USRE22115E

USRE22115E - Light-valve projection apparatus

Info

Publication number: USRE22115E
Authority: US
Priority date: 1938-04-29
Publication date: 1942-06-16
Also published as: NL58116C; BE434064A; DE760691C; FR853622A; GB527886A; US2169838A

Description

June 16, 1942. p, J, HERES-r LIGHT-VALVE PROJECTION APPARATUS TOR TELEVISION SIGNAL EEPRoDucING sYsTEMs original Filed April 29, 193e ATTORNEY Reissued June 16, 1942 LIGHT-VALVE PROJECTION APPARATUS FOR TELEVISION SIGNAL-REPRODUCING SYSTEMS Philip J. Herbst, Fort Wayne, Ind., assigner to Hazeltine Corporation, a corporation of Dela- Ware Original No. 2,169,838, dated August 15, 1939, Serial No. 204,959, April 29, 1938. Application for reissue May 2, 1941, Serial No. 391,571

16 Claims.

This invention relates to television signalreproducing systems and particularly to new and improved light-valve projection apparatus useful in such systems. The invention is especially directed to the provision of an improved lightvalve projection apparatus of the scanning-ray tube type whereby the transmission of light from an independent source may be controlled by the scanning ray to reconstruct a transmitted image with a higher intensity of illumination than is generally attainable in scanning-ray tubes.

This type cf light control is generally referred to in the art as electrical transparency control. It has heretofore been proposed to employ such a control in connection with signal-reproducing tubes of television systems for the purpose of reconstructing an image suiiiciently bright to permit of its being projected in an enlarged size on a screen spaced from the tube. In general,

systems previously proposed to provide control of this type have been subject to various objections including instability and the fact that they involve impractical or complicated apparatus.

It is an object of the present invention, therefore, to provide an improved light-valve projection apparatus of the scanning-ray tube type for use in a television signal-reproducing system whereby a practical electrical transparency control may be obtained.

ln accordance with the invention, a television signal-reproducing system includes a light-valve projection apparatus comprising masking means including a plurality of interspersed elementary transparent and opaque areas, and lens means adapted normally to direct light from a source substantially-only onto said opaque areas of the masking means, whereby the opaque areas normally intercept substantially all o! the light directed onto the masking means by the lens means. The projection apparatus includes television signal-responsive means for varying the focal lengths of incremental areas of the lens means, whereby the masking means transmits light from the source in accordance with the television signal.

In accordance with one form of the invention, a light-valve projection apparatus of the type described comprises masking means of transparent material and the opaque areas thereof comprising a photonegative surface determined by the lens means, whereby it normally intercepts substantially all of the light from the source.

In accordance with a preferred form of the invention, a light-valve projection apparatus of the type described is in the form of a target (Cl. TIS-7.5)

comprising a multiple lens system including a plurality of juxtaposed lens elements. A mask or screen is disposed adjacent the lens system and the lens elements are adapted individually to focus light rays from a given source onto restricted areas of the screen. Each of the lens elements has the property of varying its focus with respect to the screen in response to excitation by a scanning ray. When the target is scanned by a ray, therefore, the foci of the successive lens elements are varied so as to permit the light rays from the independent source to pass through the screen adjacent their respective opaque areas.

In accordance with one approved embodiment of the invention, the target comprises a transparent plate having one of its surfaces formed to provide a plurality of convex juxtaposed incremental areas which serve as the lens elements. The focal lengths of these elements are substantially equal to the thickness of the plate so that the lens elements are adapted normally to focus the light rays from the source on individual areas at the opposite surface of the plate. The screen is preferably formed as a film of photographic emulsion disposed over the focal surface of the plate. The screen, while generally transparent, is developed and fixed, after exposure to light from the source focused thereon by the lens elements, so as to vprovide the opaque portions over the individual focal areas of the lens system and, therefore, to be normally substantially completely opaque to light from such source.

For a better understanding of the invention, together with other and further objects, reference is had to the following description taken in connection with the accompanying drawing, and its scope will be pointed out in the appended claims.

In the accompanying drawing, Fig. l is a schematic diagram of a portion of a television receiver embodying the present invention; Figs. 2, 3, and 4 are fragmentary plan views of portions of the light-valve projection or target structure of the present invention, Fig. 2 showing the lens system separately, Fig. 3 the screen separately after development, and Fig. 4 the lens system with the mask or screen applied thereto; while Fig. 5 is a diagrammatic fragmentary end view of a portion of the light-valve projection or target structure.

Referring now more particularly to Fig. l, the portion of the television receiver there illustrated 55 includes a light-valve projection apparatus applied to a cathode-ray signal-reproducing tube I and line-frequency and field-frequency generators and |2 having their output circuits connected to scanning coils I3 and Il, respectively. The cathode-ray signal-reproducing tube I. includes the usual electron gun comprising a cathode I5 having a heater element Il, a control grid l1, an accelerating anode or screen Il, a focusing anode Il, and a second anode 2li, which generally comprises a conductive coating on the interior surface of the envelope. 'Ihe electron gun serves to develop, accelerate, and focus a beam of electrons or cathode rays, indicated at C, toward a target 2| which comprises a lightvalve projection apparatus and which embodies the present invention and will be hereinafter described in detail.

Proper operating potentials are applied to the various electrodes of a cathode-ray tube from a suitable source, for example, a voltage divider 22 connected across a source of unidirectional voltage as indicated, by way of connections to the various electrodes from suitable points on the voltage divider. A connection 23 is provided for applying the video-frequency modulation voltages to be reproduced to the control grid I1 by way of a suitable leak resistor 2l.

In conventional cathode-ray signal-reproducing tubes, the target 2| usually comprises a iluorescent screen which becomes luminous when excited by the cathode ray during the scanning operation. 'Ihe operation of the system just described, assuming for the moment that a conventional iiuorescent screen is employed as the target, is well understood in the art and a detailed explanation thereof is unnecessary. Briefly, however, a cathode ray is developed, accelerated, and focused by the electron gun toward the target in the well-known manner. Deilecting currents developed by generators Il and I2 are applied to the scanning coils I3 and il to provide magnetic fields to deflect the cathode rays horizontally and vertically, thereby to scan successive ilelds of horizontal parallel lines on the target. During this scanning action, the intensity of the ray is varied in accordance with the videofrequency modulation voltage applied to the control grid Il, corresponding to diiferent values of light and shade in the successive elements of images being transmitted, so that the images are reconstructed on the fluorescent screen by s`uccessive spots of light of varying intensity. While a fluorescent screen cathode-ray tube, such as iust referred to, has proven generally satisfactory, the size of the tube necessarily limits the size of the picture that can be reproduced thereon. Moreover, such a uorescent screen ordinarily does not provide a sufficiently intense light to permit projection of the reconstructed picture and enlargement thereof on a separate screen.

In accordance` with the present invention, therefore, the improved target or light-valve projection apparatus 2| is provided whereby a practical electrical transparency control is obtained. To this end, a source of illumination, as indicated by the lamp 25, is disposed adjacent the transparent end of the tube I! opposite the target 2|. A suitable source 2G of filament voltage supply is provided for the lamp 25, while a reflector 2l and condenser lens 2B may be disposed adjacent thereto to concentrate the light from the lamp and focus it in parallel rays on the inner surface of the target. Adjacent the opposite end of the tube a projecting lens system i9 is preferably disposed,

so that light images reconstructed by the light-valve projection apparatus, as presently to be described, may be projected on a screen (not shown) to provide an enlarged reproduction of the image.

Referring now more particularly to the target 2|, its construction and operation may best be explained with reference to Figs. 2-5, inclusive. Preferably, the target comprises a transparent plate III having one of its surfaces formed to provide a multiplicity of separate minute convex juxtaposed lens elements 3|. A portion of the plate and its lens elements alone are shown in Fig. 2. 'I'he lens elements are so shaped as to have local `lengths substantially equal to the thickness of plate lll, so that normally they focus parallel light rays received from the source 2l by way of the lens system 28 on restricted areas at the opposite surface of the plate III. A mask or screen 32. a portion of which is shown separately in Fig. 3, is disposed over the outer surface of the plate ll. The screen is generally transparent but is opaque, as indicated at 32a, over the individual areas on which the light rays are normally focused by the lens system. Thus, the screen or mask comprises a plurality of interspersed elementary transparent and opaque areas, In Fig. 4 the portion of the plate shown in Fig. 2 is shown superimposed on the corresponding screen portion shown in Fig. 3. Preferably, the opaque portions oi' the screen are determined by, and complementary to, the lens system itself and, in accordance with the preferred embodiment of the invention, this is accomplished by the particular manner in which the screen is constructed.

Referring more particularly to the construction of the target, the plate 30 and its lens elements may, for example, be formed by disposing a layer of spherical transparent elements of quartz or other suitable material over a sheet of transparent material, such as glass. This structure may be then heated to incipient fusion and the spherical elements pressed into the glass sheet so as to form a substantially integral structure. The cathode-ray tube may then be assembled with the plate-like lens structure forming one end thereof as shown in Fig. l. As the iinal step in the tube construction, a suitable coating of photographic emulsion may be applied to the outer surface of the plate 30. The emulsion may thereupon be exposed to rays of light from the source 25, focused thereon through the lens system 28, and subsequently the emulsion may be developed and fixed, thereby to provide the screen 32 constituting a photonegative surface which is generally transparent but includes opaque areas complementary or corresponding and determined by, the lens system itself, thereby avoiding the leakage of light through the screen that would result from any failure of the focal areas of the lens system to register with the opaque areas which might otherwise result due to the minute size of the lens elements Il.

The substance of the lens elements is such as to give them the property of varying their focus with respect to the screen in response to excitation by a scanning ra thereby to permit the light rays to pass through the screen adjacent their respective opaque areas. More particularly, changes in temperature or the well-known piezo-electric eil'ect caused by the impingement of a scanning beam. such as a cathode ray, on the lens elements, eil'ect variations either in the physical configuration of the lens eements or in their indices of refraction, or both.

The lens elements 3| comprise a cathode-ray sensitive element of the lens system and may be of any suitable material, such as quartz in the crystalline stage, which exhibits sensitivity to electron bombardment, both as to changes in its dimensions and its index of refraction and which is also quite satisfactory for the purpose of sealing in vacuum. Also certain salts, such as Rochelle salts, may be used. The latter, while more sensitive to electron bombardment than quartz, is not, however, as adaptable for use in high vacuum apparatus, which musi generally be exhausted at high temperatures. The individual lcns elements may be formed by grinding small crystals in a continuously rotating mill, until they assume the required spherical form.

In Fig. 5 a portion of the target is shown with parallel light rays, indicated by the broken lines, passing through its lens elements. Under normal conditions, the rays are focused by the lens elements 3| on the opaque portions 32a of the screen, as shown, whereby the opaque areas 32a intercept substantially all of the light directed on the masking means by the lens system. A cathode ray, however, indicated at C, is shown impinging upon one of the lens elements and varying its focus, as described above, so that the defocused light rays pass through the screen at the portions adjacent the opaque portions corresponding to this particular lens element.

In the operation of the receiving apparatus embodying the present invention which is shown in Fig. 1, the light rays from the source are projected by means of the lens system 2B in parallel rays on the inner surface of the target ZI. Due| to the focusing of the rays by the elcments 3| and the complementary opaque por tions of the screen 32, however, no light normally passes through the mask or screen 32.

However, as the television signal-modulatedelectron beam C is deflected to scan a series of parallel lines or fields on the target, it successively impinges upon the lens elements 3| and effects a variation in their foci, thereby successively varying the focal lengths of incremental areas of the lens system to an extent corresponding to the intensity of the electron beam as controlled by the video-modulation signal applied to the control grid of the tube. This defocusing action thus permits the light rays to pass through the areas of the screen adjacent the opaque portions corresponding to the particular lens elements on which the beam is focused, the

amount of the light transmitted. through each incremental area being dependent upon the amount of defocusing of the lens elements included in such area and thus on the 'intensity of the cathode-ray beam. Thus, the mask or screen 32 transmits light from the source 25 in accordance with the television signal. The transmitted image is thus apparently reconstructed on the outer surface of the target. Moreover, the brightness of this image is suiciently intense to permit its being projected by the lens system 29 upon a suitable screen spaced from the target, thereby to provide an enlarged image. The size of the lens elements will be substantially smaller than the size of the cathode-ray spot, preferably having a diameter of the order of one-tenth the diameter of the spot to ensure uniformity of the lens action.

While there has been described what is at present considered to be the preferred embodiment of this invention, lt will be obvious to those skilled in the art that various changes and modifcations may be made therein without departing from the invention, and it is, therefore, aimed in the appended claims to cover all such changes and modifications as fall within the true spirit and scope of the invention.

What is claimed is:

l. In a television signal-reproducing system, a light-valve projection apparatus comprising, a multiple lens system including a plurality of juxtaposed lens elements, a screen adjacent said lens system, said lens elements being proportioned to focus parallel light rays on individual separate areas of said screen, said screen being generally transparent but opaque over said areas, each of said lens elements having the property of varying its focus with respect to said screen in response to excitation by a scanning ray, thereby to permit said light rays to pass through said screen adjacent its respective opaque areas.

2. In a television signal-reproducing system, a light-valve projection apparatus comprising, a multiple lens system including a plurality of juxtaposed lens elements, a screen adjacent said lens system, said lens elements being adapted to focus parallel light rays on said screen, said screen being generally transparent but having opaque areas determined by, and complementary to, said lens system, whereby said target is normally opaque to said light rays, each of said lens elements having the property of varying its focus with respect to said screen in response to excitation by a scanning ray, thereby to permit said light rays to pass through said screen adjacent its respective opaque areas.

3. In a television signal-reproducing system, a light-valve projection apparatus comprising, a transparent plate having formed on one of its surfaces a plurality of convex juxtaposed incremental areas comprising separate lens elements having focal lengths substantially equal to the thickness of said plate, whereby said lens system is adapted to focus parallel light rays on individual areas at the opposite surface of said plate, a screen disposed over said opposite surface, said screen being generally transparent but opaque at portions corresponding to said focal areas, each of said lens elements having the property of varying its focus with respect to said opposite surface in response to excitation by a scanning ray, thereby to permit light rays to pass through said screen adjacent its respective opaque areas.

4. In a television signal-reproducing system, a light-valve projection apparatus comprising, a transparent plate having formed on one surface thereof a multiple lens system including a plurality of juxtaposed lens elements, a screen comprising a lm of photographic emulsion disposed on the opposite surface of said plate, said lens system being proportioned to focus parallel light rays on individual areas at the opposite surface of said plate, said screen being generally transparent but developed and fixed after exposure to light rays focused thereon by said lens elements to render said areas opaque, each of said lens elerr ents having the property of varying its focus with respect to said screen in response to excitation by a scanning ray, thereby t0 permit said light to pass through said screen adjacent its rerpective opaque areas.

5. In a television signal-reproducing system, a light-valve projection apparatus comprising, a transparent plate having formed on one of its surfaces a plurality of convex juxtaposed incremental areas providing separate lens elements having focal lengths substantially equal to the thickness of said plate, whereby said lens elements are adapted to focus parallel light rays on individual areas at the opposite surface of said plate, a screen comprising a nlm of a photographic emulsion disposed over saidopposite surrace, said screen being generally transparent but developed and iixed after exposure to said light rays focused thereon by said lens elements to render said areas opaque, each of said lens elements having the property oi varying its focus with respect to said screen in response to excitation by a scanning ray, thereby to permit said light rays to pass through said screen adjacent its respective opaque areas,

6. In a television signal-reproducing system, a light-valve projection apparatus comprising, masking means including a plurality of interspersed elementary transparent and opaque areas, lens means including only substantially rigid lens elements and adapted normally to direct light from a source substantially only onto said opaque areas of said masking means, whereby said opaque areas normally intercept substantially all of the light directed onto said masking means by said lens means, and television signalresponsive means for varying the focal lengths of incremental areas of said lens means, whereby said masking means transmits light from said source in accordance with said television signal.

"I. In a television signal-reproducing system, a light-valve projection apparatus comprising, masking means including a plurality of interspersed elementary transparent and opaque areas, lens means including a. cathode-ray sensitive element and adapted to direct light from a source substantially only onto said opaque areas of said masking means, whereby said opaque areas normally intercept substantially all of the light directed onto said masking means by said lens means, and television signal-responsive cathode-ray means for scanning said lens element in a predetermined pattern successively to vary the focal lengths of incremental areas of said lens means, whereby said masking means transmits light from said source in accordance with said television signal.

8. In a television signal-reproducing system, a light-valve projection apparatus comprising, masking means including a plurality of interspersed elementary transparent and opaque areas, lens means adapted normally to direct light from a source onto restricted areas of said masking means, said masking means being of transparent material and said opaque areas thereof comprising a photonegative surface dete N ed by said lens means, whereby it normally intero ts substantially all of the light from said source, and television signal-responsive means for varying the focal lengths of incremental areas of said lens means, `whereby said masking means transmits light from said source in accordance with said television signal. Y

9. In a television signal-reproducing system, a light-valve projection apparatus comprising, masking means including a plurality of interspersed elementary transparent and opaque areas, lens means including an element of transparent material adapted normally-to direct light from a source onto restricted areas of said masking means, said masking means being oi' transparent material and said opaque areas thereof comprising a photonegative surface determined by said lens means, whereby it normally intercepts substantially all oi the light from said source. and television signal-responsive means tor varying the index of refraction of incremental areas of said transparent material to vary the focal lengths of incremental areas of said lens means, whereby said masking means transmits light from said source in accordance with said television signal.

10. In a television signal-reproducing system, a light-valve projection .apparatus comprising, lens means including a substantially rigid lens element adapted to have a light-transmission characteristic of elemental areas thereof modified in response to excitation by a scanning ray, masking means arranged in cooperative relation with said lens means normally to mask a substantial part of the light transmitted thereto by said lens means from a light source, and television signal-responsive scanning-ray means for modifying said light-transmission characteristic of elemental areas of said lens means to permit an increased amount of light from said source to pass said masking means.

l1. In a television signal-reproducing system. a light-valve projection apparatus comprising, lens means adapted to have the index of refraction of elemental areas thereof modiiied in response to excitation by a scanning ray, masking means arranged in cooperative relation with said lens means normally to mask a substantial part of the light transmitted thereto by said lens means from a light source, and television signalresponsive scanning-ray means for modifying the index of refraction of elemental areas of said lens means, to permit an increasing amount oi light from said source to pass said masking means.

12. In a television signal-reproducing system, a light-valve projection apparatus comprising, lens means including a plurality of lens elements one of which comprises effectively a mosaic of elemental substantially rigid lenses, masking means arranged in cooperative relation with said lens means normally to mask a substantial part of the light projected thereto by said lens means from a light source, and television signal-responsive means for modifying a light-transmission characteristic of incremental areas of said one element to permit an increasing amount of light from said source to pass said masking means in accordance with said television signal.

13. In a television signal-reproducing system, a light-valve projection apparatus comprising, lens means including a plurality of lens elements one of which comprises effectively a plurality of juxtaposed elemental substantially rigid lenses, masking means arranged in cooperative relation with said lens means normally to mask a substantial part oi' the light projected thereto by said lens means trom a light source, and television signal-responsive means for modifying a lighttransmission characteristic of incremental areas of said one element to permit an increasing amount of light from said source to pass said masking means in accordance with said television signal.

14. In a television signal-reproducing system, a light-valve projection apparatus comprising, masking means including a plurality of interspersed elementary transparent and opaque areas, lens means including only substantially rigid lens elements and adapted normally to focus light from a source substantially only onto said opaque areas of said masking means, whereby said opaque areas normally intercept substantially all of the light directed onto said masking means by said lens means, and television signalresponsive means for varying the focal lengths of incremental areas of said lens means, whereby said masking means transmits light from said source in accordance with said television signal.

l5. In a television signal-reproducing system, a light-valve projection apparatus comprising, a light source, a viewing means, masking means having a plurality of interspersed elementary transparent and opaque areas and interposed in the optical path between said source and said viewing means, lens means including only substantially rigid lens elements and adapted normally to focus substantially all of the light from said source onto said opaque areas of said masking means, means for ell'ectively altering the optical path-length of elementary portions of the optical path through said lens means for varying the amount of light masked from said viewing means by said opaque areas of said masking means, and means for controlling said lastnamed means in accordance with said television signal to form on said viewing means a visible image corresponding to said television signal.

16. In a television signal-reproducing system, a light-valve projection apparatus comprising, a transparent plate having formed on one surface thereof a multiple lens system including aplurality of juxtaposed lens elements, said lens elements being proportioned to focus parallel light rays on individual areas at the opposite surface cf said plate, a screen disposed adjacent said opposite surface of said plate, said screen being generally transparent but opaque at said individual areas and being also opaque over all areas corresponding to the areas of said transparent plate not covered by said lens elements, each of said lens elements having the property of varying its focus with respect to said screen in response to excitation by a scanning ray, thereby to permit said light to pass through said screen adjacent its respective opaque areas.

PHILIP J. HERBST.