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1.13.3 
1.14.2 
Lines per millimeter mean dark lines per millimeter or light lines 
per millimeter. The resolving power is equal to the reciprocal of the 
centre to centre distance in millimeters for lines of the same shade. 
For annuli it is the reciprocal of the mean ring diameter. 
Averaging. 
Average resolving power shall be obtained from a set of readings 
at various field angles by weighting each resolution value by the pro 
portion of the total format area which it represents. 
Resolving power on radial lines and resolving power on tangen 
tial lines may be averaged by taking the geometric mean. 
1.15.2 
1.15.2.1 
1.15.2.2 
1.15.2.3 
1.15.3 
note: Averaging resolving power on radial lines and on tangen 
tial lines is mentioned since it is currently done. The geometric 
mean is not a true measure of merit as is clearly established by 
asking if a lens which resolves 25 lines by one line is as good as 
one resolving 5 lines by 5 lines. 
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 average resolving power. 
Characterization Tests. 
For characterization of a lens and camera type at least the follow 
ing information shall be given. 
A description of the test method including target, filter, focus 
setting, apertures, emulsion, and development. 
The resolution along the field diagonal for at least three lens 
apertures. These results shall be obtained for a range of focus settings 
and the position of best average resolution shall be established relating 
to visual axial minimum fringe focus. 
Unambiguous expressions such as “resolving power on radial 
lines” or “tangential lines” shall be used in the report. Terms such as 
“radial” or “radial resolving power” shall be avoided as they do not 
show whether the reference is to the direction of the lines or the direc 
tion of the resolved separation. 
Calibration. 
Calibration should preferably be done photographically under 
conditions approaching closely that which the camera will encounter 
in service. A visual method will be permissible if it has been establish 
ed that it gives the same values as the following photographic method 
to within the required accuracy. 
2.2.3 
2.2.4 
2.2.5