PHOTOGRAPHIC RESOLVING POWER OF AERIAL RECONNAISSANCE LENSES AS A FUNCTION OF TARGET MODULATION

Abstract

A simple functional relationship was found between normalized photographic resolving power (RN) and target modulation (M) given by RN = Mn, where RN is the ratio of the resolving power at a modulation (M) to the resolving power for M > 0.98 and n is an arbitrary constant. Since this equation provides a useful approximation to most of the measured curves, the resolving power dependence on target modulation for a given lens -film combination can be specified by the high contrast AWAR and the constant n. The value of n was found to lie between 0.46 and 0.62 for the AWAR versus target modulation curves of the 10 lens -film combinations analyzed. The effects of such factors as development, filter, and exposure on this relationship were found to be generally weak and seldom simply predictable. In tests to determine typical values of resolving power reading differences, an 8% average difference in photographic resolving power was encountered over 240 readings by three observers on Plus -X Aerecon film. A comparison of photographic resolving power versus target modulation curves obtained from experiments using seven test targets with those obtained from experiments using fewer targets showed that four targets, with modulations of approximately 0.11, 0.29, 0.73, and 0.98 +, were sufficient to determine the resolving power dependence for M > 0.05.