US2251786A

US2251786A - Television recording apparatus

Info

Publication number: US2251786A
Application number: US232486A
Authority: US
Inventors: David W Epstein
Original assignee: RCA Corp
Current assignee: RCA Corp
Priority date: 1938-09-30
Filing date: 1938-09-30
Publication date: 1941-08-05
Anticipated expiration: 1958-08-05

Description

"Aug, 5, 1941. D. w, EPSTEgN 2,251,785

TELEVISION RECORDING APPARATUS y Filed sept. 3o, 193e :s sheets-sheet 1 CLOSED CL 065D 3 mentor David W Epstein,

Aug- 5, 1941- D. w. EPsTElN 2,251,786

TELEVI S ION RECORDING APPARATUS Filed sept. so, 195e s sheets-sheet z F1 6.40,. 172654Z?.

F0767' F'AE'LD SECOND FIELD FVLM f77/VME X F1a.. 4c. F1a. 4d.

Tl//YD FIELD FOURTH F'IL'LD Zmventor David WEP'tezln Aug. 5, 1941.

D. W. EPSTEIN TELEVI S ION RECORDING APPARATUS Filed Sept. 50, 1938 5 Sheets-Sheet 5 Z4 'ec'.

1 RECgRD/NG TIME -P l %00 .sec P/39 l car/lows: Ray cu'r orf' Smaent r.. David W Eynstein;J

Gttorneg Patented Aug. 5, 1941 TELEVISION RECORDING APPARATUS David W. Epstein, Merchantville, N. J., assignor to Radio Corporation of America, a corporation of Delaware Application september so, 193s, serial No. 232,486 l (ci. 17a-6.1)

Claims.

My invention relates to picture recording apparatus and particularly to means for recording television pictures occurring at a certain' frame frequency on moving picture film which is being moved at a different frame frequency.

For record purposes, it is desirable to make a moving picture of studio scenes which are being transmitted from a televisiontransmitter. The obvious way of doing this isto photograph the scene directly, but such procedure is undesirable since a recording camera cannot be located in the same place as the television camera (i. e., cannot occupy the same space) and, as a practical matter, cannot be used for many scenes during the television transmission.

Also, it is desirable to provide some method of recording which is less expensive than photographing the scene directly with the aid of a special group of movie technicians.

The picture being transmitted could readily be Irecorded by focusing a movie camera on the end of a cathode ray receiver tube, such as a monitor tube or a cathode ray tube of the projector type at the transmitter, providing the frame frequencies of the television picture and movie camera vwere the same. Obviously, it is desirable to have the pictures recorded at a standard frame frequency, 24 per second for example, so that they may be projected later in a standard projector, o

Television pictures, however, should be transmitted at a frequency which is equal to or which is a submultiple of the power line frequency. In the United States, the standard power line frequency is 60 cycles per second and, accordingly, it is preferred television practice to transmit pictures having a frame frequency of 30 per second.

Preferably, double interlaced scanning is employed whereby the field frequency or frequency of vertical deflection is double the frame frequency or, in the example given, 60 per second. It will be apparent that a 24-frame picture cannot be recorded merely by focusing the camera upon a 30-frame television picture and operating the camera in the usual way.

It is, accordingly, an object of my invention to provide an improved method of and means for recording at one frame frequency, such as 24 per second, pictures which are being produced at a diierent frame frequency, such as 30 per second.

In practicing my invention, I photograph a certain number of picture fields, such as two, on one frame of film, next close a shutter or block the cathode ray of the television tube for a fraction of a picture field, such as one-half, and simultaneously pull the next frame of film into position and on this second frame photograph the remainder of the last-mentioned picture field, al1 of at least one more picture field, and enough of one more picture field, one-half for example, to complete or fill in the field which wasA not completely photographed due to the required pulldown time.

The invention will be better understood from the following description taken in connection with the accompanying drawings in which Figure 1 is a view oi apparatus illustrating one embodiment of my invention,A

Figure 2 is a view, on a slightly larger scale, of a shutter disc included in the apparatus shown in Fig. 1,

Figure 3 is a diagram illustrating the time relations employed in practicing a specific embodiment of my invention, v

Figures tatto 4f are views representing the sequence in which the television picture fields are photographed, these views being referred to in explaining the invention,

Figure 5 is a view of apparatus illustrating another embodiment of my invention, and

Figure 6 is a diagram which is referred to in explaining the operation of the apparatus shown in Fig. 5.

Referring to Fig. 1, there is indicated at l a cathode ray tube upon the endjofwhich there appears a television picture whichis to be recorded on movie film indicated at 2. `Ihis television picture may be recorded by a suitable camera comprising an intermittent mechanism 3 which pulls the film 2 through a film gate 4 at the rate of 24 picture frames per second, for example. A

A suitable camera optical system represented generally at 6 forms an image of the vtelevision picture upon the film 2.

The intermittent mechanism 3 may be driven by a motor 'l through a suitable gear drive indicated at 8.

In place of the usual camera shutter, a suitable shutter such as the disc A9 may be driven by the motor l in a fixed time relation with the intermittent mechanism. In the example being described, as shown in Fig. 2, the shutter 9 is designed to interrupt the passage of light to the film 2 for one-fifth of the period of a single film frame.

The time relations of the television picture, the shutter and the intermittent mechanism will be better understood by referring to Fig. 3.

the recording of the television picture is begun at the start of a picture field. It should be understood, however, that the recording may be begun at any point in the picture field.

Referring to Fig. 3, the fluorescent screen on the end of tube i is scanned twice while the shutter 9 is open and the rst two fields are recorded on one frame of the film 2, this taking place in 17%,@ second. The shutter then closes and the nlm 2 is pulled down in 1,620 second, bringing the second frame of lm into position for recording. At the end of the pull-down, the shutter opens.

With the shutter again open, recording begins on the second film frame, the recording beginning in the middle of the third field. On this second frame, there is now recorded the last half of field number 3, all of field number 4, and the first half of field number 5. At this point, the shutter again closes while the third film frame is being pulled into position for recording thereon and the cycle of operation is repeated beginning with field number 6.

The way in which the television picture is recorded on the nlm 2 is illustrated in Figs. 4a to 4f, the cycle of operation just described being assumed.

Figs. 4a and 4b show how the first and second fields are recorded in sequence on the rst film frame. The solid and dotted slanting lines represent the scanning lines for even andV odd fields, respectively, only a few scanning lines being shown in order to simplify the drawings.

Figs. 4c, 4d and 4e show how the last half of the third field, all of the fourth field, and the first half of the fifth eld are recorded on the second nlm frame. It will be seen that a portion of the fifth field fills out the portion of the film frame which was not exposed during the first part of the third eld.

The cycle begins toV repeat with the sixth field as shown in Fig. 4f.

In Fig. there is illustrated another embodiment of my invention where the picture appearing on the fluorescent screen 20 of a cathode ray tube 2i is recorded by a standard camera 22 which has its shutter removed.

The tube 2i may be of a well known type having an indirectly heated cathode 23, a control grid 24, a first anode 26 and a second anode 21'. The grid 24 may be maintained at a suitable negative bias by means of a battery 2B connected in series with a grid resistor 2S., Picture signals are impressed upon the control grid 24 through: a coupling condenser 3l,

In this embodiment, in place of a shutter which closes the camera during the film pull-down period, the cathode ray in the tube 2l is blocked during the pull-down period by driving the grid 24 highly negative. To accomplish this, periodically recurring negative impulses may be generated by means of a light source indicated at 32, a photoelectric cell 33 and a shutter disc I4 which interrupts the beam of light from source 32 except i'or the short time an aperture 36 passes between the source 32 and cell 23. The disc 34 is rotated in a fixed time relation to the action vertical deflection.

In Fig, 3 there are shown the time relations,

of the film pull-down mechanism in the camera 22, both disc and camera being driven by a motor 31.

The photoelectric cell Il is connected in the input circuit of an amplifier n in the output circuit of which appears the negative voltage impulses indicated at I8. These impulses are applied to the control grid 24 through a conductor ll in the example shown, and are of sufficient amplitude to bias the cathode ray tube beyond cut-off. Obviously, the negative blocking impulses 39 may be applied to the grid 24 in other ways as by means of a transformer or coupling impedance in series with the condenser 3l and the grid 24.

The operation of the apparatus shown in Fig.

5 may be in accordance with the chart in Fig. 3,

the dur-ation of the negative impulse 39 corresponding to the closed shutter period indicated in Fig. 3.

A slight variation'of the timing shown in Fig. 3 may be practiced as shown in Fig. 6. Here the same field and frame frequencies are assumed as in Fig. 3. The negative impulses 38 are made to. last for one-half field plus the return time of a This is approximately M00 second in the case illustrated.

It will be understood that additional time for the film pull-down may be obtained in the same way with the apparatus shown in Fig. 1, the shutter closing near the end of field number 2 just as the vertical return deflection begins.

A shorter pull-down time than indicated in Fig. 3 may be desirable for the purpose of insuring that there is no gap between lines at the spllce, that is, where the lines of one field, such as the fifth field, meet the lines of a preceding fleld, such as the third field. Specifically. the pull-down period may start a little later than ybut end at the same time as indicated in Fig. 3, whereby there is always a slight overlap of scanning lines at the splice. Thus, considerlng the fifth field, slightly more than one-half of the fifth field will be recorded on the second nlm frame. Since recording began at one-half of the third field, the result is a Slight overlapping of lines.

The time relations illustrated in Fig. 3 may be represented as follows: Let m be the number of the film frames per second. Let n be the number of television picture frames persecond where n is greater than 1n. Then the nlm is exposed during l/n seconds and is not exposed during (l/m-l/n) seconds. In other words. the film is exposed for the fraction m/n of a film frame and is unexposed for the fraction il-m/n) of a film frame.

It will be understood that the claims which specify certain time relations in terms of m and n are intended to cover slight departures from the exact relations shown in Fig. 3, such as the departures previously described.

I claim:

i. Apparatus for recording television pictures occurring at a certain frame frequency non a film being moved at a different frame frequency m where n is greater than m, said apparatus comprising means for moving said nlm intermittently at said frequency m, and means operating in a fixed time relation with said first means for exposing said lm to said television pictures for substantially'l/n seconds and for preventing exposure of said nlm for substantially i/m-l/n seconds.

2. The invention according to claim 1 where n equals 30 and where `m equals 24.

3. The method of recording television pictures occurring at a certain frame frequency on a lm being moved at a different frame frequency which comprises recording on one frame of said film one television picture frame, pulling said film into the next frame position without exposing the film during the pull-down period, said pull-down period being a certain fraction of the second television picture frame, and next recording on the film the remainder of the second television picture frame and a portion of the following television picture frame which is equal to said certain fraction.

4. The method of recording television pictures occurring at a frame frequency of 30 per second.

on a moving picture film being moved at a. frame frequency of 24 per second which comprises recording one television picture frame on one film frame, pulling the next film frame into position for recording without exposing the film during the pull-down period with the pull-down period such that recording can begin approximately at the end of one-fourth of the second television picture frame, and recording on the second film frame three-fourths of said second television picture frame and one-fourth of the next television picture frame.

5. 'I'he method of recording television pictures occurring at the frame frequency of n per second on a film being moved intermittently at a frame frequency of m per second where n is greater than m, said method comprising moving said film intermittently at the frequency m, exposing said film to said television pictures for m/n of a. film frame, and preventing exposure of said film for l-m/n of a film frame.

DAVID W. EPSTEIN.