US2147555A - Scanning device - Google Patents

Description

Feb. 14, 1939. K. SCHLESINGER 2,147,555

Filed Oct. 22, 1935 4 Sheets-Sheet 1 Feb. 14, 1939. K. SCHLESINGER SCANNING DEVICE 4 Sheets-Sheet 2 Filed Oct. 22, 1955 y/wen/or:

Feb. 14, 19 3 9. sc s R 2,147,555

SCANNING DEVICE Filed OQt. 22, 1935 4 Sheets-Sheet 3 Feb. 14, 1939. K SCH ESINGER 2,147,555

SCANNING DEVICE Filed Oct. 22; 19:55 4 Sheets-sheaf 4 Patented Feb. 14, 1939 UNITED STATES PATENT OFFICE SCANNING DEVICE Steglitz, Germany Application October 22, 1935, Serial No. 46,126 In Germany October 25, 1934 2 Claims.

Although this distortion has not been found to be troubling in all cases in the earlier television art, the same becomes intolerable in the modern method of transmitting images free of flickering effect. As is well known, this method consists of the superimposition of two scanning areas with interlaced lines. As will be readily appreciated, the trapezoidal distortion leads to the fact that the two part-images do not fit one over the other.

The objects of this invention are optical methods and means to compensate the said distortion.

The invention will be described and best understood with reference to the accompanying drawings which will serve for explanation of the several features.

Fig. 1 shows a scanning disc with spirally arranged apertures, while in Fig. 2 the trapezoidal form of the scanned area is shown.

Figs. 1 and 2 serve to explain the distortion mentioned above.

Figs. 3 to 9 are illustrating the scheme of several exemplary embodiments of the present invention.

In Fig. 1, I is the spirally apertured disc, the apertures of which scan a surface 2, which is confined by two arcs 3 and 4 and two radii 5 and 6 and accordingly possesses substantially a trapezoidal form. If a film is scanned, the image of which is always rectangular, this may be so projected, for example, over the scanned surface that the film picture I possesses the same base line as the inner, i. e., smaller are 4. The upper edge of the film picture I, 3' is then somewhat smaller than the are 3.

This incongruity of the areas 2 and I causes a distortion of the received images, as shown in Fig. 2, presumed a Braun tube per se furnishing a rectangular image 8 is used. As the time required by an inner scanning aperture to pass over the width of the film I, is longer than the time required by an outer aperture, there is produced at the receiver a reproduction of the film area I and area I, which is narrower at the upper edge of the image than at the bottom. Two black triangles 9 and 9' supplement the trapezoidal area I to form the complete rectangular area 8. The missing amount corresponds to the difference in radius at the commencement and the end of the spiral on the transmission disc I. The, latter amounts in the case of discs of approximately m., in diameter to approximately 3%, as much as 6 image points in a ZOO-line image.

According to the invention the distortion is eliminated by a contrary distortion of the projection of the filmimage onto the apertured disc.

Fig. 3 will serve for explanation. In the same ID is the plane of the film being transmitted and I I the lens which reproduces the image Ill on the plane of the disc I.

According to a law which is known in itself in geometrical optics, there results from an original I0 inclined to the plane of the lens I I at the angle on a sharp reproduction 'I inclined at an angle 5 in relation to the plane of the lens. If these two inclinations are eifected, there is produced from a rectangular image II] a trapezoidal reproduction 1, and by adjustment of on and ,8 it may readily be accomplished that the reproduction of the film rectangle assumes exactly that trapezoidal form H on the disc that coincides with the scanned surface 2 on the disc I. The distortions described are then all eliminated, and even complicated methods of scanning, such as the stated method free of flickering effect, may be performed with spirally apertured discs.

Methods making use of Nipkow discs are also known, in which the light source does not light first of all the film, but the disc, and in which the lens II projects an image of the spot of light in the disc on to the film. In these methods the same difficulties naturally occur because the scanning points describe on the film a trapezoidal area as surface scanned by the disc. The difliculties, therefore, are overcome by the same optical measures as in the first method using a flood-lit film.

In practice the inclination of the film and the Nipkow disc in relation to the vertical is rather inconvenient, particularly on account of the fact that these angles of inclination cc and 13 are by no means small. There is accordingly set forth in Fig. 4 an embodiment of the invention, which avoids the disadvantage of a tilted disposition of the film and Nipkow disc, and also offers the advantage of ready adjustment of the degree of distortion. In Fig. 4, I0 is again the surface of the film, which this time is exactly perpendicular, and I is the Nipkow disc, which is also disposed vertically. The lens II is likewise situated in a vertical plane, but its axis, however, is raised in relation to the common axis of the film image In and reproduction I by an amount I2, which is made approximately equal to the diameter of the lens I I. By reason of the double mirror arrangement I3, I 3a and I4, I4a according to the invention it is accomplished that the tilted planes of IO and I shown in Fig. 3 are made the vertical. For this purpose, if the mirrors I3 and I4 are tilted less than 45, they must be at an angle of a/Z and 5/2 to the mirrors [3a, I 40!, respectively. Owing to the somewhat longer path of the light it is necessary to reduce the distance between film and disc. In the case of a fixed spacing it would be necessary to employ a lens II of greater focal distance. All of these conditions are capable of being readily derived per se from geometrical optics. By varying the relative inclination of the two double-mirrors it is possiblein each case to adjust a desired degree of trapezoidal distortion. The sharpness of the edge is maintained over the entire area.

As has been explained in the above it is essential for certain television transmission methods to compensate, by optical means, the errors occurring by reason of the trapezoidal scanningarea of the Nipkow disc. These are'the methods of transmission in which an image is produced by the superposition of two or more part-images having staggered lines. It has been shown in the above that the desired trapezoidal distortion of a rectangular image area is to be obtained fundamentally by disposing the surface of the object and the surface of 'the image in opposite inclination in relation to the plane of the lens. In the practical execution, however, it is found that the inclinations which-are required in order to produce a trapezoidal angle of 4 (disc-with 90 apertures) or even 8 (disc with45 apertures) are comparatively large, and that accordingly it is hardly possible in practice to mount the film and the Nipkow disc in such an inclined position. There have been set forth as remedy two systems each consisting of 2 nonparallel reflectors, with which an upright arrangement of the planes of the object and the image is rendered possible. In practice difiiculties are frequently encountered'by the usually very short free path of light between the object and the first lens on the one hand and between the image and the second lens on the other hand. A second factor hinders the execution of the optical distortion according to the invention: Between'the Nipkow disc and the film-guiding means of a film transmitter there is a comparatively long path of light, which is caused by the fitting of the driving motor and other machine parts. The path of light amounts of 50 cm. or more. The projection of the light, therefore, over a long distance of this kind can hardly be a satisfactory one with one single lens, and two or even more lenses are required.

A further feature of the present invention is the correct embodiment of the projection of the light with two ormore lenses with the ultimate result that the inclinations of the planes of the object and the image, in accordance with the invention, in relationto the vertical are very small, and accordingly may be adjusted in practice by the mounting thereof even without the use of correcting reflector systems. Further the light intensity of the projected image is very good. An additional embodiment of the idea'according to the invention making use of a lens permits of the use thereof in its application to scanning transmitters.

In Fig. 5, I again represents the plane of the film, which is lighted by a condensing reflector 2 from a light source 3. The Nipkow disc 4 is situated at the stated comparatively large distance of approximately metre or more from the plane .tween the lenses.

of the film I. To obtain a very bright reproduction on the disc 4 at least two lenses 5 and 6 are required. According to the invention, the focal lengths of these lenses are selected to be so small and their location to be at a spacing amounting in each case to one-quarter of the total optical length 1 between the planes of the object and image I and 4, that a tangible real intermediate image 1 results at the centre be- The focal lengths necessary for this purpose amount, as well known, in the case of a scale of reproduction of 1:1 to f= /8Z. Accordingly in practice they are approximately 6 to 8 cm.

Fig. 6 explains the manner in which with an optical arrangement of this kind the trapezoidal distortion takes place. The plane of the objective 5 is designated 5 and, in the same manner as the plane 6 of the lens 6, is disposed vertically upright. A rectangularly defined image I is tilted in relation to this plane to the extent of the angle on. There accordingly results from I a reproduction I, which (1) possesses an inclination a relative to I, and (2) already has a trapezoidal distortion, which isshown in Fig. 6. With a scale of reproduction'of 1:1 the angles of inclination of l' and 'I are equal to each other. This inclined intermediate image I is now reproduced by the second-lens 6, a new image occurring in the plane 4 with the following properties: In the first place the plane of 4 is also tilted in relation to the vertical to the extent of an angle 7. This angle, with a scale of 1:1, is not of a greater order than the previously stated inclinations, but is just as largeas these. Secondly, the reproduction'is trapezoidally distorted to twice the extent as compared with the intermediate image I. This may be readily appreciated from the fact that a rectangular intermediate image figure would have resulted, owing to its inclination B, in a trapezoidal image area at 4 with the inclination 7. Since, however, the intermediate image I already represents a-trapezium, the final image 4' must accordingly result in a correspondingly more distorted trapezium. The degree of trapezoidal distortion may be increased, therefIore, step by step by the series arrangement of lenses with real intermediate images. Vice versa, a given distortion may be obtained in the final image with a correspondingly smaller inclination ofthe image planes. Thirdly,- the'undesirable variation 'in scale in the vertical illumination occurs only to very small extent, becausethe inclination of the image planes is a smaller one. A practicalembodiment is, therefore, quite'possible in simple fashion without-deflectors with the intermediate optical system according to the invention in the manner shown in Fig. 7. For mechanical reasons the plane of the disc 4 is disposed exactly vertically. The lens axis 8 is tilted downwards in relation to the normal position of the disc 4 to the extent of the normal angle 7 of approximately 5-10", which is simple to deal with in'practice. The lenses 6 and 5 in the same man her as the are 3 with the condenser 2 are directed in a straight line with the axis 8, whilst the film I, or-its guiding means, is inclined in relation to 8, this inclination in the case of a reproduction of 1:1 also again amounting to exactly so that the film is also almost perpendicular. A loss of light obviously does not occur with this construction. The intermediate image 'I is indicated in its inclination.

The use of the optical distorting system as described for the scanning transmission art is shown in Fig. 8. If it is desired to transmit an object 9 situated at a desired distance, this in accordance with the invention must first be brought to a fixed position I by a reproducing. lens I0. I is the plane in which the stated optical distortion takes place. It is only objects which are reproduced sharply in this plane that will be reproduced without distortion of shape on the disc 4 by the lens arrangement 5 and 6 according to the invention, which arrangement is dependent only on the scanning area of the Nipkow disc 8. The lens [0, therefore, should be so adjusted in each case that a sharp image of the object 9 is produced in the plane I. In view of the above the distorting lenses 6 and 5 should be so arranged that the plane I is parallel to the plane of the disc 4, i. e., is also vertical. If owing to otherwise determined dimensions in the projecting apparatus this is not possible, the reproduction of 9, with'the assistance of a doublerefiector arrangement H, l2 having non-parallel reflectors, may be moved into any desired plane I" which is not perpendicular.

According to the invention, the distortion is eliminated by the fact that a corresponding purely optical distortion of the film reproduction is introduced by way of compensation. Fig. 3 will serve for explanation. In the same ID is the plane of the film being transmitted, and H the lens which reproduces the image I 0- on the plane of the disc I. According to a law which is known in itself in geometrical optics, there results from an original ll), inclined to the plane of the lens II with the angle oz, a reproduction I, the plane of which, if I is to have marginal lines, also requires to be tilted, viz., in the opposite direction, to the extent of the angle 13 in relation to the plane of the lens are effected, there is produced from a rectangular image In a trapezoidal reproduction I, and by adjustment of a and s it may readily be accomplished that the reproduction of the film rectangle assumes exactly that trapezoidal form on the disc that coincides with the scanned-surface 2 on the disc I. The distortions described are then all eliminated, and even complicated methods of scanning, such as the stated method free of flickering effect, may be performed with spirally apertured discs. Methods making use of Nipkow discs are also known, in which the light source does not light first of all the film, but the disc, and in which the lens ll projects an image of the spot of light in the disc on to the film. 'In these methods the same difficulties naturally occur because the scanning point describes on the film a trapezoidal area as the surface scanned by the disc. The difiiculties, therefore, are overcome by the same optical measures as in the first method using a flood-lit film.

In practice the inclination of the film and the Nipkow disc in relation to the vertical is rather inconvenient, particularly on account of the fact that these angles of inclination a and 3 are by no means small. There is accordingly set forth in Fig. 4 an embodiment of the invention, which avoids the disadvantage of a tilted disposition of the film and Nipkow disc, and also offers the advantage of ready adjustment of the degree of distortion. In Fig. 4, I0 is again the surface of the film, which this time is exactly perpendicular, and I is the Nipkow disc, which is also disposed vertically. The lens H is likewise situated in a vertical plane, but its axis, however, is raised in relation to the common axis of the ameter of the lens II. By reason of the doublemirror arrangement l3, [3a and I4, Ma according to the invention it is accomplished. that the tilted planes of i0 and 1 shown in Fig. 3 are made the vertical. For this purpose, if the mirrors l3 and it are tilted less than 45, they must be at an angle of g and to the mirrors l3a, Ma respectively. Owing to the somewhat longer path of the light it is necessary to reduce the distance between film and disc. In the case of a fixed spacing it would be necessary to employ a lens I I of greater focal distance. All of these conditions are capable of being readily derived per se from geometrical optics. By varying the relative inclination of the two doublemirrors it is possible in each case to adjust a desired degree of trapezoidal distortion. The sharpness of the edge is maintained over the entire area.

As has been explained in the above it is essential for certain television transmission methods to compensate, by optical means, the errors occurring by reason of the trapezoidal scanning area of the Nipkow disc. These are the methods of transmission in which an image is produced by the superposition of two or more part-images having staggered lines. It has been shown in the above that the desired trapezoidal distortion of a rectangular image area is to be obtained fundamentally by disposing the'surface of the object and the surface of the image in opposite inclination in relation to the plane of the lens. In the practical execution, however, it is found that the inclinations which are required in order to produce a trapezoidal angle of 4 (disc with 90 apertures) or even 8 (disc with 45 apertures) are comparatively large, and that accordingly it is hardly possible in practice to mount the film and the Nipkow disc in such an inclined position. There have been set forth as remedy two systems each consisting of 2 non-parallel reflectors, with which an upright arrangement of the planes of the object and the image is rendered possible. In practice difficulties are frequently encountered by the usually very short free path of light between the object and the first lens on the one hand and between the image and the second lens on the other hand. A second factor hinders the execution of the optical distortion according to the invention: Between the Nipkow disc and the film-guiding means of a film. transmitter there is a comparatively long path of light, which is caused by the fitting of the driving motor and other machine parts. The path of light amounts of 50 cm. or more. The projection of the light. therefore, over a long distance of this kind can hardly be a satisfactory one with one single lens, and two or even more lenses are required.

A further feature of the present invention is the correct embodiment of the projection of the light with two or more lenses with the ultimate result that the inclinations of the planes of the object and the image, in accordance with the invention, in relation to the vertical are very small, and accordingly may be adjusted in practice by the mounting thereof even without the use of correcting reflector systems. Further the light intensity of the projected image is very good. An additional embodiment of the idea acfilm image [0 and reproduction l by an amount cording to the invention making use of a lens l2, which is made approximately equal to the dipermits of the use thereof in its application to scanning transmitters.

In Fig. 5, I again represents the plane of the film, which is lighted by a condensing reflector 2 from a light source 3. The Nipkow disc 4 is situated at the stated comparatively large distance of approximately metre or more from the plane of the film I. To obtain a very bright reproduction on the disc 4 at least two lenses 5 and 6 are required. According to the invention, the focal length of these lenses are selected to be so small, and their location to be at a spacing amounting in each case to one-quarter of the total optical length 1 between the planes of the object and image I and 4, that a tangible real intermediate image 1 results at the centre between the lenses. The focal length necessary for this purpose amounts, as well known, in the case of a scale of reproduction of 1:1 to f= Z. Accordingly in practice they are approximately 6 to 8 cm.

Fig. 6 explains the manner in which with an optical arrangement of this kind the trapezoidal distortion takes place. The plane of the objective 5 is designated 5 and, in the same manner as the plane 6' of the lens 6, is disposed vertically upright. A rectangularly defined image I is tilted in relation to this plane to the extent of the angle on. There accordingly results from I a reproduction l, which (1) possesses an inclination {3 relative to I, and (2) already has a trapezoidal distortion, which is shown in Fig. 6. With a scale of reproduction of 1:1 the angles of inclination of l and I are equal to each other. This inclined intermediate image I is now reproduced by the second lens 6, a new image occurring in the plane 4' with the following properties: In the first place the plane of 4 is also tilted in relation to the vertical to the extent of an angle 7. This angle, with a scale of 1:1, is not of a greater order than the previously stated inclinations, but is just as large as these. Secondly, the reproduction is trapezoidally distorted to twice the extent as compared with the intermediate image I. This may be readily appreciated from the fact that a rectangular intermediate image figure would have resulted, owing to its inclination ,6, in a trapezoidal image area at 4' with the inclination 7. Since, however, the intermediate image 1' already represents a trapezium, the final image 4' must accordingly result in a correspondingly more distorted trapezium. The degree of trapezoidal distortion may be increased, therefore, step by step by the series of lenses with real intermediate images. Vice versa, a given distortion may be obtained in the final image with a correspondingly smaller inclination of the image planes. Thirdly, the undesirable variation in scale in the vertical illumination occurs only to very small extent, because the inclination of the image planes is a smaller one. A practical embodiment is, therefore, quite possible in simple fashion without reflectors with the intermediate optical system according to the invention in the manner shown in Fig, 7. For mechanical reasons the plane of the disc 4 is disposed exactly vertically. The lens axis 8 is tilted downwards in relation to the normal position of the disc 4 to the extent of the normal angle 7 of approximately 510, which is simple to deal with in practice. The lenses 6 and 5 in the same manner as the arc 3 with the condenser 2 are directed in a straight line with the axis 8, whilst the film I, or its guiding means, is inclined in relation to 8, this inclination in the case of a reproduction of 1:]: also again amounting to exactly so that the film l is again almost perpendicular. A loss of light obviously does not occur with this construction. The intermediate image I is indicated in its inclination.

The use of the optical distorting system as described for the scanning transmission art is shown in Fig. 8. If it is desired to transmit an object 9 situated at a desired distance, this in accordance with the invention must first be brought to a fixed position I by a reproducing lens ill. I" is the plane in which the stated optical distortion takes place. It is only objects which are reproduced sharply in this plane that will be reproduced without distortion of shape on the disc 4 by the lens arrangement 5 and 6 according to the invention, which arrangement is dependent only on the scanning area of the Nipkow disc 8. The lens I0, therefore, should be so adjusted in each case that a sharp image of the object 9 is produced in the plane I. In view of the above the distorting lenses 6 and 5 should be so arranged that the plane I is parallel to the plane of the disc 4, i. e., is also vertical. If owing to otherwise determined dimensions in the projecting apparatus this is not possible, the reproduction of 9, with the assistance of a doublereflector arrangement H, l2 having non-parallel reflectors, may be moved into any desired plane I which is not perpendicular.

I claim:

1. In a television transmitter comprising a rectangular image to be transmitted and a spirally apertured disc parallel to said image, said disc having a trapezoidal scanning screen, an optical arrangement between said image and said disc, said arrangement consisting of two pairs of mirrors inclined to each other and a lens device between both pairs of mirrors displaced to the straight line connecting said image and said screen, the inclination of the mirrors being so chosen that the distorted projection of the image coincides with the said trapezoidal screen;

2. In a television transmitter comprising a rectangular image to be transmitted, a spirally apertured disc having a trapezoidal scanning screen and a lens device arranged between said image and said disc projecting said image onto said screen, the planes of said image and of said disc being inclined to the plane of said lens device so that the distorted projection of the image coincides with the said trapezoidal screen, the lens device consisting of two separate lens devices of such a focus that a real image arises between them.

KURT SCHLESINGER.

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