US2101932A - Exposure control - Google Patents

Description

Dec. 14, 1937.

J. EGGERT AL 2,101,932

EXPOSURE CONTROL Filed April 19, 1935 2 Sheets-Sheet 1 In ven fors:

By Afforneys Dec. 14, 1937. J. EVGGERT AL 2,101,932

EXPOSURE CONTROL Filed April 19, 1935 2 Sheets-Sheet 2 Afforneys m, W

- ilnvenfo rs:

Patented Dec. 14, 193'] um'rso STATES PATENT OFFICE I r f 2,101,932 v John Eue Leipzig-Gohlis, and Hans Friedrich u, Germany, assignors to I. G.

Farbenindustrie Aktlengesellschaft, Frankforton-the-Main, Germany Application April 19, 1935, Serial No. 17,318 In Germany April 20, 1934 lOlaim.

Our present invention relates to exposure control and more particularly to an apparatus for the application 01' a dosed exposure in the photographic reversal process and in the photographic printing process.

One of its objects is to provide an improved apparatus for exposure control. Another object is an apparatus of this kind which is more efiicient than those hitherto known. A further object is an apparatus for exposure control which is operated exclusively optically and electrically and is therefore operated with a minimum of in ertness. Further objects will be seen from the detailed specification following hereafter. Reference is made to the accompanying drawings in which:

Fig. 1 shows a diagram of the connections of an apparatus according to this invention,

Fig. 2 shows a diagram of the connections of an apparatus according to this invention as shown in Fig. 1 with the diiference that a special relay has been provided for holding the required contacts closed when the galvanometer has a too great deflection,

Fig. 3 shows a diagram of the connections of an apparatus according to this invention in which the intensity of the printing light is regulated over a heavy current valve,

Fig. 4 shows a modified apparatus according to this invention,

Fig. 5 shows an apparatus as shown in Fig. 4 but provided with a back coupling,

Fig. 6 shows an apparatus as shown in Fig. 5 with a modified back coupling, and

Fig. 7 shows a diaphragm as usedin the apparatus shown in Figs. 4 to 6.

In the second exposure in the production of a reversed film it is necessary to adjust the quantity of light projected on the film in accordance with the density of the photographic image. So also in the printing process the illumination must be selected in dependence on the density of the negative.

A known arrangement for producing an automatic adjustment of the light consists in placing on the other side of the film to be illuminated a device whereby the transmitted light excites a photo-electric cell the current from which moves directly or indirectly a diaphragm in the path of the rays from the illuminating lamp. These devices have the drawback that they are comparatively slow because considerable masses have to be moved, with the disadvantage that in the majority of cases the film or a greater part of it is incorrectly exposed.

According to this invention the exposure of the film is regulated exclusively electrically and optically. With the apparatus herein described it is not only possible to control the intensity of the printing light in any desired proportion, but it is also possible to adjust the intensity of the printing light according to the density of the film to be exposed while having regard to the specialproperties of the used film and the used photocell. A particular advantage of the apparatus according to this invention is its little inertness which guarantees a rapid adjustment of the intensity. Photo-electric cells of the regenerative type that is to say such which are capable to convert light into electric energy are preferred, for instance, photo-electric cells in which a layer of a finely subdivided semi-conductor is in contact with a layer of a conductor, as in the cuprous oxide cells. However, also the other photo-electric cells may be used. The use of non-regenerative photo-electric cells that is to say such in which only the resistance to an electric current is changed by the influence of light are less practical because they need a special source of electric current and an amplifier.

In using the apparatus for dosing the intensity of the source of light in the second exposure of a reversal film it is not necessary to scan the whole breadth of the pictures. The desired width which must, however, not include the perforation row, is blocked out by a mask. In order to obtain correct density of the print at least one picture length must be scanned, preferably there are scanned 4 to 5 picture lengths.

The modifications of an apparatus for exposure control according to this invention have the common feature that the light projected, for instance, through the bleached reversal film excites a photo-electric cell. The current of the photoelectric cell actuates a galvanometer provided with a mirror. According to the variations of power of the current the galvanometer is more or less deflected and, therefore, the beam of light projected from a source of light on the mirror. This beam of light may be used directly or indirectly for exposing the film. For using it directly the beam of light falls on a fixed mask having a suitable aperture which according to the degree of deflection transmits more or less light which is evenly distributed on the film plane to be exposed. When using the beam of light indirectly it falls on photo-electric cells which by means of relays switches-in or cuts out resist-' ance in the circuit of the source of light.

In printing from a finished negative or posi- The principle of the indirect method will now be explained with reference to the accompanying drawings. The indicesof the switches are the same as those of relays by which they are actuated. The reversal film F which is to be exposed is passed between a source of light and a photo-electric device in such a manner that the photo-electric cell is excited by the light passing through the film. The current produced by the light in the photo-electric cell actuates a galvanometer G provided with a mirror. The mirror reflects a light ray of the source "of light Lg- The position of the mirror determines the direction of the reflected light ray. Thus the direction of the light ray is dependent on the density of the scanned picture. .With a certain deflection of the mirror of the galvanometer the light is projected on a'photo-electric device B1, which actuates a relay C1. The relay initiates the adjustment of the required intensity of the source of light which serves for the second exposure of the film. There are arranged several photoelectric devices B1, B2 B11 directly side by side or at suitable distances, each photo-electric device actuating a special relay. In accordance with the relay which is actuated a oertain intensity of the source of light for exposing the film is produced.

The arrangement represented in Fig. 2 shows one of the many possibilities. If the relay C1 is actuated by light projected on B1, a second relay D1 is energized so that it closes the switch df, Hereby the resistance R1 is short-circuited so that the current supplied to the source of light L11 is increased and the intensity of the source of light likewise is increased. If the relay C2 is actuated R2 is short'circuited over czDzdg. The intensity of the source of light 1111 is further increased. Thus, the intensity of the source of light may be regulated to difierent values which are determined by the value of the resistance R.

In the following manner the efiectiveness may be further increased. The pencil of light projected on the photo-electric devices B1, B2 and so on is made so large that when the pencil of light passes from one photo-electric device to the next two adjacent relays are actuated (apart from the first and the last photo-electric device). By closing the switch d5 with the actuation of the relay D1 the relay is kept in action also when 01 is not actuated by C1. This involves the advantage that when the pencil of light emanating from the mirrorin moving back from E2 to E1 the switch 01 is closed without being under tension. Furthermore d; is closed, so that on actuation of d? only the partial resistance R2 is switched on or switched ofl. This would not be the case if, for instance, the galvanometer G is operated so quickly that the relay cannot follow immediately. This involves a steady operation, little wear, and increased reliability in service. It is not desired that all relays are in operation; the switches d which are actuated by the relays D having the-corresponding indices switch off all relays except two which are in operation.

' If the galvanometer G has no abutment which prevents deflection of the pencil of light so that it passes beyond .1311 it is possible to provide a devicex which retains the relay D11 in its operative position when the pencil of light is deflectedbe-- yond B11. For this purpose that relay has a coil D11 which is actuated over a switchdfi of the relay D11 and an open circuit contact c11'-1'of the relay C'11 1. If the pencil of light wanders from B11 to EH, 3111-: the relay D11 must be switched ofi. If it wanders in the opposite direction the relay D11 must remain in operation. Thus, the maximum intensity of the source of light 1111 which may be required cannot be surpassed.

Another possibility of control consists in applying difierent grid voltages to the grid of a heavy-current control valve by means of the relays C1 C11. The switching onof diilerent voltages may be obtained in difierent manners, for instance, by means ot a potentiometer, a battery from which different voltages can be taken, a transformer from which different voltages can be taken or an apparatus by which a phase lead or a phase lag is produced. Thealternating current which flows through the heavycurrent control valve is directly or after transformation conducted to the lamp which serves for the exposure of the sensitive film.

The direct method provides a rapid adjustment by using a stationary diaphragm and changing the direction of the light rays so that more or less light is projected upon the diaphragm.

The accompanying diagrams of Figs. 4, 5, and 6, illustrate three arrangements in accordance with the invention. 1

Referring to Fig. 4, the film F is illuminated by the source of light L1. The transmitted light excites the photo-electric cell A, the current from which actuates a mirror galvanometer G.,

This mirror reflects the cone of rays from the lamp L2. In the path of this reflected light is the diaphragm B, the form of which is preferably such that a certain ratio between the density curve of the image and the gradation of the 'strength of illumination is obtained. The diaform there may be used a diaphragm with the interposition of a suitable grey wedge or there may be used a grey wedge alone. The diaphragm is advantageously placed at a position in the path of the rays where the diameter of the cross section of the cone of light corresponds with about the greatest breadth of the diaphragm.

If the current passing through the galvanometer becomes stronger in consequence of a smaller density of the image, the cone of rays moves gradually behind the diaphragm, the reverse being the case when the density of the image becomes greater. The galvanometer mirror may be so adjusted that there is always a certain minimum quantity of light passing through the diaphragm.

There can, however, be provided a separate passage for the light. Advantageously, the lamp Li,

which serves for providing the transmitted light,

may have such photographic activity that it pro- 5 duces the smallest necessary illumination. The light passing through the diaphragm falls upon the ground glass screen D by which the film is luminated. The loss of light which occurs at the ground glass must be taken into account in selecting the intensity of the source of light. In order to avoid loss of light the path of the light between the ground glass screen and the film is surrounded by reflecting surfaces E.

Fig. 5 shows an arrangement for increasing the sensitiveness of the device by mea s of an auxiliary current.- n the left hand si e is the lamp L that provides the light rays to be transmitted by the film, and on the right the illuminating lamp vN. In parallel with the photo-electric cell A, 20 which actuates the galvanometer G, there is inserted a second photo-electric cell H, which is excited by the illuminating lamp N. The light necessary for the actuation of the photo-electric cell H may be taken from the trace of the rays of the 25 printing light N at any place behind the dia phragm B. This may be done by introducing a suitably inclined mirror into the trace of the rays.

The photo-electric cell H may, as shown in Fig.

be arranged behind the film and a too great in- 30 tensity of the light passed through the film may be reduced by the insertion of a. suitable mask. The regulation of the additional energy obtained from the cell H may also be achieved by the re sistance RH- For regulating any fluctuations in the illumination of the lamp L or of the lamp N the following devices are provided:-In series with the photo-electric cells A and H, which serve for regulating the illumination, are inserted two like cells J and K with interposition of resistances RJ and Rx; these are directly illuminated by the lamps L and N. When, for example, the candle power of the lamp diminishes, the countercurrent from the cell J or K through the galva nometer diminishes. The device has still another advantage. According to experience the density of a film which is to receive a second exposure varies very little. Correspondingly the light falling on the photo-electric cell A changes only in small degree; so also does the current from the photo-electric cell which actuates the galvanometer. One can think of these currents together as a constant and one which changes with the density of the image. This constant current is a disturbing factor and is advantageously removed by an equal, opposed current in the gelvancmeter. This is derived from the photoelectric cell J or K. A correct magnitude of the current is secured by a diaphragm N or O or by the resistance R; or RE.

A further possibility for producing the auxiiiary energy is shown in Fig. 6. Here the light that is transmitted through the film and the illuminating light are so close to each other that they inpart overlap, whereby the auxiliary energy is produced. The current is adjustable by a diaphragm P placed in front of or behind the film F. For this purpose the diaphragm can be laterally displaced. Advantageously the diaphragm has reflecting faces. This illuminating device has the advantage that it is very simple and operates very quickly. Obviously instead of a single source of light for producing the transmitted rays and for the illumination there may also be used two sources of light.

What we claim is:

An apparatus for exposure control comprising in combination a source of light for scanning a picture, a photo-electric device which receives the light varying in intensity with the density of said picture thereby causing a variation of an electric current, a galvanometer deflected in accordance with said variations of electric current, a mirror provided on said galvanometer, a second source of light projecting a pencil of light on said mirror, said pencil of light being reflected by said mirror, a series of photo-electric devices arranged one beside the other Within the reach of said reflected pencil of light at a distance smaller than the breadth of the reflected pencil, relays arranged in a circuit with said photo-electric devices, a further series of relays actuated by said first named relays, a source of light for exposing a photographic layer, a resistance arranged in a circuit with said source of light and switches actuated by said relays for switching on and switching off parts of said resistance for varying the intensity of said source of light for exposing said layer in accordance with said variations of electric currrent, a wire coil arranged on the relay situated farthest towards the end of the reach of said reflected pencil of light when said mirror is most deflected, and switches actuated by said wire coil for keeping switched off the whole resistance in the circuit of said source of light for exposing said layer when said refiected pencil of light passes beyond the last photo-electric device of said series.

JOHN EGGERT. HANS FRIEDRICH NISSEN.

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