Suspendable camera mounts are connected to the platform via lines or poles that are free to swing, pivot, or flex, so that the camera is removed to some extent from erratic motions and vibrations of the lifting platform. Ideally the mounting system should hang in a stable, level position. Two different solutions are the pendulum and Picavet suspensions. Both may be combined with a cable-car system in kite aerial photography, or directly attached to a kite line or to a balloon or blimp envelope.
The Picavet suspension is a string-and-pulley cable system that attaches to a kite line or a blimp keel at two points (Fig. 7-10). It was devised by a Frenchman, Pierre Picavet, in 1912 as a self-levelling platform for a camera rig suspended from a kite (Beutnagel et al., 1995). Various methods may be used for threading the line through the pulleys or eye bolts of the Picavet cross (e.g., Hunt, 2002; Beutnagel, 2009) as well as various means of attaching the two end points to a kite line (Fig. 7-11). A typical Picavet suspension hangs 1-2 m below the kite line or blimp keel, and the two attachment points are spaced a similar distance apart, resulting in a triangular arrangement.
The other main suspension type is the pendulum, which may be an aluminum staff, carbon rod, or even flexible wire. Figure 7-12 shows the pendulum suspension used by IM and JBR together with a sledge-and-pulley system running on the kite line (see Chapter 8.4.3). Although a Picavet suspension may be attached to such a sledge as well, the resulting comparatively short distance between the suspension points to some degree decreases the stabilization
FIGURE 7-9 Dual-camera rig for kite or blimp aerial photography. Two SLR film cameras are mounted bottom-to-bottom for simultaneous pictures of the same scene in color-visible and color-infrared formats. Total weight of this rig and cameras is 1.5 kg. Rig built by B. Leffler (California, United States).
effect. There are two great advantages of the sledge system: (a) launching and landing of the kite can take place without the camera attached, and (b) the camera can be retrieved for changing exposure settings, film, storage card, or lens without having to bring the kite down.
By grievous experience, the authors have learned that aluminum is a good electrical conductor. Mysterious camera malfunctions, which were observed during several surveys in hot and dry environments, were finally found to be caused by electrostatic charging from the friction of the sledge wheels on the kite line. This problem was resolved by replacing the original aluminum wheels with ceramic wheels and inserting a plastic barrier into the pendulum staff.
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