Sunday, August 17, 2008

The British Achievement In Aeroplane Cameras.

The progress made during the war in the design and manufacture of cameras for photographing from aero planes has hitherto remained undisclosed except by the few and somewhat sensational statements which were published now and again in the lay Press, and which, it may be said, were usually wide of the mark. Misers, Brock and Holat, in the paper which we reprinted in our issue of February 21 last, made certain sweeping claims to priority which in the following issue provoked denial n the part f two correspondents, both exceptionally well-informed as to what has actually been done in the production of cameras for the British air forces. Since the appearance it paper we hare had an opportunity of inspecting at the Kid Brooke camp of the Royal Air Force cameras representing the whole range of instruments which have bean used daring the war from the earliest days until its termination. The paper by Major Charles W. Gamble at the Optical Society on March 13 last has also set forth in try great detail the steps by which aero plane photography has been raised to great stats of perfection. It is therefore well that tone account be given of what has been accomplished and of the stages through which the aerial camera has passed.
At the outbreak of war photographs bum aero planes or airships had been taken only in quite a casual and amateur way, and the military authorities were low to recognize the great service which aerial photographs would reader to the Intelligence Branch of the Army. Within a law months, however, the value of the aerial photographs received recognition, and cameras specially made for the purpose were first need early in 1915. The first or A model, long since abandoned, was of a quite primitive type, consisting of wooden square-section cone-shaped body, carrying a lens of eight or tea inches local length and fitted with a Mackenzie- Wisbart adapter for envelopes taking 5x4 plates- The camera had to be held in the hand and pointed vertically or obliquely downwards by the observer as he stood up in the aero plane. The Mackenzie-Wisbart system allowed of a considerable supply of plates being taken up, but the relative fragility of the envelopes in the circumstances of their being handled by a wearer of thick gloves, coupled with a want of sufficient precision in bringing the plate accurately into the local plane of an f/4.6 lens, caused this form f plate-holder to be abandoned.
Early in 1916 a modified pattern, the C model, of the first instrument was put in the hands of airmen. It differed chiefly from the previous model in the means adopted for holding and changing the plates. The camera was fitted with two magazines, one containing eighteen 6x4 plates, in metal heaths, which was placed immediately over the local plane, and the ether (empty) magazine below it and to one side, the camera, of course, pointing downwards. By means of a horizontally moving metal plate, the lowermost of the plates awaiting exposure was pushed to one side and was received in the lower magazine, the operation of thus changing the plate also reciting the local-plane shutter under cover of the moving metal plate. The principle of mechanically changing plates by discharging from a holder placed mouth downwards into one placed mouth upwards has been retained in later models in which the changing mechanism it self has been further improved.
The two foregoing cameras mere both of wood, the disadvantage of which, as pointed out by Major Gamble in his paper, was the liability to expand or contract under the very wide range of temperature and climatic conditions to which the cameras are exposed. Inasmuch as a very slight alteration of the distance between an f/4.5 lens and the sensitive surface may disturb the definition, recourse was had to cameras of all-metal construction or to one consisting of wood framework, constructed so as to obviate expansion and covered with metal mounted thereon so as to cause no stresses in the structure in the event of its expansion. The E camera of the R.F.C.; introduced in 1917 was an all-metal camera of this type, and was fitted with a changing mechanism similar to that of the C model, but with the difference that the plate was changed by pulling a cord, and, the occulting metal plats being thus dispensed with, the camera included a capping shutter to cover the aperture in the local-plane blind during re-setting. A further new device first introduced in this model was an adjustable lens cone by which lenses of from 8 to 10(1/2) inches focal length could be fitted and readily brought into use.
Up to this point all the cameras employing plates were operated, as regards changing the plate, entirely by hand, a system which had considerable disadvantages. Simple as an ordinary photographer would regard the operation of the changing mechanism, the fact that it had to be placed in the hands of men entirely unfamiliar with photographic apparatus called for a changing device which would be free from mishandling by the human operator. It need hardly be said that the airman has many other things to do besides taking photographs, and that he carries on his work always under the conditions of fire from enemy anti-aircraft batteries and of attack from enemy machines. Thus the next step and one which brought the aero plane plate camera almost to its most perfected form, was to provide a mechanical means of changing, operated by power other than that of the airman and brought automatically into operation immediately alter an exposure had been made. This was done in the L camera first used by the K-F.C. early in 1917. With it the operator had simply to use Bowden release in order to make an exposure: the rest- resetting the shutter and changing the plate was done mechanically and automatically. The ingenious device introduced for this purpose consisted of a small propeller mounted on the aero plane and connected to the camera by a flexible shaft. This provided sufficient power for the operation of the plate-changing mechanism, the changing gear coming into operation on the observer releasing the Bowden lever.
An improved model of this camera came into use in 1913 as the LB and has proved the most successful of aerial instruments. It differs from the type just mentioned in being fitted with a self-capping focal-plane shutter which can be entirely removed and replaced by another in case of derangement. Moreover it can be adjusted as regards slit-width by an external lever, and there is the further provision of operating the plate-changing by hand or power as necessary and of instantaneously altering it for use by one or the other means. A further improvement was the series of most rigidly made and finished lens cones, enabling lenses of 4, 6, 8, 10, and 20 inches focal length being used on the one camera.
The principle of a propeller drive for the mechanical changing of plates was also applied to a camera of much larger size, for 18 x 24 cm. plates, first used by the R.A.F. in 1918. The camera, which perhaps may be said not to have been quite fully perfected at the time of the Armistice, is fitted with lens cones allowing the use of objectives of from 7 to 20 inches focal length.
Other cameras of simpler type have been used both in the Royal Flying Corps and the Royal Naval Air Service for purposes more or less special to the requirements of these services. Certain of these are cameras fitted with a stout handle or grip, by which the instrument can be held and pointed obliquely in order to produce a type of photograph distinct from that obtained with a vertical direction of the lens axis. Thus in preparing for operations with tanks in France, photographs taken obliquely are necessary in order to yield an idea of the nature of the ground over which the attack is to be delivered; and similar oblique pictures are taken for many purposes of the Admiralty, for example, in order to obtain records of the correctness with which the masters of ships proceeding as a convoy are carrying out their instructions as to formation.
But perhaps the camera evolved for aero plane work which would provoke the greatest admiration of a connoisseur in mechanical devices is that known as the F, and first used by the Royal Flying Corps in 1916, after having passed through its trials at Farnborough during 1915. This is a camera taking a continuous series of 5 x 4 pictures on a roll of film sufficient for 120 exposures. The mechanism is operated by a propeller to that as the aero plane travels the photographs are automatically taken at intervals corresponding with a certain number of revolutions of the propeller. Simultaneously with the exposure of each section of film a tiny record is made on each (by means of a small supplementary lens) of the reading of the height of the machine and of its compass bearings so that each negative is provided with a record of the direction of flight over the territory which is being photographed.

No comments: