Summary 
After a short review of the purposes and methods for testing 
optical systems, the importance of OTF-measurements for the 
evaluation of image quality is emphasized. The disadvantage of the 
necessity to use carefully designed and highly sensitive instruments 
and the difficulties arising from the large number of data to be 
handled are discussed. e. 
For aerial mapping lenses, some examples are given how to reduce 
the necessary OTF-curves to a rather small number by using field 
curvatures as an additional means for testing the image performance. 
Some OTF-values and field curvatures of old and new lenses and 
cameras are demonstrated. Possibilities of deducing figures of merit 
from OTF-data are mentioned.