest 
emulsion types are characterized by considerably greater infrared speed and 
still more moderate grain and good resolving power. Such films are especially 
suitable for haze penetration in oblique long distance photography and for 
camouflage detection. Color films for reconnaissance purposes are to be found in 
several types. The more conventional of these, which is intended to be presented 
as a direct positive photo has, during the last few years, acquired still greater 
sensitivity and more natural color rendering. But even the special color film, 
which is developed to a negative in order to reproduce the terrain with its 
complementary colors, has been considerably improved and very widely used, 
especially by the UN forces in Korea. The negative color system has the ad- 
vantage that either color or black and white prints may be. made from the 
negatives. Special methods for processing such color films in field laboratories