meaningful even if only very few collimators would be available for the lens distortion 
determination, as this is the case for longer-focal-length lenses. For example, camera calibration 
at the National Research Council of Canada is carried out with collimators located at T, = —g i, with 
{=0 to 10. For lenses with f = 86, 153, 210, 305 and 610 mm the number of available callimators 
at off-axis angles is, respectively, 10, 8, 6, 4 and 2. 
The introduction of standard lens distortion curves defining lens distortion throughout the 
useful image format would also reduce the potential problems resulting from the extrapolation of 
lens distortion values for radial distances larger than that of the last available collimator 
image. For the example given in the preceeding paragraph, such extrapolation would, for a useful 
image format of 225 mm by 225 mm with a semi-diagonal of 159 mm, be necessary for radial distances 
exceeding approximately 129, 153, 140, 126 and 121 mm respectively. In an ideally flown 
photogrammetric block with 602 forward overlap and 20% sidelap, four of the nine essential image 
locations would be located at a radial distance of 130 mm and require lens distortion extrapolation 
for three of the five types of lenses. 
3.7. Filters 
Any filter normally used on the camera shall be in place during the test. If more than 
one filter may be used in service, the camera shall be tested with each. Any filter used on 
the camera during tests shall be fully identified in the report. If its orientation on the 
camera is not well established by marks or indexing devices it shall be recorded in the 
report. 
Discussion 
A microdensitometer trace should be made and recorded of the antivignetting coating located on 
the lens side of the camera's filter. A copy of this trace (a sample is given in Fig. 1) should 
accompany the camera calibration report to determine if any deterioration has occured to the 
antivignetting coating since the last calibration. 
  
Fig. 1 Filter Gradient Density Coating 
Microdensitometer trace of the antivignetting coating on a camera's 
filter, lower trace shows deterioration from normal service. 
The deterioration of these coatings due to normal cleaning changes the relative illumination 
or light fall-off in the image plane from the axis to the edges of the format area. It is not 
unusual, to find the coating reduced or completely removed after a few years of service. 
2.8 Apertures 
Tests shall be made at full aperture and at any other apertures for which data are 
desired. The apertures used shall be specified in the report. For full characterization 
of a type of camera tests shall be made at three or more apertures, except where the 
camera mechanism provides fewer than three apertures. 
No comment. 
2.9. Negative Material 
2.9.1. The emulsion used should preferably be the same as is used in service. However, an emulsion 
of similar spectral sensitivity and gamma but with different grain characteristics is 
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