2 
The scale of the S.A.P. can be determined from the 
existing aerial survey photos. The scale control procedure 
js illustrated in Figure 3, diagrams a, b and c. Diagram 3a 
shows the 35-mm negative projected onto the survey photo 
covering the same area. The enlarger is adjusted until the 
projected detail coincides with that in the survey photo. 
When the enlarger is in this position, the scale of the S.A. 
photo is the same as that of the survey photo (356) and an 
enlargement can be made. The interpretation marked on this 
enlargement can then be transferred onto the map with some 
type of "sketchmaster" (3c). 
TECHNICAL CONSIDERATIONS 
Camera 
Any camera is. suitable for 8S.A.P. if it is equipped 
with a good-quality lens and has reasonably fast shutter 
speed (preferably 1/1000 sec). The equipment naturally will 
set a limit on the range of application. Motorized assem- 
blies are available which make possible an adequate overlap 
even at low altitudes. The following considerations are 
made for the purpose of obtaining optimum results. 
The resolving power of the lens used is most impor- 
tant in this operation because the final product will be 
magnified considerably. 
The normal focal length for 35-mm cameras is 50 to 
55 mm. These, however, provide a narrower angle of view 
and a larger scale than is used in conventional photography. 
The flight altitude must therefore be greater in order to 
obtain the same coverage as in conventional photography. 
Wide-angle lenses are the most practical in S.A.P. 
because they can simulate conventional photography from the 
same altitude (Figure 4). 
  
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Figure 4.—The above diagram shows the identical focal Length 
to picture format ratio for both 24-mm and 150-mm lenses.