62 REPORT OF COMMISSION VII
for infrared photography. They should be provided with exchangeable magazines
which make possible a quick exchange of film types while photographing, and
perhaps even prepared for periscope photography (see Figure 1). A transport-
able, photographic laboratory with equipment for processing and even enlarg-
ing, is part of such reconnaissance equipment. The material must not take up
too much room, and ought to be easy to establish in a covered van or small
type bus. Instruments for photo-interpretation should also be included in the
equipment.
Cameras of great accuracy, with a co-ordinate scale which will be exposed
in the film are preferably used for the presentation of panoramas. As an exam-
ple, a panorama camera has recently been constructed at the Research Insti-
tute of Defence in Stockholm, for taking strip panoramas with an expanse of
360° or more. Measuring horizontal angles on the photos is carried out with about
the accuracy of an angle minute. The apparatus is built according to the prin-
ciples of a continuous strip-camera. When photographing, the camera rotates
round a vertical axle through the optical center of the lens. During this move-
ment it must be levelled with the optical axle in the horizontal plane. In the
focal plane of the lens, and through the optical axle there is a slit, about 0.5
mm. wide, arranged vertically, past which a strip of film travels at the same
speed as the image during the rotation. Through a special arrangement, the
measurement of angles, with the help of the co-ordinated scale exposed in the
film, will be independent of the shrinkage of the film base when drying. The
focal length is 5.3" (13.5 cm.), and the size of the panorama about 2.3" X 34.3"
(6X87 cm.). A special measuring apparatus has been constructed for taking
angles on the negative, or a contact-diapositive with a movable microscope
which enlarges 7 times, in the horizontal and vertical directions of the panorama.
This arrangement permits the direct reading of 6,300 parts of the circuit.
Furthermore, an apparatus for enlarging, constructed according to the same
principles as the camera, is included in the equipment. The degree of enlarge-
ment is permanently fixed at 2.5 times, but this can be changed. During the
enlarging, the negative of the film is drawn past the slit at a regular speed at the
same time that the paper is made to pass the slit 2.5 times faster in the opposite
direction. The enlarged panorama has a size of about 6X86” (15X218 cm.)
when enlarged to the above mentioned extent.
When photo reconnaissance is carried out from ships, or from positions ashore
with uninterrupted visibility towards targets at sea, the distance is calculated
in thousands or tens of thousands of meters. This photography 1s called long
distance photography. Cameras with very long focal lengths, chosen in consider-
ation of the normal range of the reconnaissance in question, and the desired
photo scale, are often used for this form of reconnaissance.
In the same way that a sector of the front in the terrain can advantageously
be kept under observation through photo reconnaissance, such activity can also
be used for keeping a watch on, and observing a coast, or an area of water at
great distances. Thus, for example, one ought to remember how, during World
War II, the Germans followed the Allied sea traffic on the English side of the
Channel, through long distance photography from the French coast.
Long distance reconnaissance is always executed with the help of color
filters from yellow to infrared, and with suitable negative material. When taking
photos at great distances, the picture is diffused, due to the fact that the sun-
light which the object reflects is bent to a greater or lesser degree, by solid,
liquid or gaseous particles which exist in the air. Generally, the long-wave
rays are less affected by the particles in their path than is the case with the short-
wave ones. The more particles that are met, for instance, when the distance is
