US2437470A - Impulse recording optical system - Google Patents

Description

FIG- I {ii -iii 7 x9 mas -470 March 9, 1948. 2,437,470

- INVENTOR JOHN AMAURERJA WWW AGENT x, v 9 "ml 4 w March 9, 1948.

J. A. MAURER, JR 2,437,470 IMPULSE RECORDING OPTICAL SYSTEM Original Filed Aug. 2, 1940 3 Sheets-Sheet 2 FIG. l5

FIG. l2

uvmvm JOHN A. MA unsn, JR.

AGENT PatentedMar. 9, 1948 )1 UNITED STATES PATENT OFFICE IMPULSE macoanmqop'rrcar. SYSTEM John A. Maurer, In, New York, N. Y.', aslignor to J. A. Maurer, Inc., New York, N. Y., a corporation of New York Original application August 2, 1940, Serial No.

849,515. Divided and this application November 21, 1944, Serial No. 564,453

1 Claims. (01. 88-24) modulates a light beam in accordance with the.

electrical impulses to be recorded. The mirror oscillograph recording optical systems known heretofore, however, have the disadvantage that the light flux from the recording light source, such as the filament of an incandescent lamp, is not efiiciently utilized therein. This unfavorable condition is due to the fact that the aperture of the oscillograph mirror is the limiting aperture in the two co-ordinate planes of the known optical systems, and that it cannot be enlarged beyond a certain degree since the physical size of the mirror must be comparatively small in order to avoid distortions due to its mass. For a given light source, therefore. the amount of light flux reaching' the moving film is unduly limited in those optical systems, and this limitation makes itself particularly felt when filters are used at some position in the optical system,

for example, for selecting light rays of a certai wave length, or for other purposes.

Another drawback of the known mirror oscillograph recording" optical systems is that a portion of the light flux from the recording light source is not effectively prevented therein from falling on parts other than the oscillograph mirror, or on the structure housing the optical system. This portion of the light flux is to some extent reflected diflusely, thus forming stray light even though the surfaces on which it is incident may be black. Such stray light is objectionable because it may cause an additional-exposure of the moving film, which should be exposed only to light flux modulated by the oscillograph mirror.

,Itis, therefore, the primary object of the present invention to provide a mirror oscillograph recording optical system which is highly efficient as regards the utilization of the light flux from the recording light source.

Another vobject of the invention is the provision of such an optical system whose limiting aperture cam-in one oi its co-ordinate planes, be

of such an optical system which is particularly satisfactory as regards ease of manufacture and convenience of adjustment.

Another object of the invention is the provision of such an optical system which may be built with small physical size and at comparatively little cost.

Still other objects of. the invention include those which are hereinafter stated or apparent, or which are incidental to the invention.

In the optical system according to the invention, the oscillograph mirror is adapted to vibrate about a horizontal axis while the film moves past the recording point in a substantially verti cal direction, the recording point being the point at which the optical axis of the systemstrikes the film, The optical system also has means for forming a light spot of vertically graded light flux. Further means are provided in the optical system which effect an imagery of this light spot in such a manner that it is conjugate to the recording point in both the vertical and horizontal planes of the optical system. Otherwise, however, the imagery of the light spot is different in the two co-ordinate planes. In the vertical plane, the light spot is first imaged at a horizontal slit by imaging means acting in the vertical plane and then at the recording point by imaging means acting in only the vertical plane, the horizontal slit being placed between the oscillograph mirror and the recording point. In the horizontal plane, on the other hand, an intermediate image of the light spot is formed substantially on the mirror by first imaging means which act in only the horizontal plane. The intermediate image, in its turn, is imaged at a position beyond the recording point by second imaging means which act in only the horizontal plane, and re-imaged at the recording point by third imaging means which act in the horizontal 'plane. By virtue of this arrangement, the mirror macro mediate image. is formed substantially on the oscillograph mirror as has been explained hereinabove. Atthe same time, an image 01' the light source is formedsubstantially on the mirror by the actionof a condenser lens in the vertical plane. In this manner, substantially all the light fiux entering the optical system through the opening is, controlled by the oscillograph mirror whereby the formation or stray light is reduced to a, negligible amount.

In the ioregoing brief explanation of the state of the art and summary of the invention, and throughout the present specification, the term "co-ordinate planes designates two planes 'at right angles to each other whose line or intersection is the optical axis of the system. The

horizontal plane is the co-ordinate plane which contains the axis or .the oscillograph mirror and the slit, while the vertical plane is the coordinate plane at right angles to the horizontal plane. The plane of the slit, finally, is the plane which contains the slit, and is at right angles to both the vertical and horizontal planes.

In the present specification, the terms vertical and "horizontal" thus are not used in any absolute sense but. merely in order to distinguish between two planes, or directimis, at right anglesto one another, and choice between those terms has been determined solely by convenience in description and illustration.

The invention will be better understood when the following description is considered with the accompanying drawings of certain presently preferred embodiments thereof, and its scope will be pointed out in the appended claims.

In the drawing Fig. l is a diagrammatic perspective view of an optical system embodying the invention,

Fig, 2 is a diagrammatic longitudinal section in the vertical plane of the optical system shown in Fig. 1, the optical-axis being represented as a straight line and an oecillograph mirror as an aperture,

Fig. 3 is a corresponding section in the horizontal plane,

Fig.4isanelevationof apartoftheoptical system of Figs. 1 to 3,

Figs. 5 to 100 show in elevation modifications or the part shown in Fig. 4,

Fi 11 is a diagrammatic perspective view of a modification of the optical system shown in Figs. 1 to 3,

Fig. 12 is a perspective view of a modifica-v tion of apartshowninl'ig. 11,

Fig. 13 is a perspective view of a modification 1)! aanother part of the optical system oi Figs.

to l

Fig. 14 is a diagrammatic longitudinal section in the vertical plane of another modification of the optical system of Figs. 1 to 3, and

Figs. 15 and 16 are perspective views or modifications of two more parts of the optical system of Figs. lto8.

Referring first to Figs. '1 to 3, these figures show, by way of example, a variable area recording optical system which embodies the invention. The optical system has alight source such as the filament ll of an incandescent lamp H. The light fiux from lamp filament l0 uniiormly illuminates a triangular opening I! in a screen it so that a uniformly illuminated triangular light spot is formed at screen ll. The light beam defined by lamp filament l0 and opening I! proceeds through the optical system and is deflected by the mirror ll of an oscillograph gaivanometer (not shown) or similar de- Nice for translating electrical impulses into mechanical vibrations. It thus has a part which is incident from opening it upon mirror I1, and a part which is reflected from mirror l1 towards the recording point 21. Recording point 21 is the point at which the optical axis or the system strikes the film 23, and film 23 moves past recording point 21 in a substantially vertical direction as indicated by the arrow 2|.

More particularly, opening i3 is an isosceles triangle whose base extends horizontally, and mirror I1 is adapted to vibrate about an axis I8l8 which likewise extends horizontally. Furthermore, a horizontal slit 2! is formed in a screen 22 which is placed between mirror I! and recording point 21.

A spherical condenser lens I2 is placed between lamp H and screen it, and a cylindrical lens ll which has its cylinder axis vertical, is placed between screen M and mirror H. In front of mirror il there is-placed asecond spherical lens it which acts on the reflected as well as the incident part of the light beam proceeding through the optical system. A second cylindrical lens 42 which also has its cylinder axis vertical, is placed between mirror l1 and screen 22, while between screen 22 and recording point 21 there is placed a third spherical lens 43. Between spherical lens 43 and recording point 21, finally, there is placed a third cylindrical lens ll which has its cylinder axis horizontal.

These six imaging means have focal lengths relative to the other parts 0! the optical system as follows (see Figs. 2 and 3) Spherical lens l2 has one of its conjugate feel at lamp filament l0, and the other substantially at mirror l1, that is, either on mirror H or at a position close thereto. Cylindrical lens II has one of its conjugate foci at opening II, and the other substantially at mirror ll so that an intermediate image of opening I3 is formed substantially on mirror [1. Spherical lens I! has one of its conjugate foci at opening II, and the other at slit 2|. Cylindrical lens 42 has one of its coniugate tool at the intermediate image of opening it, and the other at a position A beyond recording point 21. Spherical lens 43 has one of its con- Jugate tool at position A, and the other at recording point 21. Cylindrical lens 4 I. finally, has one of its conjugate foci at slit 2i, and the other at recording point 21.

By virtue of the arrangement described hereinabove of its various parts, the following imagery is performed in the optical system of Figs. 1 to 3:

In the vertical plane (Fig. 2), spherical len I! forms an image of the uniforml illuminated opening II in the plane of the horizontal slit 2|. This image of opening It moves vertically across slit 2! when mirror i1 vibrates about the horizontal axis 12-". As much of slit 2| as is illuminated by the image of opening II, is imaged at re- Q ror I! with light and also aiding in the uniform illumination of opening it by lamp filament III.

In the horizontal plane (Fig. 3), cylindrical lens |5 forms substantially on mirror 11 the intermediate image of opening l3, and an image of the intermediate image is formed by cylindrical lens 42 at position A. The image at position A, in its I turn, is imaged at recording point 21 by spherical lens 43. By virtue of this successive imagery of opening I! in the horizontal plane, the horizontal line image at recording point 21 has, in addition to its sharp and distinct horizontal boundaries, also sharply defined ends.

Lenses l2 and I9 are spherical and hence have powerin the horizontal as well as in the vertical plane. But their actions in the horizontal plane can be disregarded for the following reasons:

On account of its position and relative focal I length, spherical lens |2 tends to image lamp filament 10 substantially on mirror |1 also in the horizontal plane. The action, however, of cylindrical lens l5 interferes with this imagery to such an extent that it becomes immaterial for attaining the objects of the present invention. On the other hand, the power of spherical lens IS in the horizontal plane has no effect uponthe actions of cylindrical lenses l5 and 42 on account of the proximity of spherical lens I9 to mirror H which is, in the horizontal plane, substantially at a com-' mon focus of cylindrical lenses l5 and 42. No actions, therefore, of spherical lenses l2 and I9 have been indicated in Fig. 3.

Lens 43 is likewise spherical and hence has power in the vertical as well as in the horizontal plane. But its action in the vertical plane is immaterial because, in this plane, its power is small compared to the power of cylindrical lens 41-. No action, therefore, of spherical lens 43 has been indicated in Fig.2.

planes. In the vertical plane, horizontal slit 2| is, with respect to spherical lens I9, conjugate to a horizontal line through opening It, for. example, the broken line a-a shown in Fig. 4. Since, furthermore, recording point 21 is in the vertical plane conjugate to slit 2| with respect to cylindrical lens 4|, it is also conjugate to line a-a.. The line image at recording point 21 hence is an image of line a-a as far as its vertical extension. or width, is concerned, and it is, according to a well known property of conjugates, made up of the light flux emanating from line H. Moreover. this light flux is brought to a focus at recording point 21 also in the horizontal plane,

namely- -as has been explained hereinabove-by the successive actions of cylindrical lenses I5 and 42 and of spherical lens 43. The line image at recording point 21 hence is an image of line a--a also as far'as its horizontal extension, or length,

6 horizontal line is long-as is, for example, the broken line c-c in Fig. 4.

The particular horizontal line through opening i3 to which recording point 21 is conjugate, is determined by the-angle of inclination of mirror |1. Normally, mirror I1 is adjusted so that at its rest position, that is, when no electrical impulses are applied to the oscillograph galvanometer on which it is mounted, recording point 21 is conjugate to line a-a, which line passes through opening it halfway between its tip and its base. vWhen then theeiectrical impulses to be recorded are applied in known manner to the oscillograph galvanometer, mirror |1 vibrates in accordance therewith about the horizontal axis |8-|8 and in such a manner that, when the amplitude of its vibration is a maximum, recording point 21 is conjugate to line 12-17 at the one extreme of its motion and to the line c-c at the other extreme thereof. The length of the line image at recording point 21 hence varies in accordance with the vibration of mirror l1 and, therefore, the electrical impulses to be recorded. A variable area track 28 thus is produced on film 23 as it moves past recording point 21.

As has been explained hereinabove. recording point 21 is conjugate to opening l3 or, more exactly, to a horizontal line through opening IS, in the horizontal as well as the vertical plane of the optical system of Figs. 1 to 3. The imagery, however, which results in this condition, is different in the two co-ordinate planes. In the vertical plane, opening I3 is imaged at slit 2| by spherical lens I 9 which acts in the vertical plane, and silt 2| is imaged at recording point 21 by cylindrical lens 4| which acts inch-1y the vertic'al plane. Since spherical lens I9 is placed in front of mirror I1 and images opening l3 immediately at slit 2|, the light flux from opening zontal axis |8--|8, thereby selecting, in co-op-- eration with the horizontal slit 2|, horizontal lines through opening l3 which become conjugate to recording point 21..

In the horizontal plane, onthe other hand, an intermediate image of opening I! is formed substantially on mirror H by cylindrical lens l5, and this intermediate image is imaged at position A by cylindrical lens 42 and re-imaged at recording point 21 by spherical lens 43 which acts in the horizontal plane. 'Since cylindrical lenses I5 and 42 act in only the horizontal plane, mirror I1 is substantially at a common focus of two imaging means which act in only the plane containing its axis of vibration |8|8. For any given angle ofinclination of mirror l1, therefore, the amount of light flux from opening i3 which is acted upon by cylindrical lens 42, is limited by the aperture of this lens rather than the aperture of mirror |1. Moreover, since the light flux acted upon by cylindrical lens 42 is brought to a focus at posi-. tion A and thence-focussed at recording point 21 by the action of spherical lens 43, the limiting aperture in the horizontal plane is not the actual aperture of cylindrical lens 42, but its apparent aperture'as seen from recording point 21. The apparent aperture of cylindrical lens 42, however, may-in view of the action of spherical lens 43-be made at least twice as large as its actual aperture which, in its turn, may be made as much as five times'as large as the aperture which it is practical to give to mirror l1. The limiting ailerture in the horizontal plane of the optical system of Figs. 1 to 3 hence can easily be made at least ten times larger than the aperture of mirror 11.

The result thus obtained by means or the novel imagery embodied, by way of example, in the mirror oscillograph recording optical system of Figs. 1 to 8 represents a marked advance over the prior art. In the known optical systems, the light flux from the entrance position corresponding to opening it is diffused at ,the oscillograph mirror in the two co-ordinate planes so that the mirror aperture is the limiting aperture of the optical systems also in the co-ordinate plane which contains the mirror axis. Since the physical size of the oscillognaph mirror must be comparatively small in order to avoid distortions due to its mass, the above condition has been a serious obstacle to an eificient utilization of the light fiux in the prior art optical systems. The advantage gained in this respect by the imagery according to the invention is considerable because, as is well known to those skilled in the art, the eillciency with which the light fiux from a given light source is utilized in an optical system, is approximately proportional to the product of the limiting apertures in the two co-ordinate planes of the optical system.

Another advantage of having, in the optical system of Figs. 1 to 3, mirror I1 substantially at a common focus of two imaging means which act in only the horizontal plane, is that small deviations of mirror I! about a vertical axis have a negligible efiect on the imagery in the horizontal plane. Mirror I! need therefore be accurately adJusted only about the horizontal axis l8--l8. This greatly increases the ease of adjustment of the optical system, and is particularly important when it is necessary to replace the oscillograph gaivanometer on which mirror I1 is mounted.

A further advantage of the imagery performed 1 in the optical system of Figs. 1 to 3 resides in the fact that there is formed substantially on mirror I! an image of lamp filament It by the action of spherical lens I2 in the vertical plane, and simultaneously the intermediate image of opening I 3 by the action oi. cylindrical lens I! in the horizontal plane. It thus is possible so to control the light flux entering the optical system through opening II that it is all incident within the working aperture of mirror II. This result is best obtained when the focal length of spherical lens I! and the position of lamp I i are chosen so that the image of lamp filament l has a vertical dimension no larger than that of mirror 11, and when the focal length of cylindrical lens l5 and the position of screen H are chosen so that the largest horizontal dimension of the intermediate image is no larger than the horizontal dimension of mirror ll. If these conditions are fulfilled, all the light flux passing through opening i3 is subject to control by mirror i1, whereby the formation of stray light in the optical system is reduced to a negligible amount.

The employment, finally, of cylindrical lens ll in the portion of the optical system between .screen 22 and recording point 21 has certain inherent advantages: Cylindrical lens I may have a short focal length so that the optical system may be built with small physical size. Moreover, a cylindrical lens of short focal length is less expensive than a spherical lens, or lens system, well enough corrected to form, over the same distance, an equally sharp line image. The optical system of Figs. 1 to 3 may hence be built with greater compactness and at less cost than the 8 mirror oscillograph recording optical systems known heretofore.

The optical system shown in Figs. 1 to 8 as an embodiment of the imagery according to the invention may be modified, without affecting the basic principles or its operation, as follows:

(1) Opening II in screen It is shown in Figs. 1 and 4, and has been described hereinabove, as being an isosceles triangle whose base extends horizontally. However, any other opening whose horizontal extension varies in a vertical direction, may be substituted for opening I! to pro- 'duce a variable area track on film 22. For example, the opening in screen it may be a rightangled triangle with one of the sides adjacent to the right angle extending horizontally as is the opening 20 shown in Fig. 5, or there may one or more sawtooth projections extend into it as they do into openings ii and 22 shown in Figs. 6 and 7, respectively,

However, in the case of opening it the line image at recording point 21 is a horizontal line of light whose length varies at both its ends so that the variable area track produced on film 28 is symmetrical as is the track 28 shown in Fla. 1. With opening 30, on the other hand. the line image is a horizontal line of light whose length varies at only one of its ends so that the variable area track produced on film 23 is of the unilateral type in this case. With opening 3i, furthermore, two horizontal lines of light, each I varying in length at only one of its ends, are

formed at recording point 21 so that two unilateral variable area tracks are produced on film 23. With opening 32, finally, there are formed at recording point 21 three horizontal lines of light, each varying in length at both its ends, so that three symmetrical variable area tracks are simultaneously produced on film 23.

Tracks of the type known as push-pull" may also be produced on fihn 23 by combining in screen it two openings of the kind described hereinabove. For example, the two openings may be two isosceles triangles 33a and 23b arranged as shown in Fig. 8, or two right-angled triangles 34a and 84b arranged as shown in Fig. 9. With openings 33a and 23b, a class B pushpull symmetrical variable area track is produced, and with openings 34a and 341: a class B pushpull unilateral variable area track. Class A push-pull variable area tracks may be produced, for example, by providing in screen it two rightangled triangles adjacent to each other along a common side dd so that together they form a parallelogram 35, as shown in Fig. 10. In a preferred arrangement for the production of class A push-pull variable area tracks, however, a portion Ila of screen It separates the two rightangled triangles 35a and 35b, as shown in Fig. 10a.

As in Fig. 4, the broken line H indicates also in Figs. 5 to 10a the horizontal line through the opening, or openings, in screen it which is normally conjugate to recording point 21 when mirror I1 is at rest.

The openings of vertically varying horizontal extension shown in Figs. 4 to 10a, and described hereinabove, all are bounded by one or more straight 'edges which are inclined with respect to the horizontal plane of the optical system. Since, furthermore, the variation in length of the horizontal line. or lines, of light at recording point 21 is eiiected only by those inclined edges, the lower portion of screen it may be omitted-1r desired, as indicated in Fig. 5 by the broken line e--e, for example.

When'any of-the openings, or pairsof open a. uniformly illuminated light spotwhose horizontal extension varies in a vertical direction,

' or a pair of such light spots. The light flux emanating from this light spot, or light spots,

' hence is vertically graded.

Light spots of vertically graded light flux, however, may also have a uniform horizontal extension and a vertically varying illumination. Means for forming a light spot of this type are well known in the art. They may consist, for

example, ofthe means-disclosed by G. L. Dimmick in his U. S. specifications 2,095,317 and 2,095,318. These means include, an opening 33 which is a rectangle with one of its sides extend ing vertically, and a penumbra stop 31. as shown in Fig. 11. But the illumination of rectangular opening 33 may also be varied vertically by astermediate image of the opening screen i4 substantially on mirror I! and, simultaneously, images the intermediate image at position A.

The angle at which the light beam is incident upon mirror. I 1, may be made sufficiently small by considerably lengthening the optical system mechanically. However, this end may be accom-' plished in a more convenient way which, at the sametime, provides for a very-compact mechanical design of the optical system and which is shown, by way of example. inFig. 14. It consists of placing a reflecting prism I0 between screen l4 and mirror l'l whereby the light beam is folded so that it is incidentv upon mirror I! at a small angle. and cylindrical-lens H is traversed by both the incident and reflected parts or the light beam. In place of prism 10 there may be employed other suitable beam folding means such a mirrors, or the like.

(4) Whenever it is desired to employ for the imagery inthe horizontal .plane oi the optical system two lenses instead of the single cylindrical sociating with opening 36 a vertically graded light shading member 33 such as is disclosed, tor example, in myU. S. specification 1,955,386'and shown in Fig. 12 of this speciflcatio When these or other suitable means for forming a light spot of uniform horizontal extenslon'and vertically varying illumination are substituted for opening I; in the optical system of Figs. 1 to 3-as shown by way of example in Fig. l1-the line image at recording point 21 is a horizontal line of light whose length is constant. but whose illumination varies in "accordanoe with the vibration of mirror i1. Hence, a

variable density track 38 is now produced on film 23 as it moves past recording point 21.

(2) It has been'explained hereinabove that, while spherical lens I!) has power in both the vertical and horizontal planes, its action in the horizontal plane can be disregarded. Spherical lens l9 may therefore be replaced by a cylindrical lens 66 which has its cylinder axis horizontal and hence acts in only the vertical plane. Like spherical lens I9, cylindrical lens 33 has one of its conjugate foci at the opening in screen l4, and the other at slit 2 l.- Cylindrical lens 66 may,

furthermore, have the same position as spherical lens l9, in which position it is shown in F18. 13. But since it acts in only the vertical plane, it may also have any other position between screens l4 and 22 which is consistent with its function to image the opening in screen H in the plane of slit 2|. Spherical lens IS, on the other hand, should be placed close to mirror H, as shown in Figs. 1 and 11, lest it interfere with the imagery in the horizontal plane.

(3) When the light 'beam defined by lamp filament l0 and the opening in screen i 4 is incident upon mirror I! at a sufficiently small angle, a single cylindrical lens H may be substituted for the two cylindrical lenses I 5 and 42. Like cylindrical lenses Hand 42, cylindrical lens H has its cylinder axis VerticaL-and it is placed so as to be traversed by the reflected aswell as the incident part of the light beam proceeding through the optical system. The relative focal length of cylindrical lens H is so chosen that the opening in In this manner cylindrical lens H forms thein-J lens 1|, cylindrical lens 42 may be replaced by a spherical lens 15 which, however, must be placed adjacent to screen 22 as shown in Fig. 15. When sphericallens i3 is so placed. its action in the vertical plane is barred by screen 22 so that it acts in only the horizontal plane. Spherical lens 13 may be placed on either side of screen 22, but must be close thereto in both cases lest it interfere with the imagery in the vertical plane.

Like cylindrical lens 42, spherical lens 15 has one of its conjugate loci at thelintermediate image of the opening in screen l4, afid the other at position A. The substitution of spherical lens 15 for cylindrical lens 42 has theadvantage that a spherical lens at screen 22 is cheaper, and easier to "adjust, than a cylindrical lens. The use of cylindrical lens 42, on the other hand, has the advantage that its position can be chosen independently of the position of screen 22, whereby the design of the optical system is facilitated,

(5) It has beenpointed out hereinabove that, while spherical lens 43 has power in both the vertical and horizontal planes, its action in the vertical plane is immaterial. Spherical lens 43 may therefore be replaced by a cylindrical lens 44, shown in Fig. 16, which has its cylinder axis vertical and hence acts in only the horizontal plane. Like spherical lens 43, cylindrical lens 44 is placed between screen 22 and recording point 21 and has one of its conjugate fool at position A, and the other at recording point 21. The efl'ect of cylindrical lens 44 upon the imagery in the horizontal plane thus is the same as that of spherical lens 43.

(6) Whenever the optical system of Figs. 1 to 3 is employed for producing a variable area track on film 23, it is desirable that the boundary, or boundaries, between the opaque and transparent portions of which this track consists, be sharp and well defined. The horizontal line, or lines, of light formed at recording point 21 must, therefore, be sharply defined atits. or their. ends. For that reason, cylindrical lenses I5 and 42, and spherical lens 43. should preferably be well corrected for spherical and chromatic aberration, and for coma: This applies also to their substitutes, namely, cylindrical lens ll, spherical lens 15, and cylindrical lens 44. However, if any or all of the above lenses are not so well corrected,

the beneficial results accruing from their employment in accordance with the present invention may still be had, although to a lesser extent than if they are well corrected.

(7) If it is desired to employ the optical system of Figs. 1 to 3 for recording sound in accordance with the method generally known as "noiseless recording," the well known ground noise reduction systems may be used in conjunction therewith, as will easily be understood by those skilled in the art.

What is claimed is:

1. In an optical system, the combination of means for forming a light spot of vertically graded light fiux; a mirror adapted to vibrate about a horizontal axis; means forming a horizontal slit; a recording point past-which a film may move in a substantially vertical direction; first imaging means placed between said light spot and said mirror, and having first and second conjugate foci; second imaging means placed between said mirror and said slit forming means, and having third and fourth conjugate foci; third imaging means placed between said slit forming means and said recording point.,and having fifth and sixth conjugate foci; fourth imaging means placed in front of said mirror, and having seventh and eighth conjugate foci; and fifth imaging means placed between said third imaging means and said recording point, and having ninth and tenth conjugate fool: said first imaging means acting in only the horizontal plane and having said first focus at said light spot, and said second focus substantially at said mirror so that an intermediate image of said light spot is formed substantially on said mirror: said second imaging means acting in only the horizontal plane and having said third focus at said intermediate image. and said fourth focus at a position beyond said recording point; said third imaging means acting in the horizontal plane and having said fifth focus at said position, and said sixth focus at said recording point; said fourth imaging means acting in the vertical plane and having said seventh focus at said light spot, and said eighth focus at said slit; and said fifth imaging means acting in only the vertical plane and having said ninth focus at said slit, and said tenth focus at said recording'point.

2. The combination defined in claim 1 wherein said third imaging means is a spherical lens.

8. The combination defined in claim 1 wherein said second imaging means is a cylindrical lens having its cylinder axis vertical, and said third imaging means is a spherical lens.

4. The combination defined in claim 1 wherein said first and second imaging means are each a cylindrical lens having its cylinder axis vertical, and said third imaging means is a spherical lens.

6. The combination defined in claim 1 wherein said third imaging means is a cylindrical lens having its cylinder axis vertical.

6. The combination defined in claim 1 wherein said first and second imaging means are each a cylindrical lens having its cylinder axis vertical, said third and fourth imaging means are'each a spherical lens, and said fifth imaging means is a 12 cylindrical lens having its cylinder axis horizontal.

7. In an optical system, the combination of a light source: a screen with an opening whose horizontal extension varies in a vertical direction. said opening being uniformly illuminated by said light source; a mirror adapted to vibrate about a horizontal axis; means forming a horizontal slit; a recording point past which a film may move in a substantially vertical direction; a first spherical lens placed between said light source and said screen, and having first and second conjugate foci; a first cylindrical lens placed between said screen and said mirror, and having third and fourth conjugate foci; a second cylindrical lens placed between said mirror and said slit forming means, and having fifth and sixth conJugate foci; a second spherical lens placed between said slit forming means and said recording point, and having seventh and eighth conjugate foci; a third spherical lens placed in front of said mirror, and having ninth and tenth conjugate foci; and a third cylindrical lens placed between said second spherical lens and said recording point, and having eleventh and twelfth conjugate foci: said first spherical lens having said first focus at said light source, and said second focus substantially at said mirror; said first cylindrical lens having its cylinder-axis vertical and having said third focus at said opening, and said fourth focus substantially at said mirror so that an intermediate image of said opening is formed substantially on said mirror; said second cylindrical lens having its cylinder axis vertical and having said fifth focus at said intermediate image, and said sixth focus at a position beyond said recording point; said second spherical lens having said seventh focus at said position, and said eighth focus at said recording point; saidthircl spherical lens 2 having said ninth focus at said opening, and said tenth focus at said slit; and said third cylindrical lens having its cylinder axis horizontal and having said eleventh focus at said slit, and said twelfth focus at said recording p int.

JOHN A. MAURER, Ja.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS

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