SLOWING DOWN RAPID MOVEMENTS
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.
[3] See "Moving Pictures: How they are Made and Worked," Chapter XXIV.,
page 264.
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.
[Illustration:
_By courtesy of the Marey Institute._
MAREY'S APPARATUS FOR TAKING MOVING-PICTURES OF RAPID
MOVEMENTS.
(For explanation see p. 112.)]
[Illustration:
_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
C^1 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.
[Illustration: 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.