ЯЖНЙ 
Hsess&pssäi 
1. the choice of optimum photo scale, including the choice of camera type, 
format size and focal distance; 
2. construction of the best possible flight plan and its perfect execution; 
3. planning for the optimum tone reproduction for the specific purpose; 
4. obtaining sufficient sharpness-recognition of micro detail. 
Influence of photo scale and choice of aerial camera 
The influence of the photo scale seems, at first sight, rather simple: 
a. the image size is a linear function of the scale number; 
b. the “interpretability” does not vary linearly with image size, but changes 
approximately with the surface area of detail - i.e. is a square root function 
of the scale number; 
c. the number of photographs necessary to cover a certain area varies with 
the square of the scale number. 
If, however, we look a little further into this matter, it becomes evident that 
the scale ratio or the scale number is not an independent parameter, but that it 
is also related to the flight height, the haze layer and constitution, camera size, 
focal length, etc. 
Some examples: 
If we change the photo scale by taking another flight height (keeping the 
same camera type, size and f) then we also change the influence of the haze, 
thereby changing the contrasts in the shadows as far as the haze influences the 
contrast reduction in the shadow areas particularly. 
We may vary the photo scale while conserving the same flight height and 
influence, by choosing another focal length (for instance choosing a somewhat 
smaller f for the same photo size). We then, however, change the terrain sur 
face area, the angle of incidence and stereoscopic vision in the corners. 
Conserving the same stereoscopy we may vary the scale by keeping the aper 
ture angle of the camera constant and varying the camera size and f in the 
same ratio, but we will thereby also influence the photo size and the overall 
sharpness. 
We may even conserve the same scale and camera aperture angle, but 
change the flight height considerably by choosing another photo size and f. 
In short: A variation of the photo scale, a change in flight height or in size 
or in f by a certain factor does not necessarily change the interpretational value 
by this factor alone, but will change it according to a complicated function 
that involves many variables other than the photo scale. This function is, as 
yet, not completely known. 
Flight plan and flight execution 
SYMPOSIUM PHOTO INTERPRETATION, DELFT 1962 
After the photo scale and the camera choice have been decided upon, the 
flight plan proper must be designed. Flight planning is a field in itself and we 
will limit ourselves to a few remarks.