en field 1.13 
‚ation of 1.13.2 
icient to 
»solution 
that the 
sion sur- 
a test. If 
ith each. 
rably its 
or which 
For full 1.13.3 
| or more 
'ee aper- 
1.14 
1.14.1 
jal as is 
S closely 
r slightly 
s and all 1.14.2 
hange in 
be fully 
  
| for the 
itable 
have 
nd by 1.15 
18,10 1.15.1 
all field 
"Wer. 
1.15.2 
1.15.2.1 
found in 
be stated 1.15.2.2 
Reading 
When reading the target images, magnification and illumination shall be 
adjusted to obtain maximum resolving power values. A low power stereoscopic 
microscope will be found suitable for most reading. 
Resolving power shall be stated in lines per millimetre relative to a flat distor- 
tion-free image. When the ratio of the camera and collimator focal lengths is being 
used to compute the resolving power at the image which corresponds to a certain 
size of test object, correction off-axis shall be made only for the “cos” and “cos?” 
factors affecting resolving power values on radial and tangential lines. 
  
NOTE: If a lens is deliberately designed with large negative distortion to 
improve field of view or image illumination the resolving power values 
which can be obtained by actual measurement of line separations in “com- 
pressed” areas on the film are misleadingly large. These areas have to be 
expanded before used to give a distortion-free image as is obtained in con- 
ventional systems. This expansion reduces the resolving power. 
The use of “cos” and “cos?” correcting factors can be made unneces- 
sary by using a variety of off-axis targets which have been deliberately 
distorted in accordance with these factors to suit the angles at which they 
are used. 
  
  
  
Lines per millimetre means dark lines per millimetre or light lines per mil- 
limetre. The resolving power is equal to the reciprocal of the centre to centre 
distance in millimetres for lines of the same shade. For annuli it is the reciprocal 
of the mean ring diameter. 
Averaging 
If it is wanted, average resolving power shall be obtained from a set of 
readings at various field angles by weighting each resolution value by the propor- 
tion of the total format area which it represents. 
For the purpose of the preceding section, resolving power on radial lines and 
resolving power on tangential lines may be averaged by taking the geometric 
mean. 
  
NOTE: Averaging resolving power on radial and tangential lines is 
mentioned since it is currently done, although the geometric mean is not a 
true measure of merit. 
  
  
  
Presentation of Results 
Routine Tests 
For routine tests of a well-known lens and camera the report shall give at 
least a description of the test method including target, filter, focus setting(s), 
apertures, emulsion, and development, and a statement of the resolving power 
along a diagonal. Where radial and tangential lines are used, data shall be given 
for both. 
Characterization Tests 
For characterization of a lens and camera type at least the following infor- 
mation shall be given. 
A description of the test method including target, filter, focus settings, aper- 
tures, emulsion, and development.