US2349298A - Television receiver - Google Patents

Description

y 3, F. OKOLICSANYI 2,349,298

TELEVISION RECEIVER Filed July 31, 1940 3 Sheets-Sheet l y 3, 1944. F, OKOLICSANYI 2,349,298

TELEVI S ION RECEIVER Filed July 31, I940 3 Sheets-Sheet 2 3% 3/ 6 t as divided by the and the light beam increased by Patented May as, 1944 -Ferenc Okollcsanyi,

land, assignor to America, New

Delaware Application July a1, 1040, Serial No. In Great Britain August 3, 193

11 Claims.

The present invention relates to television receivers employing mechanical scanning members such as mirror drums, oscillating mirrors or moving lenses. The invention relates particularly, though not exclusively, to receivers of this type in which a supersonic wave light modulating device is employed.

The definition of the reproduced picture in a given scanning direction, for a given quantity of light transmitted to the sreen from a given light source and for a given scanning angle will depend upon the size of the scanning member producing the scanning motion in this direction. This fact can be shown from the following considerations: Referring to Fig. l of the drawings consider a light sourcel of size S, a lens 2 adapted to form an image of size S of the source on a screen 3 of size 'R and situated at a distance d from the source, and a scanning member t situated close to the lens 2 and adapted to move the image over the screen. Obviously the lens itself can act as as the scanning member, but in any case it will be assumed that the 'lens and scanning member are so close together that they both can be regarded as being distant d from the light source. Then the definition D can be defined as being the distance moved by the image on the screen of motion, 1. e.

RRd

screen. Now

where a is the scanning angle,v i. e. the angle subtended at the by the image on the screen, and hence ad h Now if p is the size of the lens (or the scanner) subtends an angle b at the lens, then the light (assuming alight source of unit brilliancy) i From these two expressions it will be seen that, 11' D is to be kept constant, F can only be insize of the image in the direction.

Remington, London, Eng- Scophony Corporation of York, N. Y., a corporation 01 Now in a practical apparatus, these are the two values which are least suitable to increase. In-

crease in the scanner size p by a factor it means be varied are d and S, and it will be seen that for both these factors, any increase produced in one of the factors F or D is ofl-set by a corresponding decrease in the other.

At first sight, it might seem that this difficulty could be avoided by forming a reduced intermediate image of the light source, and by treating this smaller virtual light source as the original' light source, thereby obtaining a smaller value for s in the above formulae without any light loss. This is not so, 'for the light cone issuing from the new light source is increased by the same factor that the size (if the light source is reduced. Consequently, to grasp this new lightcone, the size of-the scanner p must also be increased by a corresponding amount.

An object of the present invention is to avoid this disadvantage and to enable an increase in the definition to be obtained without light loss 0 and without increase in the size of the scanning member in the direction of its scanning motion.

According to the present invention this is achieved by providing in the plane oi! the light source or in the plane of an intermediate image g g-thereof, a divided field lens system comprising scanner by the distance moved flux of the-system is given by creased by increasing 1;; the scanner size the value of which as can be seen does not aflect D. And if F is increasing a, the scanning angle.

to be kept constant D can only bea plurality of similar lenses situated one above the other in the scanning direction, the optical centres of the lenses being displaced laterally with respect to one another at right angles to the seaming direction, whereby the focussed light cones issuing from the lenses diverge with respect to each other in a direction at right angles to the scanning direction, a second divided optical member being provided in the path of the light cones at a point where they have become fully separated from one another, each portion or this second divided member being adapted to receive one of the light cones and to direct it on to the receiving screen or on to some intermediate plane in such a way that all the light cones strike the plane in the same straight line which is at right angles to the direction of the scanning motion.

to numberof components or the field lens system,

limited. *The only two values which can easily- 2 and the definition is increased by a corresponding factor, without any or with only very slight light loss or any increase of the size of the scanning member in the direction of its scanning motion.

The second divided member can beconstituted by the focussing lens itself, which in this case comprises a plurality of identical lenses placed side by side in the scanning direction and having their optical centres displaced relative to one another in the direction of the scanning motion.

The present invention is particularly applicable to the optical system for producing the frame scanning component of a television receiver employing a supersonic wave light modulating device.

Such receivers usually comprise a supersonic wave cell situated between two optical stops and two spherical lenses, one on each side of the cell. the first of which collimates the light from the first stop and the second of which collects this light after it has passed the cell and focusses it on the second stop in such a way that the light which is diffracted by the action of the supersonic waves in the cell is separated from the non-diffracted light, one of these portions of the light (usually the former) being allowed to pass the second stop. This selected portion of the light is utilised to form the scanning spot on the receiving screen, this spot being in the form of a strip of light having its longer dimension in the direction of the scanning lines. This strip of light is actually an image of the illuminated area of the supersonic cell itself, but the ratio of the length of the strip to its width must be much greater than the ratio of the length to width of this cell area, since the width of the strip determines the picture definition in the frame scanning direction and hence must be small, whilst, on the other hand, the width of the cell area cannot be equally the cell on the surface of this drum, whilst the third'lens (the line width focussing lens) is situ-' ated between the high speed drum and a low speed drum and focusses an image of the illuminated faces of the former on the receiving screen. A television receiver of this type is illustrated in Figs. 3 and4 of Britishpatent specification No. 496,964. The second lens can be dispensed with, in which case, the line width focussing lens forms directly an image of the cell on to the receiving screen.

In passing it may be pointed out that in the case of a receiver employing a supersonic wave light modulating device with immobilisation pf the wave images, the limitations of definition and light flux discussed above no longer hold in the line scanning direction, since these quantities are related in quite a different way since the definition is no longer a function of the optical aperture, but of the wave length of the waves in the cell, and other factors to do with the properties of supersonic waves.

Further in both frame and line scanning directions the use of an astigmatic lens system, which forms a narrow image on a scanner in the axial direction, enables the size of the scanner in this direction to be made small as desired. Therefore with this system, the only remaining limitation is in the frame scanner, in its direction of motion.

Thus considering now the action of the receiver in the frame scanning direction, it is seen that small without seriously cutting down the light transmitted through the cell. It is not possible to make these two ratios equal to one another without such a serious loss of light, since the maximum length of the cell area is determined solely by the maximum length of the supersonic wave train which can be usefully employed and is thus given a definite upper limit;.hence the ratios could be made equal only by reducing the width of the cell area and not by increasing its length.

In practice, no attempt is made to equalize these ratios. Instead, the optical system which forms the strip of light is astigmatic and has a greater magnifying power in the line scanning direction than in the frame scanning direction, thereby producing the necessary reduction in the width of the focussed area relative-to its length.

there is in effect a light source (the illuminated area. of the supersonic cell), a focussing lens (the line width focussing lens) and a scanning memher (the low speed scanner), and since the size S of the light source is given by the height of the supersonic cell, this size is-relatively large. Consequently in accordance with the above formula, to obtain adequate definition in the frame scanning direction, the line width fccussing lens and the slow speed scanner must be placed at a considerable distance from the cell, and must therefore be very large if no light is to be lost.

The present invention can be applied to overcome this particular difllculty in various ways,

some of which will be described by way of example vention to a form of television receiver employing a supersonic wave light'modulatlng device; Fig. 2 being a side view and Fig. 3 a plan view,

Figs. 4 and 5 are optical diagrams explaining the operation of part of the apparatus of Figs.

2 and 3,

This optical system usually consists of three cylindrical lenses. The first lens (the line length focussing lens) has optical power in the line scanning direction, is situated between the supersonic cell and a high speed mirror drum, and forms a x cylindrical image of the supersonic cell on the receiving screen in the line scanning direction.

The mirror drum moves the light beam falling on it in such a manner that the images on the screen of the moving waves in the cell are immobilised on the screen. The second and third lenses have optical power in the frame scanning direction and -co-operate to form a cylindrical image of the supersonic cell on the receiving screen in the frame scanning direction. The second lens is situated between the supersonic cell and the high speed drum and forms an intermediate image of Fig. 6 is a perspective view of part of the apparatus of Figs. 2 and 3,

Figs. '7 and 8 show an application of the invention to a' television receiver employing a Kerr cell as light modulator; Fig. 7 being a side view and Fig. 8 a plan view,'and

Figs. 9 and 10 show a side and plan view respectively of a further form of receiver employing a supersonic wave light modulating device and embodying the invention.

Referring now to Figs. 2 and 3, in which the plane of Fig. 2 lies in the frame scanning direction, and the plane of Fig. 3 in the line scanning direction, there is provided a light source l0, which illuminates an aperture I l in a screen I! in front of which is a lens l3, having power in the plane of both figures. The supersonic wave cell [4 is provided with a spherical lens I 5 on the side asea'aee nearest the light source it, and on the other side with a divided lens it (the first divided element of the invention) [AI]. optical stop I! separates the diffracted from the undifiracted light and passes the former to a lens which is composed of a part It having power in both planes and a divided part 19 having power only in the plane of Fig. 2, the frame scanning plane. After the lens is follow a high speed scanner 20, a cylindrical line width focussing'lens 2! having power only in the plane of Fig. 2, a slow speed scanner 22 and a screen 23. In Fig. 3 the planes of the scanners 20 and 22 are indicated by dotted lines 20 and22'.

In the known arrangements the divided lenses it and H! are single lenses, and in that case the apparatus operates as follows:

I In the plane of Fig. 2 the lenses i3, i8 and it (together) and 20 act as focussing lenses, and the lenses i and i6 as field lenses. The lens l3 forms cell M. (i. e. a

an image of the light source it in the he lens I8, it forms an image of the cell second image of the light source) on the face of the scanner 20. The lens 2i images the scanner 2% on the screen 23 and so forms a third image of the light source there. In the plane of Fig. 3. the lens l3 forms an enlarged image of the light source in in the cell M, and this image is focussed on to the receiving screen 23 by the lens IE to form the picture line. form an image of the aperture II on the stop ill, so that only'the difiracted light passes it.

Now, as previously stated, in the plane of Fig. 2 the image sing lens 2i, the slow speed scanner 22 and the screen 23 are equivalent to the arrangement of Fig. l, and suffer from the disadvantages discussed in relation to that figure. The present invention obviates the disadvantages in the manner described in the following, in which reference is also made to the explanatory Figures 4, 5 and 6.

The lens l6 comprises two elements I Go and Nib. The element I60. covers the upper halfof the aperture of the cell M, the vertical direction being taken as the frame scanning direction, i. e. the direction of the plane of Fig. 2. It is part of a cylindrical lens whose optical centre lies on the line dividing the cell into an upper and lower half, andto one s de of the centre of the aperture. The lens iBb covers the lower half of the cell and is a portion of a spherical lens having its optical centre on the same dividing line, and placed symmetrically to the other side of the centre of the aperture. In'Figs. 5 and 6 the optical centre of the lens Ilia is at the point Pa and the optical centre of the lens Nib is atthe point Pb. In Fig. 4, the centres lie on the line passing through the point P vertically to the plane of the paper. I

"The'lens i9 is also divided and comprises two elements Ma and l9b. The elements are both cylindrical, and their optical centre lines are at right angles to the plane of the paper in Fig. 4, and pass through the points Qa and Q11 respectively. In Fig. 5 both l nes are parallel to the line H, one above and one below the plane of the paper. Fig. 6 shows a perspective view of the arrangement.

Now in the plane of Fig. 5, the lens the light passing through it into a lid focusses cone which is indicated by the full lines, and fills the aperture of the lens l9a only. The lens libproduces a cone of light which fills the lens llb. The optical stop i i of Fig. .3 consists of two parts, Na and i122 and the lenses Ilia and I6!) form The field lenses I 5 and i6 on the scanner. the line width focusto the plane of Fig. 5 will 3 images of the aperture ii on the stops Ila and ill: respectively. Here the light diffracted by the waves is separated from the undiifracted light. a

Now in this plane, only the lens 58 has focussing power. This lens will form an image of the whole aperture of the cell on the screen 23, and since the lenses Ilia and Nib are only field lenses, their particular optical properties will not in any way alter, the focussing effect of the lens i8. The only difference the divided lens system will make compared with a single spherical field lens, is in the distribution of the light in the beam between the cell and the screen. In both cases all the light eminating from any line vertical be focussed into a corresponding image line on the screen 23.

In the plane of Fig. 4 light passing through lens Ida is formed into an image at 24, which is an image of the aperture of the lensifia. This aperture is filled by half of the image of the light source .10. Hence the image formed at 2 3 is an image of half the light source. The optical centre of the lens lea is displaced from the optical axis of the whole system by an amount sumcient ton bring the image 24 centrally on this axis. Now the lens i9b forms a similar image at 24 of the aperture of the lens 86b. These two images are not fully coincident, but, as can be seen from Fig. 5, will lie side by side in that plane.

Referring again to Figs. 2 and 3, the image formed at 243 falls on the high speed scanner 20. The remainder of the optical system functions as described above for the case of the known ar rangement, that is to say the line width focussing lens 2! focusses an image of the high speed scanner face 2!] on to the screen 23, this image being swept across the screen by the low speed scanner 22.

Now it w ll be seen, by comparing the arrangementof the present invention with the diagram of Fig. l and the description thereof, that the size of the aperture at the high speedscanner face 23 has been halved in the frame scanning direction without loss of light, in other words S of Fig. '1 has been halved without decreasing S, and hence the definition may be increased or the size of the scanner, decreased, or both, without loss of light. It will be noted that this has been achieved at the expense of the size of the aperture in the high speed scanning direction, and therefore at the expense of the scanner size in this direction. As has already been mentioned, owing to the large aperture in this plane, and the properties of supersonic waves, this scanning direction presents no problems, and an increase in the size of image in this direction can be tolerated. In many constructional forms of appa-. ratus, the high speed scanner is made larger than is required by the optical system, for practical reasons.

Figs. 4-6 illustrate the general principle of the invention, which may be applied to television arrangements other than the particular embodiment described. The surface 24 of these three figures may be any surface. such as a receiving screen, or a field lens, or may represent merely the plane in which an intermediate image is formed in a larger optical system. The relative dimensions of the apertures in the two planes are immaterial, for the invention may be applied to reduce the length of an image of a long narrow aperture, instead of being used to reduce its width (or increase its possible maximum width) as described above. Furthermore the inin this figure corresponds with the field lens vention is not limited to the use of two elements in each divided member. Three or more elements may be used, preferably arranged symmetrically about the optical axis of the system; thus where an odd number of elements are used, the central elements in each divided member has its optical centre on the optical axis of the system. In this specification, an arrangement of two divided optical systems of two or more elements each, such as is shown at lGa, l6b, Na and l9b in Figs. 4-6 will hereinafter be referred to as a beam converter.

The invention may be applied to arrangements employing a Kerr cell as a light modulating device. In the case of a Kerr cell, there is an optical limitation in one direction due to the fact that the electrodes have to be close together to avoid high modulating .voltages. Electrical requirements do not impose any serious limitation in the other direction, but owing to the fact that the aperture of the cell or some similarly shaped aperture has to be focussed on the screen as a single scanning spot of element size, the aperture in the direction parallel to the electrodes is s also limited to a size approximately the same as the distance between the electrodes.

In Figs. '7 and 8 there is shown an arrangement employing a Kerr cell, Fig. '7 being a view in the, frame scanning direction, and Fig. 8 being a view in the line scanning direction. In Fig. 8, light from a light source is collected by a cylindrical condenser lens 3| and directed on to a Kerr cell 32, having two electrodes 33, 33. An image of this cell is formed by the focussing lens 34 on to the screen 35. The cell is provided with field lenses 36 and 31; the construction of the field lens 31 [6 as seen in Figs. 3 and 5, but differs from these previously described arrangements in that it consists of three elements a, b, and 0, two of which a and 0, have their optical centres displaced from the optical axis of the system, and the third of which, b, has its optical centre on the optical axis of the system. These three field lens elements direct beams .of light on to the elements e, I and g of the focussing lens 38, which with the lens 31 forms the beam converter. In the plane of Fig. 7 the lens 31 is shown divided into its three elements, and each of the three elements of the frame width focussing lens 38 focusses an image of the part of the aperture of the cell from which it is receiving light on to the same part of the screen 35. The scanning devices have not been shown in this arrangement, but they may be placed between the-lens 38 and the screen 35 according to the usual practice. The system may be modified by the incorporation of further focussing lenses as desired, and it is not essential that the image formed by the lens 38 is the final image formed on the screen. It may be an intermediate image which is focussed by a further optical system on to the screen.

In this Kerr cell arrangement, the advantage due to the beam converter over known arrangements is that the aperture in one direction (clearly in this case, the-line and frame scanning directions are interchangeable optically) can be increased without impairing the definition in this direction-i. e. S has been increased without in-, creasing S'. Clearly this implies that if the light is suflicient in the known arrangement, the present invention makes possible the use of a smaller fcamierior the same amount'of light-or if s be kept the same, an improvement in the definition may be obtained without loss of light. 1

' to L124 are formed on the stop tween lenses 49 and 50, and between lens 50 the screen 23 there is a. considerable distance, indicated by the zig-zag lines A-A,'BB, C--C Comparison of this Kerr cell arrangement with the supersonic cell arrangement of Figs. 2 and 3 will show that in the Kerr cell arrangement, the image in the plane of Fig. I, in which the beam conversion takes place, and the image in the plane of Fig. 8, in which thetocussing is the same as if there were no beam converter present, are formed at the same distance from the cell", namely on the screen 35. In the supersonic cell arrangement however the images are formed at different distances from the cell; in the plane of Fig. 2, on the high speed scanner, and in the plane of Fig. 3 on the screen. Now this indicates that by using an astigmatic lens system one is free to choose where one may, for the beam conversion, by arranging a larger aperture in the plane in which there is no beam conversion. In Fig. 8 this "payment" is made by the large size of the lens 34 and an increase of at least one scanner in the axial direction; in Fig. 3 by a larger high speed scanner. An alternative embodiment of the invention, in which the beam converter is applied to a receiver employing a supersonic wave light modulating device and an optical system adapted to form an image on a screen situated a long distance from the receiver is shown in Figs. 9 and 10. Fig. 9 is a view in the frame scanning direction and Fig. 10 is a view in the line seaming direction. From the light source to the supersonic cell the arrangement is the same as that shown in Figs. 2 and 3.

The cell l4 has affixed to it a simple spherical lens 40; then in order along the axis come the following elements; an optical stop 4 I, cylindrical lenses 42 and 43, the high speed scanner indicated by the dotted line 20', cylindrical lenses 44 and 45, spherical lens 48 being the first-divided member of the beam: converter, cylindrical lens 41, cylindrical lens 48 being the second divided member of the beam converter, the slow speed scanner indicated by dotted line 22, cylindrical lenses 49 and 50, and finally the screen 23. Be-

and

and D-D.

In the plane of Fig. 9 and 50 have power. In lenses 42, 45, 46 and 41 have power.

In Fig. 9, the frame scanning orvertical direction, points where are indicated by Svl, S02, S123 etc., and points where images of the aperture ll (Lv) are Lvl, m2, L03 etc. In Fig. 10, the line scanning or horizontal direction the light source images are indicated at Shl, SM, SM and the images of the aperture I I at Lhl, Lhl. The images Svl to Svi are formed in the cell l4, on the high speed scanner 20', on the lens 46, on the lens 49 and the screen 23 respectively. The images Lvl 4|, lens 45, lens 41 and lens 50 respectively. Images Shl, Sh! and SM are formed in the cell l4 on the lens 48 and the screen respectively. Images LM, and LM are formedon lens 42 and lens 41 respectively. The lenses on which images of the light sourceaperture H on the iocussing lenses, and there is a field lens at each image of the light source, except in the case of the image 8222 formed on as it were pay lenses 43, 44, 48, 48, 49 the plane of Fig. 10 the images of the aperture So of the light source are formed formed are indicated by 2,849,298 the high speed scanner. This image is so small that no field lens is required. It acts in efiect like a pin-hole camera. A field lens effect may be produced by curving the mirrors of the scanner in this plane.

It will. be seen therefore that on the face of the divided lens 49 there is formed an image of the light source in both planes. In the line scanning plane, ince the high speed scanner has been passed, this image is an immobilised image of the waves, and in fact corresponds to ,the image formed on the screen in Fig. 3. It is an intermediate line image. An image of this field lens M is, in the plane of Fig. 10, formed on the screen by the line width focussing lens il. In the plane of Fig. 9, the elements of the divided lenses 418 and 49, forming the beam converter, form a reduced image of the light source on the field lens 49, an image of which is focussed on to the screen 23 by the final projection lens 59.

The invention is of particular advantage in receiving. arrangement in which there is no mechanical high speed scanner, such as are described in United States patent specification No. 2,158,990 and in co-pending application Serial No. 251,844 filed January 19, 1939. An arrangement of the kind shown in Patent No. 2,158,990 may be described with reference to Fig. 2; the high speed scanner 29 now comprises a stationary mirror, and immobilisation of the waves is car:-

ried out by means of a light source it which flashe once every line period, and for a time of the order of element duration. The cell in this case must be long enough to accommodate a wave train bearing the modulations of a full line of the picture. The beam convertor is as ,described, except that it may comprise many more than two elements-for example ten or more. There is now no limitation at all in the plane of Fig. 3, and the cell can be as wide as possible in the plane of Fig. 2. 9

Similarly in the case of the arrangements of Figs. '7 and 8 andFigs. 9 and 10, more than three elements in' the members of the beam convertor may be employed. 1

The invention may be used in any part of a television receiver in which an optical limitation exists in one direction, and-comparative freedom exists in another; the invention may also be applied, as will be quite obvious, to the optical system lying between the light source and the light modulator, or other aperture which must be narrow in one direction.

In the embodiments described, the divided field lens member of the invention has been shown as a spherical lens. matic, in which case the second divided member and the single focussing lens co-operating therewith may be spatially separated. For example in Figs. 7 and 8 the lens 31 may be cylindrical, having power only in the plane of Fig. 8, and

This field lens may be astig- 'tion I is laid on an improvement in definition, it will the lens 38 may be suitably adapted to 'form the image on the screen.

Inany embodiment of the invention in which a scanner is used, the scanning direction of which s that in which the divided focussing member of the beam converter is split, this iocussing member may be placed after the scanner; the elements of the focuss'ing member will oicourse have to be large enough to include the beam in both extremities of its deflection. In other respects however the arrangement will be the same. The field lens, which is divided into sections made by planes taken at rightangles to the scanning direction must be before the scanner, that is the beam fall- 5 ing thereon should have no motion in a direction at right angles t the planes in which the lens is divided.

From the formulae deduced from Fig. 1, it will be seen that the light flux (F), the definition (D) and the size of the scanner in the scanning direction (:2) are all mutually dependent on one another. Hence in any receiver in which all these three factors have been brought to the optimum values, any attempt to improve the value of one of them must result in a corresponding deteriorain the values of one or both of the others.

Therefore this improvement can only be obtained at the expense-of some other member in the resize of this scanner is reduced to the minimum,

the percentage improvement in F, D or p in the scanning direction will result in a proportionate increase in size of the scanner in the axial direction. This will be so in the case of the type of receiver shown in Figs. 9 and 10. The size of the low speed scanner 22 is reduced to the minimum by the fact that an image of the high speed scanner or a plane very near the high speed scanner is formed on the low speed scanner in the plane of Fig. 10. In this case the width of the scanner is in the case where a beam converter is used in n times the size where simple lenses are used, where n is the number of elements into which the divided members of the beam converter are split. In the case of the arrangement of Figs. 2 and 3 the increase will not be proportional, since the low speed scanner in the axial direction is considerably longer than necessary, since no attempt is made to focus any small aperture on it in the plane of Fig. 3.

Though in the embodiments described, stress be quite clear that either F, D, or p, or any two or all three of these factors may be improved. Which of these factors is considered to be improved will of course depend entirely on with what known arrangement or design the comparison is made.

' I claim:

. 1. In a television receiver employing a mechanical scanner, an aperture an image of which is to be moved by said scanner, an optical focussing member having power in the scanning direction of said scanner and situated between said aperture and said scanner and being divided along planes parallel to said scanning direction into a plurality of focussing elements having their optical centres displaced relatively to one another in the scanning direction, a divided lens member inthe plane of said aperture projecting light passing through each element thereof on to a corresponding element of said focussing member and an optical system having power in a ning direction for forming with said focussing member a final image of said aperture.

2. In a television receiver employing a mechanical scanner, an aperture an image 01' which is to be moved by said scanner, an optical. focussing member having power in the scanning direction or said scanner and situated between said aperture and said scanner and being divided along planes parallel to said scanning direction into a plurality oi focussing elements having their opdirection at right angles to said scancomprising a plurality of their optical centres of the modulating device on of said intermediate image tical centre's displaced relatively to one another in the scanning direction, a field lens member in the plane of said aperture and being divided along planes parallel to a second direction which is at right angles to said scanning direction into sponding focussing element, and optical focussingmeans having power in said second direction for forming an image of said aperture.

3. A television receiver as claimed in claim 1 wherein said optical system lies at least partly between said scanner and said final image.

4. In a television receiver, a receiving screen, a scanner, a light modulating device an imag of which is to be formed on said receiving screen and moved over said screen by said scanner in a scanning direction, a divided optical focussing member for forming an image of said modulating device on said screen in said scanning direction and optical elements adjacent one another in a second direction 'at right angles to said scanning direction and having displaced relatively to one another in the scanning direction, a divided field lens member comprising a number of optical elements adjacent one another in said scanning direction and having their optical centres displaced relatively to one another in said second direction for projecting light passing therethrough on to a corresponding element of said focussing member, and optical focussing means having power in said second direction for forming an image of said light modulating device on said screen in said second'direction.

5. A television receiver comprising a supersonic wave light modulating device, a high speed scanner, a low speed scanner and a receiving screen, a line length focussing lens for forming an image the screen in the line scanning direction, a iocussing member having power in the frame scanning direction for forming an intermediate image of the cell on the high speed scanner, a line widthfocussing system havirame scanning direction for forming an image of the high speed scanner on the screen, and a field lens for directing light emerging from said modulating device into the said focussing member, wherein said focussing member comprises a plurality of elements placed side by side in the line scanning direction and having their optical centres displaced in the frame scanning direction to form a plurality of images of the light source lying side by side in the line scanning direction to form a plurality of images of the light source lying side by side inthe line scanning direction, and said field lens comprises a plurality of elements having their optical centres displaced relatively to one another in the line scanning direction for directing light passing through difierent sections of said light modulating device taken along planes parallel to the line scanning direction on to the corresponding elements of said focussing member.

6. A television receiver comprising asupersonic wave light modulating device, a light source, a slow speed scanner, and an optical system for forming an intermediate image or said light source, a divided field lens system in the plane ing power in the rality or identical lenses situated one above the other in the scanning direction,

and comprising a pluthe optical oen-.

tres oi the lenses being displaced laterally with respect to one another at right angles to the scam ning direction, whereby the Iocussed light cones issuing from the lenses diverge with respect to each other in a direction at right angles to the scanning direction, a second divided optical member being provided in the path or the light cones at a point where they have become fully separated from one another, each portion or this second divided member being adapted to receive one of the "light cones and to direct it onto an image plane in such a way that an the light cones strike the plane in the same straight line which is at right angles to the scanning direction.

'7. A television receiver having a narrow width between the electrodes thereof and a longer length,

of the cell for forming an image thereof on a receiving screen, a second focussing system having power in the direction of the length of the cell for'forming an image thereof on said receiving screen, said second focussing system including -a divided member comprising a plurality oi elements situated side by'side in the, direction of the width of the cell and having their optical centres relatively displaced in the direction of the length of the cell, and a divided field lens situated on said cell to direct light from different portions 01 the length thereof on to corresponding elements of said divided member. I

8. A television receiver employing a supersonic wave light modulating device, means for forming an intermediate immobilised image or the waves in said device, and an optical system for forming a final image of said intermediate image on a receiving plane, and slow speedscanning means this direction, a divided optical system having power in said scanning direction for forming coincident images of portions or said intermediate image lying at right angles to said scanning direction in said final image plane, and a field lens system in the plane or said intermediate image for directing light from said portions on to the corresponding divisions of said divided optical system. 9. A television receiver comprising a supersonic wave light modulating device, means for forming an immobilised diffraction image of the waves in said device, a slow speed scanner, optical focussing means having power in a direction at right angles to the scanning direction of said scanner for forming a final image or said diflractlon image, divided optical focussing means comprising elements having power in said scanning direction for forming coincident images of portions of said difiraction image made by sections taken at right angles to said scanning direction, and a field lens element in the plane of said diffraction image for each or said strips for projectinglight therefrom on to a corresponding element or said divided optical focussing means.

10. A television receiver according to claim I wherein the elements of divided optical tocussinl means are such that they form intermediate images having definition in the scanning direction, and wherein there is provided an optical projection system for forming a final image of said intermediate images.

employing 51 Kerr cell i a first focussin system having power in the direction of the width forming in this direction a final image of said intermediate image, frame scanning means, divided line width tocussing means comprising elements having power in the frame scanning direction for the plane of said in forming images in a second intermediate plane 0'! portions of said first mentioned intermediate image made by sections taken parallel to the line scanning direction, a field lens element for each for projecting the light therefrom or said strips on to a corresponding element of said divided optical focussing means and for forming a plurality of images of secondary images of said aperture on said frame scanning means, and optical projection means having power in the frame scanning direction for forming a final image of said second mentioned intermediate images.

FERENC OKOLICSANYI.

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