US1699169A - Projection machine - Google Patents

Description

mmE/vrqR: wwfrze 3 Sheets-Sheet 1 c. THURSTONE PROJECTION momma Filed 00 6. 9, 1925 Jan. 15, 1929.

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C. THURSTONE PROJECTION MACHINE Filed Oct. 9, 1925 3 Sheets-Sheet 5 Patented Jan. 15, 1929.

UNITED STATES PATENT OFFICE.

CONRAD THURSTONE, OF PITTSBURGH, PENNSYLVANIA.

PROJECTION MACHINE.

Application filed October 9, 1925. Serial No. 61,398.

This invention relates to projection machines and more in particular to moving-picture projection machines.

One of the primary objects of this invention is to provide a moving picture machine whereby the pictures are projected from a continuously and uniformly moving film and wherein the use of intermittent shutters is eliminated by means of a novel arrangement of prisms. Another object of this invention is to provide a projection machine which enables the film to be run at a considerably lower speed than that required in machines now in common use, thereby effecting a great saving in film material and greatly reducing the wear on the latter owing to the reduced speed and uniform motion thereof. A further object is to produce a projection machine whereby flickering of the projected image is practically eliminated, as far as the perceptibility of the human eye is concerned. Still another object is to provide a projection machine which is well adapted to be used in conjunction with so-called phonetic-films,

. and for the projection of pictures in natural colors. Additional features and advantages of this invention will appear from the following description considered in connection with the accompanying drawings forming a part of this application, and in which:

Fig. 1 is a side elevation of my moving picture machine with the front wall of the casing removed, or assumed transparent, to better show the working parts of the machine.

Fig. 2 is a top-plan view of Fig. 1 with the film-door and film-guide-plate removed.

Figs. 3, 4 and 5 are diagrammatic views showing the refraction of light rays through various positions of a revolving prism used in the machine.

Fig. 6 is another side view of the so-called controller of my projection machine.

I am aware of the fact that many inventions have been patented in this and other countries in which moving transparent refractors have been proposed, but it seems to me that in all these patents due consideration to what may be called the refractive periodicity caused by these refractors has not been given, and for this reason these patents may well be considered as practically inoperative. Experience has proved that optical aberrations caused by said periodicity can best be corrected by optical means, and for that purpose I have evolved a new combination of revolving, oscillating and reciprocatingprisms operating as hereafter described. Owing to the fact that such refracting bodies are usually called prisms and that my proection machine differs so greatly in construction and operation from the now generally used types of moving picture projecting machines, I have found advisable to designate my machine by the more descriptive name of prismograph.

Referring to the various drawings, the optical system of my prismograph may be briefly described as follows: The line X-Y represents the optical axis on which is located the source of light 1 the rays of which pass successively through the condensing lenses 2, the oscillating prism 3, the stationary triangular prism 4, the reciprocating triangular prism 5, the revolving-prism 6 and finally the objective lenses 7, before being projected on a screen.

The machine may be operated in any suitable manner such as by means of a crank 8 secured at one end of the drive-shaft 9 which is mounted for rotation in the bearings 10, 11 and 12 suitably located and fastened on the walls 13, 14 and 15 respectively of the front housing 16 of the machine. On this driveshaft is mounted the spiral drive gear 17 which meshes with the right angularly disposed spiral gear 18 secured on the longitudinal shaft 19. The latter is parallel to the optical axis XY and rotates in bearings 20 mounted on he bridges 21 fastened to the walls 14 and 15 of the front housing and to the walls 22 and 23 of the rear housing 24.

The downward feeding of the film 25 is effected by means of a spiral gear 26 mounted on the longitudinal shaft and which meshes with another spiral gear 27 secured on the lower sprocket shaft 28 running in the bearings 29, 30 and 31. Upon this shaft is properly mounted the driving-sprocket 32 whereby the film is driven. The upper film sprocket 33 is secured on the shaft 34 rotatably mounted in the bearings 35, 36 and 37 and is driven by means of the two similar gears 38 and 39, respectively keyed on the shafts 28 and 34. The active portion of the film moves vertically at right angles to the optical axis, as it passes the aperture-plate 40, the guide-plate 41 and the film gate 42. These various parts may be of the same design as usually found in ordinary moving picture machines and, therefore, need not b described in detail.

Close engagement of the film on the lower and upper film sprockets is insured by the ressure- rolls 43 and 44 respectively. The ormer rotates between two parallel arms 45 rockably mounted on the cross-bar 46 secured to the walls 13 and 14. A coil-spring 47, having one end attached to one of the arms 45 and the other end to a stationary pin-support 48 fastened to the wall 13, is used to press the roll 43 against the lower sprocket. The upper roll 44 is similarly mounted on arms 49 rockable on the cross-bar 50 and is forced against the upper sprocket by the coil-spring 51 fastened to one arm and to the pin-support 52, secured on the wall 14. The above described erection of the rolls enables them to be easily lifted out of engagement with their respective sprockets for the purpose of introducing a new film in the machine.

The illumination during the projection on a screen of the successive pictures of a film is governed by means of the controller 53 which takes the place of the shutter mechanism now used in most moving picture machines and makes possible the continuous (i. e. the non-intermittent) operation of the film. This controller is cylindrical in shape and comprises the cylindrical shell 54, preferably made of transparent material, in which the upper and lower portions 55 and 56 are made opaque so as to leave an intermediate space forming the transparent helix 57 the pitch of which must bear a definite relation to the speed of the downward travelling film, as will be explained later. The controller is open at the top and has a circular bottom 58 to which the shell is secured. The tilting position that is given to the controller is for the purpose of lowering the upper edge farthest from the film, so that the pencil of light carrying the image from the film, may pass undisturbed over that edge. The controller is also given a small transversal inclination the object of which is to ive'to the portion of the transparent helix directly behind the film aperture-plate a horizintal position corresponding to that of the upper and lower sides of the aperture 59. The width of this aperture is equal to that of the film picture and the height is equal to that of two film pictures, one above and one below the optical axis.

The driving mechanism for revolving the controller comprises a spiral gear 60 meshing with the drive-gear 17 and mounted on a transverse shaft 61 journaled in the bearings 62, 63, and 64 secured to the three vertical walls of the front housing. Upon this shaft is keyed the spiral gear 65 which drives a similar gear 66 fastened on the inclined shaft 67 which is rotatable in the bearings 68 and 69 of the standard 70 secured to the bottom 71 of the front housing by means of screws 72. A second spiral gear 7 3 is keyed on said shaft to drive the spiral gear 74 fastened on the controller spindle 75 at the upper end of which the controller is secured by means of a hub 76, mounted centrally on the underside of the bottom 58, and the adjusting set-screw 77. The controller spindle is rotatably mounted in the lower journal-block 78 screwed on the bottom 71, and in the upper bearing 79 fastened by means of the screws 80 on a bridge 81 which extends between the walls 13 and 14 to which it is secured in any desired manner. The shafts 67 and 75 are respectively held in position in their bearings by means of the collars 82 and 83.

The front housing is permanently secured on the general base 84 by means of screws 85 which are inserted through suitably disposed apertures provided in the bottom 71 of said housing.

The driving connections for operating the various prisms are all mounted in the rear housin 24 of the machine and form a substantially self-contained group. Suitably placed on the longitudinal shaft 19 is the spiral gear 86 which is longitudinally adjustable thereon by means of the set-screw 87, for a purpose to be described hereafter. This gear meshes with the spiral-gear 88 keyed on the shaft 89. This shaft rotates in the bearings 90 and 91 respectively mounted on the walls 22 and 23 and carries at its inner end a flanged hub 92, secured by means of a set-screw 93. Upon the flange 94 of this hub is cemented the revolving-prism 6 positioned centrally upon the optical axis XY.

' Mounted on the other end of the shaft 89 and outwardly of the rear-housing is the cam disc 95 which is adjustably secured by means of a set-screw 96. This cam-disc is shown in Fig. 2 as being built up of a central disc 97, an inner disc 98 and the outer disc 99 fastened together by cementing or otherw1se.

In the outer disc is cut an endless groove 100 having the irregular shape shown in heavy dotted lines in Fi 1. This groove serves to operate the osci lating-prism 3 by means of the following mechanism: 101 is a pin which engages the groove, preferably at a point substantially level with the optical axis to reduce friction to a minimum. This pin is secured at the lower end of the normally vertical arm 102 which is keyed at its upper end to the rocker-shaft. 103, running in bearings 104 and 105 respectively secured in the walls 22 and 23. The rocking motion to the rocker-shaft is transmitted, preferably in an intensified degree, to the oscillatingshaft 106 by means of a set of meshing gearsectors 107 and 108, the former being secured on the rocker-shaft and the other on the oscillating-shaft. The later is journalled in the bearings 109 and 110 mounted in the walls 22 and 23. At the inner end of said shaft is adjustably secured, by means of the set-screw 111, the flanged hub 112 to which is fastened the oscillating prism 3.

The oscillating-prism must be of sufiicient size to cover the field of the image in the pencil of light. Its construction need not necessarily be rectangular. A square prism will function as well. Upon the thickness of the prismto be traversed by the light beam depends the shape of the cam-groove. The thicker the prism, the less its oscillation, and consequently the less curvature in the cam groove, because the oscillation of this prism must only be enough to correct by refraction the difference between the uniform linear downward movement of the film-picture, descending at a constant speed, and the variation with which the image is thrown upon the screen while refracted by the revolvingprism, which variation is due to the fact that said refraction by the revolving-prism varies according to the sine of the angle of incidence, and that said angle is continually changing while the revolving-prism is in motion.

The reciprocating-prism 5 is operated by means of an endless, suitably shaped, groove 113 provided in the inner cam-disc 98. This groove is engaged by a pin 114 positioned at the end of the arm 115 secured at the other end of a shaft 116 to which a rocking motion is imparted on account of the shape of the groove 113. This shaft rocks in the two wall bearings 117, 118 and in the bearing-pedestal 119 fastened on the bottom120 of the rear-housing by means of the screws 121.

A second arm 122 is secured on this shaft; this arm terminates with a fork 123 between which is introduced the prism-supportingrod 125 having an enlarged portion 126 provided with an oblong slot 127 which is engaged by the connecting-pin 128 secured in the fork. The prism-supporting-rod is rovided at the top with a fiat base 129 on w iich is cemented the reciprocating-prism. This rod is guided in its reciprocations by the guide-bushing 130 provided on the standard 131 fastened to the bottom 120 by means of the screws 132. The inclination of the guidebushing is such as to enable the reciprocatingprism to travel in the diagonal plane corresponding to the hypothenuses of said prism and to that of the stationary triangular prism 4. The latter is securely cemented to a special cross-bridge 133 rigidly secured to the walls 22 and 134.

The rear-housing is fastened to the generalbase 84 by means of screws 135 which engage oblong apertures 136 cut in the bottom 120. The reason for making these apertures 0blong is for the purpose of varying the position of the various prisms along the optical axis according to the relation between the revolving-prism and the size of the image, due to the converging of the pencil of light.

Operation. As stated above, the film and all the-various movable elements of the machine are operated in the present illustration from the crank 8. When the latter is rotated, the film 25 is moved downward by the lower sprocket 32, and the controller 53 revolves with its spindle 75, causing the illumination to descend, through the transparent helix 57, in synchronism wit-h the descending picture on the film, thus controlling the projection of but one film picture until the'bottom of that picture reaches the lower edge of the aperture in the aperture-plate 40, at which instant there willbe two film-pictures in front of said aperture. The projection on the screen of the lower will then be quickly excluded by the lower, opaque, portion 56 of the controller and at this same time the upper end of the transparent helix will allow the projection of the upper, or succeeding, film-picture on the screen.

The transparent helix 57 may be arranged to accommodate one or more film-pictures for each revolution of the controller, the speed of which would be calculated accordingly. In the present embodiment of my machine, the controller has two transparent hel-, ices to accommodate two film-pictures for each revolution, each helix covering one half of the circumference of the cont-roller.-

The rei'olving-prism 6 keeps the image on the screen practically still by refraction. although the picture on the film is descending. The driving-gears for the revolving-prism are so proportioned that one side thereof will correspond to one film-picture, the next following side, in the sense of rotation, corresponds to the next film-picture, and so forth.

Figs. 3, 4 and 5, show successive steps of refraction as the film is moved downward and the prism 6 revolves counter-clockwise. In Fig. 3, the film 25 presents three pictures marked I, II and III, respectively. Each picture is marked with the letter A on its lower half and the letter B on its upper half. In Fig. 3, the lower half (A) of picture II is refracted downward by the prism; and the upper half (B) of picture I is refracted upward, Hence it will be seen that a complete image (A-B) is emerging from the prism to the objective lenses and projected on the screen. The revolving-prism 6, is marked with letters C, D, E and F at the corners, for the purpose of illustrating its movements.

In Fig. 4, the revolving-prism has changed position, and the film has advanced downward a distance equal to one half of a filmpicture. The picture II is now occupying the center of the aperture in the aperture-plate 40, Fig. 1, and passes through the prism without refraction.

In Fig. 5, the revolving-prism has further changed position, and the film has advanced another step. In this position, the lower part (A) of picture III is refracted downward, and the upper part (B) of the picture III is refracted upward, with the result that a complete picture (AB) emerges from the prism.

In the next succeeding steps, the position of the prism, and also of the film, would be advanced another step, and the picture III would then pass through the prism without refraction.

The size of the revolving-prism 6 may be so calculated, according to the refractive index of the material used, that it refracts two half-film pictures, as shown in Figs. 3 and 5, when the prism is placed near to the film.

The pencil of light, emerging from the condensin lenses, and carrying the ima e from the film, is converging toward the o jective lens, and if a revolving prism of the size and shape just indicated, is moved along the optical axis to about half the distance between the film and the objective lens, (the position of prism and film otherwise remaining as in Fig. 3), that prism will retract the full picture I and II; and these two full pictures will superimpose each other on the screen.

Hence it will be seen that if the position of the film in Fig. 1 be the same as represented in Fig. 3, the opaque part 56 of the controller 53 shuts off the illumination from the film-picture I, while the transparent helix 57 permits the illumination of the filmpicture II, and when the mechanism is set in motion, the descending picture is illuminated on the screen until the illumination is changed by the controller 53, facilitating the transition of pictures by the transparent helix 57.

\Vhile a square prism is used in these figures for illustrative purposes, it is evident that any other form of prism, having an even number of fiat parallel sides, may be used.

It is also obvious that a revolving-prism of smaller size can be used by placing it nearer toward the objective lens, where the pencil of light is more concentrated. In order to make it possible to use revolving prisms of different sizes in the same machine, the shaft 19 is given a location parallel with the optical axis. By this arrangement the gear 86 can he slid along the shaft 19 and be fastened by means of the set-screw 87 at any place where it may be desirable to locate the shaft 89, on account of the size of the revolvingprism. This shaft, together with the prisms 3, 4 and 5 and their respective moving elements, are therefore mounted together on the axially movable rear-housing 24, so that all these parts can slide together without disturbing their relative posltion.

Fig. 6 shows the position of the controller 53 when the revolving-prism and the film occupy positions indicated in Fig. 4. In this position the picture II occupies the center of the aperture, and the prism admits the image to pass through it without refraction. The controller (Fig. 6) now presents the transparent helix 57 in the center, ust passing the optical axis X--Y. From. these figures it is evident that the revolving-prism would admit a constantly changing stream of light to pass over and below the desired image. Such light would disturb the projection, but it is excluded by the opaque parts of the controller.

In my construction of the controller I had particularly in view to eliminate the objectionable features of the large disc, such as used in the Patent No. 729,375 to Marvin et al. in which the width of the slot of the mat is exactly equal to that of a picture of the film. The spiral aperture in that disc will not give sufficiently straight horizontal lines at the upper and lower edges of the image on the screen, unless the disc has a diameter of about eighteen inches or more, extending at least sixteen inches above the optical axis. A disc of that size would be objectionable, as it would hinder the freedom of work necessary for the purpose of changing film-reels, mending films, oiling, adjusting and general attending of the machine. If a frail construction be used, it would be a constant source of irritation to the operator and very likely often be knocked out of order. If a strong construction be used, or if it be protected by some housing, it would occupy still more space, forming a heavy and cumbersome part, out of proportion in relation to other parts, and be particularly objectionable in portable machines.

The controller 53 in my construction, gives sufliciently straight horizontal lines at upper and lower edges of the image on the screen, even when the drum 54 is less than six inches 1n diameter, and it can be built to extend less than three inches above the optical axis. It is very rigid and can even be covered or built in without causing any undue weight or bulk.

While the image from the descending filmpicture is being refracted through the revolving-prism 6, it is evident that the angle of incidence is constantly changed, and that the refraction is changed accordingly, From the position shown in Fig. 3, with a high degree of refraction, the refraction decreases gradually until there is no refraction as shown in Fig. 4, and then again it increases until the position as shown in Fig. 5 is reached, with refraction similar to Fig. 3. In this operation the movement of the film at a constant speed is linear, while the rectification accomplished by the prism varies according to the sine of the angle of incidence, thus involving a problem of trigonometry and optics combined. These variations are causing a vibration or movement on the screen, proportional to the difference between the linear film movement and the rectification by the prism.

Such variations between the film movement and the movement of the refracted image, gives a vertical swaying, or vibration, to the image on the screen. If an octagonal rism be used, this vibration is very small,

ut enough to disturb the projection. A hexagonal prism gives more vibrations, and a square prism still more. From a square rism this vibration is more than an inch, in projection at a distance of thirty feet.

The refractive periodicity is corrected by the oscillating-prism 3, operated by the camgroove 100 in the manner heretofore described. When the pin 101 is moved toward the center of the cam, the oscillating-prism 3 turns in a clockwise sense and the image on the screen is raised; the opposite rotation of this prism will, of course, lower said image.

When the revolving-prism is in the position indicated by Fig. 3, and revolves anti-clockwise to a position halfway between Figs. 3 and 4, while the film is moving downward, the refraction by the revolving-prism is more than necessary to correspond with the movement of the film, and therefore, any certain part on the film (for instance a letter in a printed text) is moved up a little by the revolving-prism, which movement through the objective lens is shown as a downward movement on the screen. A slight movement clockwise by the oscillating-prism will ac-.

complish the desired correction and hold the letter fixed on the screen.

While the revolving-prism passes from the position halfway between Figs. 3 and 4, to a position halfway between Figs. 4 and 5, the refraction by the revolving-prism is less than necessary to correspond with the downward movement of the film. During this period it is necessary to give the oscillating-prism an anti-clockwise movement in order to hold the image fixed on the screen. In other words, while two opposite corners of the revolvingprism are passing the optical axis, the refraction by that prism is more than needed, and while two opposite surfaces of the revolvingprism are passing the optical axis, the refraction is less than needed. In the positions indicated by Figs. 3, 4 and 5, the oscillatingprism should have the position shown in Fig. 1. At the oscillating turning point halfway between Figs. 3 and 4, the oscillating prism has a position slightly tilting to the right (after a clockwise movement from the previous position). From this position it moves anti-clockwise to the other oscillating turning point halfway between Figs. 4 and 5, where it presents a slight inclination to the left, etc.

The cams shown inthe drawings are comparatively large in diameter. The object of this is to facilitate the exact correction of errors in the revolving-prism, experience having shown that perfect prisms are very difficult to obtain at commercial prices. For

this reason it becomes necessary to establish the correct shape of the cam-groove experimentally for all sides of the selected revolving-prism.

Proper synchronization of the movements of the revolving and oscillating prisms is assured by mounting the cam-disc on the shaft of the revolving-prism, as shown.

If the revolving-prism shown had its four angles exactly equal, a smaller cam, making one revolution for each side of the revolvingprism, would be preferable. The function of such a smaller cam would be only to correct vibrations caused by the variable angles of incidence as the prism revolves. But even the smallest variations in the angles or sides of the revolvingrism form a new source of periodical vibrations which can best be corrected by a cam large enough to give a certain sector to each side of the revolving-prism, and thus correct all irregularities emerging from the different sides of the prism.

When the prism 6 revolves, its relation to the pencil of light is constantly chan ing. In the position shown in Fig. 3, the lig t beams travel a longer distance through the prism than in the position shown in Fig. 4. Such variations in distance of the light-path through the denser body, has influence upon the focus, and also upon the size of the picture. Considering an ordinary size picture refracted by a revolving-prism with a refractive index of about 1.52,the distance traveled by the light beams in Fig. 3, would be about three eight-s of an inch longer than in Fig. 4. If the objective lens be placed so as to give clear focus when the revolving-prism is in a position halfway between Figs. 3 and 4, the distortion is only about three-sixteenths of an inch each way. The depth of focus in the objective lense helps to overcome this distortion, and thus make possible projection of a small image at short distance. At lon distance, however, the projection is spoiled, particularly by the change in size, or the alternating linear contraction and expansion of the image. It is therefore obvious that corrective means are necessary. For that reason I have inserted a com ensato or focus equilizer, consisting o a pair of triangum'isars 4and 5 the latter moving diagonally an operated by the cam 95, in a manner described before, and in such a way that the two prisms together resent variations in thickness to compensate for snmlar variations presented by the different positions of the revolving prism.

When the reyolvin rism 6 has its opposite corners in the op ica axis as shown in Fig. 1, the pin 114 in the cam-groove 113 is nearest to the edge of the cam, thereby causing the prism 5 to be held down in-such a position that the two prisms 4 and 5 present the shortest distance for the light beams to traverse, while the revolving prism presents the longest distance, or most refraction. In the position shown in Fig. 4, the revolving prism 6 presents the shortest distance to be traversed by the light beams. Then the pin 114 is lifted up higher by the cam-groove so that the prism 5 takes the position shown by the dotted lines, and thus the two prisms 4 and 5 present an increased thickness to be traversed by the light beams.

The location and the movements of the prisms 4 and 5 must be such that the outer vertical sides (one facing the oscillating and the other facing the revolving prism) alwaysare at right angles with the optical axis.

By this arrangement a reciprocating relation is maintained between the revolvingprism 6 and the focus equalizing prisms 4 and 5, so that these prisms together present at all times a practically constant distance of the light path through the denser media, and the focus is therefore undisturbed.

The rocking movement of the oscillating prism is so small that it need not be taken into consideration in regard to its influence upon the focus.

While the prismograph projects the film photographed with the intermittent moving picture camera, it is obvious that it also is applicable to devices for taking animated pictures, particularly when sound records are desired in conjunction with the film pictures; because with the uniform movement of the film, the photographed sound record can be obtained side by side with just that film picture to which that sound belongs, and onsequently perfect synchronization secured.

\Vith the shutter machine it is necessary to run fast (at least 16 pictures to the second) in order to deceive the human eye, and make the transitions invisible during the dark intervals. The prismograph makes invisible transitions in full and continuous light, even when it runs as slow as 8 or 10 film pictures to the second. One result of this is that a certain subject matter can be projected by the prismograph with much shorter film, or in other words that the prismograph can save 25 to 50 per cent of the capital usually invested in films.

While the prismograph is thus pointing the way to a film saving slow-running moving picture photography, and a correspondingly slow running projection, it can also be used equally well for the projection of films photographed at the usual fast speed.

Moving picture photography at slow speed has the advantage of saving film, and also of a better utilization of available light, which is very important when operating the camera under difficult light conditions. With slow running and continuous motion of the film, it is reasonable to expect that a much cheaper film band material could be used, and the expense thus be further reduced.

The prismograph also offers special facilities for photography and projection of moving pictures in natural colors, by insertion of color-screens in the controller instead of the transparent helix used for ordinary, black and white, projection, or else covering said helix with such colors.

In the projection of moving pictures in natural colors, the color-screens inserted in the controller should practically correspond in order and in shades of colors to such colorscreens as were used in photographing the film being projected. It should be considered, however, that the persistence of vision and the constant overlapping during the swift color transitions in the human eye, may, for some films, require a slight deviation from the screens used in photographing the film. The length of the transparent helices gives ample space for adjustment or arrangement of the color-screens in such order and such shades of color as will best correspond to the needs of the film being projected, in order to produce images in natural colors.

Where only two color-screens are needed, the controller should be geared just as indicated in the drawings presented herewith, in which the controller accommodates two film pictures during each revolution. If three or more color-screens should be desired, the speed and gearing of the controller can be arranged accordingly. The speed of the prismograph can be reduced below the normal speed of sixteen film pictures er second, for ordinary, black and white, pro ection, because of invisible transition in open illumination; but in color projection it is necessary to increase the speed, because the persistence of vision in the eye requires each color-screen to appear at least sixteen times per second in order to have a good blending or resemblance of natural colors.

While I have illustrated and described herein the present embodiment of my invention, and one which I have found by actual test to be operative, it may be thought desirable after continued experience to make slight changes in the construction and arrangement of the details of my invention, and I intend to include in this application all such variations as fall Within the scope of the appended claims.

I claim:

1. In a projection machine of the character described, a source of light; a moving picture film; a rotary controller adapted to control the exclusive projection of each successive picture of said film; said controller comprising a cylindrical shell having two opaque peripheral zones and a transparent zone of uniform width and helical form therebetween, and unitary means to feed said film at a uniform speed and rotate said controller synchronously therewith.

2. In a projection machine of the character described, a source of light; a moving picture film; a rotary controller adapted to control the exclusive projection of each successive picture of said film; said controller comprising a cylindrical shell having two opaque peripheral zones and a plurality of identical transparent zones of helical shape and uniform width positioned therebetween, and unitary means to feed said film at a uniform speed and rotate said controller synchronously therewith.

3. In a projection machine of the character described, a source of light; a moving picture film; a rotary controller adapted to control the exclusive projection of each successive picture of said film; said controller comprising a cylindrical shell having two opaque peripheral zones and a transparent zone of uniform width and helical form therebetween; the pitch of said helical zone being equal to the length of a film-picture, and unitary means to feed said film at a uniform speed and ro tate said controller synchronously therewith.

4. In a projection machine of the character described, a source of light; a moving picture film; a rotary controller adapted to control the exclusive projection of each successive picture of said film; said controller comprising a cylindrical shell having two opaque peripheral zones and a plurality of identical transparent zones of helical shape and uniform width positioned therebetween, the pitch of said helical zones being equal to the length of a film-picture and the high point of each of said zones being immediately above the low point of the adjacent zone, and unitary means to operate said film at a uniform speed and rotate said controller synchronous ly therewith.

5. In a projection machine of the character described, a source of light; a moving picture film; a rotary controller positioned in the focal axis of said light and adapted to control the exclusive projection of each successive picture of said film; said controller comprismg a cylindrical shell having two opaque peripheral zones and a transparent zone of uniform width and helical form therebetween; the pitch of said helical zone being equal to the length of a film-picture; said controller being rearwardly inclined to allow the passage of said light through the portion of the transparent zone nearest to said light and allow the undisturbed passage of said light over the rearward edge of said controller, and unitary means to feed said film at a uniform speed and rotate said controller synchronously therewith.

6. In a projection machine of the character described, a source of light; a moving picture film; a rotary controller positioned in the focal axis of said light and adapted to control the exclusive projection of each successive picture of said film; said controller comprising a cylindrical shell having two opaque peripheral zones and a plurality of identical transparent zones of helical shape and uniform width positioned therebetween, the pitch and width of said helical zones being equal to the length of a film-picture and the high point of each of said zone being immediately above the low point of the adjacent zone; said controller being rearwardly inclined to allow the passage of said light through the portion of the transparent zone nearest to said light and allow the undisturbed passage of said light over the rearward edge of said controller, and unitary means to feed said film at a uniform speed and rotate said controller synchronously therewith.

7. In a moving picture machine of the character described having uniform filmmovement, a single refractor revolving at constant speed and an objective lens, the combination of means adapted to compensate the variation in optical distance between the film and the objective lens caused by the rotation of said refractor, said means comprising a pair of similar triangular prisms disposed in relatively reversed position and relatively reciprocable along the plane of their hypotenuses, and means for reciprocating said triangular prisms.

8. In a moving picture machine of the character described having uniform film-movement, a single refractor revolving at constant speed and an objective lens, the combination of means adapted to compensate the variation in optical distance between the film and the objective lens caused by the rotation of said refractor, said means comprising a stationary triangular prism and a movable triangular prism, both these prisms being similar and positioned in relatively reversed relation to each other, and means for reciprocating said movable prism along the plane of the hypotenuse of the stationary prism.

9. In a moving picture machine of the character described having uniform filmmovement, a single refractor revolving at constant speed and an objective lens, the combination of means adapted to compensate the variation in optical distance between the film and the objective lens caused by the rotation of said refractor, said means comprising a stationary triangular prism and a movable triangular prism, both these prisms being similar and positioned in relatively reversed relation to each other; means for reciprocating said movable prism along the plane of the hypotenuse of the stationary prism, and means to guide the movements of said movable prism.

10. In a moving picture machine of the character described having uniform filmmovement, a single refractor revolving at constant speed and an objective lens, the combination of means adapted to compensate the variation in optical distance between the film and the objective lens caused by the rotation of said refractor; said means comprismg av the hypotenuse of the stationary prism in synchronized relation with the movement of the revolving refractor.

11. In a moving picture machine of the character described having uniform filmmovement, a single refractor revolving at constant speed and an objective lens, the combination of means adapted to compensate the variation in optical distance between the film and the objective lens caused by the rotation of said refractor; said means comprising a stationary triangular prism and a movable triangular prism, both these prisms being similar and positioned in relatively reversed relation to each other; means to guide said movable prism for reciprocating movement able triangular prism in synchronized speed relation. J

12. In a moving picture machine of the character described having uniform filmmovement, a single refractor revolving at constant speed and an objective lens, the combination of a pair of similar triangular prisms disposed in relatively reversed position and relatively reciprocable alon the plane of their hypotenuses, and a roc lrable prism adapted to correct therefractive periodicity caused by the rotation of the revggving refracto'r; said revolving refractor, trl ggular prisms and rockable prismsbein p sitioned in the optical axis of the machine, and unitary means to operate the the film and the various prisms in synchronized speed relation.

In testimony whereof I afiix my signature.

CONRAD THURSTONE.

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