US2352214A - Optical system and method - Google Patents

Description

' June 27 1944. D. R. LlGI-l 2,352,234

OPTICAL SYSTEM AND METHOD Filed Feb. 25, 1941 4 SheetSSheet [rzvenZ'or DAVID R.LIGH

6y 7&2 aiiarne ys DISPLACEMENT June 27 1944.

D. R. LHGIHI 511F114 OPTICAL SYSTEM AND METHOD Filed Feb. 25, 1941 4. Sheets-Sheet 2 2O 6O '70 BO DEG- ROTATION Tic fi.

lizverzar DAVID R. LIGH )zzis a'ai-orizeya' June 27, 1944. D. R. LIGH OPTICAL SYSTEM AND METHOD Filed Feb. 25, 1941 4 Sheets-Sheet 4 X w J 35 O 32 I ,i Y J) r/ 221 I W I\ \a lizv eniar Tiqlll DAVID R. LIGH 2 2221s aiivrzzeys Patented June 27,

or'rrcsr. srs'rms sun un'mon David a. Ugh, New Deep, N. Y2,

Industrial Management,

ford, Conn.

amignorto-Darli a Hart- Application February 25, 1941, Serial No. 380,541

16 Claims. (Cl. as-icsi This invention relates to an optical system and 7 method for recording or portraying motion, in which either the object or the image projected therefrom is held in a stationary location while the conjugate is moving constantly; and more specifically the invention relates to motion picture projectors or cameras using a constantly moving film, or other apparatus embodying optical rectiflers. The object of the invention is to produce a practical method and means of diverting the light rays passing between an object and an image. the system being of the type employing planar retracting means to cause the rectification. It is characteristic of the invention that a plurality of planar retracting media are employed together so as to compensate for the sine ratio characteristics of the light displacement for each separate medium, giving a net displacement otthe rays which is linear in relation to the rotation thereof and in synchronism with the uniform movement of the moving object or image.

In the drawings:

Fig. 1 is a geometric diagram of the retraction of a ray by a planar retracting medium such as can be used in the present invention;

Fig. 2 is a similar geometric diagram illustrating the parallel but displaced condition of the ray as it leaves the retracting medium;

Fig. 3 is a sheet of graphsillustrating the sine ratio character of the displacement of a light ray caused by rotation of a planar retracting medium, and the compensating efiect produced by the present invention 'to make the rectification linear;

]'igs.4to'7 areaseriesotdiaeramsshowing the rotation of two planar'refracting media op rated in accordance with the present invention to illustrate the principle of compensated displacement of a ray as used in a motion picture machine; Fig. 4 showing the displacement at 30 of rotation from the vertical position of the first re- Iracting medium; Fig. 5, the displacement at 60 of rotation; Fig. 6, the displacement at 120 of rotation; and Fig. 7, at 150 or rotation;

Fig. 8 is a diagrammatic view in side elevation of the essential parts of a motion picture projector made in accordance with this invention;

Fig. 9 is a view similar to Fig. 8, of a preferred form of motion picture projector made in accordance with the present invention; while Fig. 10 is a front elevation of the shutter blade of the projector of Pig. 9.

It has heretofore been known to attempt projection of a motion picture film moving constantly, i. e.. non-intermittently. and rectifying for this continuous movement of the film by using a plane parallel plate or retracting prisms to retract the light to give the necessary optical displacement to follow the film movement: but such efforts have revealed defects in the resulting screen images and methods of producing them which until the present invention have been incurable. According to the present invention, a plurality of such platw. optical flats or planar retracting media are employed in such a manner and location as to produce the necessary linear motion concurrently with the film movement by a compensating action which avoids the defects of the prior art.

Owingtotheiactthatthespeedoflightray's varies according to the medium through which they pass. when a light my strikes the surface of another medium at an angle other than normal to thatsuriacaitisreiractedasshowninldg. l. lnthisfl urethelightnylisshownentering a planar retracting medium ll, namely. lass, at an angle i from the normal N, H, and the glass being denserthanaintherayisretractedor benttowardthenmmalsothatitsangleri'rom the normal is less than the angle of incidence i. Theanglesiandrareknownastheanglesof incidence and refraction, respectively, and the ratio of their sines is constant and is called the index of refraction. The ratio of the sines of air and any other medium gives the constant which is the index of retraction for that other medium. It is well known that in an optical flat or other glass having two parallel surfaces, theretractedrayftwillbebentawayimmthe normal on entering the glass and towards the normal on emerging. to amounts such that the emerging beam will be parallel to the incident beamI. liowevenwhiletheem il sbeamwill beparalleltotheorighialbeam,thereisalateral displacement D, as shown in Fig. 2. Starting from this geometric premise. using glass with the preferred index of refraction of 1.60483 and the thickness '1 of the planar retracting medium as 1 inch, the displacement oi. the beam varies with th incident angle i in accordance with the following table:

Incident angle Displacement device, on the one hand, or a camera, on theother; but it has not proved practical to vary the rate of angular turning of the planar refracting medium in accordance with the displacement curve to keep the rate of rectification of the projected light rays constant. I

As will now be described in an optical system according to the present invention, it has been found possible to compensate for the displacement curve variation in the rate of rectification of the light beams so as to produce a linear or constant rate of displacement of the light beams while rotating the planar refracting media at a uniform angular speed. Thus, although the dis-' placement in the prior art is not a linear function of the degrees of rotation of the retracting medium and therefore the projected picture of a film frame moving at uniform rate hasv been iumpy," it has been found possible by using the present invention to reach the ideal, wherein the retracting medium turning with uniform anular rotation operates in a concurrent or synchronous relation with th film moving at a constant speed across the aperture of the light of the projector. The principle employed will be described with particular reference to Figs. 4, 5, 6 and 7, which show the application of the prin-- ciple to a motion picture camera. Thus these figures show a ray of an image being diverted for presentation to the moving film. By reversing the direction of the light ray, the figures would be applicable to a motion picture projector.

A multiplicity of planar retracting media are employed in such a way that they compensate and offset the non-linear psrtions of each other with the result that linear displacement, accurate well within practical limits, is obtained from uniform angular rotation of the reiracting media. Basically it is necessary to have only two such media or plates, and the same have been identified in Figs. 4to '7 incl. as plates A and B, respectively. Each plate rotates on its own individual 18113 which lies in a direction normal to therays. Both plates rotate in the same direction, and in these figures it appears as counterclockwise rotation. The angle of incidence i for each position of the plate is indicated beside each figure, identified as M and 1B for the platoon and B, respectively, and there is also indicated the degree of rotation from the position in which plate A was vertical. When plate A is vertical, plate B is horizontal, for plate 13 is always in a position 90' behind plate A, with the same angular 90 relation maintained at all times. While 90' is the most effective compensating angle, and the construction and calculations in the examples given are based on this angle, it should be understood that compensation can be obtained from angles which differ somewhat from 90". In other words, lines normal to the planes of the two plates are always at right angles to each other, with the second plate through which the rays pass always lagging. It will be noted in Figs. 4 and '7 that the sun: of the angles of incidence equals 90 and that this is true'for all positions of applicant's device. In order that Figs. 4 to I may be properly considered with relation to the chart comprising Fig. 3, it is noted that plate A starts at rotation at the midpoint on the left side of the sheet, which is the vertical position of that plate, and at that time plate B is 90' rotated from that position. As shown in Figs. 4 to 7; the light beam coming from the other elements in the optical system passes through first the left plate and then the right plate before going to' the other main elements of the optical system. The result of this successive passingthrough these two planar refracting media in succession gives the desired compensatory eifect. By compensation broadly is meant that the displacement D caused by one plate always is in the opposite direction from the displacement D caused by the other plate. It is the particular net displacement from my apparatus which is used to synchronize or cause concurrent movement of the film and the projector. To explain this in more detail, a table is given here showing by plus or minus signs whether the displacement of each plate is above or below the original or incident ray at the various angles of the two plates, as the rays, plates and displacements appear in Figs. 4 to 7.

Degrees rotation andialgebraic displacement s gn Incident angle Displace Displm Plate A ment Sign Plate B ment in Actually it is found that the net displacement, taking cognizance of these algebraic plus and minus signs, approaches so closely to a straight line (as shown in'Fig. 3) as to be well within the limits of tolerance of motion picture projection. (It might be noted that in passing through a cycle of 180 of rotation of the two plates, two

the ideal linear displacement and the extremely small deviation from the ideal caused by this compensatory method.

U T Detyiation in arm rom Incident angle or angle 3 33 225? linear uniform of rotation 5 displacelinear ment displacement In the above table it will be noted that for a complete cycle of 90 rotation the theoretical displacement D is two inches. It will be noted .that the displacements vary from minus 1 to tion of the plates. In such a projector each picture frame is .30 inch high, and the displacement D will therefore be .30 inch for each cycle. In line of the table given above, the deviation from true linear displacement by the use of the smaller plates will have as its maximum .00056 inch. Assuming that the picture is magnified sixty times on the screen, this would introduce a possible picture jump of about of an inch. This is well within the limits necessaryfor a steady picture.

With further reference to the refraction of the horizontal pencils of light by the plates as shown in Figs. 4 to '7, it should be noted that the effective angles through which the combined plates may be rotated are limited by several factors including (a) the aperture of the objective lens; (b) the size of the picture frame; and (c) the movement of the film. Furthermore the effective angle of rotation is limited by the size of the plates and the obvious fact that as the plane of a plate approaches the direction of the incident beam, its refractive effectiveness is limited as it changes over to receiving the rays on its .other face. In this connection it should be noted that when the angles of the plates are plus or minus 45 from the vertical, 1. e., 45 from normal to the rays, the net image displacement is 0. It has been found that in a practical design of 16 mm. projector under these various limitations, an angle of 38% out of each 90% is available for use, i. e., a light transmitting time efliciency of 42% can be obtained. A shutter can be used to stop the light when it is not desired and also to introduce a sufllcient number of alternate periods of light and dark to reduce the apparent fiicker."

The embodiment of my invention in the motion picture projector shown in Fig. 8 will now be described. The central feature of the machine is the refracting or rectifying means, which in this case comprise two optical flats" H and II. It should be understood that while I prefer to use planar refracting media, such as optical flats,

' any refracting media which by uniform rotation will provide displacement and compensate for each other so as to provide constant or true linear displacement, can be used. These refracting media will hereafter be referred to as plates. Iprefer to mount them in the machine without the intermediary of optical means such as converging or diverging lenses between them. Each plate rotates about its own axis 13, ll, which axis is normal to the direction of the rays, the axes themselves preferably lying at right angles to the direction of movement of the film. The plates have rotation relatively to each other, the rotation being maintained so that the plates or their planar normals are 90 apart at all times. The film IS in Fig. 8 moves downwardly and the two refracting plates II, I! therefore revolve in a counter-clockwise direction, as indicated bythe small arrows. The plates are each mounted extending laterally from a gear wheel l6, I], re spectively, and are driven in synchronism with the movement of the film by means of a large gear wheel 18, a small gear wheel 19, a worm!!! and the film motor 2|. The film I5 is given continuous linear movement by a sprocket wheel 22 mounted on the same shaft with the gear wheels l8 and I9 and revolving in synchronism therewith, the film being led past the plates II, I! on the side of an aperture plate 23 away from the plates and passing over the guide rollers 24, 25 as it approaches and leaves the aperture plate. It will thus be seen that the speed of movement of the film I5 is accurately synchronized with the rotation of the refracting plates ll, l2 and the parts are made of such dimensions and so arranged that in the case of a 16 mm. projector,

as the film moves down the distance of one pic- A source of light '26 is indicated at the left of the figure, the diverging rays from this source of light passing through a converging or condenser lens 21 which efficiently transmits the.

light through the optical system. This lens brings the rays into a concentrated relation which is maintained preferably untilafter the rays have left the refracting plates! I, I2. After the rays have left the refracting plates H, l2, they pass through the objective lens 28 which focuses the light on a screen 29. I

In the construction shown in this figure, there is a shutter located between the condenser lens 21 and the aperture plate 23 for the purpose of cutting on the light rays when either of the refracting plates is in a change-over position. In the construction shown it has been found that this results in having the light for about 42% of the time. The shutter comprises a pair of plates 30 projecting laterally from the side of a gear II, the two plates being arranged parallel to each other a distance apart slightly greater than the opening of the aperture plate 23. The

gear 3| is driven by the gear it of the adjacent refracting plate II, and the widths of the plates 8| are such as to cover the aperture and cut off v the light for the desired period of time.

From the description just given it will be obvious that in the projector of Fig. 8, as the plate ll revolves from the vertical position the net displacement of the two plates will move down, synchronized with the movement of the film. For each 90' of rotation, the film advances one frame and the compensated net displacement rectifles the picture frame to a stationary image on the projection screen. An aperture plate It may also be provided between the objective lens 28 and screen 28, if desired, to cut off any rays outside the central picture.

A preferred form of shutter is shown in Figs. 9 and 10. In this construction there is a single shutter plate 35 lying in a plane perpendicular to the rays of light which originate at the lamp and are projected by the condenser lens. This shutter I! can be mounted on a shaft 32 which is an extension of the shaft carrying the main drive worm gear 20 so that its rotation can be accurately synchronized with the rotation of the refracting plates. As can be seen in Fig. 10, the peripheral portion of the shutter, which is the portion lying in the path of the light, consists of spaced blades ll, 34, there being four small blades 33 spaced apart a distance equal to their width, and a very much wider blade I4 spaced from the four narrow blades a greater distance. In the construction shown in Fig. 9, I prefer to revolve this shutter ll once for each movement of the picture frame. This means that the shutter revolves four times for each complete revolution of the retracting plates II, II. Since there are five blades I3, it altogether and a corresponding number of spaces between them, it follows that the light is interrupted with a frequency of five times per frame movement, so that if the film moves at the rate of 24 frames per second past a given point, these shutter blades interrupt the light 120 times a second. I find that this arrangement of blades produces the minimum amount of flicker. It may be pointed out that the large blade I on the periphery of the shutter is interrupting the light while one or the other of the refracting plates is revolving through any non-operating position or change-over, while the four small blades 38 are merely to balance up or equalize the intensity of the light during the time that the image appears on the screen with relation to the dark period to minimize the "fiicker.

If the invention is to be embodied in a camera for taking motion pictures, the object rays of light are displaced by means of the revolving refracting plates to conform with the moving film, andthere is no necessity for balancing up the intensity of the light by the small blades 33. The shutter arranges for the exposure of the film in regular timed succession and in proper relation to the operative and non-operative positions of the refracting plates. The principle of image displacement by optical refraction utilizing the in-. vention above described can, as above intimated, be used not only in motion picture projectors and motion picture cameras of standard or high speed persistence of vision is used to show the motion of a constantly moving object, whether such ob- Ject be shown directly or through a series of images in a film, on the one hand, or on the other, in the case of the moving picture camera the projecting of the image on the moving illm.

or television projectors. It is applicable wherever I claim:

1. In an optical system, means maintaining light rays in a concentrated relation, in combination with two efiective rotating planar refracting media adapted successively to cause displacement of the rays from the projecting means, and means rotating the media at uniform angular speed but at lag in angular relation to each other, whereby uniform linear displacement of the rays is obtained.

2. In an optical rectifier system, the combination of a plurality of refracting media each adapted to displace a ray of light in the same manner, said two media being adapted to rotate each about its own axis but at such relative angles that their displacements of the ray are in compensating phase, and obturating means synchronized to cut off the rays when either of the media is at an inoperative angle to the ray.

3. In an optical rectifier system transmitting a series of images of an object, or vice versa, where one is at a stationary location and the other at constantly changing location, the combination of two planar refracting media and means rotating them in the same direction with uniform angular speed, with the planes of one medium at a 90 angle to the other, whereby the displacement of light rays by one medium is compensated for by the other and uniform linear displacement results.

4. In an optical system for obtaining a stationary image from a moving one, or vice versa, the combination of two planar refracting media with means rotating them in the same direction and with uniform angular speed but with a 90 lag in the normals to their axes, whereby uniform linear displacement of the image received or projected is obtained.

5. In an optical system wherein uniform linear displacement of image is desired at one end of the system, the provision of two planar refracting media mounted in successive relation to the light path, in combination with means rotating them in the same direction about separate axes and with uniform angular speed but with a 90 lag in the normal axes of the media, and a shutter to obturate the light rays intermittently.

6. In a method of operating an optical refracting system, the rotation of two planar refracting media each about its own axis but in the same direction and with constant angular speed, holding their planar normals 90 apart, whereby the linear displacement of rays passing through the two media is made uniform.

7. In a method of operating an optical refracting system containing rotating planar re fracting means, the steps of presenting rays to a planar refracting medium while rotating same with constant angular speed and subsequently presenting the refracted rays to a planar refracting medium at an angle 90 removed from the angle of the first incident ray, whereby the net linear displacement-of the double passage of the rays is made uniform.

-8. In a motion picture projector, means advancing a film in non-intermittent or constant speed manner and two planar refracting media located successively in the path of the image rays, in combination with means giving uniform angular rotation in th same direction to the media sesame 5 with a 90 lag between the normal axes of the two media, whereby uniform linear dishlacemeut of image synchronizeciwith. the film movement is obtained.

9. In an optical rectifier system, the QOmbiZlQ." tier; of two optical flats whose inolices of reirac tion are in the order of 1.605 and which are located successively in the path of the light rays, and means rotating them at a uniform speed in the same angular direction but with their planar normals 90 apart, whereby the rays will. be cliverted from positions having uniform linear dis placement to a stationary location, or vice versa.

10. in an optical rectifier system having" film and. relying on persistence orvisiori, the com-= bination of two critical flats located successively in the path of the light rays, and means to give the normals of said. flats uniform angular rotation synchronized with the film movement, while maintaining the normals in ac relation to each. other, and shutter to ohturate the rays of light during change-over position.

'11. In an optical rectifier system relying on persistence of vision, a lens adapted to maintain. rays in concentratecl relation, and two optical flats of about 1.8% liiclices of refraction arranged to receive the rays successively from the lens, in combination with means rotatihgthe flats at untform angular speerl alcout ti: ir separate out with the planar normals maintained about 93 apart in corrirsensatirig relation to ratio displacement curves, whereby the linear displace merit of the rays from the second. will be uniform.

12. in an optical rectifier system relying on persistence of ViSiOlfl, two optical lists oi about 1.605 indices oi street-ion arranges to receive the rays successively i'rcii the lens, anti ro toting the flats at uniform angular speeci about their separate axes but with their planar normals maintaiheti about 9% apart in compensating? relation as to shoe ratio curve characteristics of linear displacement or" the rays, whereby the linear displacement of the rays emerging irom the-second. that will be uniform, in combination with a shutter actor-atlas any rays passing when one of the is at as luefifeetive angle.

13. In an optical rectifier system relying on the persistence of vision, two retracting plates having similar light displacement qualities and whosetotal cycle displacement equals the sum of the thickness of the two plates, in combination with in linear displacement of the rays is obtained.

14. in an optical rectifier system, two retracting plates having similar light displacement quali= ties, in combination with means rotating the plates on ares normal to the path of the light ray and with. the plates at such relative angles that the sums of the angles of incidence of the light rays at the two plates equals 90?, whereby the total cycle displacement of the light rays is independent of the index of refraction of the 26 plates,

iii. In an optical rectifier system, two retracting plates having similar light displacement qualities, in. combination with means rotatingthe plates on axes normal to the path or" the light rays and with the plates at such relative angles that the sums of the angles of incidence of the light rays at the two plates equals so", whereby the cycle displacement of the light rays is oh the thicm ess of the plates and independent of the index oi refraction of the plates.

, 16. in an critical rectifier system,-two retracting plates having similar light displacement qualities and whose total cycle displacemen equals the sum of the thickness or") the two plates, anal photographic film, in combination with means rotating the plates on axes parallel to the plane oi the film at uniform. angular unidirectional speed, the relative angles of the two plates being such that the sums of the angles of incidence a equal 90, and the glass in the plates having an index of refraction of about 1.605, whereby the intra-cycle displacement caused by said plates is meal-s uniformly linear and the cycle displacement of the rays is equal to the cyclic movement of the DAHD R.

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