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machine with a precision of 1 micron is being obtained to cover all format sizes 
up to 9 inches square. This machine will also have a device for measuring the 
flatness of suction backs, etc. 
For instruments in which a calibrated focal length is used it is defined on 
the basis of zero distortion at a distance of 5 cm off-axis for the 13 x 18 cm 
negative, or a distance of 8 cm off-axis for the 19 x 19 cm negative. 
The principal point used in testing is the principal point of auto-collimation. 
For photographing cameras the same principal point is used but it is required in 
addition that no asymmetrical distortion higher than 2 milligrads (6 sexagesimal 
seconds) occur relative to it. In plotting cameras if asymmetry is present the 
principal point used is the centre of symmetry for four points 90° apart at a 
selected distance from the axis. In the acceptance testing of new lenses it is 
required that their average distortion should not depart by more than one-half 
centesimal minute (16 sexagesimal seconds) from that of a standard lens of the 
same type and that they should not have more than one-half centesimal minute 
(16 sexagesimal seconds) variation in distortion at any given field angle. Testing 
is done with a photo-goniometer with a 2-32 metre collimator. 
Germany 
Camera calibration in Germany is done usually by the manufacturer but 
sometimes by a government laboratory. The principal point is defined as the 
point of auto-collimation. Camera calibration includes visual focussing and 
measurement of principal distance and distortion by means of a goniometer 
method. Some details of the concepts used in German calibration are given by 
W. Roos 11 . Collimator focal lengths are 3,000 mm and 1,250 mm. 
India 
The Eagle IX cameras used in India are calibrated by the manufacturer. 
Other cameras are calibrated by the user. 
Italy 
The Santoni and Zeiss cameras are calibrated by the manufacturer and by 
the user. Calibration procedure is photographic using a collimator of 250 mm 
focal length. The calibrated focal length is that which gives zero distortion at a 
certain field angle. Distortion relative to this focal length is determined and 
the principal point is chosen as a point of symmetry. The Nistri cameras are 
calibrated in the manufacturer’s laboratory using a photographic method with 
collimators of 1-50 metre focal length. 
Netherlands 
The Wild RC-5 cameras used in the Netherlands are calibrated by the 
manufacturer and checked at the Delft Institute. The calibration in the 
Netherlands is done with virtually the same apparatus and the same tolerances 
as at the Wild factories. The principal point is determined by an auto-collima 
tion method. The principal distance and the distortion are determined with a 
visual goniometer as descrbed by R. Roelofs 12 . Other publications on this 
subject are by H. Kasper 13M and R. David 15 . The Wild RC-7 camera and the