jhical Section, 
who developed 
was based on 
other straight 
control points, 
could be then 
eral's office to 
id to traverse, 
plotting from 
hod had to be 
phy in Canada 
)hs taken each 
mber 
1,248 
2,169 
8,143 
9,071 
1,889 
4,163 
ecial attention. 
1e view of the 
Henceforth, he 
apping and to 
At the time, it 
] value of air- 
eodetic Survey 
ique cameras, 
Nelles and his 
he overlapping 
this method of 
Y 
y in the instru- 
d established a 
1g instruments. 
era, to provide 
(7) 
constants for use in the experimental mapping then commencing. Adaptations 
of the methods already in use for calibrating ground survey cameras were em- 
ployed and these followed essentially the same principles as those upon which 
all modern calibrating equipment is now based. From about this time all 
cameras employed in governmental mapping operations in Canada were checked 
in the laboratory, and a record kept of their measured constants for office use. 
A re-calibration is made after major repairs or other disturbances. 
Concurrently, the original suggestion of J. A. Wilson has been followed 
right from the beginning and a record made of each photograph taken on behalf 
of the Government, as well as many others. Prints of these photographs are 
filed in the Canadian National Air Photo Library, which now contains nearly 
3,000,000 photographs of Canada depicting some 90 per cent of the land area. 
The early establishment of this Library was probably one of the wisest steps 
taken in the pioneer days of air photogrammetry. Not only are the prints 
from the Library of great value to technical users, but there has been a constantly 
increasing demand for prints from the general public. The present rate for the 
total demand is some 500,000 prints per year. 
The first available cameras were rather crude military instruments, which 
were adapted in the laboratory for mapping purposes by the insertion of focal 
plane markers to indicate the principal point. Later, in 1923, Fairchild (U.S. A.) 
cameras of improved design (the K3 model) were obtained by the Royal Canadian 
Air Force. These were marked in the Surveys Laboratory by an etched cross 
on the glass focal plane plate to indicate the principal point. 
In the design of the first Fairchild cameras, perhaps insufficient thought was 
given to strictly photogrammetric requirements. For instance, the K3 camera 
consisted of three components — a lens cone, permitting lenses, of different focal 
lengths with their cones to be employed at will, a body, containing the driving 
motor, etc., and a magazine. One defect was that the three components were 
not located to one another as precisely as was desirable. Another was that 
each magazine had its own glass focal plane plate, bearing the register marks. 
The lack of precision consequent to these factors was brought to the attention 
of the makers, who at once designed modifications to meet the criticisms and 
produced, as a result, the F3 camera in which the cone, lens mount, etc., were 
all located by steel dowels and the glass focal plane plate was rigidly attached 
to the body. Hence, the calibration constants had now only to be determined 
for the body-cone combination, while a far better degree of permanency was 
achieved for those constants. The F3 camera, despite its great advantages for 
perspective measurements, was not widely used in the U.S.A. It was adopted 
as standard for mapping purposes by the R.C.A.F. and for some years was 
known as the “Canadian” camera. One difficulty that might be mentioned with 
these early cameras was the range in the actual focal lengths for nominally 
similar lenses. This necessitated a greater range of grids in the office for plotting 
operations than otherwise would have been necessary. 
Static discharges, which marked the film, gave much trouble in early photog- 
raphy. It was investigated in various ways and the makers were consulted.