ud 
4.3 
> 
c1 
4.6 
MT 
— 
The percent veiling glare shall be calculated for each position in the field 
and variation of average veiling glare with off-axis angle shall be presented in a 
table or a graph, for each aperture tested. Any significant asymmetries shall be 
recorded. 
IMAGE ILLUMINATION 
Image illumination shall be measured in the following manner, or by a method 
from which equivalent results are obtained. 
Source 
A source equivalent to an infinite uniformly bright Lambert's Law surface 
shall be placed in front of the camera. The illuminant shall be as specified in 
section 1.4. 
Photometry 
The camera shall be used to photograph this source on the usual aerial emul- 
sion held in the camera's film plane in the usual manner. Well-controlled methods 
of photographie photometry shall be used to obtain the image illumination. The 
source luminance if required shall be obtained by photographing it with a well- 
baffled lensless camera having a relative aperture about the same as the camera 
being tested. This relative aperture shall be determined by measuring the size of 
the entrance aperture and its distance from the emulsion. The source luminance 
shall be calculated from the illumination on the film at the camera axis. 
  
NOTE: If a truly uniform source cannot be obtained, a somewhat non- 
uniform one may be calibrated this lensless camera, as explained by 
Tate. *) 
  
  
  
Filters 
If a routine test is requested, 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. For full characterization of a type of camera, it shall 
be tested alone and with any usual operational filter(s). Any filter(s) used shall 
be fully described in the report. 
Apertures 
The camera shall be tested at full aperture and at any other aperture 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. 
Presentation of Data 
A curve or table shall show average illumination against distance from the 
centre of the format. Any significant asymmetries shall be described. Illumination 
may be given as relative to the centre value and/or relative to the source lumi- 
nance. In the latter case, units shall be such that a lens of 10096 transmission and 
the maximum theoretical aperture (f : 0.5) would represent 100 on axis. The cor- 
responding relative apertures for a perfect non-absorbing system should also be 
shown (T-stops). If a graphical presentation is used distance along the abscissa 
should be proportional to picture area. The average T-stop shall be calculated 
from the average illumination over the entire area of the format. 
*) P. A. Tate, *Illuminance in the Focal Plane of Aerial Cameras", Photogram- 
metric Eng., March, 1951. 
EIS ERES 
m