CHAPTER IX SLOWING DOWN RAPID MOVEMENTS

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During the past few years much effort has been spent upon adapting the cinematograph so that it will record exceedingly rapid movements, such as a bullet in flight. Some popular films of this character have been placed on the market, and, in order to attract the public, have been colloquially described as "quicker-than-thought" or "quicker-than-the-eye" movements. Strictly speaking both the latter designations are erroneous, especially in regard to the eye, inasmuch as if a bullet fired from a rifle were brilliant white the eye would be able to follow its flight with ease, notwithstanding the fact that it may issue from the muzzle with a travelling speed of 2,000 feet or more per second.

So far as the moving-picture camera is concerned it is obvious that the ordinary machine could not be operated with sufficient speed to film a bullet in flight, or even to catch the flap of the wings of a small insect, such as a house-fly or bee. It would be impossible to jerk the film through the gate with sufficient speed to take perhaps five thousand pictures per second—the mechanism, and more particularly the film, would break down before a fiftieth of the number of pictures were taken in the space of one second.

Accordingly, great ingenuity has been displayed by cinematograph investigators in the evolution of a means of snapping such extremely rapid movements at sufficient speed to make the films interesting or scientifically useful. This particular branch of the craft was developed first by Monsieur Lucien Bull, of the Marey Institute, who designed a novel and ingenious camera capable of taking up to two thousand pictures per second.[3] With this apparatus many wonderful films have been obtained, and such a fascinating field of study has been revealed that attempts are being made in all directions to secure "quicker-than-thought" films that would have been thought ten years ago to be photographically impossible. Monsieur Bull is developing his idea in order to be in a position to obtain longer records of a subject, and also to take the photographs at a higher rate of speed. Professor Cranz, a German experimenter, also has carried out some novel experiments on the same lines, and has designed a system whereby he is able to take a photograph in the ten-millionth part of a second.

This particular phase of cinematographic investigation is wonderfully fascinating, and from the private worker's point of view it is additionally attractive because it offers him an opportunity to display his ingenuity. It is only by individual effort and the mutual communication of ideas that perfection can be achieved, and in this one field there is great scope. There are many problems which have to be solved, many of which are peculiar to this particular study. It involves a combination of the electrical and cinematographic expert, since dependence has to be placed upon the electric spark for illumination, and also upon electricity for operating the mechanism.

In such work as this the time factor is a most important feature. Obviously, from the scientific point of view, it is essential to have some reliable means of determining the fraction of a second in which each picture is taken and also the period which elapses between the successive pictures. In the system devised by Monsieur Lucien Bull a tuning-fork is used. The vibrations of this fork per second are known, and as the two ends of the fork are reproduced in each image, it is by no means difficult to calculate the time factor.

Dr. E. J. Marey insisted strongly on the importance of this registration of time. It is obviously essential in many kinds of scientific work. Marey during his life investigated some very rapid natural movements such as those of a pigeon's wings during flight. Such a film would have been useless from the scientific point of view, unless there were some means of showing in what interval of time each successive picture was taken, and also the period which elapsed between each exposure. Knowledge of these two facts enables one to tell the time occupied in making a complete flap of the wing, and the physical changes which take place in the shape of the wing to accommodate the bird to different conditions, and it also enables the investigator to trace the motion photographically lost while the lens is eclipsed to permit the film to be moved forward.

To this end Marey devised an interesting type of clock. It consisted of a dial provided with one large revolving hand which was driven by ordinary clockwork. The face of the dial was marked off into twenty equal divisions, each of which corresponded to one-twentieth part of a second. This "chronoscope" as it was called, was placed near the object under cinematographic study, so that both the movement of the clock-hand and that of the object were photographed simultaneously. This system of timing motions it may be pointed out has been revived in a similar form by Mr. Frank Gilbreth in connection with "micro-motion" study described in another chapter.

By courtesy of the Marey Institute.

Marey's Apparatus for taking Moving-pictures of Rapid Movements.

(For explanation see p. 112.)

By courtesy of the Marey Institute.

Cinematographing Rapid Movements.

The complete beat of a pigeon's wing secured by Dr. Marey in eighteen pictures, and taken, according to the "chronoscope" in the corner, in 3/20ths of a second.

Marey also evolved a means of adapting the camera so as to enable him to take the pictures at a speed exceeding sixteen per second. He did not change the mechanism of the camera very radically, but was able to secure as many as one hundred and ten pictures per second. His arrangement of the camera was very simple, as shown on the plate opposite. The film travelled intermittently, its arrest for each exposure being very abrupt. In the camera were two cylinders C and C1 between which the film passed, and these cylinders revolved in opposite directions and towards one another. As the two peripheries of the cylinders were brought together the film was gripped and was moved forward by friction, somewhat in the manner of the clutch-action which was adopted in the very first moving-picture cameras. But each cylinder was provided with eight flattened sections, of equal length, disposed equidistantly. Consequently, when two opposing flat surfaces came together the grip on the film was momentarily released, and the film stopped, though the cylinders continued their rotary motion. By the incorporation of gear trains the number of revolutions could be varied up to about seventeen or eighteen per second. In the camera, above the lens was a small device whereby the sudden and complete stoppage of the film was assured during the periods when it was not gripped by the cylinders below. Another similar device was introduced at F above the window, through which the mechanism at the gate was visible, and this also pressed lightly upon the film to counteract all the vibrations set up from its quick intermittent movement. The unexposed film was mounted upon a spool in the removable box R in the usual manner, but before being fed into the camera it passed between two other friction disks D and K, and was then fed through the camera mechanism and out at the bottom into a second removable spool box L, where it was wound in after exposure. This lower box also contained two friction disks similar to those in the unexposed film box, and the larger of these cylinders in the lower box, like D in the upper or unexposed box, was driven by the revolving handle, through belts and pulleys.

It was a very simple apparatus. Although it was open to the objection that the film might slip while photographs were being taken at high speed, Marey proved strikingly successful in his use of it, his pictures being wonderfully steady, even when taken at a speed of one hundred and forty per second. In photographing the beat of a pigeon's wings he secured a complete cycle of motion in eighteen pictures, which, by reference to the chronoscope visible in the same field, shows that they were recorded in three-twentieths of a second.

Such an adaptation of the camera could be used successfully to-day for what might be described, somewhat paradoxically, as slow rapid movements. But it would be better to secure a more positive and simple means of moving the film forward. Of course the main advantage of the friction disk system is that the film suffers no damage as it moves. In an ordinary camera, working on the conventional claw principle, there would be a tendency to tear the perforations when the pictures exceeded sixty or so per second, and it would prove difficult in some instances to ensure the absolute quiescence and steadiness of the film during exposure. With the Geneva stop system of moving the film, a steady smooth movement is more easily obtained than with the claw mounted upon a sharp eccentric.

For such work where there is no desire to exceed two hundred pictures or so per second, the ideal camera is that which has been perfected by Monsieur M. P. NoguÈs, of the Marey Institute. In general appearance this camera resembles the ordinary machine. It was designed specially for the purpose of field work, for which Monsieur Bull's camera is not suitable. In Monsieur Bull's camera the illumination is effected by means of the electric spark, and it is impossible by this means to light a large field.

Fig. 8.—Mechanism of the NoguÈs camera, wherewith up to two hundred and forty pictures per second can be taken.

In Monsieur NoguÈs' camera there are two claws, each mounted upon its own eccentric, and the film passes between them. The claws do not work together. That is to say, they do not engage the film simultaneously on both sides, but work alternately. When one is engaged with the film the other is in the out position. Without entering into a technical description of the mechanism it may be stated that there is an articulated lever system, so designed as to give the claws an irregular D-shaped trajectory, which is very rapid and abrupt, the ascent of the claw to re-engage with the film being sharper and quicker than is possible in the orthodox design. The general design of the claw mechanism and its method of operation may be gathered from a reference to Fig. 8, wherein the paths described by the moving parts are indicated clearly. The handle whereby the camera is operated is turned at the normal speed of two revolutions per second, but this, owing to the gearing, causes ninety or more downward jerks to be imparted to the film F during each second. This makes one hundred and eighty film movements by the two claws per second, and consequently one hundred and eighty exposures.

Notwithstanding the high speed at which the celluloid ribbon is moved through the camera, there are no signs whatever of tearing. Furthermore, the film, during the brief period of exposure—from 1/360th to 1/480th part of a second—remains perfectly steady and quiet in the gate.

The first camera built on this principle had a maximum speed of one hundred and eighty pictures per second, but by modifying certain details it was found possible to increase the velocity in a subsequent machine to two hundred and two hundred and forty pictures per second. This represents a far higher speed than has ever yet been attained with the ordinary moving-picture apparatus. The machine is no larger than the ordinary type, although, owing to the rapidity with which the pictures are taken, the externally fitting film-box system is adopted, so as to provide a supply of about 700 feet of film for exposure.

In projection on the screen the speed is reduced to about one-twentieth or more of the rate of the exposure. The results are far superior to any which have yet been seen upon the screen. The movements are steadier and more continuous, inasmuch as the proportion of lost movement is about one-twentieth of what it is with the orthodox instrument. The result is that one sees upon the screen many phases of movement which otherwise escape detection or are only partially shown under present cinematographing conditions. Owing to the gearing and the balance of the moving parts the operation of this camera is not more fatiguing than that of the ordinary instrument; indeed, it runs far more easily and lightly. The camera has been evolved for the express purpose of reinvestigating many of the studies conducted by Marey, which, owing to the imperfect appliances at his disposal, are possibly incomplete.

But it may be asked, where is the demand for pictures taken at such a speed? In reply it is only necessary to point out that such photographing speeds are indispensable in studying the motions of the smaller members of the animal kingdom. For instance, an amateur recently prepared a film showing the life and habits of lizards. They were taken at the normal speed of sixteen pictures per second, which the operator judged to be sufficient. But when the pictures were shown upon the screen, the very motions which are the most interesting, such as the movement of the tongue, jerk of the head, and so forth, were lost. Similarly, another film depicted the chameleon, but failed to catch the instantaneous throw of its tongue. On the other hand, when the pictures were taken at the accelerated speed of fifty to eighty per second, the results were strikingly different. Not only were they more complete, but they were smoother, more continuous, and more natural; in fact, they were practically identical with those which the human eye observes in the creatures themselves.

Phases of natural movement, capable of being recorded at speeds ranging between eighty and two hundred per second, are the most promising spheres of moving-picture activity at the present moment. Nature study never fails to arouse enthusiasm, while from the operator's point of view it is indescribably fascinating. Something unexpected is secured at every turn of the handle. The portrayal of Nature stirs the emotions of wonder, it is true to fact, and it often introduces the spectator to something about which he has read but which he never has seen. Consequently, so far as life is concerned, the pictures should never be taken at less than forty to fifty per second, unless one is contented to have a mere distorted impression of what actually takes place. Even moving-pictures of the snail or tortoise, generally considered to move very slowly, should never be photographed at a less speed, because these have actions which cannot be caught at sixteen pictures per second.

Generally speaking, the smaller the live subject under investigation, the more rapid should be the photographing speed. The movements of a bee's wings cannot be caught at sixteen or even two hundred pictures per second. This was proved some time ago when Monsieur Lucien Bull, by the aid of his electric spark system, and special camera, obtained a series of photos showing how a bee regains its normal balance when it is upset. For this purpose a bee was launched from the special apparatus used in connection with the camera, with its equilibrium very seriously disturbed. So rapid was its recovery that twenty pictures taken in succession at the above speed served to illustrate the whole operation, the final photograph showing the bee in normal flight. This was the first occasion wherein this peculiar phenomenon had been photographically recorded, and the unique character of the achievement may be realised from the fact that the bee regained its balance in the infinitesimal period of approximately the hundredth part of a second.

Even in photographing a man, to show rapid walking motion, a speed of sixteen pictures per second is far from adequate. If he happens to be walking at four miles an hour quite 75 per cent. of the motion is lost, and the movement portrayed under these conditions is spasmodic and jerky. For a natural cinematographic record of a man walking, at the present orthodox rate of sixteen pictures per second, his pace should not exceed a mile an hour. Therefore to film a man walking at four miles an hour the photographing speed should not be less than sixty-four pictures per second.

Though the ultra-rapid movement involves the use of intricate electrical apparatus, it is a peculiarly absorbing study. The appliances required are necessarily expensive, but, since it is virtually an untouched province, enormous opportunities await the patient worker. It is additionally attractive because each worker is to a very great extent dependent upon his own ingenuity in the design of efficient auxiliaries and secondary apparatus. It is this wide scope for individual initiative which causes rapid cinematography to be so keenly appreciated by investigators, and, as results have shown, their discoveries when popularised make a very deep impression on the public.

Of course, in projection, it is useless to attempt to throw the successive pictures upon the screen at anything approaching the speed at which they were snapped. If the flight of a bullet recorded at say ten thousand images per second, were projected at a corresponding speed, nothing would be seen. So, in projection, the speed is slowed down; the subject photographed at two thousand pictures per second is thrown upon the screen and brought to the eye at the rate of sixteen pictures per second. The bullet moves across the screen with the pace of a snail. The wings of a dragon fly, which in life make several hundred oscillations per second, appear to move as sluggishly as those of a barn-door fowl. But the detail and the complex movements are recorded; the eye sees and follows something which has formerly been beyond its powers.

If it is desired to reduce the speed to its absolute slowest point, so as to facilitate even closer study, the operator can take advantage, to an extreme degree, of the phenomenon of the persistence of vision. This has been done by Monsieur Lucien Bull. It is impossible to reduce the speed of projection to less than sixteen pictures per second, for this is the lowest rate at which the laws of persistence will allow of an appearance of continuous motion. Yet there is an ingenious way of obtaining the equivalent of a speed of eight pictures per second, and this without either disturbing the apparently lifelike movement or producing any flicker. The method is by duplicating each separate picture of the negative upon the positive. That is to say each negative picture is printed twice in succession upon the positive, so that 12 inches of film, which normally would carry sixteen successive and different pictures carries in this case only eight. When projected upon the screen, at the rate of sixteen pictures per second, the eye fails to detect that it is seeing every picture twice. This might almost be described as an optical illusion, and it makes another interesting proof that the eye can be deluded by cinematography. Monsieur Bull, after having found that the eye did not observe that two identical pictures were shown in succession, endeavoured to carry multiplication still farther. He found, however, that a pair of pictures was the limit. When three identical pictures were shown in succession the impression upon the eye was too long. The movement from triplet to triplet gave a disjointed effect such as arises in ordinary projection when the speed is too slow.


                                                                                                                                                                                                                                                                                                           

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