US 2056761 A
Description (OCR text may contain errors)
Oct. 6, 1936.
J. L. BAIRD TELEVISION AND LIKE APPARATUS Filed Nov. 10, 1931 5 Sheets-Sheet 1 .fo/4N Loa/E BA leo,
Oct. 6, 1936. J. L, BAIRD 2,056,761
TELEVISON AND LIKE APPARATUS Filed Nov'. 1o, 1931 -s sheets-sheet 2 [Q IQ n 1 n 1 INVENTOR. JoHN oe/E BA1/2D,
oct. 6, 1936. J. BAIRD 2,056,761
TLEVISION AND LIKE APPARATUS Filed Nov'. 1o, 1951v s sheets-sheet s JOHN oe/E BA/QD,
Patented Oct. 6, 1936 UNITED STAT-Es vPATENT OFFICE Application November 10, 1931, Serial No. 574,114
In Great Britain November 12, 1930 3 Claims.
This invention relates to two-way television apparatus, that is to say, apparatus by means of which two persons situated at a distance may see each other at the same time. The invention relates more particularly to apparatus for enabling two people who are telephoning to each other to see each other simultaneously.
In systems which have hitherto been proposed for the purpose, it has been impossible for two persons to look directly at each other; that is to say, if one were looking straight into the screen, the other would see, not a full face view of him, but a partly side face, as the transmitting apparatus would be in a direction different from that of his line of vision.
To make this difficulty clearer it will be understood that in present systems of television the subject being transmitted is viewed by a lens (where oodlighting is used) or is scanned by a beam of light (where spotlighting is used). In hitherto proposed two-way television systems it has been found necessary to place the receiving screen outside the solid angle formed by the moving beam of the transmitter. Therefore, when the person being transmitted looks at the receiving screen to see the person to whom he is speaking he has to turn his eyes, or even his head, away from the viewing lens of the transmitter so that on the screen at the receiving 3 station he does not appear to be looking at the person to whom he is talking. It is highly desirable in two-way television that the operators Should be able to look straight at each other and this invention is concerned with devices with this object.
According to the present invention, the actual or virtual position of the receiving screen at each end of a two-way television system lies Within the solid angle formed by the scanning 40 beams of the co-terminal transmitter.
According to a feature of this invention the operator at each end of a two-way television `system is scanned from the same direction as that in which he sees an image of his co-operator.
In combination with these features the present invention also contemplates the contemporaneous scanning of the operator and reconstitution of an image for his beneiit at each station, the processes of scanning and reconstitution being substantially coinitial and concurrent as regards commencement and completion of traversal.
It will be appreciated by those skilled in the art that when an image is reconstituted within the Vangle of the scanning rays, it may become inconvenient or impossible for the operator to observe this image by reason of the superior brightness of the scanning beams employed in spotlight transmission, compared with the brightness of the image-forming rays.
Accordingly, in order to avoid dazzling the op- Yeratorat each of apair of co-operating stations, it is further proposed to employ radiation of low or substantially zero luminous value for scanning each operator when a spotlight method of traversal is used, in conjunction with devices sensitive to radiation particularly in the appropriate spectral region.
For instance, in one embodiment ofthe present invention I may use a transmitting disc with two spirals of holes; through one spiral the light passes; behind the other spiral are little mirrors at right angles tothe plane of the disc and directed towards the centre or the periphery of the disc. Near the centre or the periphery of the disc is a plate neon tube modulated in accordance with the currents from the transmitting station. The light from this neon tube is directed by the little mirrors through the holes in the disc Vcorresponding to the receiver. Now, the effect vof this is that the person being transmitted looks into the lens and sees the image caused by the light from the neon tube being reflected through the spiral of holes, but at the same time he is scanned by the beams coming through the other series of holes adjacent to the receiving holes. Thus he can look directly into the lens and see the image while he is Vbeing Viewed full face by the transmitting device, a similar arrangement being used at the other station.
It will be obvious that the beams of light will tend to dazzle the persons being transmitted, and to overcome this I use screens passing the infra-red rays only, as described in prior British Patent No. 288,882, and well known under the name of Noctovision.
In another form of this device, I use two discs, the receiving disc kbeing nearer to the observer than the transmitting disc and having perforations in it to permit the beams from the transmitting disc to pass through it without interruption, as both discs revolve, this disc `having affixed to it mirrors at an angle, or prisms to enable the light vfrom the neon tube to pass through the apertures in it, the neon tube itself being so situated as to be outside the solid angle made by the image beams.
YIt will be understood that, although I have described a beam of light passing over the subject, a similar effect would be obtained with floodlighting, only instead of objective beams I would have a moving coneY of light, the cone .being that subtended by the small elemental area into which the image is divided. u
In another form of this device, I may produce the received image by Vcausing a spot of light with an attendant moving screen to be placed within the cone of the light beams, the moving screen upon which the spot is projected being so arranged with perforations that as it revolves, the image beams pass freely throughit at all times. A mirror-drum., for example, may be used to project a point of light on to this screen, the two scanning devices and the screen being so arranged that the screen does not interfere with the scanning beams.
In another form of device, I place va screen at an angle across the solid angle made by the image beams, this screen reflecting the visible light and transmitting infra-red light. Thus the observer, looking at this screen from an Y angle as properly arranged, looks at the reflection of the image of a television receiver seen on the infra-red screen. The person can be so adjusted that when he is looking directly at the reflected image, he is looking directly into the scanning lens.
. An ordinary filter possesses this property of relecting visible light to a certain degree, and may be used; or the effect may be enhanced by using a partly silvered screen, so long as the opacity of the Yscreen is not such as to destroy the eiect of the transmitting beam. Y
In order that the details of construction and action of the present invention may be the more clearly understood, reference is made to the accompanying drawings in whichrf- Figure l represents a perspective View of the one embodiment of the invention,
Figure 2 is a plan of Figure 1, showing the rays of both scanning beams, Y
Figure 3 is a plan of a further embodiment of the invention,
Figure V4 shows a perspective view of yet another embodiment of the present invention and Figure 5 shows a further embodiment of the present invention in which a single mirror drum scanning and reconstituting device is used in place of the pair of drums shown in Figure 4.
In Figure l, light from a powerful Asource I passes through an aperturedmask 2, and then .through a iilter 3 which may be a thin sheet of ebonite so that only infra-red light is transmitted. This infra-red light is focussed on to the observer 5 by the large lenses l spirally arranged on the scanning disc 5, sothat on rotation'of the disc the observer 6 is scanned systematically by a spotl of intense infra-red light. The diffused light from the observer is received by the light sensitive devices 1,' which or cells of the thalium sulphide type. In addition to the spiral of large lenses the disc also has a spiral of small apertures V9 arranged so that. a small aperture is situated between two adjacent large lenses. Be`
hind these small apertures are small reflectors l0, arranged at such an angle that they reflect light from an electric glow lamp 8 to the eye of the observer 6. Now the lamp 8 is being modulated in Vaccordance with the image signal of the observer at the distant station. Hence, to look straight at his co-observer at the distant station the observer 6 stares at the traverse area of the small apertures and is therefore looking straight at the infra-red scanning beam and therefore his image appears full face at the distant station. Figure 2 shows more clearly the arrangement of the reectors I0 behind the small apertures 9; each reflector being xed at an angle such that the light from the glow lamp is reflected towards the observer in the same direction as the invisible spot-light scanning beam.
In connection with the scanning disc of the two co-operating stations, it is important to notice that when a large lens is in operation at one station, a small aperture must be in operation at the other station. For example, suppose the relative arrangement of the large and small apertures at the near station is such that a large aperture comes into operation very soon after a small aperture, then at the distant station a small aperture must come into operation an equally short time after a large aperture. In terms of the arrangement of the apertures on the; discs, this means that `each disc is made and operated in such a way that a large aper (not shownin the drawings) falls upon the mirror-drum and is focussed (as an intense light spot) upon the observer 6. Thus, on rotation of the drum Vthis light spot is systematically kpassed over the observer, and part of the diffused light is receivedon the cells 'I in the usual Way. Between the mirror-drum I2 and the observer is a lterV I5 which transmits chiefly or exclusively the invisible component of the light. This iilter has the side towards the observer highly polished and is set at an angle of to a scanning disc IIIV which is mounted parallel rto the drum and maybe on the same shaft. Behind the disc I4 is an electric Vglow lamp 8, the light from which is reflected by the polished surfacesv of the filter I5 towards the vobserver 6. This glow lamp is modulated by the image signal from the distant station so thatV the observer 6, in looking at his co-operator, is caused to look directly into the invisible scanning beam as before.
In Figure 4 members I5' and I Gare two mirrorf drums mounted on the same shaft and running in connection with the disc 5I. This disc has arranged upon it large clear apertures II intercalated with large apertures I8 which are covered with light diffusing screens, such as ground glass or frosted gelatine. The method of operation is as follows: Light from an intense source I passes through a lter 3, which transmits only the infra-red (or other invisible) components, and is reflected at the mirror-drum I5 on to the observer 8, having passed through one of the clear apertures in the disc 5I. This lightV is focussed as an intense spot by means of the lens system I9 and the light diffused fromvthe observer is received by the photo-electric cells 'I in the usual manner. Light from the electric glow lamp 8|, which may be for example, the well known hot cathode type of lamp, is focussed by the lens system 20 so as to form, vafter reilection at the mirror-drum I6, a real image `the observer 6 gatathe plane of the disc :5I; thus when the llight diffusing-screen intersects its lpath Aa bright spot is seen in the plane of the disc. The lamp 8| isimodulated by the image signals from thedis- Ytant-station. The rotation of the mirror-drums 4|.5and I6 and the disc 5| .is Varrangedby means YVof anappropriate system of gears, so that during "the;period that a clear aperture is Vin line with and the drums, light from the vdrum I5 scans one strip of the image of the Thus the observer E sees an image of as before,'in'gazing at this imagehe is also looking :straight into the spot-light scanning beam.
In this last-mentioned embodiment of the present 'invention it will be seen that strips from the images of the two operators may be transmitted alternately by appropriate masking and these intercalated signals may be transmitted over a single channel in the manner described in my co-pending British application No. 6712/31. The same method of scanning may be effected by the embodiments illustrated in the other drawings. For example, in the apparatus illustrated in Figure 1, this end may be attained by making the spot-light traverse area twice the height of the observer to be scanned, by masking the unused part of the scan and receiving and reconstituting the image signal from the distant station during the intervals in the spot-light scanning.
In Figure 5 light from an arc lamp I passes through an aperture 2 I, in a mask or diaphragm 2, and is transmitted by a lens ISI on to a mirror drum |5I whence it is reflected by way of apertures |`|I in a disc 52 on to the subject of the transmission or observer 6. The apertures 1| are preferably covered with iilters which are opaque or substantially opaque to radiation in the visible portion of the spectrum of the arc. Radiation diffused from the exposed surface of the subject 6 becomes incident upon sensitive cells 1 and becomes operative in transmitting signals by way of Aan amplifying system 38 to a line or channel of communication 39.
In the mask 2, there is an additional aperture 22, having a small reflector 23, co-operating therewith to pass light from a glow discharge lamp 8|, in the direction of the lens I9I and thence to the mirror-drum |5I. Now if the centres of the apertures 2|, 23 are arranged to lie in a plane at right angles to the axis of the drum |5| then image-forming beams will be reflected by the mirrors of the drum in the same direction as the scanning beams, but not in general, coincident therewith. These image forming beams impinge upon coverings of diifusive material in the apertures I8 of the disc 52, and serve to reconstitute an image of the subject or observer at the distant station when the glow discharge lamp 8| is modulated in accordance with the signals received from that station by Way of the line or channel of communication 40 and the amplifier 4I.
It will be understood by those skilled in the art that the distance between the centres of the apertures 2|, 22 is so chosen that the image forming beams strike the coverings of the apertures I8, while the scanning beams pass through the filters of the apertures |1I. Further, the optical distance of the glowing crater or aper- 'ture oftheglowdischarge lamp,8| from the lens IQI A'is such that an image :of the said crater is brought sharplyto focus inthe plane o'f the disc 52, while the distance of the aperture .2| vfrom the lens |.9I is such that an image of theaper- `ture 2| Vis .brought to a focus substantially in the plane of the subject or observer` 6. The aperture .2| may be regarded as the source of `.light for scanning the object, and a condenser-lens system may be employed to concentrate light vfrom an varc or other intrinsic source thereon.
The crater of the glow discharge lamp 8| or its 4limiting aperture, which is usually incorporated within the same transparent envelope, maybe regarded as thesource of light for Yreconstitution. The extent of the field of View on the disc is limited by means of a mask as indicated ,by the rectangle 31.
I may use a single line or channel of .com-
munication for carrying two-way television `si'- nals in a system according to the present invention, by using different carrier frequencies according to practice well known in the art of telegraphy and telephony, for the signals proceeding from each of the co-operating stations.
It will be appreciated by those skilled in the art that the term scanning beam is equally applicable to both floodlight and spotlight methods of television transmission. In the case of spotlight transmission the scanning beam, which may be of visible or invisible radiation, are those proceeding from the scanning device in the direction of and impinging upon the object, and serving to dene at any instant that portion of the object of which the diffusiVity-value for the particular kind of radiation employed is integrated (over the elemental area on which the radiation impinges at that instant) by light sensitive devices adapted to receive directly part of the diffused radiation. In oodlight transmission, on the other hand, the scanning-beams are those rays of the flood-radiation (diffused from that elemental area of 'the object which at any one instant in the conjugate focus or hypothetical image of the photocell aperture or its equivalent; which lie between the object and the light-transmitting devices of the scanning means. In this case the scanning beams are subjective, and are the rays selected by the scanning means at any instant for conveyance to the light sensitive device.
While preferred embodiments and methods of operation have been described in the foregoing specification, I am aware that numerous changes of construction and operation may be made without departing from the spirit and scope of the invention, and I, therefore, do not wish to be understood as limiting myself by the positive terms employed in connection with the description. For example, although I have illustrated an electric glow lamp as the modulated source of light, an electric arc used in connection with a Kerr cell may replace it.
Having described my invention, what I claim as new and desire to secure by Letters Patent is:
1. A television apparatus for the simultaneous transmission and reception of images, such apparatus including a disk formed with a spiral series of scanning apertures, adjacent apertures being respectively for transmitting and reproject, a glow lamp, and means whereby such lamp is caused to project its rays through the reproducing apertures of such disk 2. A television system for simultaneously transmitting and receiving images at different stations, such system including substantially identical apparatus at each station, such apparatus in each instance embracing a disk formed with a spiral series of scanning apertures, adjacent apertures being respectively for transmitting and reproducing purposes,v a light source, Vmeans whereby light rays from such source are Ycaused to pass through the transmitting apertures of such series and to the object which is to be reproduced,` light sensitive means adjacent such object, aV glow lamp, means whereby such glow lamp is caused to project its rays through the reproducing apertures, the lamp of one unit of apparatus being connected to the light sensitive means of the other unit, and means whereby when the transmitting aperture of one disk is in operative position, the reproducing aperture Yof the other disk will be in similar position.
3. A television apparatus for the simultaneous transmission and reception of images, including a disk formed with scanning apertures, a mirror to move in synchronism With such disk and including a plurality of reflecting surfaces, a light source embodying rays to be reected by the surfaces of such mirror towards the object to'be reproduced for scanning the same, a further and angularly disposed mirror interposed between such reiiecting mirrors and such object, such latter mirror having light filtering characteristics,V a glow lamp disposed adjacent such mirror and so that its rays will pass through the apertures of such disk and be reflected by the surfaces of the mirror towards the object, and a light sensitive means adjacent such object.
J. L. BAIRD.