The new lenses for the P31 and P32 Terrestrial Cameras are also described. 
All these lenses have minimum distortion and are universal in application, i.e. they can be used with all types 
of emulsion in photogrammetry and photointerpretation. 
The paper gives a general description of the characteristics and performance of these lenses together with some 
results obtained with the first models of the new lenses. 
33. Smedberg, A. 
Bergman, A. 
Sweden 
EXPERIMENTS WITH AERIAL PHOTOGRAPHY 
USING DIFFERENTLY COLOURED SIGNALS 
The use of aerial photography in colour in connection with mapping on large scales, 1:400 - 1:2000, is common 
in Sweden and, at present, about 40% of the coverage for this purpose is in colour. When carrying out aerial 
photography of densely built-up areas it has become common to mark the main underground system of 
drainage, water supply and electric cables, etc. with signals in various colours to make it possible to more easily 
identify them at the stereoplotting stage. 
In order to choose suitable colours for the signals and also to study whether the colour of the signals influences 
the result of the measurements in the stereoplotters the Geographical Survey Office of Sweden has carried out 
a number of experimental studies. Signals painted in different colours were placed on the ground against 
different backgrounds and photographed from 600 m and 900 m altitude. Black and white, colour and to some 
extent IR-colour films were used. 
A study concerning identification of the signals in the pictures has been performed both on single pictures and 
in stereomodels using a Wind A7 stereoplotter. 
The heights of the signals were determined by both spirit-levelling in the field and in a stereoplotter and the 
influence of the colour on the measurements has been studied. 
This paper describes the methods used and some results from the investigation are presented. 
34. Smedberg, A. 
Welander, E. 
Sweden 
THE CALIBRATION OF AERIAL CAMERAS 
FOR PRACTICAL PURPOSES 
The Geographical Survey Office’s aerial cameras are tested in the laboratory and under operational conditions 
before each field season. In the laboratory the mechanical and electric functions are checked and measurements 
of the flatness of the pressure-plates and the focal-plane frames are carried out. 
The results of measurements over a number of years are presented and discussed. 
In the central parts of Sweden there are many lakes which in the early spring are normally frozen and free from 
snow. The ice surfaces which are generally absolutely flat and rich in details are very suitable as test fields for 
aerial photography and are, therefore, used for the final testing of the cameras. Each camera is tested in 
combination with three cassettes. As an alternative to the ice photography the Oland test field and a test field 
on Bromma Airport are also used. 
The paper describes the test method used and results from several years are presented. 
The tests require no field work and can be quickly carried out in the same manner and with the methods as 
are used for the utilization of aerial photographs for practical stereoplotting with the advantages that this 
entails. 
13