(116) 
2.3 Focus Setting. 
Cameras shall normally be supplied for calibration and for use 
focussed to give best average photographic resolving power. A differ 
ent focussing criterion may be used only if it is clearly justified by a 
user requirement and is stated in the report. 
2.4 Target. 
The target shall be a high contrast cross, dark on a bright back 
ground. 
2.5 Collimators. 
Each target shall be placed at the focus of a collimator. A single 
collimator which is set at various angles relative to the cameras may 
be used, or an array of collimators providing all the necessary field 
angles. Collimator lenses shall be of sufficient quality and focal length 
and shall be focussed accurately enough that displacements of the 
camera lens which still permit of it being entirely filled do not intro 
duce significant errors in measurement. 
note: Spherical aberration or small focussing errors could intro 
duce significant inaccuracies. Such effects should be checked 
carefully. 
2.5.2 Auxiliary illuminating collimators shall be used when necessary 
to provide light to print images of the fiducial marks. 
2.5.3 The collimator apertures and the positions of the collimators 
relative to the camera shall be such that the entrance pupil of the 
camera lens is filled with light from every part of the illuminated 
collimator field. 
2.5.4 Luminance shall be uniform over the collimator field and of the 
spectral quality specified in section 1.4. 
2.6 Number of Field Angles. 
Targets shall be photographed at the principal point of autocolli- 
mation and along the two diagonals of the image format. They shall 
be photographed at a sufficient number of off-axis angles (at least 6) 
in each half field to permit accurate plotting of the distortion to the 
limit of the field. 
2.7 Filters. 
If a filter correcting for vignetting and cos 4 effect is normally used 
on the camera it shall be in place during the test. The use of any other 
operational filter on the camera during test is optional. Any filter used 
on the camera during test shall be fully identified in the report and its 
orientation on the camera established. 
2.8 Apertures. 
Tests shall be made at full aperture and at any other apertures for 
which data are desired. The aperture used shall be specified in the 
report. For full characterization of a type of camera tests shall be made 
at three or more apertures. 
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