HOW THE PICTURES ARE SHOWN UPON THE SCREEN.
Having obtained the positive film, with its string of consecutive
pictures, we now proceed to reproduce upon a large scale the animation
which has been, so to speak, harnessed by the camera. For this purpose
three essentials are necessary--a projecting apparatus, a powerful and
brilliant illuminant, and a white surface or screen, upon which the
pictures are thrown.
In its general appearance the projector resembles the magic lantern,
which before the advent of the cinematograph held the field as a
favourite source of amusement. It has the small box or cabinet in
which the light is placed, and the condenser whereby the rays from the
illuminant are converged into a powerful beam to be thrown through
the picture and the lens upon the screen. This part of the apparatus
is practically the same as that required for the purpose of showing
still-life lantern slides. It is the mechanism required to bring the
consecutive pictures singly before the lens in rapid succession that
constitutes the real difference between the modern projector and the
old stereopticon.
The projecting mechanism has the same task as the camera for securing
the pictures. That is to say, a small section of film corresponding
to the dimensions of a picture has to be brought into position before
the lens in such a way as to permit the powerful concentrated beam
of light from the lantern to pass through it and throw an enlarged,
brilliant, and clearly defined picture upon the screen. The image rests
on the screen for the fraction of a second, to be followed by the
next picture. One does not observe the change from one picture to the
other, as there is a revolving shutter, the opaque blade or blades of
which cut across the screen at regular intervals. While the shutter
is passing the lens, thereby interrupting the passage of light to the
screen, the succeeding picture is brought into position; and when the
opaque blade has passed, it is exposed in its turn and makes way for
the next picture, this alternate action continuing until the end of the
film is reached. It will be seen that an intermittent motion has to be
given to the film in projection, in precisely the same manner as is
required in the camera for exposure.
Although the evolution of a smooth-working and perfect camera taxed
mechanical ingenuity to a high degree, the proportions of the task were
not to be compared with those involved in the design of the projector.
Many factors had to be taken into consideration. In the first place,
it was imperative that each picture should be superimposed exactly
upon its predecessor, that when the image reached the sheet it should
stand as steadily and as still for the minute fraction of a second as
if it were a lantern slide, and that the change from one picture to the
other should be carried out in such a way as to render the change as
imperceptible as possible to the spectator. In short, every effort had
to be made to reproduce by intermittent motion the effect obtainable
with the _camera obscura_.
The perfection of this illusion has demanded years of unremitting
experiment and research. When animated pictures first came before the
public they had a violent flickering, oscillating, and jumping motion,
which proved exceedingly painful to the eyes. The effect was somewhat
similar to that produced by gazing at a picture which is vibrating,
and blinking rapidly meanwhile, or when a flicker-disc is rotated very
rapidly before the limelight centred upon a stage scene and actors.
By dint of persistent effort and the perfection of mechanical details,
this serious flickering and jumping effect has been eliminated; that
is, so far as is possible with an apparatus designed to convey the
impression of continuous motion by intermittent action. The projecting
mechanism is of substantial design, while the moving parts subjected
to wear and tear are made of the strongest metals. The wear and
tear, however, is tremendous, and as all the moving parts are liable
to displacement they must be fitted with adjusting devices whereby
all slackness can be taken up and the apparatus be kept tuned to a
high pitch of efficiency. Great ingenuity has been displayed in the
conception and manufacture of these details, and the cinematograph
projector of to-day is a wonderful piece of mechanism.
[Illustration:
[_By courtesy of Messrs. Butcher & Sons, Ltd._
FIG. 9.--THE OPTICAL PRINCIPLE OF THE CINEMATOGRAPH.]
The optical principle of the cinematograph is exactly that of the magic
lantern. Reference to Fig. 9 will explain it fully. The illuminant is
represented by _L_ and the centre of the light is opposite the centre
of the condensers _C C_, which receive the rays and condense them, the
point of convergence being in the lens or objective _O_, from which
they pass out in the form of an expanding cone of light to fall upon
the screen. The rays in passing from the condensers penetrate the
picture _F_ on the film in position before the lens. It will be seen
that the lens has to be mounted so that its longitudinal axis is level
with the light. The distance of the light _L_ from the condensers, and
similarly the distance of the lens or objective _O_ from the picture
_F_ is governed by the focus of the objective.
It is obvious, therefore, that the picture to be projected must be
brought to a stop in a position central to the lens, and for this
purpose there is a film trap or gate, where it makes a momentary halt,
in precisely the same way that the unexposed film is arrested in its
progress through the camera.
The film to be projected is carried upon a spool mounted on an arm or
bracket above the mechanism, with the pictures upside down as in the
ordinary magic lantern. The spools used are of the open or the closed
type. The former is permissible in countries where there is no rigid
legislation governing cinematograph displays, or where non-inflammable
films are used; but in Great Britain the film must be wound upon a
spool enclosed in a metallic case, to provide protection against fire.
The best spool boxes are lined with asbestos, which ensures a greater
degree of safety.
From the spool the film is threaded over a toothed sprocket, which
engages with the perforations, and also under a spring grip roller
which keeps the film in contact with the sprocket. A loop is then
formed, and from this the film passes into the gate behind the lens.
This gate consists, as in the camera, of two pieces, one rigid, the
other swinging and hinged to the first, so that it may be opened to
enable the film to be introduced. When closed, the film is held flat
and rigid. As the shutter passes across the field of the lens, cutting
the picture off the sheet, the film is given a sharp jerk downwards
to bring the next picture into exactly the same position in the gate
before the lens as that occupied by the preceding image. The descending
film passes round a second toothed sprocket, with its grip roller, and
thence into the second spool box, where it is coiled upon the bobbin.
The machine is operated either by hand or by power and belting passing
over a pulley.
I have described the broad principle upon which the projector
operates; the details of the mechanism vary according to the ideas of
various makers. There are several excellent projecting mechanisms on
the market, each possessing departures in detail, to some of which
reference is made later.
The great difficulty was to impart intermittent motion to the
mechanism which feeds the film to the lens at regular intervals from a
continuous rotary drive, the handle being revolved at uniform speed.
It occurred to Paul, who was the first man in England to attack the
problem scientifically, that it might be feasible to employ the type of
intermittent gear used in watches, known as the Geneva stop. He decided
to adopt this mechanism.
The driving wheel when it completes a revolution falls into a notch
of the driven wheel, and in continuing its rotary movement moves the
latter forward the extent of one notch, but no more, owing to the
convex space between each notch, or concave rim of each tooth, which
coincides with the curve of the driving wheel and fits closely against
its circumference. When the driving wheel makes its second revolution
it engages with the second notch, and so on, with the result that in
this case the driving wheel makes seven revolutions to one of the
driven wheel. Each notch coincides with a picture; that is to say, each
time the driving wheel forces the second wheel forward one notch, a
picture on the film is brought before the lens for projection.
This novel gear gave the desired result, but it underwent considerable
modification, the number of teeth in the driven wheel being ultimately
reduced to four. The driving wheel was also altered. Instead of being
notched as in the Geneva stop movement, it was fitted with a pin,
which, when the wheel made a complete revolution, fell into one of the
deep notches in the driven wheel, and so moved it forward. By this
modification the gearing was reduced to 4 to 1; the driving wheel made
four revolutions to one of the driven wheel, and each notch of the
latter corresponded to a picture. Owing to the fact that the notches in
this driven wheel resemble a Maltese cross in form, the device became
known as the “Maltese Cross” movement. It is in use to-day. The notched
Maltese cross wheel is attached to the spindle of the sprocket wheel
below the lens, and the movement forward of one notch suffices to jerk
the film down smartly three-quarters of an inch or the depth of one
picture.
The advantage of this movement is that the film is pulled down very
quickly, and as a result the flicker is reduced to a negligible
quantity. The gear is noiseless and enables a very steady picture
to be obtained upon the screen. On the other hand, not being a true
mechanical movement, the forward motion of the film is accompanied by
a certain degree of shock, which not only imposes a strain upon the
fragile film, but at the same time sets up great wear and tear in the
mechanism itself.
For these reasons another system of bringing the film into place was
evolved. A wheel having an eccentric movement is introduced below
the film gate. This wheel carries a projecting roller, and with each
revolution the roller strikes the film which passes over the wheel, and
pulls it down the depth of a picture. This type of action is known as
the “dog” movement, and is incorporated in a variety of ways for the
purpose of facilitating the smooth and regular movement of the film
through the gate. Its disadvantages are that it is noisy; and secondly,
that it is almost impossible to secure a steady picture upon the
screen, as the dog strikes the film so smartly as to set up a vibration
which is communicated to the picture in the gate. But it is simpler
than the “Maltese cross” movement, while the wear and tear upon the
mechanism itself is so slight as to be almost non-existent.
These two movements have divided the cinematograph world into two
camps, one adhering to the “Maltese cross,” the other staunch in its
support of the “dog” movement. But the former appears to be increasing
in favour, despite its acknowledged defects. Some years ago Paul
indicated an improvement on it which demands attention because it
converts an indifferent mechanical movement into one scientifically
correct. The principle is shown in Fig. 10. Instead of having four
notches or slots in the driven wheel, as in the Maltese cross, he has
only three slots. The driving member _A_ has an arm _C_ carrying a
roller _E_ at its outer edge. The driving member _A_ when it completes
a revolution, enters the slot _c_ in the driven wheel _B_, and at the
moment of entering the slot is at a tangent to the circular path _a_
of _E_, with the result that the roller _E_ enters the slot without
setting up any shock whatever, carries the wheel _B_ round, and leaves
the slot at a similar tangent to its path, at the same time bringing
the next slot tangent to the path of the roller _E_ on arm _A_. Thus
the film is given increasing speed without the slightest strain, and as
the movement enables the images to be changed rapidly without jarring,
it is possible to reduce the period of eclipse to almost nothing.
For this reason, the opaque sector of the shutter can be cut down to
one sixteenth of the area of the circle described by the shutter.
With the other movements the sector of the shutter must cover at
least one-quarter of the superficies. In other words, the three-slot
wheel cuts down the period of eclipse to less than one-quarter of
that possible by any other mechanism, and as the sector only covers
one-sixteenth of the circle, the period of light thrown through the
film on to the screen is increased, with an accompanying increase of
brilliancy and a complete absence of flicker.
[Illustration: FIG. 10.--PAUL’S IMPROVED “CROSS” DRIVING MECHANISM.]
The shutter is one of the most important features of the projector. In
the majority of cases it is placed before the lens, but in the Gaumont
“chrono” machine it is placed between the condenser and the picture.
In order to secure the best results, the area of the opaque surface
covering the lens while the next picture is brought into position
should be reduced to the minimum, and the eclipsing action should be
so carried out as to reduce the flicker, which is directly due to
the cutting off of one picture to enable the next to be brought into
position. In the early days the shutter had one blade only; when a
brilliant light was used, the alternate periods of light and darkness
could be easily distinguished, and the eyes suffered accordingly. An
effort to remedy this disastrous effect was made by the introduction
of a violet-coloured sector of similar area to the opaque sector, and
set opposite to the latter, which gave the shutter the appearance of
a two-bladed propeller. This is effective to a certain degree; but it
has been superseded by a shutter having three blades. The shutter is
mounted upon a spindle in front of the lens, the distance therefrom
being determined by the focus of the objective.
The heat concentrated upon the film by the converging rays of light
from the condenser is tremendous. The effect is identical with that
produced by focussing the sun’s rays with a lens upon a piece of paper.
If the rays are permitted to play upon one part of the celluloid film
for four or five seconds it will become ignited. So long as the film is
moving little apprehension need be entertained; the danger arises when
the film is stopped to attempt focussing with a stationary picture,
or the film breaks during projection and stops in the gate. Several
disastrous catastrophes have arisen from the firing of the film during
projection. It is impossible to lay too great a stress upon the danger,
for the average operator is little more than a cog in the machine,
and fails to concentrate attention upon the work in hand so as to
anticipate and meet emergencies.
Manufacturers have tried to remove the danger by the evolution of what
is known as an automatic safety cut-off. This is a second shutter,
which, when the projector is at rest, drops between the light and
the lens. The shutter is connected to the balls of a governor. As the
revolving speed of the governor is increased by the turning of the
driving handle, the balls assume a horizontal circle of rotation, and
in so doing, lift the shutter until it rises clear of the aperture in
the gate, through which the light strikes the picture. In the same way,
as the revolving speed of the governor is decreased, the balls fall and
the shutter descends.
The introduction of this automatic cut-off is somewhat to be deplored.
It makes the operator less careful; he trusts blindly to his automatic
friend, which, though it functions admirably, is, like all such
mechanisms, liable to fail at a critical moment. When such a breakdown
does occur, the average operator is invariably caught napping, and the
film is fired before he realises what has happened. The older system,
whereby the cut-off, a shutter working upon a hinged flap principle,
had to be operated manually, was far safer. Its opening or closing
constituted a part of the cycle of operations in the preparations for
projection, thus calling for a definite movement on the part of the
operator.
The most efficient safety appliance yet associated with the projector
itself is the Urban-Joy-Harris anti-firing device, Fig. 11, a very
simple arrangement, whereby the rising and falling gate is converted,
to all intents and purposes, into a fire-proof box. When the film
is threaded through the gate, only that part before the lens, upon
which the light rays are converged, is exposed to the air on the side
nearest the light. On the opposite side the exposure hole is contained
in a tube, holding the lens, which consequently forms an air-tight
chamber upon that side. Should the film catch fire while stationary
in the gate, the air contained in the lens chamber _A_ becomes
heated suddenly, and expands, so that the products of combustion are
discharged through the exposure hole of _H_ into the air. The fire
cannot creep up and down the film, as small bars exactly above and
below the exposure hole successfully prevent such action.
[Illustration:
FIG. 11--THE URBAN-JOY-HARRIS ANTI-FIRING DEVICE. THE DOTTED
LINES SHOW ACTION OF MECHANISM CLOSING SHUTTER _C_ WHEN
FILM _F_ BREAKS AT _K_.
]
In addition there is the Harris safety shutter, which in the event of
the film breaking below the gate, and thus preventing its own passage
owing to the interruption in the driving effort, shuts off the light
from the film, and also stops the electric motor, should the machine be
driven by electricity. This safety-shutter _B_ holds a semi-circular
flap _D_, which is connected by a small lever to a rectangular flap
_C_. The flap _D_ is so adjusted as to hang over the loop in the film
_E_ between the sprocket and the entrance to the film gate. Under
normal conditions the loop _E_ does not come into contact with the
shutter _D_, but when the film _F_ becomes broken below at _K_, the
loop _E_ is enlarged suddenly owing to the film not being able to pass
through the gate, with the result that it forces the flap _D_ to a
vertical position, and this in turn throws the flap _C_ down over the
exposure hole. There is a tube _I_ which contains about half-an-ounce
of mercury with an electrical contact at either end, the object of
which is to change the centre of gravity of the flap _D_, and also to
cut off the supply of electric energy to the motor. When the machine is
running smoothly this tube _I_ is in a horizontal position making the
electrical connection at either end, but when the flap _D_ rises, owing
to the enlargement of the loop _E_ in the film, the weight of mercury
is thrown to one end of the tube, causing it to cant in such a way as
to retain the flap _D_ in a vertical position. If the film should take
fire, only the picture before the lens is consumed. Even the perforated
edges remain untouched, so that the film is not severed, and can
continue its travel through the machine when the breakdown is repaired.
To supply the light necessary to projection, acetylene, the
oxy-hydrogen limelight, and the electric arc have all been used; but
the last is the illuminant most generally favoured. It enables the
maximum amount of light to be collected by the condenser. When the
projection of moving pictures was first attempted an arc light was
unavailable, because that form of lighting had not been adapted to
the magic lantern. The late T. C. Hepworth, the eminent authority
on the lantern, was wrestling with the problem, but there was no
commercial apparatus suited to the cinematograph. In using electric
light a resistance is required to absorb or dissipate in the form of
heat the current over and above that required for the light. Many
types of resistances have been devised for this purpose, to suit
varying requirements. This method of dealing with the surplus current
is, however, distinctly wasteful, and accordingly, where picture
projection is being carried out on a large scale, a motor generator is
adopted. The current derived from the supply main is utilised to drive
an electric motor, which in turn actuates a dynamo, whereby current
is furnished for the light. This seems a roundabout process, but it
effects a great economy in the consumption of electricity.
The mounting for the lantern is also important. As there is continual
movement in the mechanism owing to the communication of driving
effort, either by hand or by power, the mounting chosen must be of a
sufficiently massive character to absorb all the vibration set up.
Paul devised an iron pillar, to one side of the top of which the
lantern was fixed, while the projector was attached to the other.
The principle was similar to that used for the mounting of a machine
gun, and although the idea met with considerable criticism, yet Paul
succeeded in producing steadier pictures than were possible with other
forms of mounting. That his idea was sound is witnessed to-day, for
the principle he advocated has been resuscitated in the Brockliss
Motiograph, which is mounted on a rigid pillar, and undoubtedly throws
a steadier picture than is possible from any other system of supporting
the projector.
In the majority of projecting mechanisms a second lens is mounted
upon the frame, in line with and beside the cinematograph objective.
This second lens is used for the projection of lantern slides for the
illustration of a song, title announcement, or other purposes. In order
to bring the light of the lamp into line with this second lens the
lantern is moved bodily sideways the requisite distance; the projector
itself is not touched--it remains a rigid fixture.
Paul also adopted a driving system which might be revived profitably
to-day where manual operation is practised. Instead of the small handle
placed somewhat high, calling for quick rotation and fatiguing wrist
movement, he used a large wheel mounted at such a height that the
operator, when standing beside, had the lowest travel of the handle
almost at arm’s length. The wheel being of large diameter, a slow,
steady revolution was sufficient, which caused no fatigue, the drive
being transmitted through a pulley or chain to the projector. In many
of the latest picture palaces, however, the apparatus is driven by
an electric motor, which yields a more uniform speed and conduces to
steadier projection.
I will now take up the distinctive features of some of the best
known makes of projector. A comparison of the latest Edison model,
the “B Underwriter,” with the first kinetoscope, affords a striking
illustration of the advance of cinematography in twenty years. The new
machine is constructed throughout of metal, is wonderfully compact,
and the mechanism has been reduced to the acme of simplicity. All
moving parts subject to heavy wear and tear are made of lignum vitæ.
The shutter is of the three-bladed type, while the intermittent action
is conveyed by the Maltese Cross movement. Being rigidly mounted upon
a heavy stand, the picture projected is very steady and free from all
disconcerting lateral and vertical movement.
In the “Gaumont Chrono” projector, the salient characteristic, as I
have mentioned already, is the position of the shutter, which is placed
between the film and the condenser. The film-trap is worthy of notice
because it conduces very materially to the steadiness of the picture
thrown with this machine. The edges of the film are gripped by means
of burnished steel runners or vertical clamps, and they secure it in
position during exposure with the exact degree of tension required
to obtain steadiness, yet without hindering the travel of the film
through the gate, or inflicting injury upon the celluloid. The trap is
fitted with an asbestos shield, which serves to insulate the film while
passing through the trap from the intense rays of the light, which is
continually playing upon the metal around the exposure hole.
The dog movement has been adopted in this apparatus, but upon an
improved principle. Instead of striking the film one smart blow to jerk
it through the gate, it imparts a steady pushing action. The result is
that the film does not suffer any injury. A massive dog striking the
film heavily is apt to produce cracks across the perforations at the
points of impact, which in time become weak spots in the film. This
well-conceived machine has met with remarkable popularity among moving
picture theatres in this country; it is an excellent example of French
engineering skill, wherein lightness is combined with strength and
simplicity.
[Illustration:
The projector and mechanism. The complete projecting installation.
THE LATEST EDISON DEVELOPMENT IN CINEMATOGRAPHY.
This outfit is in striking contrast to the original “peep-hole” machine
facing page 32.]
The Ernemann “Imperator” projector commands deserved attention. It is
built stoutly so as to last and withstand rough usage. Steel forms
the constructional material throughout, and a noticeable feature is
that motion is communicated to all driving parts through heavy gearing.
In this machine the “Maltese Cross” movement has been brought to its
highest pitch of perfection, being of large substantial construction,
and so designed as to obviate the objections to its use. The driven
part is made of hardened silver steel, and there are means of taking
up all slack arising from wear directly it becomes manifest. Instead
of the cross being struck by a pin on the driving wheel, the latter
carries a roller which picks up the slotted wheel without jar or noise.
The mechanism is kept cool by running in an enclosed oil bath, which
tends to reduce the wear and tear to a minimum, while at the same time
the machine is light and easy running, a feature which appeals to the
operator.
[Illustration: THE “CHRONO” PROJECTOR.
The main feature of the Gaumont lantern is the position of the shutter
between the film and the light, instead of outside the lens.]
[Illustration:
_See page 319._
OUTSTRIPPING THE HUMAN EYE.
The Greene di-optic projector which shows on the sheet what the organ
of sight misses during blinking.]
Another machine which possesses many interesting points is the “Silent
Knight,” its chief claim to attention being, as its name implies,
quietness in running, combined with easy operation and steadiness of
the pictures projected. It has the fire-proof gate already described,
and also aluminium fire-proof spool boxes. The movement is the Maltese
Cross. Simplicity has been studied to the last degree, and the
necessity to withstand hard wear and tear, as well as rough handling in
inexperienced hands, has not been overlooked. All the vital parts are
made of chilled steel running in an oil bath, with the necessity for
adjustments reduced to the minimum, though capable of being carried out
easily when the necessity arrives.
The foregoing by no means exhausts the variety of machines on
the market. There is the Pathé machine, a masterpiece of French
manufacture; the Kamm projector, the “Empire,” remarkable for its many
ingenious devices to secure protection against fire, the chief of which
is a contrivance whereby the light is cut off automatically in the
event of the film breaking, although the machine is still running, and
so on. In every instance the direct aim is the evolution of a projector
which will produce an absolutely steady picture, free from flickering
and fluttering, and as noiseless in operation as human skill can
contrive. In this particular field England and the Continent are ahead
of the United States manufacturers. Except in one or two instances the
American product is distinctly inferior. It looks attractive, but its
results fail to stand comparison with the British and French machines.
The projecting features of the moving picture industry in the United
States have not advanced to the high state of excellency attained in
Europe.
In projecting, the pictures have to be thrown upon the screen at the
same speed as that at which they were taken by the camera, that is, if
steady continuous motion is to be secured. The average speed is, as
I have said, about sixteen pictures per second, and it is essential
that the handle should be rotated at a regular uniform pace. Outside
influences appear to exercise a distinct effect upon this manual
action, just as we have seen them do in the process of taking the
original picture. The musical accompaniment is likely to induce the
inexperienced operator inadvertently to accelerate or retard the speed
of projection. For this reason, power driving is coming more and more
into use, the motion being communicated to the mechanism by means of a
small electric motor. The results are far superior to those produced
by the average operator, though not comparable to projection by a
practised and intelligent hand. The latter can tell the approximate
speed at which the pictures were taken, and can adjust his speed to
a far greater nicety than is possible by a mechanical agency which
maintains a constant speed.