US2489299A

US2489299A - Color television projector

Info

Publication number: US2489299A
Application number: US662378A
Authority: US
Inventors: Christian C Larson
Original assignee: Farnsworth Research Corp
Current assignee: Farnsworth Research Corp
Priority date: 1946-04-15
Filing date: 1946-04-15
Publication date: 1949-11-29
Anticipated expiration: 1966-11-29

Description

Nov. 29, 1949 c.- c. LARSQN 9 2,439,299

COLOR TELEVISION PROJECTOR Filed April 15, 1946 INVENTOR CHRISTIAN C. LARSON ATTORNEY Patented Nov. 29, 1949 UNITED STATES PATENT OFFICE cows ELEV N RQJE Christian C. Larson, Fort Wayne, Ind., assignor, by mesne assignments, to Farnsworth Research Corporation, a corporation of Indiana Application April 1o, 1946, Serial No. 662,378 5 Claims. (Cl. Nil-5.4)

This invention relates to television systems and particularly to an optical device for use in producing a television image in color. A color television system which is commonly u d employs a sin e c thode r y tube fo oducing in succession a plurality of partial images. Each partial image represents one of a number of primary color components of the television subject. Each of these partial images is reproduced in black andwhite on the screen of the tube. A colored discor drum is rotated between the fluorescent screen of the cathode ray tube and the observer, so that as each black and white representation of one of the primary color cornponents of the subject is reproduced on the screen, a correspondingly colored filter element of the di or d m s' iiwss he ob r e a d t e screen. The final result is a colored reproduc tion of the television subject.

All of such systems require, in the first place, a movable color filter device either in the term of a disc, a drum or the like. The filter apparatus m be rotated o otherwise mo e in si nr tial synchronism with the successive reproduc tions of the partial'television images. Such appar n it u s to operaa a relati high Speed r th d ice m st c ps-S et Isle: tiv ly l r n mb r Pi @9 91" fi t e eme ts it order to produce the desired effects.

Ordinarily, a television receiver is provided with a cathode ray tube which, when'directly viewed, will produce only a relatively small p c: ture. It is becoming ihcreasingly desirable to Pr ct i es rmnsuch tub si's t a a m: tively a e ture ma b P duc d vi ing screen. One of the most satisfact y ,opt s em' f r e i a t evis on mol s er a c on of the hm dt ame aus t $9 2 as: tent heretofore in astronomical telescopes and the like. A

In orderto use a r fle tion pe 9 antics} s st suh a at sed nth lscbmi in a television receiver for projecting c,o images upon a viewing screen, it nsuallyhas been necessary to sacrifice a substantial portion .oi' the i t in -prop r i o su h, o t m sts tem. For example, in one pr osed ns'e of a Schmidt Optical system a c. 9 te r s oc P ajection receiver, a color filter drum having e. great many color filters is rotated in close pros imity to the fluorescent screen of the cathode ray tube. Inasmuch as this screen must also face he spherical reflecting member of the optical system, it has been .necessaryto thread the color fil r hro h uitahlei ats-inilw salient reflector. Then when the desired color filter is passing before the screen of the cathode'ray tube, the proper 1y colored light representing the'corre} spondin'gcolor component of the television subject is projected onto the spherical reflector. In that section of the reflector through which the filter drum operates the desired colored image is reflected back through other segments of the color drum. If the desired color is say red, the rays of light reflected from the central portion of the reflector will impinge upon green and/ or blue filter segments. The reflected red rays which impinge upon these green and blue filter segments are absorbed to a great extent thereby and, therefore, do not materially impair the color relproduction. Alternatively, it has been proposed to mask these filter segments whch are not in use at any given instant so that the colored light rays reflected from the mirror will not impinge upon these segments. In any case, a substantial portion of the spherical mirror is not used for the enlarged reproduction of the image. In other words, the otherwise efficiently operating Schmidt optical system is not employed at maximum efiicie cy'.

It, therefore, is an object of this invention to provide an optical system of the reflection type which will function at high efiiciency in a television projection system.

Another object of the invention is to provide optical apparatus for use in conjunction with a Schmidt optical system for projecting colored television images onto a viewing screen without materially reducing the efficiency of the Schmidt stem In accordance with this invention, there is provided the usual concave reflecting mirror and preferably, in addition, an aspherical correcting plate if the concave mirror is spherical as in the Schmidt camera. A number of cathode ray re pro-ducing tubes are directed generally toward the central axis of the system at a point between the concave mirror and the focal surface area thereof. In addition, there are provided a number of plane reflectors, one for each tube, which are located relative to the concave mirror and to the respective tubes in such a manner that they will reproduce in the focal surface area of the concalvemirror a plurality of virtual images exactly in register corresponding to each of the cathode ray tube screens; In a color television system some or all of the images may be of different elementary colors.

For a better understanding of the invention, together with other and further objects thereof,

, 3 reference is made to the following description, taken in connection with the accompanying drawlugs, and its scope will be pointed out in the pended claims.

In the accompanying drawings:

Fig. 1 is a side elevational view showing diagrammatically one form of apparatus embodying the invention; and

Fig. 2 is a sectional view taken on the line 2-2 of Fig. 1.

Having reference now to the drawings, there is shown a concave reflector Pref rably, as in the Schmidt camera, this reflector is spherical. There also is provided a light refractive device |2 such as a lens having a particular configuration to correct for the spherical aberration of the reflector The corrector plate I 2 is located substantially coaxially with the spherical reflector and is spaced therefrom at such a distance that it lies substantially in the same plane as the center of curvature of the reflector. The spherical reflector has a predetermined focal surface area which also has a spherical configuration and is represented by the broken line 53.

The optical system in accordance with this invention also is provided with a pluralit of plane reflectors which, in the illustrative embodiment, comprise three contiguous faces of a cubical member M. The plane reflectors which are used comprise the faces 55, i6 and 5?. All three of these plane reflectors meet at a common point which is located on the central axis E8 of the projecting optical system. The plane reflectors are located between the spherical reflector ii and its focal surface area l3 and face 3'5..-

generally the concave reflecting surface of the spherical reflector.

The system also includes a plurality of cathode ray television reproducing tubes. In the case where three plane reflectors are used, there are employed three tubes l9, 2| and 22. The tube |9, for example, is arranged so that the fluorescent screen which is formed on the face of the tube is directed toward the plane reflector E5. The tube I9 is located at such an angle with respect to the plane reflector If) that the image of the fluorescent screen of the tube is reflected from the plane reflector l5 onto the spherical reflecting surface of the reflector H in such a manner that the light rays which impinge upon the reflector appear to originate at the focal surface area i3. In other words, the tube 59 and the plane reflector i5 are so located relative to one another and to the spherical reflector N that a virtual image of the fluorescent screen of the tube 59 is formed in the focal surface area In a similar manner, the tubes 2i and are located respectively relative to the plane reflectors i6 and H to effect reflected reproductions of their fluorescent screens in the spherical reflector Ii. The tubes 25 and 22 likewise are located so as to produce virtual images of their respective screens in the focal surface area [3.

Between the fluorescent screen of the tube i9 and the plane reflector l5, there is mounted a color filter 23. Similarly placed color filters 2 and 25 are provided in conjunction with the tubes 2| and 22 respectively. Depending upon the particular mode of operation of such a device, as will be explained in greater detail subsequently, the color filters 23, 24 and 25 each may be different from the others or each may have other forms to be described. In one form of the invention, the color filter 23 may be red, the filter 24 green, and the filter 25 blue, for example. In

7 conventional.

42 such a case the filters will be mounted in a sta-' tionary mamier in front of the associated tube SCIEGllS.

Inasmuch as there are provided a plurality of cathode ray tubes in accordance with this invention, the fluorescent screens of these tubes each may be formed by different phosphors so that the images reproduced on the screens may be in the desired elementary colors. In such a case, the color filters may be eliminated.

Referring now to a preferred mode of operation of the described apparatus embodying the invention, assume that the color filters 23, 24 and 25 are respectively red, green and blue. In such a case, the are stationary. The television communication system employed to operate the cathode ray tubes l9, 2| and 22 may be entirely Such a system operates by transmitting in succession trains of video signals representing respectively red, green and blue partial images of a subject. In such a case, the video signals representing the red partial image are impressed upon the tube I9. These signals produce on the screen of the tube l9, a black and white representation of the red portion of the subject. The light emanating from the face of the tube passes through the red color filter 23 to produce a red colored partial image on the plane reflector l5. By reason of the described relationship between the tube IS, the plane reflector I5 and the spherical reflector II, this red partial image is projected by the optical system comprising the spherical reflector H and the corrector plate l2 onto a viewing screen (not shown).

In like manner, the video signals representing the green portion of the subject are impressed upon the cathode ray tube 2| which, in conjunction with its associated green filter 24, produces a green partial image on the plane reflector l6.

Similarly, the video signals representing the blue portion of the subject are impressed upon the tube 22 which in cooperation with its associated color filter 25 produces a blue partial image on the plane reflector ll.

Inasmuch as the cathode ray tubes and the plane reflectors are located relative to one another in the manner described to produce, respectively, virtual images of the fluorescent screens in the focal surface area l3, all of the partial images will be reproduced on the viewing screen exactly in register.

In order to operate the tubes I9, 2| and 22 sequentially in the manner described, a switch which preferably should be electronic may be used to transfer the video signal circuit from one tube to another as the corresponding color signals are received. Alternatively, three separate signaling channels may be provided, one for each of the color components of the picture so that all of the video signals may be transmitted and received for each of the colors substantially simultaneously.

If the plane reflectors l5, l6 and H form three contiguous faces of a cube as illustrated and described, the cathode ray tubes |9, 2| and 22 will be arranged substantially as shown. In such a case, the image of the screen of the tube 9 which is reflected by the plane reflector l5 will use less than the entire surface of the spherical reflector Similarly the tubes 2| and 22 each will not utilize the entire surface of the spherical reflector. However, other angular positions of the plane reflectors may be used as subsequently described, whereby greater portions of the spherical reflector surface may be used by eachth tube It may be desiredto increasethe brilliancy of the reproduced picture. In this event, the received video signals 'may be applied simultaneously-to all of the tubes, This will necessitate the use of color filters associated with each of the tubes which will include all three colors. They will reguire rotation or other movementin the usual manner to coincide with the image which is being reproduced by the tube. 1 Synchronism between the moving color discs, drums or the like may be effected-in the usual manner. Nevertheless, by means of the present invention the color filters may be located entirelyout of the path of any reflected light rays.

It obviously is not necessary to employ plane reflectors which form three faces of a cube. If such a structure is used, the plane reflectors, of necessity, are mutually disposed at right angles. Other angular relationships between the plane reflectors may be employed within the scope of this invention. For example, each of the reflectors may be placed more nearly in a plane perpendicular to the central axis IS. The cathode ray tubes associated with such reflectors will be located closely to the spherical reflector H. In some cases, it may be desirable to so position the plane reflectors that the cathode ray tubes will be located behind the spherical reflector. In such a case, suitable apertures maybe provided in the spherical reflector to enable light to be projected from the tube screen onto the associated plane reflector. In cases where the plane reflectors are set in planes more nearly perpendicular to the central axis of the system, the light which is reflected therefrom will fall upon a greater surface area of the spherical reflector II. More efficient operation may be obtained in some cases by so locating the plane reflectors and their associated tubes. Substantially any desired location may be employed so long as the relationship between each of the plane reflectors and its associated cathode ray tube is such that there is produced a virtual image of each tube screen in the focal surface area I3.

Obviously, the apparatus embodying the present invention is not limited to the use of three plane reflectors. Other numbers of plane reflectors either greater or smaller may be used with equal facility in order to obtain special effects without departing from the spirit of the invention.

While there has been described what, at present, is considered the preferred embodiment of the invention, it will be obvious to those skilled in the art that various changes and modifications may be made therein without departing from the invention, and it is aimed, therefore, 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:

1. An image projecting device for a color television system comprising, a concave spherical reflector having a predetermined focal surface area, a plurality of plane reflectors angularly disposed relative to one another and facing said spherical reflector, a plurality of cathode ray television reproducing tubes having the fluorescent screens thereof directed toward respective ones of said plane reflectors, said tubes and said plane reflectors being so located relative to one another and to said concave reflector as to produce virtual images of said fluorescent screens substantially in re ister he focalsurface area of said concave reflector, and means for directins differentlycoloredlighti from each of said plurality of tubeszonto its corresponding plane reflector.

2. An imageprojecting device for a color tele-i vision system comprising, a concave reflector having a predetermined focal surface area, an auxili-. ary reflecting device facing said. spherical re-y hector, said auxiliary reflecting device comprising aplurality ofplane'reflectors, a pluralityof cathode ray television reproducing tubes having the fluorescent screens thereof directed toward re spective ones of said plane reflectors, said tubes. and said plane reflectors being so located relative to one another and to saidconcavezreflector as to. produce a plurality of virtual images of said fluorescentscreens.substantially in register in the focal surface area of said concave reflector, and means associated with each of three of said tubes in conjunction with the corresponding plane reflector to produce three partial images of said television subject in three different colors.

3. An image projecting device for a color television system comprising, a concave spherical reflector having a predetermined focal surface area, a light refractive device facing said reflector for correcting the spherical aberration of said reflector, an auxiliary reflecting device located between said spherical reflector and its focal surface area, said auxiliary reflecting device comprising a plurality of plane reflectors symmetrically disposed around the central axis through said spherical reflector and said refractive device, a plurality of cathode ray television reproducing tubes having the fluorescent screens thereof directed toward respective ones of said plane reflectors, said tubes and said plane reflectors being so located relative to one another and to said spherical reflector to produce of plurality of partial virtual images of a television subject in the focal surface area of said spherical reflector, and colored light filters located between each of said tubes and its corresponding plane reflector.

4. An image projecting device for a color television system comprising, a concave spherical reflector having a predetermined focal surface area, a lens facing said reflector and spaced therefrom for correcting the spherical aberration of said reflector, an auxiliary reflecting device located between said spherical reflector and its focal surface area, said auxiliary reflecting device comprising three plane reflectors angularly disposed relative to one another in a symmetrical manner about the central axis through said spherical reflector and said lens, three cathode ray television reproducing tubes having the fluorescent screens thereof directed toward respective ones of said plane reflectors, said tubes and. said plane reflectors being so located relative to one another and to said spherical reflector as to produce three respective virtual images of said flourescent screens in substantial register in the focal surface area of said spherical reflector, and a differently colored light filter located between each of said tubes and its associated plane reflector.

5. An image projecting device for a color television system comprising, a concave spherical reflector having a predetermined focal surface area, a spherical aberration corrector plate facing said reflector and spaced therefrom, an auxiliary reflecting device located between said spherical reflector and its focal surface area, said auxiliary reflecting device comprising three plane reflectors mutually disposed at right angles, the common point of said three plane reflectors being located on the central axis through said spherical reflector and said corrector plate and being pointed toward said spherical reflector with the plane reflectors disposed symmetrically about said axis, three cathode ray television reproducing tubes having the fluorescent screens thereof directed toward respective ones of said plane reflectors, said tubes and said auxiliary plane reflectors being located suitably relative to one another and to said spherical reflector to produce registering virtual images of said fluorescent screens in the focal surface area of said spherical reflector, and :a diflerently colored light filter element located between each of said tubes and the corresponding plane reflector.

CHRISTIAN C. LARSON.

8 REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Australia June 1, 1939