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*
4
Fig. 2 - Installation of the Wild RC-9 Aerial Camera,
Wild Horizon Camera, and Zeiss Statoscope
in a DC-3 Aircraft
Fig. 2a - Outside View of the RC-9 and Horizon Camera
Installation in a DC-3 Aircraft
The horizon photographs are synchronized with the vertical
photographs in two ways:
(a) by zeroing exposure counters on both the RC-9 and the horizon camera before
each flight. Both counters are operated by the same electrical impulse,
and the same exposure number appears on both negatives (9x9 inches and
35 mm. )
(b) by recording the time on both negatives at the moment of exposure. The
clocks on the vertical camera and on the horizon camera are synchronized
before each flight.
2.2 Technique of Obtaining Horizon Photographs
To obtain acceptable horizon photographs under variable atmospheric
conditions, much attention must be paid to the choice of proper emulsions and
filters. The horizon that appears on the negatives is not a true horizon but a
vapour horizon, or a very distant cloud layer. Pictures of the true horizon
can be obtained only over water or under certain atmospheric conditions, when
flying at low altitudes. However, it is not important whether the true horizon
or a vapour horizon be photographed since we are determining the values of
relative tip and tilt. It is important that the horizon appear on the
negatives as a sharp, well-defined line that can be measured under magnification.