US2218498A

US2218498A - Telecine system

Info

Publication number: US2218498A
Application number: US174122A
Authority: US
Inventors: Bunger Walter; Kosche Erich
Original assignee: FIRM OF FERNSEH AG
Current assignee: FIRM OF FERNSEH AG
Priority date: 1936-11-12
Filing date: 1937-11-11
Publication date: 1940-10-15
Anticipated expiration: 1957-10-15
Also published as: FR829035A; US2265264A; BE424562A; CH202379A; GB505574A; NL60010C

Description

Oct. 15, 1940.

' w. BUNGER ET AL TELECINE SYSTEM Filed Nov. 11, 1937 2 Sheets-Sheet l INV NT (E OR;

I S/ 31 ATTORNE s.

Oct. 15, w BUNG R ET AL TELECINE SYSTEM Filed Nov. 11,' 1957 2 Sheets-Sheet 2 7 INV NTOR 0 K i Z5 B Y W WQTTORNEYS.

Patented ct.,15, 1940 TELECINE SYSTEM Walter Biinger and Erich Kosche, Berlin-Zehlen- 'dorf, Germany, assignors to the firm ofFernseh Aktiengesellschaft, Zehlendorf, near Berlin,

Germany Application November 11, 1937, Serial No. 174,122 a In Germany November 12, 1936 v Claims.

This invention relates to a method of and to devices for scanning films by means ofcathode ray tubes particularly of the dissector type. While standard sound film projectors are operated with 5 24 or 25 frames per second, it is desirable to use a higher field frequency in television in order to avoid flicker. This increasein the rate of scanning is not difiicult when a mechanical scanner is used. There are, however, great difficulties when aninterlaced scanning method is used, operating on a purely electrical principle.

There are several general possibilities of scanning; it is possible to reproduce the images on the photoelectric cathode so that they have no motion relative to the cathode, and to scan these pictures electrically in the usual manner. This method, however, requires a complicated projectionapparatus in the manner of the Mechan- Projector, as the time for changing from one picture to the next one should not be longer than about 5% of the time in which the complete image is scanned. l

Another method of scanning uses a continuously moving film and the movement of the film is compensated by the electric movement, for example by using a dissector-type tube with a fixed scanning aperture. Such a method requires three deflection frequencies, namely the transverse or high scanning frequency, the field frequency, for example 50 cycles per second, and a frequency equal to half the field frequency in a single interlace; usually called the repetition frequency. v

In a third method the image moving across the photoelectric cathode with uniform speed is scanned by a ray moving in the opposite direction in order to produce the necessary rate of scanning. If, for example, 25 frames per second are on the film and if the scanning ray is moved with a frequency of 25 cycles per second against the movement of the image, each frame is scanned twice. This method, however, has the drawback that the amplitude of the repetition frequency must be kept very nearly constant in order to obtain a correct interlace. These difficulties are discussed in detail in the following example:

The first frame of the film is scanned during the first part of the deflection period, that is, during the first second. The scanning of the second picture follows without interrupting the scanning deflection. vIf the amplitude of the deflection is not exactly equal to the height of the picture frame for a fraction of the width of a line the contents of lines lying adjacent one another on the reception side will not correspond, but lines will be adjacent which in reality are lying far apart. This happens because the repetition period of second is exactly divided in half even in case the two pictures are not scanned down to thebottom. Fig. 1 shows in heavy lines the two frames at andb. The contents of the two pictures are, an oblique line ,c. It may beassumed that the deflection amplitude is somewhat too small and that the first image is scanned only up to the line d' and the second image up; to the line e. On the reception side two images are produced whichdo not correspond exactly. The first imageshows the line 0, but the second image contains first the upper part of the first image and then adds the contents of' the second image. This results in a loss of detail, as shown in Fig.2.

According to the invention these difficulties are overcome by using the sameuscanning frequency on the transmitting side ason the reception side, that is, the scanning frequency is the field frequency and not therepetition frequency; This is achieved by projecting onto the light-sensitive layer n pictures, which are laterally displaced for 1/11 height of a frame by an optical device, and of which only one is used for scanning by interposition of a shutter device. The electrical scanning has an amplitude corresponding to 1/12 height of the frame while the frequency is equal to n times the repetition frequency. This method has the advantage that the requirements forthe electricallrelaxation generatorwlth regard to the exactness of the amplitude are lower because-the exactness of the interlace depends only on optical and mechanical adjustments. This optical adjustment is much easier to carry out than the electrical control. Besides it is possible to use a continuously moving film even in case subsequent frames are scanned a different number of times.

' The invention possesses numerous other objects and features of advantage, some of' which together with the foregoing, will be set forth in the following description" of specific apparatus embodying and utilizing our novel method. is, therefore, to be understood that our method is applicable to other apparatus and that we do not limit ourselves in any way to the appaof the problem to the solution of which this invention is directed;

Figs. 3 and 4 are schematic showings of the elements of a projection system containing a double prism and a rotating shutter;

Fig. 5 shows the shutter disc in front View;

Fig. 6 is a showing of a particularly useful arrangement containing as television analyzer a dissector tubeand representing the lateral displacement of the light rays;

Fig. '7 shows another form of the shutter disc;

Fig. 8 indicates the scanning principle; and

Fig. 9 shows an arrangement in which alternating frames are scanned a different number of times.

The film l of Figs. 3 and l moves continuously in the direction of the arrow through the gate 2 and is reproduced on the light-sensitive layer 3' of the analyzer 4. A double prism 6 is arranged behind an objective 5 dividing the frame picture into two laterally displaced images on the photoelectric cathode. A shutter disc I is rotated in front of the double prism and exposes alternatively one or the other prism. It is assumed that a film with 25 frames per second is used for a transmission with 50 fields per second of 200 lines each. Fig. 3 shows the position of a frame at the beginning and at the end of second, and Fig. 4 shows the position of the next frame at the beginning and at the end of the following second. The frame positioned in the gate at the beginning of the scanning movement is represented by the arrow 8. The arrow 9 shows the image of the frame. During 4 second the frame is moving into position l0 so that the'image is moving into position I l. During the same time the scanning ray is moving from position l2 into position l3 so that it is moving in a direction opposite that of the image of the frame. During this whole period the shutter 1 has exposed the upper prism 6. As soon as the scanningray reaches position [3 and returns, the shutter disc 1 exposes the lower prism and covers the upper prism. The following part of the movement is represented in Fig. 4. The image of the next frame I4 is indicated by arrow l5 and is scanned by ray [2 while it is moving into the position l6 during second. At the end of the stroke the next frame has reached position I! in the gate 2. This frame is scanned a second time in the same manner as the frame indicated by the arrow 8,.so that each frame is scanned twice. If an odd-line interlace is used, the two images must be displaced for exactly onehalf of the frame height; if an even-line interlace is used, the displacement must be equal to one-half the height of a frame plus one-half of the width of a line. The exact adjustment of the images is produced by an adjustment of one or both prisms. The whole prism arrangement or only one of the prisms is mounted on an adjustment device in order to permit exact positioning. The relaxation oscillator frequencies remain unchanged and may have an integral or non-integral ratio to one another.

The shutter disc is represented in Fig. 5. The double prism 6 is indicated as a rectangle of which only one-half is exposed by the slots l8 and I9 alternatively. The circumference of the disc is dependent on the fact that the change from one prism to the next one shall not take a longer time than the return movement of the cathode ray, that is, 5 to 10% of the scanning period. Half the circumference of the circle 2! must therefore be at least 10 times as long as the distance 22. The disc is rotated in the present case at 1500 revolutions per minute.

Instead of the prism 6 of Figs. 3 and 4, an optical arrangement, for instance a reflecting prism or a mirror arrangement, can be used for producing not only an overlapping of the images but also a lateral displacement or shifting of the light rays. This is of particular importance in case a dissector-type tube is used containing a fixed anode finger situated on the side of the photoelectric cathode directed toward the film. In this case the lateral displacement of the rays is used to avoid an interference of the electrode system with the light rays.

An embodiment of this kind is represented in Fig. 6. The image of the frame is split up by a double prism 23, producing a lateral shifting of the light rays. The prism has the general form of a plane-parallel prism. The prism is adjustably mounted and both parts of the prism can be moved relatively to one another so that the images produced on the photoelectric cathode can be adjusted exactly for the fraction of a line width. Such a prism arrangement is disclosed and claimed in our copending application Serial No. 189,010, filed February 5, 1938. The electrode system 24 of the dissector tube 26 is situated perpendicularly to the plane of the drawing outside of the path of the light rays.

In order to obtain transmission free from distortion it is necessary to maintain correct phasing in addition to exact synchronism between film movement, shutter disc movement and electric scanning. The synchronism between the film and the shutter disc can be obtained by a mechanical drive common to both devices or by separate driving means fed from the same mains. The phasing is obtained by an adjusting device 2'! arranged between the motor 30 of the disc and the driving mechanism 3| of the film. In order to adjust the phase of the relaxation oscillator 29 in relation to the film drive, an adjusting device 28 is provided. The adjusting device may consist for instance of a motor, the stator of which is adjustable. The oscillator 29 is fed from the same mains as the motor.

The film frame may be reproduced on the photo-cathode with a relation of 1:1 or preferably on an enlarged scale. Instead of using the rotating shutter it is also possible to use a movable prism changing its position for each of a second. It is also possible to use a movable mirror or a rotating ring prism.

Instead of covering the prisms by the shutter it is preferable to cover the film by a shutter moving closely adjacent to the film gate or in the plane of an intermediate optical image of the film frame. Such a device is represented in Figs. '7 and 8. It is assumed that, in Fig. 8, the scanning ray 45 is scanning line 46. In order to obtain only one of the pictures on this particular point of the light-sensitive layer, a part 4'! of the frame is covered by the shutter 38 so that the shaded parts of the overlapping pictures represented by

arrows

43 and 44 are not reproduced on the photoelectric layer. Each sector 39 of the shutter disc 38, in Fig. '7, must move across the gate during the time of a picture repetition, so that the relation between the scanned line and the covered part of the frame is maintained.

The cone-shaped form of the shutter disc 38 represented in Fig. '7 has the advantages that the device can more easily be arranged nearer the film gate, that the movement of the single sectors 39 is more easily kept parallel to the moveaarsncs ment. ofthe and thatthe sectors 39..have approximately rectangular form-even-when the disc has a small diameter. Instead 'ofthe disc 38 a spiral shutter maybe used coveringalways the part of the picture which is not being scanned. The optical arrangement corresponds otherwise to that of the foregoing figures, having the source of light 31, a condenser lens 36,'the mm 35, the objective 4!], the prism arrangement M and thephotoelectric cathode 42.

The arrangement of the shutter closely adjacent the gate is preferable because it is possible to use a disc of smaller diameter in comparison with the arrangement of Figs. 3 and 4, on account of the small size of the film frames. The

number of revolutions of the disc can be kept very low when the number of sectors '39 is increased. This method of scanning isnct limited to the field frequencies and repetition frequencies above mentioned, but can be used, for instance, in connection with 241 frames onthe'film and a field fre-- quency of 60. Anexample of this type is described in connection with Fig. 9.

During second the'film moves for of the height of the frame. In order toscan a complete picture field, the scanning movement must be opposite to the movement of the film and equal to of the height of the image. The scanning takes place with a frequency of 60 cycles per second, and the scanning amplitude equals the height of the image. In order to scan all frames of the film, each alternate frame is scanned three times and the frames in between two times. The movement of the film is accounted for by an optical system in the following manner. The first frame of the fllrnmay have the position of the arrow IBM. Its image appears at arrow Ill when the ratio of reproduction is 1:1. The image is moved downwardly by means of a prism IZI from the situation Ill so that the point of the arrow (the edge of the image) is situated on the line Hi6,

that is, at the place where the scanning movement represented by line I2 is starting. The shutter disc I has such a position that the light traversing the objective 5 can pass through the prism l2! only'during the first 4 second while all other prisms are covered. The prism shifts the image downwardly for of its height. The

scanning movement reaches the position I I3 at the end of the first second. The film frame moves into position I02 when the scanning movement is making the return stroke. During the next ,4 second, the image is produced without the use of a prism through the central part of the arrangement. The image is represented by arrow H2. At the end of the second second, prism It? acts to move image H3 upwardly for of the height of the image. .At the end of the third 4 second, thenext frame of the film. is reproduced, having reached the position I04. The first frame is represented by the dotted line NM. The image lid of the second frame is moved downwardly by prism [24 for /5 of the height and scanned during the fourth second. During the fifth M second the second frame, having first the position I 95, is scanned again. Its image H5 is moved upwardly by prism E25 for of the height of the image. After the fifth 4 second, the third frame is scanned in the same manner as frame MI.

The film gate has a height of .the height of the frame. Instead of the prisms represented in Fig. 9, it is preferable to usean arrangement of prisms according to Fig. 6. These prisms have the advantage of producing less distortion. In-

stead of the disc 1 a shutter, accordingto Fig. 7, may be used. The method has the advantage that the film is moving continuously past the window so that the necessity of a swiftintermediate movement is avoided.

We claim:

1. In combination, a cathode ray device comprising an envelope having a photoelectric cathode disposed therein at one end and a pencillikev anode disposed therein at an opposite end,

and means external to said envelope for creating an optical image and directing the entire optical image to said cathode along a path to one side of said pencil-like anode, whereby said anode will not cast a shadow on said cathode.

2. In combination, a cathode ray device comprising an envelope having a photoelectric cathode and a pencil-like anode, both located on the longitudinal axis of said envelope, means external to said device but located on said axis in line with said anode and said cathode for producing an optical image, and a prism located intermediate said optical image producing means and said anode to intercept an optical image from said optical image producing means and deflect the entire intercepted image around said anode onto said cathode, whereby said anode will not cast a shadow on said cathode.

'3. In combination, a cathode ray device comprising an envelope having a screen at one end and a pencil-like electrode at the other end, means for directing a beam of light in line with said electrode and said screen and means for bending said beam about said electrode to preclude casting of a shadow of said electrode on said screen, said means comprising a prism having an incident surface substantially normal to the direction of incident light, an emerging surface substantially parallel to said incident surface but laterally offset with respect thereto, and light reflecting surfaces joining corresponding edges of said incident and emerging surfaces at an angle with the normal between said incident and emerging surfaces.

4. In combination, a cathode ray device comprising an envelope having a photo-electric cathode at one end thereof and a pencil-like electrode at the opposite end of said device, means for directing a pair of optical images of a subject, on said cathode from a point'external to said device and in line with said electrode and cathode, without casting'a shadow of said electrode on said screen, said means including a pair of prisms substantially symmetrically disposed with respect to said electrode, each prism having substantially vertical incident and emerging surfaces and light reflecting surfaces joining said vertical surfaces at an angle to the normal between said vertical surfaces to cause an incident ray to emerge in a direction to miss said electrode and strike said cathode, said prisms being spaced to cast overlapping images on said cathode offset with respect to each other by at least half scanning line thickness, and means for alternately intercepting the light through one prism and then the other.

5. In a moving-picture projectorfor television use, means for two-dimensional scanning at a repetition frequency greater than the normal frame frequency of the film, which comprises means for optically deflecting the image of said film frames in the direction of film travel, means for optically deflecting the image of said film frames in a direction opposite to that of the film travel, and means for obturating said deflecting means alternately in synchronism with the movement of said film.

6. In combination with apparatus for projecting successive images from moving-picture film onto television transmitting apparatus, means for deflecting a portion of successive images on said film in the direction of film travel, and means for deflecting a portion of said film images in a direction opposite to that of film travel, comprising a plurality of prisms positioned to deflect light passing therethrough, said prisms being adjusted to provide deflections in opposite directions differing by half the width between successive scanning lines, and means for alternately obturating said deflecting means.

'7. Means for scanning motion-picture film associated with television apparatus comprising a source of projection light, means for focusing said projection light to form an optical image of said film, means for displacing said image in the same direction as that of travel of film to be televised, means for displacing said image in a direction opposite to the direction of travel of said film, an obturating shutter arranged to sequentially and alternately cover and uncover said light-deflecting means, and means' for transforming an optical image into television signals.

8. In a moving-picture projector for television use,the method of two-dimensional scanning at a repetition frequency greater than the normal frame frequency of the film, which comprises the steps of optically deflecting the image of said film frames in the direction of film travel,

optically deflecting the image of said film frames in a direction opposite to that of the film travel, and obturating said deflected images alternately in synchronism with the movement of said film.

9. In a moving-picture projector for television use, the method of two-dimensional scanning at a repetition frequency greater than the normal frame frequency of the film, which comprises the steps of prismatically deflecting the image of said film frames in the direction of film travel, prismatically deflecting the image of said film frames in a direction opposite to that of the film travel, and obturating said deflected images alternately in synchronism with the movement of said film.

10. In a moving-picture projector for television use, the method which comprises focusing light from a source to form an optical image of the film to be televised, displacing said image in a direction opposite to the direction of travel of said film, sequentially and alternately intercepting said displaced images, and transforming said images into television signals.

WALTER BiiNGER. ERICI-I KOSCHE.