US2273801A

US2273801A - Television receiver

Info

Publication number: US2273801A
Application number: US248569A
Authority: US
Inventors: Daniel O Landis
Original assignee: RCA Corp
Current assignee: RCA Corp
Priority date: 1938-12-30
Filing date: 1938-12-30
Publication date: 1942-02-17
Anticipated expiration: 1959-02-17

Description

Feb. 17, 1942. D. o. LANDIS TELEVISION RECEIVER Filed Deo. 30, 1938 4 Sheets-Sheet l :inventor 0. L an di' Daniel N .www

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dtrorneg Feb. 17, 1942. v D. o. LANDIS 2,273,801

TELEVISION RECEIVER Filed Dec. 30, 1958 4 Sheets-Sheet 2 M/Hnon v t? /acREEN Imca/VER afwas/.s d] 22 n] 20 l @E18 Z0 x ,i7 I Wl E l .I' A16//l m17 15 12 l .a/ Z1 7 l/ lnoentor Daniel 0. Lan/dus t 'Patented Febltlvh1 942 I fija-,213,801 c u fr ELEylsIoN REcErvEE Landis, Upper Darby, Pa., .assigvnor '1 of America, a 'corporation ppl'iatqinecembef 4so, 193s, seal 1410.248569 f ,1-3 ,Chi-ms. CL 173:15)

My invention relates to television receivers or the like and particularly to television receivers of the projection type. c In designing television receivers of' the projection type employing a cathode ray tube, one of the principal ldiiliculties has been in obtaining a good qualit-y'projected picture which is su`fl`1' cientlybright. A- Itis, accordingly, an object of my invention to provide an improved television receiver which will reproduce a picture of comparatively large.

sizeand of the desired brilliancy.

In practicing my invention I employ a spherical mirror for projecting the image appearing on a fluorescent screen, and provide a correcting plate to eliminate substantially all spherical aberration.

It'v has been previously proposed'v to project a l of a television receiver embodying my invention,

Figure 4 is a view, partlyin section, of a portion of the receiver shown in Fig. 3, I

Figure 5 is aview taken on the line Fig. 4, and

Figure 6 is a view illustrating another embodi` ment of myinvention.

Referring to Fig. -1v, -therefis illustrated yafspecic optical system which maybe employed in a television receiver embodying my invention,y -specic dimensions being givenY merely by Way of example. The systemcomprises a spherical 'mire' ror l and acorrecting plate 2.' The' end ofthe cathode ray tube upon which the picture appears is indicated at 3 while the`s'creen upon which ther picture is projected is indicated at 4.

Thel correcting plate is guredoto bring light' rays reflected liromeither theedge of the mirror for example, orhigher without any noticeable spherical aberration, "chromatic laberration or coma. In other words, I provide a fast lens sys,-

tem of vhigh duality. Furthermore, it ris a lens system which absorbs a minimum amount of the light produced by the cathode ray tube.

As will be explained in detail hereinafter, the correcting plate 'and spherical mirror combination resembles the Schmidt camera which'is used in astronomical work. However, in my system the correcting plate is ground or gured for a finitedistance frommirror to projection screen whereas they corresponding distance -in the Schmidt camera is infinity. Also, the object surface `f the fluorescent screen) inv my optical' system asfconstructed up to this time does not, as v in the Schmidt camera,"havearadiusV equal -to half theradius of the spherical'mirror, but, in::

stead,l it has a curve which will focus any Apoint;y

on `itsy surface on the image `surfacerwhichzordinarilyis'a projection screenvhaving a plane sur` face. f I The invention will be better understood from the following description,` taken in connection withthe accompanying drawingsin which Figures 1 and 2 are diagramsn which are rev ferred toin describing theoptical. systemv enfi-A-`v ployed in my improved receiver.

Figure 3 is a view, drawn substantially'to scale,"l

Y` projectionk screen,

or from a point 'on or near its axis into focus at the projection screen.

any one of several shapes although 4theshape illustrated is preferred. The way in which the correcting plate functions'mis illustrated in Fig. 42.

Referring to Fig. 2*, it is assumed there is a light source at the pointmarke'd focuslff' Light rays from this source-reected from the mirror ,l nearits edge would have their focus atthe point' marked normal edge focus" in theabsenc'e of the correcting plate 2. The correcting plate, however, is figured to refract these edgerays just enough to make them focus on theprojection f screen 4.

Considering the axial rays from the same light" source, it will be vseen that in the absence of the correcting plate .they focus at the point marked normal axial focus.v The correcting'plate is f gured to refract these rays the correct amount to make them focus on the screen-4.7Ihus lthe correcting plate may be sogured as rto. make all rays originating from this light source andre-- to a `focus onf-the ected 'from` the mirror come Considering rays or object 3 ofi;I the axis, the raysyfiom ac'orn'er of the',` picture in' order to l'foc'zi'isfonits corresponding corner ofk the screen l mustv have a? `shorterobjet focus andy a longer-image focus n Therefore, the v* radius of the object surface 3 -will be greater than thefaxial or central rays.

than one-half theradius ofI the mirror 'I-. Thus, in theoptical systemA shown` infFig. l*

v c As m the case' of thev i Schmidt camera, the correcting plate may have from a point 'on the 'picture/' lit 'was klvfound that'the' radius of curvatureforftlrie' fluorescent screen on theiend yof the tube should be* inches where the radius of curvature of the spherical mirror was 171/4. inches.

The curvature of the object surface 3 may not be exactly. spherical in some cases but'it will be very Vnearly so'. 0f course, this curvature should be changed if the screen 4 is given. a curvature instead of being flatas it ordinarily is. v

TheA desired curvature for the object surface I may be obtained by` placing a photographic plate on the axis of the optical system and then tracing a curve thereon by moving a spot of light, such as an electric bulb, along the projection screen and in a direction parallel to the plane of the photographic plate.

For example, referring to Fig. l, a. photographic plate may be positioned, at the focus between the mirror i and the correcting plate 2 with the emulsion side up, i. e.,`the photographic plate is in the piane of the paper. Then the light from an electricrbulb moved horizontally along the image surface I (i. e., moved in the planeof the paper) focuses on the photographic plate and traces the desired curve.

As to the technique employed in figuring and testing the correcting plate, it may be noted that, since my projection system focuses at a finite distance, it was found desirable to employ a testing procedure during the figuring of the plate based on the fact that the longitudinal spherical aberration of a high aperture mirror and the diameter oi' the pupilv ofthe eye will make light from a pin hole at the focus appear to the eye placed on the axis at the second focus as a bright ring on the surface of -the mirror. If the eye is placed on the axis at a point closer to the mirror, a ring of light of larger diameter on the mirror will be seen.

If we take a series of these annular zones or rings each having a focus on the axis and figure the correcting plate to bring them all to a focus at the same point, we have the required curve on the correcting plate. Thus, the procedure may be as follows:

Bet up the system minus the correcting plate and, after placing a mark on the mirror at about Surface.

.7 the distance from the center of the mirror to its edge, move the eye along the axis until the bright ring visible on the mirror passes through this .7 point. Adjust the foci until the bright ring passes through the .7 zone when the eye and pinhole are at the desired conjugate foci. AWhen these adjustments are acquired, the bracket used for holding the correcting plate is placed so that first principal plane of the plate is at the center of curvature of the main mirror. A ray from the .7 zone of the main mirror should pass through the finished correcting plate without deviation and fall half waybetween the maximum and minimum foci of the uncorrected main mirror.

The reason forA working from a zone'.7 of the distance from the center of the mirror to its edge is that the area of the mirror inside this .7 ring is about equal to the mirror area outside this ring. Thus, the correcting plate may be figured to have a positive power for half the light andv a negative power for the other half of the light whereby the refracting angles of the plate will be at a minimum for the desired correction. For all practical purposes, the .7 measurement may be taken on the chord from the center of the mirror to its edge. v

vI'he area of the correcting plate inside the .7 ring is then masked ofi and the negative power of the edge zone or .3 zone is increased by grindscreen about 2 inches inside the focus.

does the center or .7 zone. l 'This edge zone, of

course, is the area betweenf'the .7 ring and the edge of the mirror.

The progress of the grinding of the edge zone is checkedfrom time to time by looking at the mirror from a point on the axis and noting the change in the position from which a certain ring of light is seen (this position being the focus for this particular ring of light). l'orA example, if the eye is located on the axis at thepoint marked Normal edge focus (Fig. 2), a bright ring is seen near the edge of the mirror. After the edge zone has been Worked on some by the grinding machine, it will be found that this ring of light is now seen from a point closer to the desiredcommon focus. When this ring is seen from the desired common focus, the correction' for the particular zone of the correcting plate through which this ring of `light passes has been completed.

During the grinding of the edge zone, the other light rings of smaller diameter should be observed from time to time just as described in connection with the ring of largest diameter. When the rough grinding of this zone is finished, the entire edge zone will appear from the common focus to be covered with narrow rings.

After the edge zone is made to focus at the correct place, mask ofi' this zone and work on the center or .7 zone and increase the positive power over this area until the rays falling beyond those of the .7 zone are brought into focus at the same place as those from the rest of the In order to generate a curve continuous with that of the edge, it is best to workon the center portion beginning at the .7 zone.

It will be understood that the grinding of the center zone is checked in substantially the same way as described in connection with the grinding of the edge zone.V

So far we have the general rough curve generated on the plate and we will find the entire surface covered with narrow rings. It is necessary from the beginning of this grinding operation to see that the plate is perfectly centered and running true on the grinding machine and frequent checks should be made to determine that the plate is maintaining a true surface of revolution.

It will be found that very narrow zones'are capable of becoming tilted in relation to the general curve and may be detected by holding a A bright ring from a tilted zone will appear eccentric to the rest of the pattern. If the screen is moved to within a few inches of the plate and the finger used to cast a shadow, the zone responsible for the eccentric ring can be covered with the finger and the shadow followed from the plate to the focus as the screen is moved away. The tilted zone responsible for the ring can be interpreted into the direction of tilt on the surface of the plate which would cause the deflection of an annular cone of light creating the eccentric ring as found. Due to the fact that all errors appear in complementary illumination on opposite sides of the focus, it is best to do all testing inside the focus.

After the direction of tilt hasbeen determined and the high portion located (by a scale placed in front of the correcting plate and by a corresponding one on the grinding machine), the plate is tilted on the turntable so that most work will be ing until this zone focuses at the same place as done on this zone,

'I'he machine is arranged so that pressure is lncreased when the high zone comes under the grinding tool. After most of these narrow zones have been corrected, the plate, after being indicated true, is worked on with the largest tool possible with a radial stroke and the remaining narrow zones averaged out.

If desired, after the correcting plate has been figured as described above to bring all zones of the mirror close to the desired focus, a standard test such as the Foucalt knife edge test may be employed for figuring the correcting plate still more accurately.

It was found that much time could be saved by coating the ground surface of the correcting plate with glycerine eachv time it was desired to make a test to permit testing without having to grind the plate to a smooh surface.

One practicalembodiment of my invention is illustrated in Fig. 3.

Referring to Fig. 3, the television receiver comprises a cabinet I Il of the console type having a translucent screen Il, such as ground glass, in

the front thereof upon which the reproduced picn ture is to appear.

A cathode ray receiver tube I2 ofthe projecthe center of curvature of the mirror I4 to bring the light rays originating at the fluorescent screen I3 and reflected from the mirror I4 to a focus on the screen II as explained in connection with Fig. 2. A mirror I9 is mounted at 45 degrees to direct the light rays from the correcting plate I8 to the screen II.

Preferably, adjusting screws 20 are provided to facilitate axial adjustment of the correcting plate I8.

The loud speaker 2I and the receiver chassis 22 may be located in the receiver cabinet as indicated. With the above described receiver, a bright picture 15 inches by 20 inches of good quality may be obtained. It is assumed, by way of example, that the optical system of this receiver has the dimensions given in Fig. 1, the effective aperture being approximately .6.

It will be understood that the receiver shown in Fig. 3 may be designed to project a still larger picture upon a separate projection screen placed across across the room from the receiver, for example. In this case, the screen II is removed from the cabinet I0. Obviously. the correcting plate I8 should be figured differently for the different conjugate foci.

The mounting and adjusting means for the cathode ray tube I2 of Fig. 3 are shown more clearly in Figs. 4 and 5. The mounting supports I6 are in the form of a spider comprising four metal straps attached at their ends to thel shelf I5. A metal cylinder 35 is welded or otherwise fastened to the inner ends of the spider arms I6.

The cylinder 35 has extending upwardly therefrom three lugs 36 for supporting the connecting plate I8 at the center. desirable where the plate has been molded from a plastic such as Lucite.

The lower part of cylinder 35 has two slots'31 therein in which adjusting screws 38 may slide.

The tube I2 is supported from the cylinder 35 Such support may be lli) wedge member 42 fits into the small spacev between the neck of the tube I2 and the. yoke I1, the wedge being secured to the neck of the tube by a clamp 43.

The tube I2 and deecting yoke .I1 are supported from the cylinder 35 by means of a cylindrical member 46 which telescopes into cylinder 35 and is held in position by means of the screws 38.

The lower end of member 46 has an edge 41 spun or otherwise formed thereon which has a spherical surface conforming to the surface of member 4I. Adjusting and fastening screws 48 pass through openings in the edge 41 and fasten in the member 4I in screw threaded relation, the said openings being large enough to permit .an adjustment of the tube I2 about its lower end as a pivot.

From the foregoing, it will be apparent that by loosening the screws 38 the tube I2 may be moved axially to different positions, as indicated by the dotted lines, for the purpose of focusing the image upon the projection screen. Also, it will be seen that by loosening the screws 48 the tube I2 may be adjusted about the center of the lower end of the tube as a pivot point whereby the edgesof the picture may readily be brought into focus.

In Fig. 6 there is illustrated another embodiment of my invention, this receiver being designed to project a picture upon a screen indicated' at 28. In this figure the screen 26 is shown much ytco close to the receiver because of limited space on the drawing.

The receiver comprises a cabinet 21 which may beeither of the table model or console type. A cathode ray tube 28 is positioned in front of a spherical mirror 29 in the proper relation to project the image appearing on the end* of the cathode ray tube upon the screen 26. A correcting plate 3I, as previously described, is mounted at the front of the cabinet. The tube 28 preferablv is adjustably mounted as previously described.

If the cabinet is of the console type as illustrated, the loud speaker may be located inthe lower part of the cabinet as indicated at 32 or remotely, as desired. The receiver chassis 33 may be mounted in the top of the cabinet as shown, or it may be located along one side of the cabinet if 'the cabinet is made of suilicient width.

ceive the light issuing from the source, an l aspherical zone plate positioned to receive the reflected light projected from thelight source, said zone plate being arranged external to the light path from the light source to the reflector and axially aligned with each and adapted to correflected light rays by the reflecting surfacel whereby a sharply focused enlargement of the original finite dimension light source is developed at a plane located at a finite distance from the aspherical zone plate. y

2. An image projection device comprising a light source of flnite bi-dimensional image area emitting light according to Lambert's law, an axially aligned optical system including a concave reflecting surface of revolution positioned to receive the light issuing from the source, and an aspherical zone plate positioned external to the path of the light projected from thelight source to the reflector and positioned to receive the reected light from the reflector, said zone plate being adapted to correct for spherical aberrations introduced by the reflecting surface whereby the optical system projects a sharply defined enlarged image substantially free from spherical aberration upon a viewing surface located at a finite distance from the zone plate.

3. An image projection device comprising a cathode ray tube to produce a light image, and an aligned optical system including a spherical reflector element having its concave surface area positioned to receive the light image from the tube and an aspherical zone plate located at substantially the center of curvature of the spherical reflector element to receive the light image as reflected thereby, said zone plate being located external to the light path from the tube to the reflector and having such curvature as to correct for spherical aberration introduced into the reflected light rays by the reflector whereby the optical system including the reflector and the zone plate is adapted to form a projected enlarged image of the light image upon the cathode ray tube upon a viewing area located at a flnite distance from the zone plate.

4. A television image projection device comprising a cathode ray tube having a luminescent target area whereupon an optical image is produced, a spherical reflector` having its concave surface area positioned to receive the light of the image as produced upon the cathode ray tube, an aspheric zone plate located externalto the tube to reflector optical path and arranged to receive the reflected light from the reflector, said zone plate having its surface area of such curvature as to correct for spherical aberration due to the reflector so that a sharply focused enlarged image of the tube target area may be focused upon a viewing surface located at a finite distance from the zone plate.

5. The device claimed in claim 4 wherein the said zone plate is located substantially at the center of curvature of the reflector.

6. In a television image projecting and enlarging apparatus, a cathode ray tube having means to produce light representative of an image, an aligned optical system to receive the light image on the tube, said optical system. in cluding a substantially spherical light reflecting element having its concave surface positioned to receive the light from the light source, and an aspherical plate member located external'to the tube to reflector light path to receiv the reflected light from the reflector and located near or at the center of curvature of the reflector, said aspherical member being so curved as to correct for sphericalV aberrations introduced by the reflecting means, said plate curvature being such as to reduce the said spherical aberration to a minimum in a viewing area located a finite distance from the said plate member.

7. The apparatus claimed i'n claim 6 wherein the said aspherical plate member has a central aperture and wherein at least a portion of the said cathode ray tube projects through the said plate.

8. The apparatus claimed in claim 6 comprising in addition means for pivoting the-\cathode ray tube about a pivot point located substantially at the center of the thereupon produced light image to adjust the said tube relative to the light reflecting and projecting elements of the optical system.

9. A television image projector and enlarger comprising a cathode ray tube having a luminescent target area of ilnite dimensions whereupon a two dimensional optical image is adapted to be produced, said optical image being adapted to radiate light substantially according to Lamberts law, a substantially spherical light refleeting means yaxially aligned with the axis of the tube and so positioned that the light rays of the image upon the tube are adapted to fall upon the concave surface of the reflector, and a spherical aberration correcting means for correcting for spherical aberration introduced by the said spherical light reflecting means, said means comprising a zone plate member having its surface of predetermined curvature to compensate for the said vspherical aberration distortion and spaced from the reflector by a distance .approximately equal to the radius of' curvature of the reflector, said zone plate being located external to the light path between said cathode ray tube and the reflector and so positioned that the said tube masks only the central area of the said plate, whereby the optical system is adapted to focus an enlarged projected image of that upon the tube upon a viewing surface located at a finite distance from the light source and optical system.

10. In a television image projecting and enlarging apparatus, a cathode ray tube having a neck portion and a target portion whereupon an optical image is adapted to be produced, an optical system aligned with the tube axis, said system including a substantially spherical reflecting element positioned to receive the light from the tube target, and an aberration correcting zone plate element located substantially at the center of curvature of the reflector and having its surface so curved as to correct for spherical aberrations introduced by the reflecting means, said surface being positioned externally of the light path between the light source and the reflector and arranged to receive light dlrectly from the reflector, said plate being also so curved that the spherical aberration is a minimum upon an image viewing area located at a ilnite distance from the optical system.

11. The apparatus claimed in claim 10 wherein said zone plate has its central area apertured and wherein the said tube neck is projected through the plate aperture.

12. The apparatus claimed in claim 10 comprising in addition means for pivoting the cathode ray tube about a pivot point located substantially at the center of the thereupon produced light image to adjust the said tube relative to the light reflecting and projecting elements of the optical system.

13. In television image projection apparatus, a cathode ray tube device having a luminescent target area and means to produce on the target,

near or at the center of curvature of the light l0 reflecting element, said surface being positioned externally of the light path between the cathode ray tube light source and the reflector and arranged to receive light from the reector, and said optical system being adapted to focus the enlarged image sharply and with minimum` spherical aberration upon a, viewing plane located at finite distance from the correction plate.

DANIEL O. LANDIS.