US2905757A

US2905757A - Light correcting apparatus for electron pick-up tubes

Info

Publication number: US2905757A
Application number: US485776A
Authority: US
Inventors: James Ivanhoe John Penfound
Original assignee: EMI Ltd
Current assignee: EMI Ltd; Electrical and Musical Industries Ltd
Priority date: 1954-02-03
Filing date: 1955-02-02
Publication date: 1959-09-22
Anticipated expiration: 1976-09-22

Description

Sept. 22, 1959 J p JAMES 2,905,757

LIGHT COREbTING APPARATUS FOR ELECTRON PICK-UP TUBES Filed Feb. 2, 1955 26 FIG 3 FIG. 2.

LIGHT CORRECTING APPARATUS FOR ELECTRON PICK-UP TUBES Ivanhoe John Penfound James, South Ealiug, London,

England, assignor to Electric & Musical Industries Limited, Hayes, Middlesex, England, a British company Application February 2, 1955, Serial No. 485,776

Claims priority, application Great Britain February 3,1954

18 Claims. (Cl. 178-72) This invention relates to apparatus embodying electronic pick-up tubes.

Such pick-up tubes are frequently employed for the generation of signals suitable for television transmission purposes. In one such tube a photo-electric target electrode is provided which is arranged to be scanned by a low velocity scanning beam so that the elements of the target electrode are brought to a datum potential corresponding substantially to that of the cathode which gen erates the scanning beam. Signals are generated during scanning and signal voltages are set up across a signal impedance connected to a signal electrode associated with the target electrode. With this type of tube it is found that the sensitivity of the target electrode is not consistent at all points on the target electrode and in fact in general the sensitivity decreases towards the edges of the area scanned by the beam. In order to correct for this change of sensitivity over the area of the target electrode, it has been proposed to provide a translucency over the window of the tube through which the image is projected, such translucency being inversely proportional to the change of sensitivity of the target electrode so that when an optical image is projected through the translucency on to the target electrode, the intensity of the light image is changed so as to compensate for the change in sensitivity of the target electrode. When such a translucency is arranged in contact with the window of the pick-up tube, difliculties arise due to internal reflections at the interface and other problems also arise during the processing of the translucency.

In some apparatus a cathode ray tube is employed on which an optical image is reproduced and such image is then projected by an optical system on to a pick-up tube, the target electrode of which is scanned to generate signals from the image projected on to said pick-up tube. One example of such an apparatus is described in the specification of United States patent application Serial No. 384,704 in which three cathode ray tubes and three pick-up tubes are employed in a colour television system for converting frame sequential colour signals into simultaneous colour signals. In such apparatus not only do imperfections occur in the pick-up tubes out also in the fluorescent screen or screens of the cathode ray tube or tubes and in the optical system or systems. In a colour converting apparatus as referred to above it is particularly important that the signal response of the several pick-up tubes employed to be substantially the same although it may not be necessary to ensure that the signal response be constant throughout the Whole of the area' of the target electrode of the pick-up tubes.

The object of the present invention is to provide an improved apparatus with a view to overcoming some or all of the above-mentioned difiiculties.

According to one feature of the invention there is provided a cathode ray tube having a fluorescent screen on which images can be produced, a pick-up tube spaced from said cathode ray tube and having a sensitive surface, and an optical system for projecting images produced on 2,905,757 Patented Sept. 22, 1959 said cathode ray tube on to said pick-up tube and where means are provided in the optical path prior to said pickup tube for modifying the light projected on to said pickup tube to compensate at least in part for inconsistencies in said fluorescent screen, said optical system, or said surface.

According to another feature of the invention there is provided apparatus comprising a plurality of pick-up tubes each having a sensitive surface and an optical system for projecting light images on to said sensitive surfaces and light modifying means in the optical path prior to said pick-up tubes for modifying the light projected on to said pick-up tubes so as to make the signal response of said tubes substantially the. same.

In order that the said invention may be clearly understood and readily carried into effect, it will now be more fully described with reference to the accompanying drawings, in which:

Figure 1 illustrates diagrammatically a plurality of cathode ray tubes and pick-up tubes suitable for use in a colour conversion system and including modifying means according to one embodiment of the invention,

Figure 2 illustrates a modification of the light modifying means illustrated in Figure l, and

Figure 3 illustrates a further form of light modifying means suitable for use in the invention.

The present invention can be employed with pick-up tubes on to which an image of a scene for transmission is directly projected by an optical system and in which an optical image is projected simultaneously on to a plurality of pick-up tubes such as in some television cameras employed for producing colour signals. The invention is, however, particularly applicable to a converting system for use in colour television such as is described in the specification of United States patent application Serial No. 384,704 and will be described in the following specific embodiments as applied to such a system.

As shown in Figure 1 of the drawings, three cathode ray reproducing tubes 1, '2 and 3 are provided having fluorescent screens on which optical images representative of the diiterent colour components of an image are reproduced. Images of the scenes produced on the cathode ray tubes 1, '2 and 3 are then focussed by optical systems indicated at 4, 5 and 6 on to three pick-up tubes 7, 8 and 9. Each of these pick-up tubes may be of the type hereinbefore referred to having a photo-sensitive target electrode 10, t1 and 12 which is arranged to be scanned by a low velocity scanning beam. Such a type of pick-up tube is well-known in the art. The images formed on the

cathode ray tubes

1, 2 and 3 are reduced in size by the optical systems 4, 5 and 6 before being projected on to the pick-up tubes 7, 8 and 9.

As stated above, the photo-

sensitive target electrodes

10, 11 and 12 may not have consistent sensitivities throughout their areas and in accordance with the present invention, in order to cause the signal response of said target areas to be substantially the same for each of said tubes 7, 8 and 9, means are provided in the optical paths between the tubes 1 and the target electrodes of the pick-up tubes 7, 8 and 9 and out of focalplanes in said paths in order to modify the light projected on to said last-mentioned tubes. Where the change in sensitivity of the target electrode 10 of the pick-up tube 7 is of intensity towards the edges of the target electrode 10"so that compensation for the change in sensitivity towards" the edges of the target electrode can be effected. The member 13 is mounted on a pillar 14 which is connected by a universal joint 15 such as a ball and socket joint, to a further pillar 16. which is, in turn, mounted for ver tical adjustment in a socket I7 projecting from a pillar 18 mounted on a sleeve 19 slidably arranged to a support 20. The pillar 16 and the sleeve 19' can be retained in adjusted position by means of

screws

21 and 22. Thus, the member 13 is mounted so that its position along the axis of the optical system can be varied and so that it can be adjusted laterally with respect to the optical system and also rotated relatively thereto and for tilting movement, these facilities enabling assymetrical variations in sensitivity of the target electrode to be compensated. By suitably choosing the size of the member 13 and its position in the optical path, the change of sensitivity of the target electrode can be caused to be c nsistent throughout its area. It will be appreciated that similar members are provided in the optical paths of the

tubes

2 and 3, and 3 and 9, and by suitably adjusting the various members 13 it can be arranged that the signal response of the tubes 7, 8 and 9 can be made substantially the same, although this does. not necessarily mean that the change ofsensitivity of each of said target areas is completely compensated, since in the arrangement shown in Figure 1 it may be sufiicient for the members 13 to be adjusted so that the signal response of. each of the. tubes 7, 8 and 9 is substantially the same.

If desired the members 13 may be provided with one or more slots or holes 23 so that irregular variations of sensitivity can be compensated or the member 13. may have, a shape other than a rectangular one.

Figure 2 of the drawings illustrates a further. embodimerit of light modifying means which comprises a small sheet 24 of rubber or other suitable stretchable material which is mounted in a frame 25 of suitable shape, such as rectangular as shown, and disposed outside the optical path, the four sides of the member and the, four cor ners being connected to rods or wires 26, the ends of said wires or rods remote from the member 24. being connected to screws 27 passing through the frame and having adjusting nuts 28 whereby on rotation of said nuts the wires or rods 26 are moved longitudinally so as to stretch the member 24 so that its. shape can be readily adjusted to compensate for irregular variations in sensiivity.

1 Figure 3 of the drawings illustrates a. further form of light modifying means. which is, in the form of a translucent filter 29 which has av graded transmission factor represented by the horizontal lines 30 and which serves to. compensate for variations in sensitivity of the target electrode.

The. light modifying means referred to above can, of course, be employed for compensating for changes in the sensitivity of the fluorescent screens of the

cathode ray tubes

1, 2 and 3 and also for compensating for imperfections in the optical systems 4, 5 and 6.,

The invention can also be employed in connection with a television camera for generating colour television signals in which three pick-up tubes are employed and the scenes of an object from which colour signals are required are projected through an optical lens into a beam splitting system which serves to project images on tothe, three pick-up tubes. In such an arrangement the light modifying means may be employed after the beam has been split and prior to the projection of split-light beams on to the sensitive surfaces of the target electrodes. The invention can also be applied to the known type of pick-up tube in which an optical image is first converted into an electron image before being projected.

on to the target electrode.

What I claim is:

1., Apparatus comprising apick-up tube having a light sensitive surface the sensitivity of which is not con- Sis ent. throughout. its area. means for. projecting abe m of light onto said surface along an optical path between said means and said surface, light modifying means to spatially vary the intensity of light in said beam disposed in said optical path and remote from a focal plane in said path to compensate. at least in part for the nonconsistent sensitivity of said surface and means mounting said light modifying. means in an adjustable. manner in said light path.

2. Apparatus according to claim 1 wherein said light modifying means comprises an opaque member the area of which is. small compared with the area of said beam of light at the disposed position of said light modifying means.

3. Apparatus according to claim 1 wherein said light modifying means comprises an. opaque member which is small compared with the area of said light beam at the disposed position of said light modifying means, said opaque member including at least one aperture to compensate for irregularities in the sensitivity of said sensitive surface.

4. Apparatus according to claim 1 wherein said light modifying means comprises a sheet of stretchable material and means mounting said material to stretch said material at a plurality of points around its periphery.

5. Apparatus according to claim 1, wherein said light modifying means comprises a graded translucent filter.

6. Apparatus comprising, a cathode ray tube having a fluorescent screen on which light images can be produced, a pick-up tube spaced from said cathode ray tube, said tube having a light sensitive surface, an optical system. for projecting light images produced on said cathode ray tube in a beam along an optical path between said system, said surface and light modifying means to spatially vary the intensity of light in said beam and disposed in said optical path and remote from a focal plane in said path to compensate at least in part for an inconsistency in said fluorescent screen, said optical system or said surface and means mounting said light modifying means in an adjustable, manner in said light path. 7

7. Apparatus according to claim 6 wherein said light, modifying means comprises an opaque member the area: of which is small compared with the area of said beam. of light at the disposed position of said light modifying. means.

8. Apparatus according to claim- 6 wherein said. light. modifying means comprises an opaque member which is. small compared with the area of said light beam at the. disposed position of said light modifyingmeans, said opaque member including at least one aperture to com pensate for irregularities in the sensitivity of said sensitive. surface.

9. Apparatus according to. claim 6 wherein said light modifying means comprises a sheet of stretchable ma-- terial and means mounting said material to stretch: said, material at a plurality of points around its periphery.

10. Apparatus according to claim 6, wherein said light. modifying means comprises a graded translucent filter.

11. Apparatus comprising a plurality of pick-up. tubes, each having a light sensitive surface, the sensitivity of which is not constant throughout its area, optical means for projecting beams of light onto said surfaces along; optical paths between said means, said surfaces. and light modifying means to spatially vary the intensity of light. insaid beams and disposed in said optical paths and remote from focal planes in said paths to make the signal. re.- spouses of said tubes substantially the same and meansmounting said light modifying means in adjustable manners in said light paths.

12. Apparatus according to claim. 11 wherein said light modifying means comprises opaque members, the areas of which are small compared with the areas of said beams of light at the. disposed positions of said light modifying means.

13. Apparatus according to claim 11 wherein said light.

modifying means. comprise opaque members. which are;

small compared with the areas of said light beams at the disposed positions of said light modifying means, each opaque member including at least one aperture to compensate for irregularities in the sensitivity of said sensitive surfaces.

14. Apparatus according to claim 11 wherein each of said light modifying means comprises a sheet of stretchable material and means mounting said material to stretch said material at a plurality of points around its periphery.

15. Apparatus according to claim 11, wherein said light modifying means comprises a graded translucent filter.

16. Apparatus comprising a pick-up tube having a light sensitive surface the sensitivity of which is not consistent throughout its area, means for projecting a beam of light onto said surface along an optical path between said means and said surface, light modifying means to spatially vary the intensity of light in said beam disposed in said optical path and remote from a focal plane in said path to compensate at least in part for the non-consistent sensitivity of said surface and means universally mounting said light modifying means for adjustment in all directions in said light path.

17. Apparatus comprising a cathode ray tube having a fluorescent screen on which light images can be produced, a pick-up tube spaced from said cathode ray tube, said tube having a light sensitive surface, an optical system for projecting light images produced on said cathode ray tube in a beam along an optical path between said system and said surface, light modifying means to spatially vary the intensity of light in said beam and disposed in said optical path and remote from a focal plane in said path to compensate at least in part for an inconsistency in said fluorescent screen, said optical system or said surface and means universally mounting said light modifying means for adjustment in all directions in said light path.

18. Apparatus comprising a plurality of pick-up tubes each having a light sensitive surface, the sensitivity of which is not constant throughout its area, optical means for projecting beams of light onto said surfaces along optical paths between said means and said surfaces, light modifying means to spatially vary the intensity of light in said beams and disposed in said optical paths and remote from focal planes in said paths to make the signal responses of said tubes substantially the same and means universally mounting said light modifying means for adjustment in all directions in said light paths.

References Cited in the file of this patent UNITED STATES PATENTS 2,188,679 Dovaston et al I an. 30, 1940 2,415,981 Wolff Feb. 18, 1947 2,431,824 Poch Dec. 2, 1947 2,474,628 Hurvitz June 28, 1949 FOREIGN PATENTS 916,298 Germany Aug. 9, 1954