56 REPORT OF COMMISSION VII
length of 40” (about 100 cm). When the focal length is increased, however, the
photo field or the target area which the camera embraces, is decreased, often
with the result that the desired target is outside the limits of the field when
exposed.
Two long distance cameras for vertical photography are therefore nowadays
often used together with the optical axes of the instruments diverging some-
what, through which almost twice as great a field is reproduced. However, this
kind of mounting has a disadvantage, i. e. these near vertical photographs present
slightly oblique pictures with a varying photoscale across the photograph,
which must be carefully observed by the interpreters as soon as exact measure-
ments are to be made.
The strategic reconnaissance planes are, however, also equipped with cam-
eras with shorter focal lengths, 6"—11.8" (15-30 cm.) and embracing a greater
width for taking survey pictures of an area in which detail reconnaissance with
long distance cameras is being carried out at the same time. Between-the-lens
shutters are preferably used in these smaller cameras with relatively short
focal lengths. In this way such precision-built cameras can also be used to ad-
vantage for map making purposes. It is worth mentioning in this connection
that new and improved shutters for aerial cameras are developed by the Air
Research and Development Command, Wright Field, Dayton, Ohio (described
by Mr. A. H. Katz). With three precision-built cameras with short focal lengths,
usually 6" (15 cm.), placed in so-called trimetrogon mountings, one gets not only
verticals, but even obliques of the terrain on both sides of the direction of flight,
which are suitable to be used as a basis for quick presentation of aerial maps.
The trimetrogon method, which has been developed and perfected by the
Americans, especially at Aeronautical Chart Service, Washington D.C., makes
map making of considerable areas possible in a very short time. As an example
it can be mentioned that approximately 240,000 square miles, or about 621,000
square kilometers of Alaska were mapped by photography by the U. S. Air
Force during 1948-1949.
By day, tactical photo reconnaissance is carried out both as vertical and
oblique photography; by night, only for the taking of vertical photographs.
For day photography, cameras are used with both long and short focal lengths,
mounted for taking pictures of different types. Altitudes and methods vary
according to the nature and effectiveness of the enemy anti-air capacity. The
side which is inferior in the air is often forced to operate over its own lines, and
only take obliques in the direction of the enemy area. In such cases cameras
with long focal lengths can prove to be of value even when mounted for obliques.
The side which is superior in the air certainly does not need to pay the same
regard to the enemy air force, but it must however always operate in accord-
ance with the strength of the enemy anti-aircraft and the effectiveness of his
radar equipment. Through this, the methods of photo reconnaissance will vary
very considerably, and sometimes it may be necessary to take aerial photos
from extremely low altitudes from very fast jet planes. In such cases, all conven-
tional type cameras are useless. The so-called indistinctness through movement,
which is in direct proportion to the time of exposure, the speed of the aircraft,
and the scale at which the ground is reproduced, would completely spoil the
photographs. The only usable constructions are those which eliminate the in-
distinctness through movement through the compensating traveling of the film.
The camera developed by U. S. Air Force, the so-called "Continuous strip"
camera, also known as the ‘Sonne’ camera after the constructor, has proved
to be a particularly pleasing solution to the problem. Instead of the ordinary
