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Photographing from Balloons and Kites
Most photographs that have to be taken from the air are best taken from an aeroplane, but there are occasions when it is more convenient to take them from a kite or captive balloon. The first really satisfactory aerial photograph, from a tethered balloon, was taken by J. W. Black in October 1860 from a height of 1,200 feet over Boston, U.S.A.
Nadar was the earliest photographer to work from a balloon in 1858, but most of his pictures were taken from a moving free balloon. Since the course of the balloon cannot be predicted accurately, and it is not possible to repeat a run over the picture area, there is little point in such photography today. (The exception is the automatic photography of the earth from a stratosphere balloon from altitudes which cannot be reached by an aeroplane.) But a captive balloon or kite offers a vantage point that can be controlled within reasonable limits both in position and altitude.
A much more satisfactory method is to fly the camera from a balloon on a still day. This was the method adopted in the American Civil War, the South African War and in World War I. In these wars the photographs were taken by observers from captive observation balloons. This function has now been taken over by the highly developed air force reconnaissance units.
Where photographs are to be taken from a balloon, it is no longer necessary to use a man carrying type. The cost can be cut to a fraction by using a balloon just big enough to raise the camera and the required length of cable. If the pictures have to be taken on days when the wind is more than about 5 m.p.h. spherical balloons are useless and a properly stabilized balloon flown from a winch must be used.
By operating only when the wind is light it is possible to get good pictures using one or more spherical rubber balloons like the type used in meteorological offices. If the balloon is filled with ordinary coal gas from the domestic supply, every 1,000 cubic feet will lift roughly 50 pounds of gear, including the weight of the envelope and flying wire or cord. The camera with its release gear is housed in a box as for kite photography (above) and the box is fitted with an aerodynamic stabilizer and a small drag parachute or drogue. This unit is attached to a suspension wire or cord long enough to let the balloon be flown well clear of the ground before it is added.
When the unit leaves the ground, the slight wind drag on the drogue swings it away from the flying wire so that the wire does not appear in the picture.
The layer of atmosphere near the earth prevents photography of optimum quality of heavenly bodies from the earth. Scientists are constantly working to find ways of getting astronomical telescopes and cameras into the clearer upper layers of the atmosphere. One of the most successful methods to date is to sling the apparatus below a high-altitude free balloon.
By using a small amount of hydrogen or helium in a giant envelope of extremely light plastic sheet, photographic gear and telescopes up to 36 inches have been raised to over 100,000 feet to take photographs of the planets. When the balloon reaches its ceiling, the gas inside fills out the plastic envelope. In time the pressure builds up and the balloon bursts. The envelope is designed so that after bursting it forms a parachute which lowers the apparatus gently to the ground. Photographs taken in this way show details which were previously beyond the scope of the finest telescopes. Both polythene and foil material balloons are used today for such high altitude work.
The pioneer of this field of aerial photography was a Belgian, A. Batut, who in 1887 took photographs of the ground with a camera attached to a kite. The exposure was timed by lighting a slow-burning fuse which released a stretched rubber band attached to the shutter control after the kite had reached the desired height.
At the beginning of the century, American meteorological observatories were using clockwork operated cameras, suspended below kites, for cloud photography.
The most stable kite for this type of photography is the Cody kite-a box-form kite divided into cells and made of reinforced silk, nylon or cotton panels stretched between bamboo spars. Any weight of equipment can be lifted by simply adding kites, one below the other on the same cable.
The photographic equipment is never attached directly to the first kite. This kite always acts as a pilot. It is launched first and when it is flying well clear of the ground-at least 150 to 200 feet-the next kite is attached. If the pilot kite will give all the lift required, the camera cradle is attached to the cable. The camera cradle is a small waterproof box with a window in the bottom through which the photographs are taken. The box is fitted with air stabilizing fins and a small drag parachute to prevent it from yawing and to keep it standing clear of the cable.
The camera with its clockwork automatic release and rewind mechanism is not loaded into the cradle until there is plenty of steady tension to ensure that it will be carried clear of the ground as soon as the cable is paid out.
Equipment of this type must be flown from a mobile power-operated winch-generally mounted on the back of a truck-because the cable tension may be several hundredweights.
An amateur set-up is not difficult to contrive with two ordinary box kites flown one above the other to give stability, and a miniature camera.
The timed release is easy to arrange with either an alarm clock mechanism or the stretched rubber band and fuse mentioned above. In this case only one exposure can be made per flight.
But kites are not an ideal form of suspension for delicate photographic equipment. They are apt to yaw violently from side to side, or fall to the ground when the wind drops.
A camera with a normal angle lens will cover a square of ground approximately 70 x 70 feet when looking down from an altitude of 100 feet.
The area covered at any other height is given by Side of Square Covered = Height of Camera from Ground x 0.706
In aerial photography from kites or balloons, the camera should be at least 50 feet from the ground to keep it out of the worst of the ground wind eddies. The air is always turbulent in the lee of trees and tall buildings.
The shutter speed for such photographs should be at least 1/100 second to allow for the constant movement of the camera. When taking single shots, it saves time to make the shutter release gear operate a visible indicator, e.g., make it unroll an orange colored streamer. This provides a warning that the exposure has been made and that it is time to haul down and reset the mechanism.
From all points of view, short of using a specially designed camera, a 35 mm precision miniature is the best camera for this work; it is small, light, and easy to couple to an automatic exposure mechanism.
This photographic technique -with balloons especially- is particularly suitable for such enterprises as archaeological expeditions, site excavation, and prospecting; the equipment is cheap and self-contained and it is capable of yielding detailed plan views of relatively small areas of terrain without the difficulty or expense that would be involved in commissioning an aircraft.