- 26 - 
changes in film thickness, because the back of the 
film is used as reference 
depth distribution of the exposed grains within the 
emulsion 
lack of contact between the back of the film and the 
reference plate 
temporary film deformation during the flattening 
procedure 
In the following, these sources will be discussed further. 
Deviation of the Image Frame from a Plane 
Measurement of the image frame is an integral part of 
the Canadian camera calibration proeedure. In Figs. 9a and 
b, results of the measurements of the image frames of the 
two used cameras are given, and in Figs. 10a and b the 
resulting positional ehanges. Both image frames are composed 
of several segments with gaps for clamping of the reseau plates. 
Unflatness of the Reference Plate 
Camera manufacturers usually use a tolerance of +7 um [44]. 
Flatness within that limit ean apparently be attained 
easily [35]. Newer results, published in the last four 
years, have not come to the attention of this reporter. 
Figure lla and b show the calibration results for two of 
the magazines used in flying the example photography; Fig. 
12a and b indicate the resulting positional changes,