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2.1 The revision of Section 6 developed into a definite project 
following the 1972 Congress when specific techniques and MTF values 
were suggested as standards, but rejected by a significant number 
of members as being untenable. Brock then modified the paragraphs, 
which are reported in the following section and Welch added the 
guidelines for testing MTF of cameras. The rewriting followed 
discussions with many scientists at national, government, and industry 
laboratories. The proposed paragraphs therefore encompass general 
agreement, with no limitation of techniques or equipment imposed 
other than the physical conditions which assure unbiased data. 
2.2 It is to be remembered that the Preamble of "Recommended Pro- 
cedures of Calibrating Photogrammetric Cameras and Related Optical Tests" 
specifies control of equipment and techniques by the statement: 
"This recommendation has been prepared on the assumption that tests 
will be carried out under the supervision of scientists experienced 
in the field of optical and photographic measurements. Hence, 
it does not specify the quality of equipment which shall be used 
nor the procedural details necessary to obtain correct results." 
The substitution for the present Section 6 which follows: 
a. Updates the present paragraphs on lenses 
b. Changes the numbering system 
c. Adds paragraphs on MTF camera testing 
d. Adds references 
  
6. MODULATION TRANSFER FUNCTION AND OPTICAL TRANSFER FUNCTION 
OF PHOTOGRAMMETRIC LENSES AND GUIDELINES FOR MEASURING MTF OF CAMERA 
SYSTEMS 
6.1 Measurement of OTF and MTF 
The OTF and MTF may be measured by any of the several known 
methods, but the technique and equipment used shall be calibrated 
or qualified by measuring the MTF or OTF of known standard lenses. 
Simples lenses designed specifically for such purposes are now 
manufactured. (Ref 1) Particular attention should be paid to 
the geometrical accuracy of the test bench. 
6.2 Illuminant and Spectral Sensitivity 
The effective spectral response of the measuring apparatus 
shall be stated. Ideally the spectral product of the light source 
radiance, filter transmittance (s), and photoreceiver response used 
for OTF and MTF measurements should match perfectly the spectral 
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