2 
3. Scope of Report 
The Working Group has not been in a position to 
conduct studies specifically for the ISP. However, 
throughout the period between the Congresses, the 
members of the Group, in the course of their profess 
ional work, have been responsible for, or have had contact 
with, substantial programs of research on the measurement 
and use of transfer functions and their application to the 
design, development and production of aerial photographic 
systems. The requirements of the ISP have been kept in 
mind during these activities, which supplement many years 
of previous experience in the same field. The Working 
Group can therefore claim to speak with reasonable auth 
ority on the current state of the art. 
A symposium on Image Evaluation was held in London, 
England, in September 1966, at which many questions rele 
vant to the present subject were discussed by photogramm- 
etrists and specialists in photo-optics. A draft of the 
present report was presented at that time and gave rise 
to considerable discussion. This revised version has taken 
account of those discussions as far as possible. The 
report recognizes that the transfer function can be consid 
ered from two points of view; first, as a tool for the 
designer and research worker, and second, as a means for 
obtaining more informative measurements of the performance 
of aerial photographic lenses and other optical components 
in place of the present universally used resolving power 
test. The current state-of-the-art, and the further work 
required to obtain useful results, are not necessarily the 
same in these two areas. Briefly, the transfer function 
is already well established as a research and design tool 
and is used extensively in computational techniques. 
Measurement of transfer functions, and particularly transfer 
functions of lenses, has been practiced for many years, but 
a great deal of detailed work is still required before such 
measurements can be made with sufficient accuracy (as 
distinct from precision) to justify their universal use as 
an index of lens quality whereby tests made in different 
laboratories could be compared with confidence. These 
points are further discussed in Section 4, 5 and 6. 
While the report does not attempt to be tutorial, a 
brief account of the transfer function is given in Appendix 
I and particular aspects of the nature of transfer functions 
are emphasized in the text to support the argument at cer 
tain points. 
The resolution applies " transfer function' 1 to photo 
graphic imagery in general, whereas two terms, "optical 
transfer function" (OTF) and "modulation transfer function" 
(MTF) have been internationally recognised. (See appendix 2)