1. INTRODUCTION: History of ISP activity in Optical and Modulation 
Transfer Functions (OTF, MTF) 
The first significant work on OTF and MTF for Commission I, 
covering many years of study was conducted by Brockl, Chairman 
of the Working Group on Image Quality from 1964 to 1968. His report 
presented the theory of transfer functions, methods of measuring 
lenses, and general applications to evaluation of aerial photography. 
The report included the first correlation testing of various national 
laboratories and showed wide discrepancies. One result of this 
activity was the inclusion, as Section 6 in "Recommended Procedures 
for Calibrating Photogrammetric Cameras and Related Optical Tests," 
of requirements for OTF and MTF testing. € @ 
The work on transfer functions continued during the 1968-72 
quadrennium, primarily under Welender. His report? to the 1972 
Congress covered theory, MTF of film and noted the advantage of 
MTF analysis of aerial photography. During that same period Norton3 
investigated the use of OTF/MIF as a quality standard showing the 
complex problems associated with establishing such a standard and 
the disagreement among members as to its practicality. 
Correlation among laboratories showed improved results but 
significant variables still existed, particularly for off-axis 
values. Hopkins and Dutton* reported that differences in design 
programs could predict different MTF values. 
As of this date (1976), the status of OTF/MTF testing of lenses 
is much improved. For some manufacturers, particularly in England, 
Germany and Japan, it has replaced resolution criteria for evaluation 
of optics and for control of quality. Many of the problems of 
poor correlation have been traced to equipment where a high order & o 
of precision is requisite. Great Britain? has established certification 
of laboratories that are conducting OTF/MTF testing, to assure 
that equipment and techniques are controlled. 
As the voluminous studies on transfer functions accumulate, 
one becomes increasingly aware of the limits that define techniques 
and equipment. Simultaneously, the methods, while becoming more 
diverse, are yielding predictions and results that are more consistent. 
Edge gradient techniques are being successfully employed in the 
analysis of aerial and space photography. 
2. REVISION OF SECTION 6 OF "RECOMMENDED PROCEDURES FOR CALIBRATING 
PHOTOGRAMMETRIC CAMERAS AND RELATED OPTICAL TESTS"