US2315291A - Apparatus for and method of generating television signals - Google Patents

Description

March 30, 1943.

c. F. MATTKE 2,315,291

APPARATUS FOR AND METHOD OF GENERATING, TELEVISION SIGNALS Filed Feb. 27, 1941 7 Sheets-Sheet 1 INVENTOR CF MATT/(E ATTOQNEV March so, 1943. c. F. MATTKEA APPARATUS FOR AND METHOD OF GENERATING-TELEVISION SIGNALS E .2 m m m mm m m5 a & 7 ,Y

r 4 9 l m m F d u .1 F

A TORNEY March 30, 1943; Q E MATTKE 2,315,291

APPARATUS FOR AND METHOD OF GENERATING TELEVISION SIGNALS Filed Feb. 2'7, 1941 7 Sheets-Sheet 5 F/GI5 A TORNE V lNVE/VTOR By C. F MATT/(E sscolvos March 30, 1943. c MATTKE 2,315,291

APPARATUS FOR AND METHOD OF'GENERATING TELEVISION SIGNALS Filed- Feb. 27, 1941 7 Sh eetS-Shee t 4 IN V[ N TOR By CF MATT/(E March 30, 1943. c MATTKE 7 2,315,291

APPARATUS FOR AND METHOD OF GENERATING TELEVISION SIGNALS '7 Sheets-Sheet 5 Filed Feb. 27, l941 FOCAL AREA OF LIMITING APERTURE J6 FIG. 78

uvvmrm y Cf. MATT/(E ATTORNEY March 1943- c; F. MATTKE APPARATUS FOR AND METHOD OF GENERATING TELEVISION SIGNALS Filed Feb. 27, 1941 7 Sheets-Sheet 6 INVENTOR 6. f. MATT/(E March 30, 1943.-. IC -F IMATTKEI- r 2,315,291

APPARATUS FOR AND METHOD'OF GEXIIERATINQ TELEVISION SIGNALS Filed F313. 27, 1941. Sheets-Sheet 7 c. E MAW/r5 an I TORNEV Patented Mar. so, 1943 2,315,291 mans-ms FOR AND mnon or GENEB- ATING TELEVISIQN SIGNALS Charles F. Mattke, Jackson Heights, N. Y.,aasignor to Bell 'l'ele New York, N. Y.,

phone laboratories, Incorporated,

a corporation of New York Application February 21, 1941, Serial no. sacs-14 invention relates to signaling and partic ularly to a method of and apparatus 'for scanning motion picture film for generating television signals.

.An object of the invention is to provide an improved apparatus fo'r'scanningmotion picture 'film for television transmission.

Another object is to provide an ode ray scanning device. In accordance with improved cathare projected from the film at the same rate. However, in transmitting television images, in accordance with standards adopted ,by Radio Manufacturers Association, a field of view is scanned at the rate of 60 field scans 01. 220 lines each per second with the lines of one field scan interlaced with the lines of the preceding and following field scans so that 30 complete frame scannings of 441 lines each take place in one second. Therefore, in scanning for television transmission a motion picture film which is' moved continuously at the-rate of 24 film frames per second, it is desirable to scan the odd film' frames, for example, twice and even frames three timesrso that there are five field scans of 220% lines each in "-9, second, that is, 60 field scans or 30 completerframe scannings of 441 lines each,

interlaced, per second.

In accordance with a preferred 'embodimentof the present invention shown and described herestandard' motion picture'- .-practice a motion picture film is exposed at the .rate of 24 film (frames .per second and picturesimage dissector'tube shown and the film being shownin approximately corthe apparatus shown in for the purpose of illustration, a cathode ray image dissector tube of special construction is employed for generating a television image current under control of light projected through a continuously moving -motion picture film upon the light sensitive cathode of the image dissector. tube. The image dissector tube is provided'with an'a-pertureplate having five spaced apertures therein (instead of a single aperture heretofore employed), the centers of the apertures lying on a line substantiallyvparal lel to the direction 7 of vertical movement of the electron image which is focussed in the plane of the aperture plate, 4

and substantially parallel to the direction of motion of the motion picture film. The usual horizontal and vertical deflecting coils and the usual sourcesot current for energizing the deflecting coils are-provided but, since the motion picture film, and therefore the image projected upon the cathode o! the dissector tube, is moved continuously at a constant rate, the amplitude of the current supplied to the vertical deflecting coils is correspondingly reduced. In order that elecvidedin the path of scams. moi. ire-1.2)

trons emitted irom the cathode of the image dissector tube may pass through only one of" the five scanning apertures different apertures in succession, there is prothe light beam for projecting images from the filmupon the cathode of the image dissector tube, a rotating shutter disc having five arcuate light transmitting slots therein. The movement of the film, the rotation oi the light intercepting shuttenand the deflecting fields for controlling the deflection of the electronjmage are all maintained in synchronism so that the pictures recorded on the film are scanned at a desired rate diflerent from the rate of movement of the film.

The invention will now ence to the accompanying drawings in which Fig. 1 is a diagrammatic view at a motion picture film scanning apparatus in accordance with the present invention:

Fig. 2 is a view of the motion picture film andshutter disc as viewed from the cathode. ray in Fig. 1, the disc rect dimensional relationship; Fig. 3 is a diagrammatic view or a portion or in Fig. 1 including in plan view the electron multiplier of theimage dissector tube;

Fig. 4 is a view taken along the line 4-4 of s.3:and i Figs. 5 to 11, inclusive, are diagrams to which reference will bemade in connection with an ex planation of the operation of the apparatus shown inFlgs. 1 m4. Referring now to the drawings, a modified motion picture projector projects the successive ima es recorded on a the'cathode of a cathode ray image dissector tube.

The motion picture film I0 is driven by synchronous motor ll, through shafts l2 and I3, gearbox l4, and film sprocket IS. The motor II' is such that the film is driven continuously at thev rate of 24 frames per second.

I! is directed through condensing lens i8, through slotted rotatable disc 30 having slots 3|, 8!, 83, it and 35 therein, through the opening in name aperture plate 36 and film l0 and thence through lens 31 which focusses an image or the subjectmatter recorded on film l0 :upon the cathode oi an image dissector tube comprising an evacuated g ass housing 88 or sin stanti'aliy cylindrical shape at a time, and through be described with refer-' motion picture film l0 upon Light from sourcev are focussed to form an from which extends a side tube 39 of smaller diameter. Ignoring for the present the fact that the disc 30 intercepts a portion of the light beam,

it is seen that'the lens 31 projects an image of a picture recorded on the film upon the cathode 42, the image on the cathode being inverted with respect to the image recorded on the film, as

indicated by the arrows. The inner surface of the housing 38 has a mev tallic coating or anode 40in which is formed a aperture plate 44, multi-' film I and disc 30 are shown more nearly correctly.

Any suitable means may be employed for supplying deflecting currents of saw-toothed wave plier plates 45, collector grid 46 and anode 41.

An electromotive force is applied between c athode 42 and anode 40 through leads 48 and 49 from a circuit comprising battery 50, the positive terminal'of which is, grounded, and a network 5I made up of voltage dividing resistors 52 and condensers 53, as shown. Leads from the circuit 5I are connected to the electrodes of the electron multiplier as shown for applying appropriate potentials thereto. The electrons emittedfrom cathode 42 due to the light activation thereof electron image in the plane of the aperture plate 44 having therein five small spaced apertures I, 2, 3, 4, and 5, the centers of which are in alignment with the centers of the somewhat larger apertures GI, 52, 63, 54 and 65, respectively, in the shield 43 (see Figs. 3 and 4), the electron image being focussed by means of an axial magnetic field set up due to the current from source III flowing through the coil II which surrounds the glass envelope 3B and :vlgich extends substantially the full length of the There are provided two pairs of deflecting coils the horizontal [or high frequency deflecting coils I2 and the vertical or low frequency deflecting coils- 13. e magnetic field set up when these deflecting coilsare suitably energized cause the beam of electrons emitted from the cathode 42 and. therefore, the electron image focussed in the plane of the scanning apertures I to 5, inclusive, to be deflected along both horizontal and vertical coordinates. The electron beam reaching the apertured shield 43 s of such size that electrons can pass through only one of the apertures BI to 55, inclusive, at a time but electrons can pass through different apertures in succession due to.the action. of the rotating slotted disc 34 and to the deflection of the electron beam by the vertical deflecting field. The motion of the electron image with respect to the scanning aver- 'tures results in progressively selecting elemental areas of the image. Due to the, bombardment of the first of the plurality of multiplier plates by the electrons from different portions of the cathode 42 in succession, an image,current is set upin' the circuit including lead "I4 connected to the collector grid 46, the terminating impedform to the deflecting coils I2 and I3. As shown diagrammatically in Fig. 1 the drawings, there are provided a 26,460-cycle controlled oscillator I8 from which is derived by successive steps the submultiple frequency sources 19 and I! of 13,230-cycle and Gil-cycle waves, respectively, of generally square-topped wave form. The cycle wave from the power source I25 and the GO-cycle wave from the submultiple frequency generator I! are impressed upon the frequency control circuit I24. There is produced by the circuit I24 as the result of beating together the waves from sources I25 and IT, a control current which is impressed upon the oscillator 181'or maintaining the frequency of the wave produced cult which, in turn, controls the horizontal sweep circuit for supplying a toothed current wave to the horizontal deflecting coils I2. An arrangement of the type described for generating waves for controlling the sweep circuits which, in turn, control the deflection of a cathode ray-beam and for maintaining the waves in synchronism with an alternating current power source is disclosed in an article by A. Vs-Bedford and JohnPaul Smith on page 51 of -RCA Review for July 1940, pub- 13,230-cycle ,saw-

lished by RCA Institute Technical Press, 75,

Variclr': Street. New .York, New York. Sixty cycle pulses produced by the generator 8| under controlgof the subharmonic generator I! control th vertical sweep' circuit 82 which supplies a Gil-cycle saw-toothed current cal deflecting coils I3.

In order that the electron image produced in the plane of the apertureplitte 44 may be brought into correct vertical and horizontal alignment, there are provided 1 batteries 83 and 84 is supplied through to the horizontal and and I3, respectively.

from which direct current vertical deflecting coils I2 The operation ofthe scanning system shown In I Fig. 1 may best be understood by referring to Figs. 5 to 12, inclusive.

Referring to Fig. '5 the film I0 is moved downwardly, as viewed in the figure, at the rate of 24 film frames per second, so that, at the beginning of successive equal periods of ,4, second, the fllm is in positions marked A, 13,

lower portion of the figure. Assuming for the ,anceelement 15 and ground. This image current may be amplified by the vacuum tube amplifier I6 if desired, and transmitted over a suitable transmission medium such as a balanced.

line 11. a y

In Fig. 1, the film Ill and disc 30, for example, are not shown in their correct relative dimensions. In. Fig. 2 the relative dimensions of the ode 42 of the image dlssector tube, then the elec*- tron image corresponding to frame '1 formed in the plane of the aperture-plate 44 would appear at I. Due to the downward ID from position A to position 3, the image formed on the cathode 42 and thereforethe electron image formed in the plane aperture plate 44 Will move upwardly by a corresponding amount. that is, anamount corresponding to a filr:

wave to the verti-.

Potentiometers u and a? C, D, Eand F. spectively.- The time periods areindicated at the saw-toothed wave This vertical motion of the electron image is supplemental by deflecting the cathode beam to cause the electron image tomove through a distance corresponding to of a film frame by applying to the vertical deflecting coils II a regular 90 from source '82. f the apertures I, 2, 3, l and in the aperture plate I l, one only is effective in the process of scanning the image during a certain field scanning period,-

the apertures becoming eifective successively during successive field scanning periods. In Fig. 5

the apertures are shown aligned on equally spaced horizontal lines which are numbered at the left-hand side of the drawing. During the first field scanning period only aperture i is effective and during this period the electron image of frame Ismoves verticallywith respect to aperture i through adistance corresponding to a film frame. While the electron image is thus moved along a vertical component, it is also moved horizontally in the usual manner at the rate of 541 lines per frame scanning period of /30 second or 220 /2 lines per field scanning periods of let second by applying a saw-toothed wave current from the horizontal sweep circuit to the horizontal sweep coils I2.

At the start of the second field scanning pe-- riod, the film and the electron image are in the positions shown at B in Fig. 5. Aperture 2 is now effective and due to the continuous movement of the film l0 and the deflection of-the electron beam from cathode 42, film frame I is scanned a second time. At the beginning of the third field scanning period aperture 3 becomes effective in the process of scanning film frame 11. Aperture 4 next becomes effective in the scanning of film frame 11' a second time during the fourth field scanning period and then aperture 5 becomes effective in the process of scanning film frame II a third time. At the beginning of the sixth field scanning period, as shown by F in Fig. 5, frame IIIoccupies the position whlch was occupied by frame I and electron image 111 occupies the position which was occupied by electron iriiage I at the beginning of the first field scanning period A. Thus, alternate film frames are scanned twice and the remaining frames are scanned three times along 441 lines per frame scanning period. the lines on one field scanning being interlaced with those of the preceding or following field scanning. The film moving con-' tinuously at 24 film frames per second is thus scanned at the rate of 60 field scans per second.

As will be apparent from a consideration of Figs. 2, 6; 10 and 11, the apertures l, 2, 8, 6 and 5 in the aperture plate 46 are made effective for scanning one at a time in succession by the rotating slotted disc 30' which permits only a narrow strip of the film l0 tobe illuminated at a time the beam.

. aperture I iii and, therefore, an optical image 9| of this narrow strip to be focussed upon the cathode 62 and.

an electron image 92 corresponding to this narrow strip to be focussed in the planeof the aperture plate 64. The position of film frames '1 .and II of film it, as indicated in Fig. 6, corresponds to the condition depicted at A'of Fig. 5

and the relative positions of the disc 30 and film Iii are as shown in Fig. 2.

At the commencement of scanning of film frame I, the leading'portion (lower portion, as

viewed in Fig.- 6) of film frame I is illuminated and the light beam from this portion of the film reaches position 9| on the light sensitive surface of cathode 42, light from the first scanned line being at about the central portion of The electron beam from portion ii of the cathode is focussed upon the aperture plate 64 so that, as the electron beam is deflected, elecof' frame-'1- "trons corresponding to the elemental areas of the first scanned line pass successively through in aperture plate 44. It is apparent that if 'the of the light beam and of the electron beam would be limited only by the opening in aperture plate 38 and electrons would pass simultaneously through a plurality of apertures in aperture plate 66. The width of the slots in disc 30 is sulficiently narrow that electrons emitted from cathode 42 can pass through only one of the apertures in aperture plate M at a time. 7

During the first field scan of film frame I, the

lfihn moves downwardly, as viewed in Fig. 6, through a distance of frame and-the'slot Si in disc 30 in effect moves upwardly through a distance of frame, that is, through a distance indicated by IA in Fig. 6. During this period the light beam intercepted by cathode 42 moves from position 9! downwardly through a distance indicated by IB in Fig. 6. A saw-toothed wave deflecting field (Fig. l) is applied to the vertical deflecting coils 13 so that, as the light beam impinging on cathode 62 moves downwardly through a distance lB,.the positionof the electron beam at electrode at remains fixed with respect to the vertical coordinate, Thus electrons emitted from cathode 42 in response to light from successive elemental areas along successive lines of film frame I pass, in order,

through aperture l-in electrode 44 and impinge .upon the first multiplier electrode or target B5 of the electron multiplier 39 to set up a corresponding image current in the output circuit of the multiplier.

V In a similar manner, during the second field scan of frame I, the film is illuminated by light passing through slot 3; in disc 30, the light beam leaving the film moves upwardly through a distance indicated at 2A, the light beam impingingon'the cathode '42 moves downwardly through a distance indicated at ZB'and electronsemitted from the cathode pass through the aperture 2 in electrode 64, Similarly, film frame II is illumi nated three times during the next three field scanning periods, the light beam from the film being swept over the area indicated at 3A during the first field scan, over the area All during the second field scan,

the electrons emitted from the cathode pass through the scanning apertures 3. 4 and 5, re-

spectively, of-the aperture plate M.

'In accordance with the standards adopted by the Radio Manufacturers Association, there is an interval. about '7 percent of the field scanning period. at the end of each field scanning period during which the beam of the image producing cathode ray tube is" preferably reduced in intensity and is returned to its. initial scanning position. During this interval, frame synchronizing impulses are transmitted and no image production takes 1ace.- As may be seen from Fig. '7B, for example, there is an interval between successive field scanning periods durin which one'slot of disc 30 is moving out of alignment with. the opening in the aperture slotted disc 30 were omitted, the sizeand over the area 5A during the third field scan of frame II. During '80 at a, time about half way between alignment with the opening in aperture plate 36. In Fig. 7B, for example, slot 35 has just moved out of alignment with the opening in aperture plate 36 and slot-3| has moved. into position for scanning of thefirst line of film frame I during the first field scanning period. The length of each of the slots. 3| to 35 is preferably such with respect to the width of the opening in plate 36 that one slot can move completely out of, and a succeeding slot can move completelyinto, alignment with the opening in plate 36 within the period of about 7 per cent oi the field scanning period alotted to the vertical synchronizing impulses.

Fig. 7A shows the position of the optical image at 9| and .the position of the electron image at 92, as is shown in Fig. 6, picted in Fig. 7B and also at A of Fig. 5. In Fig. 7C is shown a saw-toothed electric wave 30. as shown in the lower part of'Fig. 1, for energizing the vertical deflecting coil 13. It will be noted that the zero point on the horizontal time axis of Fig. 7C is in vertical alignment with the scanning aperture plate 44. This is intended to indicate that at the beginning of the first field scanning. period of filmirame I the vertical deflecting saw-toothed wave is at its minimum amplitude.

Figs. 8A, 8B and 8C are similar to Figs. 7A, 7B and 70, respectively, but depict a condition encountered about ,420 second after the condition depicted in Figs. 7A, 7B and 70. As shown in Fig. 8B, at this time about the central portion of fiim'frame I is being scanned. As shown in Fig. 8A, and also in Fig. 6, the light beam is intercepted by the cathode 4-2 at a lower position 93 as viewed in the figure. As shown'in Fig. zero and V second, the amplitude of the vertical deflecting wave 90 is about one-hall. its maximum amplitude, this amplitude of the defiecting'wave causing the electron beam to be deflected so as to for the condition de-.

of each field scanning period during which the electron beam of the image producing cathode ray tube is reduced in intensity and returned to its initial scanningposition. During this interval frame synchronizing impulses are transmitted and no image production takes place. This 7 per cent of the field scanningperiod is also required for the-return sweep of the cathode ray beam emitted from the cathode 42 or the image dissector tube. In standard motion picture film the dimension along the length of the film of the frame line between two successive picture portions is about per cent of the length of an entire film frame consisting of a'picture portion and a frame line. In order to. avoid waste of transmission time, it is desirable to scan a picture portion only of a film frame during 93 per cent of a field scanning period, thus allowing 7 per cent of the field scanning period between the time of scanning the last scanned elemental area of one field scanning period and the first scanned elemental area of the succeeding field scanning period. In order that the picture portion only of the motion picture film may be scanned during 93 per cent of the field scanning period 'of onesixtieth second, the slots 3| to 36 in the disc 30 may be laid out so that a picture portion of the film is.traversed by a slot in 93 per cent of a field scanning period and the amplitude of the vertical deflecting current from source 82 reduced so that the electron image corresponding to a picture portion only of the motion picture film is scanned in 93 per cent of the field scanning period.

Thesubject-matter of this application is related to that of my application Serial No. 380,773, filed trode having a plurality of spaced apertures therereach position 92 on the aperture plate 44. Figs.

9A, 9B and 9C are similar to Figs. 8A, 8B and LC, respectively, but depicit a condition encountered just prior to the end of the first field scanning of film frame I. As shown in Fig. 93 slot 3| is about to start moving out of, and slot 32 about to start moving into, alignment with the opening in plate 36. Fig. 9A shows that at this time the light beam is intercepted by the cathode 42 at a still lower position 94, which is also shown in Fig. 6. The vertical sweep wave 90 is now at its maximum amplitude to cause the electron beam to be deflected to position 92 on the aperture plate 44. 1

In a similar manner, during a difierent field scanning period when light is directedthrough some other slot of disc 30, the light beam will be intercepted initially at some other position or cathode 42 such that the electron beam will pass through a corresponding aperture in aperture plate 44 and, as the light beam illuminates ditierent portions of cathode "in succession, the saw-toothed wave 96 impressed upon vertical defiecting coils 13 will set up a beam deflecting-field to. cause the position oi the electron image to, re-

per cent 01 the field scanningf period, at the-end 78 in through which electrons from said cathode may pass to reach said target, means for directing a light beam upon said cathode to illuminate in succession difierent areas of said cathode which may overlap in part, each area being illuminated a small section at a time and diiierent sections in succession by moving the light beam to cause electrons emitted from, different of said areas of said cathode to reach'diflerent apertures. respectively, in said electrode and means for deflecting the electron beam to compensate in part. at least for the movement of said light beam so that electrons emitted from'any section 01' a certain area of said cathode will pass through thecorresponding aperture in said electrode.

2. An image dlssector tube comprising a light sensitive cathode for emitting electrons 'inaccordancewith the illumination of elemental areas thereof, an anode, means for producing an electron image corresponding to an optical image focussed on said cathode, an electron multiplier comprising an aperture electrode having a plurality oi spaced scanning apertures therein subs'tantially in the plane of said electron image, a shielding electrode located between said aperture electrode and said cathode and having therein a plurality of apertures in alignment with said scanning apertures respectively, a plurality of multiplier electrodes, tion to be bombarded by electrons passing through said scanning apertures, and means for deflecting the electron beam from said cathode to move said .electron image with respect to said scanning apertures and to cause electrons from said cathode to the first of which is in posi field ofview upon said cathode to 3. Scanning apparatus comprising alight sensitive cathode for emitting electrons in accordance with the illumination of elemental portions thereof,-means for illuminating portions of a field of view in succession, means for directing light from the successively illuminated portions of the illuminate portions thereof in succession, an aperture electrode having a plurality of spaced scanning apertures therein through which electrons emitted irom said cathode may pass, means for focussing the electrons from said cathode in the plane of said aperture electrode, and means for causing the electrons emitted from different elemental areas or said cathode to pass in succession through one" oi saidscanning apertures and through different apertures during successive time interv 4. Apparatus for scanning continuously moving motion picture film comprising a cathode ray scanning device having a light sensitive cathode and an aperture electrode having a plurality of scanning apertures therein, means for projecting an optical image from said film to said cathtrol of electrons transmitted through said scanning apertures as the result of the scanning of the electron image by said apertures successively for producing an image current ,which may be used for controlling the production of television images corresponding to the pictures recorded on said motion picture film.

6. Apparatus for scanning continuously moving motion picture film so that each frame of the motion picture film is scanned a plurality of times comprising a light sensitive cathode and an aperture'electrode havinga plurality of scanning apertures, therein, means for projecting an optical ode while said film is in motion, means for accelerating the electrons emitted from said cathode to produce an electron beam, means for iocussing said electrons to produce substantially in the plane 01 said aperture electrode an electron image corresponding to the optical image produced on said cathode, means for causing said scanning apertures one ata time in succession to scan the electron ima'ge formed in said plane, said means comp means for deflecting said electron beam, and means under control of electrons transmitted through said scanning apertures as the result-oi the scanning by said apertures successively of the electron image landed in said plane for producing an image current which may be used for controlling the production of television images corresponding to the- -pictures recorded on said motion picture film.

5. Apparatus for scanning motion picture mm for television transmission comprising means for continuously moving the motion pictur film at image from said film upon said cathode, means for accelerating the electrons emitted from saidcathode to produce an electron beam, means i'or focussing said electrons to produce in the plane of said aperture electrode an electron image corresponding to said optical image means for de fiectingsaid electron beam'in a direction substantially perpendicular to .the direction of motion or the film to cause elemental areas in succession oi the' electron image to be scanned, means for deflecting the electron image in a direction substantially parallel to the direction or to be scanned in a period 1688i than that in which a substantially uniform rate, a cathode ray scanning device having a light sensitive cathode, means tor'projecting an optical image from said film to said cathode while said film is in motion means for accelerating the electrons from said cathode to produce an electron beam, means for Iocussing said electrons to produce in a certain plane an electron image corresponding to the opa frame of the film moves past a fixed point, the scanning apertures insaid electrode being'so positioned that an electron image corresponding to a frame oi the motion picture film is completely scanned at leasttwo times in succession bydflferentapertures, respectively, means for preventing electrons or said electron image from reaching more than one or said plurality otvapertures at atime", and means under control of electrons transmitted through said scanning apertures as the result of the scanning of the electronimage by said apertures successively i'orproducing image current which may be used for controlling the production of televisionimages. corresponding to the pictures recorded on said motion picture mm. A

- g CHARLES F. MA'ITKE.

tical image produced on said cathode, said oathode ray device comprising an electrode substantially in said plane having a; plurality of electron transmitting scanning apertures therein, means for deflecting said electron beam to cause a scan-.

Images