24 
Milton D. Rosenau, 
Electro-Optical Division, 
Perkin-Elmer Corporation, 
Norwalk, Connecticut, U.S.A. 
Madame Marquet, 
Institute d'Optique, 
Paris, France* 
Appendices 2 and 4 have been largely contributed by 
Dr. Denis Kelsall (Lincoln Laboratories, Massachusetts, 
formerly Itek Corporation) whose careful work in the measure 
ment of OTF's and analysis of the Covogon tests is gratefully 
acknowledged. 
Mr. P. D. Carman (NRC Canada) contributed helpful crit 
icisms of the draft versions of the report. 
Appendix 2 
Definition of Optical Transfer Function and 
Modulation Transfer Function 
Numerous terms, such as Frequency Response, Contrast 
Transfer Function, Amplitude Reduction Function, etc*, have 
been used to express the decline of image contrast with 
increase of spatial frequency. In 1961 an international 
committee agreed to standardize on the terms “Optical Transfer 
Function” (OTF), and “Modulation Transfer Function” (MTF) 
(Ref. 67)* While some of the earlier terms were more express 
ive for photographic purposes, it has been felt better, in 
the interests of standardization, to use the approved terms 
throughout this paper. 
The meaning of OTF and MTF for lenses, and of MTF for 
emulsions, are explained in the following paragraphs. 
Optical Transfer Function 
The optical transfer function is a statement of the 
fundamental image-forming qualities of a lens, expressed in 
terms of spatial frequency. Its derivation may be explained 
as follows: 
When a very narrow, incoherently illuminated slit is 
imaged by a lens, the light in the image is spread out into 
a particular intensity distribution. (Fig 2) If the slit is