(112) 
1.5 Collimator. 
1.5.1 The target shall be placed at the focus of a collimator. The col 
limator shall be such as to have no adverse effect on the apparent per 
formance of the lens under test. 
1.5.2 The collimator aperture and the positions of the collimator relat 
ive to the camera shall be such that the entrance pupil of the camera 
lens is filled with light from every part of the target. 
1.5.3 Effects of stray light shall be kept to a minimum by illuminating 
only the target and if necessary by diaphragming the collimator tube. 
note: It seems desirable to avoid mixing the effects of veiling 
glare into the resolving power tests. The effects of veiling glare 
on resolving power are well known. Introduction of glare cor 
responds to a decrease in target contrast. Hence, from measure 
ments of veiling glare, reduction of resolving power can be cal 
culated with adequate accuracy. 
Veiling glare also is very largely controllable by camera 
baffling and lens coating. Consequently, it seems desirable to 
measure veiling glare separately and reduce it if it exceeds per 
missible limits. This approach is similar to those generally used in 
testing camera mounts and film flatness. 
1.6 Number of Exposures. 
The target shall be photographed on axis and at a sufficient num 
ber of off-axis angles (at least 6) to permit preparation of reliable 
curves between field angle and resolving power, to the limit of the 
field. 
1.7 Focus Setting. 
1.7.1 A complete camera shall be tested as received. Other focus set 
tings may be used if desired. For full characterization of a camera (or 
lens) tests shall be made at a number of focus settings sufficient to ensure 
accurate location of the focus setting which gives best average reso 
lution (see 1.14). 
1.7.2 The position of best average photographic focus shall be establish 
ed relative to the position of visual axial minimum fringe focus for the 
same illuminant, or for other specified illuminant if the photographic 
illuminant is not suited to visual observation. Visual minimum fringe 
focus is the focus position at which the image of an opaque edge 
appears sharpest, that is, has the narrowest region of transition from 
light to dark, as determined by observing the aerial image through a 
microscope. 
1.7.3 When a lens is being tested alone it shall normally be mounted so 
that the machined face which would orient it on a camera is parallel 
to the emulsion surface. Any other method of orientation used shall 
be fully described. 
1.8 
1.9 
1.10 
1.11 
1.12 
1.13 
1.13.1 
1.13.2