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SYMPOSIUM PHOTO INTERPRETATION, DELFT 1962 
near the limit of resolution. Photographic tone reproduction is the reproduction 
of larger details - sometimes called “macro detail” - and is not very much 
affected by the scale or the size of this detail. But the reproduction of the 
smallest detail near the resolution limit - sometimes called “micro detail” - 
is much more complicated. As the image size becomes smaller, the contrast is 
also reduced, because in the reproduction of micro detail, size and contrast 
must be considered together. In this respect we may draw attention to the 
important work of Welander. His paper on the T-functions deserves more 
attention than could be given during the short time of its presentation at this 
Symposium. At our institute, Hempenius is working at the basics and the appli 
cation of the T-functions in aerial image formation. 
It is of the utmost importance that the principles of photography as a branch 
of applied physics are understood and applied in photo interpretation, because the 
photo interpreter is particularly interested in the smallest details, such as 
“texture”, and other information near the limit of recognition. 
Conclusion 
Finally it can be said that “rational planning of aerial photography for a 
specific purpose” means: 
“optimization of the complete system to that purpose”. 
To achieve such optimum conditions, experience and insight into all aspects 
are needed. But even then, part of it is still personal judgement. Gradually, 
however, we are getting to know more about the possibilities and the tolerances 
in survey navigation and we are gaining a better insight into the aerial image 
formation process. For photo interpretation it is important to use this complete 
knowledge: the application of the total complex to aerial photography leads to 
the most economical aerial photograph. 
Discussion 
J. A. E. Allum (U.K.) : After having gone to the expense of producing the aerial photography 
would it not be sensible to produce copy negatives at different scales? Answer: Photographic 
enlargements or reductions do not give more information than the original scale. The smallest 
scale which is still useful for the required purpose should be chosen. F. Ruellan (France) 
endorsed this answer by stating that each purpose requires its own scale.