US2214072A - Apparatus for the reversal of photographic negatives - Google Patents

Description

p 1940. F. BIEDERMANN 2,214,072 I APPARATUS FOR THE REVERSAL OF PHOTOGRAPHIC NEGATIVES Filed Nov. 26, 1938 in van for Fr/b drl'c/z Bl'ederm am By His Afforn y Patented Sept. 10, 1940 UNITEU STATES PATENT FHCE APPARATUS FOR THE REVERSAL OF PHOTOGRAPHIJ NEGATIVES Application November 26, 1938, Serial No. 242,627 In Germany November 29, 1937 8 Claims.

My present invention relates to the reversal of photographic negatives.

In estimating the adaptability for printing of a photographic negative it is of great advantage in various branches of practical photography to be able to produce from the negative a positive picture, enlarged or of the same size as the original, without resorting to a printing process.

10 It is known in a complete system of television comprisin a transmitter and a receiver to reproduce the negative pictures transmitted from the transmitting oscillograph as positive pictures in the receiving oscillograph. Such apparatus, however, is complex and requires a series of devices irrelevant to the purpose of the invention.

It is one object of my invention to provide an apparatus for the reversal of photographic negatives to be estimated by an electrical process.

28 Another object of the invention is to provide such apparatus which comprises a single cathode ray oscillograph in which the cathode ray beam scans the fluorescent screen point by point acting at the same time as transmitter and receiver.

A further object is the provision of an apparatus in which the light from the fluorescent screen of the oscillograph passes through the negative to be reversed, thereby scanning it point by point, and then falls on a photocell which con- 30 trols either the intensity of the cathode ray beam or the speed of scanning in such a manner that the quantity of light falling on the photocell from all the points of the picture to be reversed is substantially the same.

A still further object of my invention is to provide such apparatus which comprises a control device, connected if desired with an amplifier for controlling the intensity of the cathode ray beam between the photocell and the cathode and control electrode of the oscillograph. The control of the intensity is brought about by the influence of the output of the amplifier or the control device on the voltage between the cathode and the control grid. For controlling the speed of scanning, the frequency of the time base is influenced by a control device connected with the photocell or by the output of an amplifier connected with the control device.

Other objects of my invention will be apparent from the description following hereinafter.

Reference is made to the accompanying diagrammatic drawing, in which:

Fig. 1 represents the Whole reversing apparatus and Fig. 2 represents a circuit for the control device.

B denotes the cathode ray oscillograph having a fluorescent screen F, deflecting plates P1, P2, P3 and P4, and the usual electrodes, diagrammatical- 5 ly indicated in the drawing (anode A, control electrode G and cathode K). By the deflecting plates, which derive their voltage from the time base KG, the cathode ray beam is deflected in two directions as in television, so that it scans a definite rectangular picture on the fluorescent screen F in a definite time. The rectangle (or square) so scanned, and emitting light of the color of fluorescence of the screen, is projected by an objective 0 on to the negative N (sta- 5 tionary picture or moving film) to be reversed. The light transmitted by the negative N is projected by a lens L, if desired condensed, on a photocell Z. The photocell Z controls by way of a control device R and an amplifier V the intensity of the cathode ray beam; the output of the amplifier V provides the voltage between the control electrode G and the cathode K of the oscillograph. This control by the photocell Z is effected by the control device R in such a man- 25 her that the quantity of light falling on the cell at every instant is the same, that is the intensity of the cathode ray beam is automaticallyincreased at the dark parts of the negative, so that the parts of the fluorescent screen corresponding with the 30 dark parts of the negative are the most brightly illuminated, and vice versa. Thus the desired complementary distribution of illumination is eX- hibited by the screen, which shows a positive of the negative N placed in the path of the rays. The fluorescent picture can either be observed directly or projected.

The constancy of the light falling on the photocell may be obtained by, ior example, the circuit shown in Fig. 2. Z again denotes the photocell 0 on which the light transmitted by the negative falls. The photocell is connected with the resistances T1 and T2 and a variable resistance Tv to form a bridge circuit. With a given intensity of light a definite current flows through the cell Z and a definite voltage E is produced between the points a and b which acts as the grid voltage, or a part of the grid voltage, of a tube included in the amplifier V. If Z receives more light, a 50 becomes more negative with respect to b and the amplification factor of the tube and therewith the intensity of the cathode ray beam are reduced until the previously prevailing condition of the bridge is restored. If Z receives less light, 55

the amplification factor and therewith the intensity of the cathode ray beam are increased. To the control electrode G of the cathode ray oscillograph is fed either the amplified compensating voltage itself or an alternating voltage the magnitude of which is controlled by the control device R. The picture appearing on the screen F can exhibit the most varied gradations, depending on the intensity of light maintained by the control device. The gradation is therefore adjustable, the adjustment being made either by inserting a diaphragm or filter in front of the photocell Z or by altering the resistance Tv or the amplifier.

While the apparatus described uses control of the intensity of the cathode ray beam, the picture may alternatively be reversed in a similar manner by control of the speed of scanning. In this method the apparent brightness of a spot of light is varied by Varying its velocity on the surface of the picture, so that, in a manner known per se the impression produced at points of more rapid movement is darker than that produced at points of slower movement. The speed of scanning depends on the frequency of the time base, which is influenced by the control device R of the output voltage of the amplifier V.

The apparatus requires no synchronization. The number of points per frame can be substantially higher than in television, because the high frequencies are not'cut oil by cables and the like. Moreover,- the number of frames per second, especially in the reversal of stationary pictures, can be made quite low, the flickering being in this case avoided by a correspondingly high duration of the after-fluorescence of the fluorescent screen.

I claim:

1. Apparatus for the reversal of photographic negatives which comprises a cathode ray oscillograph provided with an anode, a cathode, a control electrode, a fluorescent screen and deflecting plates, a time base, said deflecting plates being adapted to derive their voltage from said time base and to deflect the cathode ray beam in two directions as in television so that said ray beam scans said fluorescent screen point by point, an objective between said screen and the negative to be reversed, a photoelectric cell, and a lens between said negative and said cell, said cell being adapted to control said cathode ray beam, without altering the cross-sectional size of the beam at said screen, in such a manner that the quantity of light falling on said cell from all points of said negative is substantially the same.

2. Apparatus for the reversal of photographic negatives which comprises a cathode ray oscillograph provided with an anode, a cathode, a control electrode, a fluorescent screen and deflecting plates, a time base, said deflecting plates being adapted to derive their voltage from said time base and to deflect the cathode ray beam in two directions as in television so that said ray beam scans said fluorescent screen point by point, an objective between said screen and the negative to be reversed, a photoelectric cell, a lens between said negative and said cell, and a control device connected between said photoelectric cell on the one hand and said control electrode and cathode on the other hand and adapted to control said cathode ray beam, without altering the cross-sectional size of the beam at said screen, in such a manner that the quantity of light falling on said cell from all points of said negative is substantially the same.

3. Apparatus for the reversal of photographic negatives which comprises a cathode ray oscillograph provided with an anode, a cathode, a control electrode, a fluorescent screen and defleeting plates, a time base, said deflecting plates being adapted to derive their voltage from said time base and to deflect the cathode ray beam in two directions as in television so that said ray beam scans said fluorescent screen point by point, an objective between said screen and the negative to be reversed, a photoelectric cell, a lens between said negative and said cell, and a control device connected between said photoelectric cell on the one hand and said control electrode and cathode on the other hand, forming a bridge circuit, said cell being one arm of said circuit, and adapted to control said cathode ray beam, without altering the cross-sectional size of the beam at said screen, in such a manner that the quantity of light falling on said cell from all points of said negative is substantially the same.

4. Apparatus for the reversal of photographic negatives which comprises a cathode ray oscillograph provided with an anode, a cathode, a control electrode, a fluorescent screen and. defleeting plates, a time base, said deflecting plates being adapted to derive their voltage from said time base and to deflect the cathode ray beam in two directions as in television so that said ray beam scans said fluorescent screen point by, point, an objective between said screen and the negative to be reversed, a photoelectric cell, a lens between said negative and said cell, a control device connected between said photoelectric cell on the one hand and said control electrode and cathode on the other hand and adapted to control said cathode ray beam, without altering the cross-sectional size of the beam at said screen, in such a manner that the quantity of light falling on said cell from all points of said negative is substantially the same, and means for adjusting the gradation of the reversed picture on said fluorescent screen.

5. Apparatus for the reversal of photographic negatives which comprises a cathode ray oscillograph provided with an anode, a cathode, a control electrode, a fluorescent screen and deflecting plates, a time base, said deflecting plates being adapted to derive their voltage from said time base and to deflect the cathode ray beam in two directions as in television so that said ray beam scans said fluorescent screen point by point, an objective between said screen and the negative to be reversed, a photoelectric cell, a lens between said negative and said cell, and a control device connected between said photoelectric cell on the one hand and said control electrode and cathode on the other hand, forming a bridge circuit, said cell being one arm of said circuit, and adapted to control said cathode ray beam, without altering the cross-sectional size of the beam at said screen, in such a manner that the quantity of light falling on said cell from all points of said negative is substantially the same, said bridge circuit containing a variable resistance adapted to adjust the gradation of the reversed picture on said fluorescent screen.

6. Apparatus for the reversal of photographic negatives which comprises a cathode ray oscillograph provided with an anode, a cathode, a control electrode, a fluorescent screen and deflecting plates, a time base, said deflecting plates being adapted to derive their voltage from said time base and to deflect the cathode ray beam in two directions as in television so that said ray beam scans said fluorescent screen point Fey point, an objective between said screen the negative to be reversed, a photoelectric cell, a lens tween said negative and cel control device connected between said photoelectric ceL on the one hand and said control electrode and cathode on the other hand and adapted to co trol said cathode ray bearn, without alt cross-sectional. size of he in such manner that falling on cell from a tive is substantially the and an azopli connected between conti control electrode and cathode 7. Apparatus for the re ersal of photographic negatives which comprises a cathode oscillograph provided with an anode, a cathode, a control electrode, a finer so nt screen and deflecting plates, a time said deflecting plates being adapted to derive their voltag in time base and to deflect the cathode ray beat-o1 in two directions as in television so that said ray beam scans said fluorescent screen point by point, an objective between said screen and the negative to be reversed, a photoelectric cell, a lens between said negative and said cell, a control device connected between said photoelectric cell on the one hand and said control electrode and cathode on the other hand and adapted to control said cathode ray beam, without altering the cross-sectional size of the beam at said screen, in such a manner that the quantity of light falling on said cell from all points of said negative is substantia ly the same, and an amplifier connected betwe a said control device and said control electrode and cathode, and containing a variable part adapted to adjust the gradation or the reversed picture on said fluorescent screen.

8. Apparatus for the reversal of phctogra negatives which comprises a cathode ray oscillograph provided with an anode, cathode, a con.- trol electrode, a fluorescent screen and deflecting plates, a base, said deflecting plates being adapted to derive their volta e base and to deflect the cathodoe two directions as in television 5: beam scans said fluores bv an objective between s e e tive to be revers d, a 1 1 ct between said neget'vc 9.115. said cell a control 1 1 i device connect-ed oetween sad photoelectric ce on the one hand and said control electrode o cathode on the other hand a adapted to control said cathode ray beam, wi hout altering the cross-sectional size of the beam at said screen, in such a manner that the quantity or" light falling on said cell from all points of said negative is substantially the same, and an interchangeable filter placed between said negative and said cell and adapted to adjust the gradation of the reversed picture on said fluorescent screen.

FRIEDRICH BIEDERMANN.

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