May, 1960 Commission | 173 
Occasional trouble was encountered with failure of vacuum supply to magazines. 
Wild installed vacuum gauges connected at the platen on magazines so that trouble 
would be immediately apparent before photography was wasted. 
To make drift correction easier the viewfinder graticule has been provided with 
several lines in the flight direction in place of the original single line. 
It was found that film was sticking to the vacuum-back during transport and this 
resulted in scratches on the back of the film. Wild added a modification to shut off 
the vacuum before lifting the back. 
Film take-up spool inertia, when the spool was nearly full, was causing excessive 
film transport. To correct this the stop on the metering roller was improved and a 
brake was added to the supply spool. 
A ratchet was added in the drive mechanism of the cone to permit easier hand 
testing of the shutter. 
Fiducial marks were changed from dark crosses on light background to light on 
dark so their negative image would not fill in and be lost on accidental overexposure. 
As a result of experience in Canada and elsewhere, a considerable number of changes 
were made to improve the operation, reliability, and durability of the shutters. 
To meet Canadian and other requests for a camera of RC5a quality to fit small 
aircraft, the RC8 was developed. 
Mounts for the RC5a and RC8 have been found to provide insufficient isolation 
from aircraft vibration. Efforts are being made by Wild to improve them. 
Most cameras, magazines, filters, and camera port glasses are tested for compliance 
with a Canadian “Specification for Air Survey Photography” revised in 1952 and again 
in 1959. The 1959 revision established three quality categories for cameras to provide 
formal classifications for the existing wide variations in quality. Table 1 shows some 
of the maximum tolerances permitted. 
  
  
  
  
TABLE I 
A 3 | € 
Flatness of film locating surface (microns) + 8 +13 +38 
Departure of average radial measured distortion 
from reference (microns) 5 10 40 
Difference between radial measured distortion and 
average radial measured distortion (microns) 
-about principal point of autocollimation 18 35 35 
—about center of best symmetry 5 10 10 
Tangential distortion (microns) == 5 +10 +20 
Veiling glare (%) 10 20 20 
Relative image illumination out to 42.5° (%) 30 25 20 
Filters and port glasses 
— Deviation (sexagesimal sec.) 5 10: 1 20 
Change of deviation (sexagesimal sec.) GP 2 4 
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It is found that the 6” Wild cameras with the improvements described can reliably 
meet category A requirements though all do not do so as yet. 'The Zeiss RMK 15/23, 
as far as can be judged from the few tested, meets most category A requirements. It 
seems likely that it could be brought to meet all of them consistently. 
Although no basic changes have been made in camera calibration procedures, a 
number of improvements in equipment and techniques have been made at the National 
Research Council laboratories where most Canadian cameras are calibrated. Calibration 
techniques are essentially those of the 1952 “International Specification of Methods of 
Calibrating Photogrammetric Cameras”. A new method of measuring the angular 
positions of the calibration collimators has been devised that is free of systematic