THE MOTION-PICTURE MACHINE.
A diagrammatic sketch of the essentials of a good motion picture machine
is given in Figure 28. This does not represent any machine in particular
and no machine exactly like it will be found; it does, however, show the
theoretical elements necessary to the projection of motion pictures and
the usual safety devices with which standard machines are provided. As a
variation from Figure 28, the exact method of threading the film through
the Edison machine is given in Figure 29. In Figure 28, the parts are
designated as follows:
_A_--feed reel or upper reel
_B_--feed reel magazine or upper magazine
_C_--magazine fire traps, or film valves, or fire valves
_D_--upper steady-feed sprocket
_E_--presser rollers, or friction rollers, or idlers
_F_--upper feed loop or upper loop
_G_--film-steady drum or film steadier
_H_--film gate
_I_--tension spring
_J_--automatic fire shutter
_K_--revolving shutter
_L_--intermittent sprocket
_M_--lower feed loop
_N_--lower steady-feed sprocket
_O_--take-up reel and lower magazine
_P_--framing device or adjusting lever (not shown)
_Q_--film shields
[Illustration: FIGURE 28.]
[Illustration: FIGURE 29.]
In addition to the above, there are the gearing and the belting which
transmit motion to the various sprockets and drums shown. The whole
function of the machine, however, is the proper moving of the film along
the lines indicated in the figure, the heavy black line representing the
film. The film is unwound from the upper reel by the upper steady feed
sprocket _D_. After forming the upper loop _F,_ it passes over _G,_
through the film gate _H,_ to the intermittent sprocket _L_. This
sprocket moves the film by an intermittent motion allowing the film to
remain stationary in the light for about four-eightieths of a second and
shifting it during about one-eightieth of a second. After leaving the
intermittent sprocket, the film forms the lower loop and then passes to
the lower steady feed sprocket, which prevents the take-up from pulling
the loop away from the intermittent sprocket. The object of the upper
and lower loops is to lighten the work of the intermittent sprocket as
much as possible by making it unnecessary to move anything but the film
between the two loops.
[Illustration: FIGURE 30.]
All of the sprockets and the shutter _K_ are connected together by a
train of gears (see Figure 30, which is the gearing of the Motiograph
machine) and when properly adjusted they all work in proper relation to
each other. The upper steady-feed sprocket feeds just as much film into
the upper loop as the intermittent sprocket takes away; while the lower
steady-feed sprocket takes away just as much as the intermittent
sprocket feeds to it. The film is unwound from the upper reel and
rewound upon the lower; but before it is used again, it must be rewound
from the lower reel upon another one. If it were to be exhibited from
the lower reel without this rewinding, the pictures would be exhibited
backwards.
DISCUSSION OF PARTS.
_A--Upper, or Feed Reel._--The feed reel is usually either 10 or 12
inches in diameter. A 10-inch reel accommodates 1,000 feet of film and a
12-inch reel, about 2,000 feet. The reel fits loosely upon bearings in
the upper magazine and the film is unwound from the reel, which
revolves, by the upper steady-feed sprocket. To prevent its unwinding
more film than is wanted, a small spring is arranged to cause a slight
friction. It is best to keep good reels in the operating room for use as
feed reels. A reel to be used for this purpose should be perfectly true
and in good order; reels sent out from the exchanges are often bent or
have loose parts which cause trouble. A good operator will keep a supply
of good reels always on hand.
_B--Upper Magazine._--The upper magazine is a steel box made up without
solder and fitted with a steel door on the crank side of the machine. It
exists for the purpose of protecting the film against fire or injury
from other causes. It is important that the door be kept closed for,
without this precaution, there is no fire protection. In some cities, it
is required that the door be provided with spring hinges to keep it
closed, but it is doubtful whether this is a wise provision; for since
the door must be opened to change films and since there is nearly always
great haste in making the change, it is likely that the operator will
block the door open if the spring hinges interfere with him. All doors
now swing to the side, but it seems as though it would be a great
improvement if the doors were arranged to drop down. The door would
then, even if open, prevent fire from below reaching the film. The
magazine might as well be entirely missing as to be left with the
side-swinging door open. Many operators have the habit of opening the
door to watch the progress of the reel instead of noting it on the
screen, or of preparing for a change of reel by opening the door long
before necessary and starting the new run before closing the doors.
Needless to say, this is highly reprehensible.
In order to put out a fire in case it should communicate to the reel,
the magazines have been connected with water piping and a valve so
arranged that the water could be turned on instantly thus filling the
magazines. If the door of the magazine is kept closed, the progress of a
fire will be comparatively slow.
_C--Fire Traps._--The fire traps are an important adjunct. Their object
is to prevent fire, which often occurs at the aperture, from reaching
the film on the reel. All of the various makes of fire traps have been
tested and will ordinarily prevent fire from passing through them. The
larger the roller and the smaller the space around the film, the better
the traps seem to be. The metal of the rollers has a cooling effect
upon the flame and this is undoubtedly one reason why they do their work
so well. None of them, however, is absolutely sure.
If the opening through which the film passes is made too narrow, the
film is likely to brush one side or the other and wear grooves in it, or
cut entirely through it, with the result that a splice may be caught in
the opening and the film torn. Fire traps, cut in this manner, have been
the cause of many fires. This trouble is due mainly to improper
alignment of the magazine with the fire traps. Examine them often and,
if the least wear shows, improve the alignment.
It is advisable that every operator test his traps with pieces of film
and assure himself that they will not, under ordinary circumstances,
carry fire; but he must never rely too much upon them as safeguards, for
although they will check a small blaze, such as would result from the
burning of a few inches of film, they would probably not extinguish a
fire occurring when there was much film crowded around them, as might be
the case when a take-up reel or the intermittent sprocket failed to
work. If the film catches fire and there is any possible chance to do
so, the operator should tear it off at the upper and lower magazines,
and thus break the communication. But if there happens to be a lot of
film lying loosely about, it is advisable for the operator to get away
as quick as possible.
_D--Upper Steady-Feed Sprocket._--The office of the upper steady-feed
sprocket is to unwind the film from the reel and feed it toward the
intermittent sprocket. In order that it may do its work well and relieve
the intermittent sprocket of all unnecessary strain, there must be a
loop _F_. The upper steady-feed sprocket is in continual steady motion
and feeds just as much film to the loop as the intermittent sprocket
takes from it by periodical jerks. The main trouble with all sprockets
is in the wear of the teeth, as in time they wear away near the body of
the sprocket and form hooks. The best sprockets have a number of teeth
to engage the film. In some of the older machines, only two teeth catch
the film, in which case, if two holes in the film are torn out, the film
may stand still.
_E--Presser or Friction Rollers._--The presser or friction rollers exist
merely to hold the film in its proper place. They are sometimes spoken
of as friction rollers although they have nothing to do with friction.
_F--Upper Loop._--The upper loop is provided for the purpose of storing
slack film which the intermittent sprocket may pull away with a very
rapid jerk. It avoids placing unnecessary strain upon the film. The
upper loop often causes trouble by enlarging; this occurs when the
intermittent sprocket fails to work while the steady sprocket continues
to feed. The most frequent cause of this is due to faulty films. In
order to prevent the excess film in the upper loop from falling over in
front of the light of the arc lamp (which would quickly set it on fire),
the film shields _Q_ are provided. In many machines they are too short
or too narrow to be of much use.
_G--Film-Steady Drum, or Film Steadier._--The film steadier is not found
in all machines. If the upper portion of the machine head is properly
arranged, the film may feed directly into the gate.
_H--Film Gate._--The film gate is to hold the film in position. In
order that the picture may be properly projected, the film must lie
perfectly flat and at a fixed distance from the lenses. If this distance
varies, there will be improper focusing of the picture. The film must
also be held in its proper position laterally and vertically. The film
gate has nothing to do with the height of the film. This is taken care
of by the framing device. The film gate wears quite rapidly and when
badly worn allows the film too much play. In order to avoid the wobbling
of the picture, a new gate must be provided. There should be
considerable metal surrounding the aperture and there should also be an
air space and some little ventilation. The metal surrounding the gate is
subject to the heat from the arc lamp rays and, unless properly
constructed, may overheat and damage the tension springs, if it does not
set fire to the film.
_I--Tension Springs._--The tension springs are provided to hold the film
flat against the film gate and also to check its motion as soon as the
intermittent sprocket has stopped pulling it. A certain intermittent
movement is advertised to make the change from one picture to another in
1/96 of a second at normal operating speed. The film moved at this rate
of speed acquires considerable momentum; and the office of the tension
spring is to bring it to rest as quickly as possible. If the springs are
set too tight, they will cause the machine to run hard and may also be
the cause of tearing out splices. They should be set just tight enough
to keep the picture steady; anything beyond this will merely cause
unnecessary wear of the parts, besides calling for unnecessary exertions
on the part of the operator.
_J--Automatic Fire Shutter._--The automatic fire shutter is provided
for the purpose of shutting off the light when the machine is not in
motion. It is required by most city ordinances. The ideal fire shutter
would be one so controlled by the film that it would remain up only
while the film is moving at operating speed. The shutters in use at the
present time vary widely in details of construction. Some of them are
raised and admit the light to the film the instant the handle is pressed
sufficiently to start the machine. Other types are raised only after the
machine has nearly attained its proper speed. Some operate as indicated
in the figure and others operate from the side. All of them are liable
to become deranged at times, and it is no unusual thing to find them
tied up in some way because they failed to work properly. The shutter is
a great convenience when in proper order and has probably prevented many
fires; but it is good practice to consider it as entirely absent and not
get into the habit of relying upon it. The operator should always push
his lamp to the side whenever anything is out of order. This act is
necessary in most houses at the end of every run of film showing
stereopticon slides. It would inconvenience the operator but little to
do this at all times, and then the habit would be formed and become
second nature. On the machines now in use, there is no automatic shutter
governed by the action of the film, which would give protection in case
the film should come to rest, as old films often do when their sprocket
holes are torn out, or, as often happens, when the film splits along the
row of holes. In some machines the fire shutter is made up of such thin
material and rests so close to the film that the light may heat it
sufficiently to fire the film below it. Pieces of film often become
detached at the aperture and remain in the light long enough to be
ignited. Against such occurrences as these there is no protection
whatever except the watchfulness of the operator. If the film fits
snugly into the gate and is well enclosed, such fires do not usually
spread.
_K--The Revolving Shutter._--The revolving shutter is sometimes arranged
in front of the machine and often between the film and the lenses. The
shutter _K_ is of the “barrel” type and is further illustrated in Figure
31 at the left. The object of the shutter is to shut off the light
during the time that the film is in motion so that the impressions made
upon the eye by the succession of stationary pictures may not be blurred
by the motion of the film when it is changed. The ideal shutter is one
that shuts the light off instantly and, at the expiration of the
necessary time, allows it as quickly to come to view again. The
barrel-type shutter allows the light to pass through while it is in the
position shown by solid lines, Figure 31, and has it entirely shut off
when in the position indicated by broken lines. When it is in motion,
the upper wing begins to shut off the light from the top and the lower
from the bottom, thus causing the total eclipse of light in one-half of
the time that a single wing shutter could do it.
[Illustration: FIGURE 31.]
At the right of Figure 31, we have a cone shutter such as is used in the
Motiograph. The stem and gearing of this shutter are set at an angle of
forty-five degrees to the rays of light, for the purpose of arranging
them inside of the mechanism without taking up too much room. There are
two cones of the kind illustrated in Figures 32 and 33 and they move in
opposite directions, thus shutting off the light in about the same time
that a barrel shutter could be made to do it. These two figures show the
positions of wings just before shutting off the last vestige of light
and just as they are beginning to admit it again.
[Illustration: FIGURE 32.]
[Illustration: FIGURE 33.]
The disk type of shutter is much used. It may have either one, two, or
three blades and may also be double, i.e., two disks revolving in
opposite directions so as to shut off the light from two sides of the
opening at once. Three types of disk shutters are shown in Figures 34 to
36. In order to obtain a flickerless picture, it is necessary to cut off
the light not only during the time that the film is in motion, but also
during part of the time that it is standing still. If the light were not
interrupted during the time of exposure, the light interval would be so
long that the difference between the dark period, when it is shut off
entirely, and the light period would be great enough to be noticed in
the form of a flicker.
[Illustration: FIGURE 34.]
[Illustration: FIGURE 35.]
[Illustration: FIGURE 36.]
If a single-blade shutter is used, it must make two revolutions during
the time that a single picture is exposed; once to shut off the light
while the film is being moved and once to interrupt the period of
illumination. This shutter would thus have to run twice as fast as the
two- or three-blade shutter, the three-blade shutter interrupting the
light twice during the time the film is standing still.
The three-blade shutter has one wide blade which must be in front of the
light while the film is moving and two narrower ones which interrupt the
light during the time of exposure.
The two-blade shutter must have both blades of the same size and run one
and one-half times as fast as the three-blade shutter to obtain the same
effect, i.e., cause two interruptions of light during the time of
exposure.
In order to shut the light off very rapidly with a blade, which
approaches the opening from one side only, the disk shutter must be of
sufficient size to produce great angular velocity. It can not well be
used, therefore, inside of the mechanism, but is usually placed in front
of the machine; and it is much larger than the aperture which it must
cover. The shutters must all be set so as to shut off the light during
the time that the film is in motion. When the dividing line between two
film pictures is in the center of the aperture, the shutter should have
it entirely covered. It is possible, however, to arrange the shutter so
that the film may move a trifle before the light is shut off and
continue in motion also for a very short time after the light is again
admitted. This is practicable with the “Geneva” intermittent movement
which starts and stops the film gradually.
A shutter should be adapted to the speed of the film movement. There is
no need of keeping the film covered any longer than it is in motion. A
quick film movement and a narrow shutter will add considerably to the
light obtained from a given lamp and a given current consumption. If the
shutter is not properly adjusted, there will be what is known as “travel
ghost”, “light rain”, or “halo”. These are due to the improper timing of
the shutter, allowing a part of the picture to be seen while in motion.
The travel ghost may be seen either at the top or the bottom, according
to whether the shutter is set too fast or too slow.
[Illustration: FIGURE 37.]
[Illustration: FIGURE 38.]
_L--Intermittent Sprocket._--The intermittent sprocket is a very
important part of the machine. Owing to the swiftness with which it
strikes the film, the teeth on it are more subject to wear than those on
the other sprockets. The number of teeth that engage the film is also an
important item. In order to obtain the best picture with the least
expenditure of light, the film should be moved very rapidly so as to
allow the greatest possible length of time for the stationary picture.
The film should, furthermore, be started slowly; then increased in
speed; and the speed should decrease gradually until brought to rest,
and thus avoid unnecessary jerking. It is also necessary to prevent all
motion of the film during the time the mechanism which moves it is
preparing for the next succeeding movement. All of these conditions are
admirably fulfilled by the “Geneva” movement, Figure 37. The pin wheel
_W_ is in continuous motion and the pin is so placed upon it that it
enters one slot of the cross and carries it along with it, thus causing
a quarter revolution of the cross each time the pin wheel makes one
revolution. The cam band _P_ is cut away sufficiently to allow the cross
to make a quarter revolution, but the remaining portion of it is made to
fit the cross snugly, so that when the cross is not in motion it is held
rigid. Figure 37 shows the movement just starting and Figure 38 shows it
half completed. It can be seen that the motion begins very slowly; comes
to a maximum when it is in the middle; and ends slowly; thus subjecting
the film to the least possible strain. This movement is widely used and
may be arranged with one pin, as shown, or with two. If the pin wheel is
equipped with two pins, it will move only half as fast as with one pin
and thus the proportionate time that the film is in motion will be
lengthened. By making the pin wheel large as compared with the cross or
star, the time during which the motion takes place can be reduced as
much as desired; but the characteristic feature of starting and stopping
the film gradually will be lost directly in proportion as the relative
size of the pin wheel is increased.
[Illustration: FIGURE 39.]
The “Geneva” movement requires extremely accurate construction and
careful management. If dusty or insufficiently lubricated, it wears very
rapidly. It is often arranged so that it can be immersed in oil while
running. Figure 39 shows a practical application of the “Geneva” as used
in the Motiograph. The cover shown at the right entirely encloses it.
[Illustration: FIGURE 40.]
[Illustration: FIGURE 41.]
[Illustration: FIGURE 42.]
[Illustration: FIGURE 43.]
A form of intermittent movement which has lately come out and is used on
the Powers No. 6 Cameragraph is shown in Figures 40 to 42 inclusive. The
moving element of this intermittent movement is a diamond-shaped
projection on the surface of a revolving disk. The driven element is a
cross carrying four pins--termed a “pin cross”--and is indicated by
broken lines. The raised portion _A_ of the diamond strikes one of the
pins of the cross and starts it in motion as indicated in Figure 41.
The movement of the cross can be traced by the black dot indicating one
of the pins. At every revolution of the driving disk, the cross makes
one quarter of a revolution and when not in motion is held rigidly
locked by the locking ring _R_, which fits snugly between the pins. This
movement probably moves the film in the shortest time of any. It is
entirely encased, runs in oil, and is practically noiseless. The manner
in which it is installed in the machine is indicated in Figure 43.
_M--Lower Feed Loop._--The lower feed loop is provided to prevent the
lower sprocket from pulling on the film and thus interfering with the
work of the intermittent sprocket. The intermittent sprocket feeds the
loop, by jerks, three-fourths of an inch of the film at a time; and the
lower sprocket is geared to take away that much by steady motion. Thus,
everything working properly, the loop remains of the same size. In case
the lower sprocket is not working properly, the loop may become enlarged
and the film may run onto the floor. Sometimes the intermittent sprocket
does not work properly and the lower sprocket pulls away all of the
loop.
_N--Lower Steady-Feed Sprocket._--The lower steady-feed sprocket
maintains the loop and restrains the film. If it were not for this
sprocket, the take-up mechanism would pull directly on the intermittent
sprocket and keep the film jiggling.
[Illustration: FIGURE 44.]
_O--Take-up Reel._--The take-up reel is identical with the upper reel
and, in fact, the two are generally used interchangeably. In both cases,
only perfect reels should be used; and reels delivered by exchanges are
very often untrustworthy.
The principle of the take-up mechanism is shown in Figure 44. When a run
of film is started, the diameter of the roll of film being small, the
reel must travel comparatively fast to take up the film as fast as it is
unwound from the upper reel. As more and more film is gathered by the
lower reel, the travel must become slower until finally, with a
twelve-inch reel, the number of revolutions per minute are but about
one-fourth as many as at the beginning.
In Figure 44, _A_ is the reel which is fastened to the spindle _B_; _C_
is a collar also fastened to the same spindle. _D_ is a loose pulley
capable of revolving around the spindle without imparting motion to it
and arranged so that it can be driven by a belt. _E_ is a spiral spring
which is controlled by the small collar _F_, and it presses the loose
pulley against the collar _C_. If the loose pulley is pressed against
_C_ with sufficient force, it will cause _C_ to revolve with it; and the
movement of _C_ will impart motion to the reel and wind up the film
which is fastened to it. _D_ must revolve fast enough so that, even when
the reel is empty, it will take up all of the film fed to it. As the
film is wound up, the size of the roll of film increases and the speed
must become less; thus _D_ begins to slip a little on _C_ and this
slippage increases until the end of the run.
Friction in one form or another is the only method by which take-up
reels are now operated; but in some of them this friction may be in a
belt, as well as in the two disks as shown. Sometimes a fiber washer is
interposed between the two friction disks. In the Motiograph take-up,
Figure 45, the necessary friction and slip are all in the belting.
[Illustration: FIGURE 45.]
If the take-up is not handling the film properly, it is due to a loose
belt or to insufficient tension on the spring. The take-up probably
causes more trouble than any other part of the mechanism and it should
be carefully watched. On account of the trouble incurred from it, there
are still many operators who prefer to run films into a tank; although
the take-up saves them much time. A careful operator who understands the
care of machinery would have little trouble with a take-up; while the
one who has not the faculty of keeping things in order would, perhaps,
be better off (fire hazard neglected) with a tank. With most machines,
the take-up magazine is located where it is very difficult for the
operator to watch its operation. Those machines in which it is located
in easy sight of the operator have considerable advantage in this
respect. A careless operator is often compelled to open the lower
magazine door and turn the reel by hand when the take-up tension is out
of order. Remember that the take-up can cause trouble only when it is
out of order and that a good operator will never allow it to get out of
order and he will inspect it carefully before every show.
_P--Framing Device._--The aperture in the film gate is just large enough
to fit the picture on the film. If the film is accurately placed, the
whole picture will show upon the screen. In order to bring this about,
the machine must either be provided with a means of adjustment, or a
certain part of the film must be placed upon a certain sprocket tooth.
This latter method causes considerable annoyance and waste of time;
furthermore, every splice in a film would have to be made exactly right
or the whole succeeding part of the show would be “out of frame”. In
order to avoid these troubles, every machine is provided with a
so-called framing device. Somewhere about the machine, convenient to the
operator, will be found a lever by which, during the operation of the
machine and without interruption, the position of the film with
reference to the film window and the lens may be adjusted either up or
down. The precise manner in which this is done varies with different
machines. The framing device must be capable of adjusting the film to
somewhat more than the width of one picture.
The splice should be so made that framing becomes unnecessary and this
is accomplished by cutting out full pictures so as to leave each picture
with the full four holes. If a picture is left, for instance, with only
two holes, it will appear upon the screen with the black line, which
should be hidden in the center. If this happens, by moving the framing
lever either up or down, the picture can again be centered upon the
screen.
[Illustration: FIGURE 46.]
_Q--Film Shields._--The film shield is an important part of the machine;
although it is often very much neglected and in many machines is so
small as to be practically useless. It should prevent films from
crowding out into the light when the loops enlarge. Many operators do
not take kindly to machines that enclose the film too tightly; for in
case the take-up fails to work properly, it is often a convenience to be
able to handle the film. This is also the case where very badly torn or
old film is used. Many old films are so badly worn that they will not
run properly on the sprockets and must be very closely watched.
[Illustration: FIGURE 47.]
[Illustration: FIGURE 48.]
It is not thought necessary or advisable to go into the details of
construction of any particular machine as changes are made nearly every
year so that such description would not be of great value and might, in
fact, be misleading. Any person possessing a little mechanical ingenuity
and taking an interest in such matters can readily learn the
peculiarities of any of the machines. They are, after all, when one has
mastered the principles, quite simple affairs. All progressive
manufacturers, furthermore, publish instruction books which are issued
whenever a change is made in any machine; and these are always
obtainable.
[Illustration: FIGURE 49.]
In Figure 46 we have a general view of the Edengraph machine. It will be
noticed that the total length of film between the two magazines is
exposed to view making threading of the film very easy; also that the
revolving shutter works between the objective lens and the film gate.
The well-known Edison machine is shown in Figure 47. This is one of the
best known machines; and it is very compact and durable.
[Illustration: FIGURE 50.]
The Motiograph is shown in Figure 48. The take-up, shown on the lower
magazine, is different in this machine from what it is in the others.
This machine also has a special rewind feature. By an adjustment of the
operating handle, the film, after having been run off onto the take-up
reel, can be rewound upon the upper reel without taking it out of the
magazines.
Figure 49 shows a general view of the Powers No. 6 Cameragraph
mechanism.
The Simplex mechanism is shown in Figure 50. In this machine the film is
entirely enclosed between the two magazines.