CHAPTER V.

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

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.

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.

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.

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.

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.

_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.

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.

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.

_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.

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.

_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.

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.

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.

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.