US3166674A

US3166674A - Time switch for photographic apparatus

Info

Publication number: US3166674A
Application number: US147791A
Authority: US
Inventors: Wick Richard; Schneider Othmar
Original assignee: Individual
Current assignee: Individual
Priority date: 1960-10-28
Filing date: 1961-10-26
Publication date: 1965-01-19
Anticipated expiration: 1982-01-19
Also published as: DE1146366B; BE609699A; NL270378A; GB949517A

Description

Jan. 19, 1965 R. WICK ETAL 3,166,674

TIME SWITCH FOR PHOTOGRAPHIC APPARATUS Filed Oct. 26. 1961 IN V EN TOR.

BY RICHARD WICK OTHMAR SCHNEIDER United States Patent 15 Claims. 61. 25o 217 The present invention concerns an electric time switch arrangement for controlling the duration of exposures of photo-sensitive material to radiating energy. Arrangements of this type are most conveniently applied to apparatus for making photoprints in black and white or in colors, but it may as well be applied to apparatus for making X-ray pictures.

Apparatus of the type to which the present invention is applicable contain control means for limiting the exposure time in accordance with .the amount of radiating energy impinging during an exposure on the photo-sensitive material. However, it is known that the expo-sure of light sensitive material should additionally be controlled according to the equation lt =constant, in which I indicates the intensity of the radiating energy or light impinging upon the light sensitivematerial, t is the time of exposure and p is the blackening exponent characteristic of the light sensitive material. This exponent p is well known in the art and may be equal to 1, larger than 1 or smaller than 1, depending upon the particular material.

There are known arrangements of the type set forth which comprise devices for taking the blackening exponent into account by corresponding adjustment or certain components of the arrangement.

However, it has been found that known arrangements of this type are comparatively very involved in structure and require a great number of individual and delicate devices.

It is therefore a main object of the present invention to provide for an electric time switch arrangement of the general type set forth which provides similar and more eflicient means for modifying the ordinary exposure time control depending upon the characteristic blackening exponent of the photo-sensitive material being used.

Other objects and characteristics of the invention will become apparent from the following description.

With above objects in view the invention provides in an electric time switch arrangement for controlling the duration of exposures of photo-sensitive material to radiating energy, in combination.

(a) Control means for limiting the exposure time in accordance with the amount of radiating energy impinging during an exposure on said photo-sensitive material, said control means including an electron tube controlling, upon being rendered non-conductive, the start, and upon being returned to conductive condition, the end of the exposure, the conductive condition of said tube depending upon a predetermined potential relation between two electrodes of-said tube, and photo-responsive means exposed to said radiating energy and furnishing to one of said electrodes a potential gradually varying depending upon said India"- ing energy impinging on said photo-responsive means and thereby changing the potential and said one of said electrodes; and

(b) correction means for modifying the time limiting action of said control means, said correction means includ ing means for applying a first predetermined potential to the other one of said electrodes, chargeable RC-circuit means having a predetermined charging time constant and being connected in circuit with said other one electrode for changing said first potential at said other electrode depending upon the charge potential of said RC-circuit 3,166,674 Patented Jan. 19, 1965 means, and adjustment means for varying said charge potential in accordance with the blackening exponent of the photo-sensitive material being used, the superposition of said charge potential on said first potential applied to said other electrode by said correction means modifying the time period required for establishing said predetermined potential relation between said two electrodes and thus determining the duration of said conductive condition of said electron tube and thereby the duration of the exposure.

In a preferred embodiment of the invention the RC- circuit means comprise at least two RC-circuits having time constants differing from each other, the capacitors of all of these RC-circuits being connected in series.

It is particularly recommended to connect in a twocapacitor arrangement one of the capacitors with one electrode, preferably with the cathode, of an electron tube forming part of the ordinary time control arrangement, and to connect the othercapacitor with the movable tap of a potentiometer. In this case the electron tube and a control relay controlled thereby may be arranged in a separate control circuit, while the above mentioned potentiometer forms part of the timing circuit of the time control arrangement, whereas the capacitors of the above mentioned RC-circuits are arranged in a separate adjustment circuit, each of these circuits having preferably separate power supply circuits. The potentiometer arranged in the timing circuit may be connected in parallel with a series combination comprising conventional photocell and timing capacitor of the timing arrangement.

As a further advantageous characteristic of the invention the means for changing the potential applied to one electrode of the electron tube are connected with the respective power supply in such a manner that the polarity of the potential derived from the adjustment means can be reversed. For this purpose a potentiometer is included in the charging circuit of each of the capacitors of the RC-circuits, each capacitor having one terminal connected with a fixed center tap of the respective potentiometer, while the other terminal of the capacitor is connected with the movable tap of that potentiometer. It is advisable to couple mechanically the movable taps of these potentiometers. It is further recommended to arrange the justmentioned potentiometers so that they are connected in parallel with each other and that their movable taps, when moved simultaneously, have an opposite effect on the respective potentiometers. In addition it is desirable to couple mechanically the two movable taps of the above mentioned potentiometers also with the movable tap of the previously mentioned potentiometer located in the timing circuit. Finally, all these movable potentiometer taps mentioned above may be controlled by one single control knob having an index cooperating with a corresponding scale.

If the invention is applied to photographic printing apparatus used for making color prints and therefore requiring a plurality of color component exposures, a corresponding plurality of arrangements according to the invention may be provided.

It is a remarkable advantage of the arrangement according to the invention that the adjustment of the exposure time in view of the blackening constant of the material being used is carried out exclusively by a group of potentiometers cooperating with the corresponding RC- circuits. It is further to be noted that the arrangement according to the invention requires very little electrical energy while nevertheless offering a very great range of adjustment. The voltage characteristic of the adjustment means corresponds very satisfactorily with the desired adjustment values within the above mentioned great range of adjustment.

The novel features which are considered as characteristic for the invention are set forth in particular in the appended claims. The invention itself, however, both as to its construction and its method of operation together with additional objects and advantages thereof, will be best understood from the following description of specific embodiments when read in connection with the accompanying drawing, in which an embodiment of the invention is illustrated in the form of a schematic circuit diagram.

It will be understood that the arrangement according to the invention as illustrated applies to a photographic printing apparatus, not shown, having a light source 1 connected by

lines

2 and 3 with a

general supply

4, 5 of alternating current, controllable by a main switch 6. The main purpose of the arrangement described below is to control the duration of an exposure of photo-sensitive material to the radiating energy furnished by the light source 1. The arrangement according to the invention as shown comprises three main circuits, namely a light control circuit 7, a time control circuit 8 and an adjustment circuit 9. Each of these circuits comprises a separate

power supply circuit

10, 11, 12, respectively. These supply circuits 1'0, 11 and 12 obtain energy through

secondary windings

13, 14 and 15, respectively, of a transformer 16 having a primary 17 connected to the

main power supply

4, 5. The power supply circuit co. prises in conventional manner a four-way rectifier 18 and a filter circuit composed of the capacitors 19 and 2t) and a resistor 21. The power supply circuits 11 and 12 are constructed in the same manner.

The light control circuit 7 comprises in series arrangement a control tube 22, preferably a thyratron, a relay coil 23 operating, among others, a relay switch 23a in the connection 3 of the light source 1, and a starter switch 24 movable between two

stationary contacts

25 and 26 for the purpose of briefly interrupting the light control circuit 7 when the switch 24 is moved from one of the

contacts

25, 26 to the other. The time control circuit 8 comprises a conventional timing capacitor 27 connected in series with a photocell 28 which is arranged to be exposed to the radiating energy furnished by the light source 1 and impinging on the photo-sensitive material. The junction point 29 between the capacitor 27 and the photocell 28 is connected via line 30 with the control grid 31 of the tube 22. A relay switch 23b operable by the coil 23 is connected in parallel with the capacitor 27 so that the latter is shunted when switch 23b is in closed position.

The photocell 28 may be an electron multiplier phototube. It operates in the well known manner.

The adjustment circuit 9 comprises two RC-

circuits

32, 33 and 34, 35. The

capacitors

32 and 34 of these circuits are connected in series and the pertaining

adjustable resistors

33 and 35 are arranged, as shown, in separate charging circuits for the

respective capacitors

32 and 34. The

capacitors

32 and 34 can be charged with potentials determined by the

potentiometers

36 and 37, respectively, which are connected in parallel between the

supply lines

38 and 39 connected with the supply circuit 12 and carrying direct current voltage. The junction point 40 between the

capacitors

32 and 34 is connected by a line 41 with both the fixed center taps 42 and 43 of the

potentiometers

36 and 37, respectively. The

resistors

33 and 35, however, are connected via

lines

44 and 45, respectively, with the movable potentiometer taps 46 and 47, respectively.

A relay switch 23c is connected in parallel with the capacitor 32, and similarly a relay switch 23d is connected in parallel with the capacitor 34. Both these last mentioned relay switches are also operated by the relay coil 23.

The capacitor 32 is connected by the line 48 with the cathode 49 of the control tube 22 of the light control circuit 7, while the capacitor 34 is connected by line 50 with the movable tap 52 of the potentiometer 51 of the time control circuit 8. The potentiometer 51 is connected across the

supply lines

53 and 54 of the power supply circuit 11 and at the same time in parallel with the seriescombination consisting of the timing capacitor 27 and the photocell 28. The movable tap 52 of the potentiometer 51 is mechanically coupled with the

movable taps

46 and 47 of the

potentiometers

36, 37 of the adjustment circuit 9, e.g. by means of a common shaft 55 indicated only symbolically by dash-dotted lines in the drawing and turnable by means of a control knob 56. This knob is equipped with an index or pointer 57 which cooperates with an adjustment scale or graduation 58 that may be arranged on the outside wall of the printing apparatus not shown in the drawing.

For describing the operation of this arrangement, it may be assumed that the printing apparatus is to be operated While the control knob 56 and accordingly the potentiometer taps 46, 47 and 52 are in the position shown in the drawing.

It is to be understood that, as long as the main switch 6 is in open position, the relay switch 23a is in closed position, the

relay switches

23b, 23c and 23d are in open position, and no potential difference exists between the grid 31 and the cathode 49 of the tube 22.

Consequently, upon closing the main switch 6 the tube 22 is immediately rendered conductive and causes energization of the relay coil 23 whereby the relay switch 23a is moved to open position and the

relay switches

23b, 23c and 23d are moved to closed position. This means that these relay switches are in the positions shown in the drawing as soon as the time switch arrangement according to the invention is ready for operation. Under these circumstances the cathode 49 of the tube 22 is provided across the

switches

23c and 23d of the

shunted capacitors

32, 34 with a potential available at the movable tap 52 of the potentiometer 51, while the grid 31 remains on ground potential and has therefore a negative potential with respect to the cathode 49 following the change of tube 22 to conductive condition. Nevertheless, in view of the well-known characteristics of a thyratron the tube 22 remains in conductive condition so that also the relay coil 23 remains in energized condition.

If now an exposure of the photo-sensitive material is to be carried out the starting switch 24 is moved from the position contacting the contact 25 to its second position contacting the contact 26. The movement of the switch 24 causes a transitory interruption of the circuit whereby the tube 22 is changed to non-conductive condition, the relay coil 23 is de-energized so that relay switch 23a moves to closed position while the relay switches 23b, 23c and 23d are moved to open position. By the closing of relay switch 23a the source of light 1 is switched on and the exposure of the photo-sensitive material is started. At the same time charging of the

capacitors

32 and 34 is started and continues until the capacitor 32 assumes the potential existing between the center tap 42 and the movable tap 46 of the potentiometer 36, and until the capacitor 34 assumes the potential existing between the center tap 43 and the movable tap 47 of the potentiometer 37. Since the

capacitors

32 and 34 are connected in series and since the positioning of the movable taps 46, 47 of the

potentiometers

36, 37, respectively, in relation to their center taps 42, 43, respectively, occurs in mutually opposite directions, the charging potentials of the

capacitors

32 and 34 are superimposed on each other and simultaneously added to the potential tapped from the potentiometer 51, so that the potential at the cathode 49 of the tube 22 is gradually increased in accordance with the charging rate of the

capacitors

32, 34, starting with the potential of the movable tap 52, from the start of the exposure on- Ward.

Independently, the timing capacitor 27 of the time control circuit 8 is also charged by the photo-current of the photocell 28 illuminated by the radiating energy furnished by the source 1, the charge potential of the capacitor 27 being applied to the grid 31 of the tube 22 via the line 30. I

As soon as the potential of the grid 31 of the tube 22 reaches the cathode potential, the tube 22 is rendered conductivewhereby the relay coil 23 is returned to energizedv condition and the

relay switches

23a, 23b, 23c and 23d are returned to the positions shown in the drawing. Hereby the source of light 1 is switched off and the exposure is terminated While the

capacitors

27, 32 and 34 are shunted and thus discharged. Consequently, the potential of the cathode 49 of the tube 22 drops back to the potential of the movable tap 52 of the potentiometer 51 while the grid 31 assumes again groundpotential. However, the tube 22 remain in conductive condition and the relay coil 23 remains in energized condition. In this manner the time switch arrangement is now ready for another cycle of operations, i.e. for another exposure.

The gradual raising of the cathode potential of the tube 22 in accordance with the charging of the

capacitors

32, 34 has the effect that-relative to a medium exposure'time selected for the purpose of calibration exposure times of comparatively long duration can be extended still further and exposure times of comparatively short duration can be shortened still further. The relation between the

adjustable resistors

33 and 35 and the associated capacicumstances the RC-circuit with the shorter charging time causes a substantial increase of the potential at the cathode 490i the tube 22 during the first portion of an exposure, while the RC-circuit with the longer charging time causes the potential rise at the cathode 49 to continue for a longer period commencing with the start of the exposure. Nevertheless the operating voltages involved remain comparatively low. The charging times of the RC-circuits containing the

capacitors

32, 34 can be varied by adjustment of the

resistors

33, 35, respectively, and can be adjusted arbitrarily with respect to each other.

As a whole, the potential rise at the cathode 49 of the tube 22 during an exposure can be varied by corresponding setting of the control knob 56 and is increased by turning the knob 56 in counter-clockwise direction. By turning the knob 56 and the shaft 55 increasing portions of the upper half of the potentiometer 36 and of the lower half of the potentiometer 37 are introduced into the charging circuits of the

capacitors

32 and 34, respectively, whereby the maximum charge potentials of these capacitors are increased, while simultaneously the starting potential of the cathode 49 is reduced due to the simultaneous turning of the movable tap 52 of the potentiometer 51.

However, if the control knob 56 is turned in opposite direction until its index 57 registers with the center mark 59 of the graduation 58 the starting potential of the cathode 49 is raised to a potential corresponding to the center point of the potentiometer 51 while the movable taps 46, 47 are positioned in register with the center taps 42, 43, respectively, whereby the

otentiometers

36, 37, respectively, are completely eliminated from the charging cir-v cuits of the. associated

capacitors

32, 34, respectively. In this case the

capacitors

32, 34 are not charged at all at the beginning of, and during, an exposure so that the potential at the. cathode 49 of the tube 22 remains constant irrespective of the duration of an exposure. 8

If the control knob 56 is turned further in clockwise direction portions of the lowerhalf of the potentiometer 36 and portions of the upper half of the potentiometer 37 ode 49. Consequently, in this case the potential of the.

cathode 49 of thetube 22 is decreased with increasing exposure time and the starting potential of the cathode 49 and the degree of potential decrease are both increased,

with increasing turning of the control knob 56 in clockwise direction.

It can be seen therefore that the blackening exponent characteristic of the photo-sensitive material being used can be taken into account by using the arrangement according to the invention. This applies both to blackening exponents smaller than 1 as well as to blackening exponents equal to 1 or larger than 1. In using the arrangement described above it is advisable to take into account not only the blackening exponent of the photosensitive material being used but also a possibly existing mismatch between the photocell 28 and the photo-sensitive material. Such a mismatch exists when the spectral sensitivity of the photocell 28 does not agree with the spectral sensitivity of the photo-sensitive ma erial. It occurs frequently that the sensitivity of the photocell extends over a wider spectral range than that of the, photo-sensitive materal which condition is called under-matching. The opposite condition is called over-matching. The effect of a mismatch is similar to that defined bythe blackening exponent, namely in the case of under-matching long exposure times are too short andshortexposure times are too long, while the opposite is the effectof over-match ing. However, also these efiects can be taken into account together with the blackening exponent by correspondingly setting the control knob for determining the desired correction of the exposure time.

it is of particular importance to take into account the blackening exponent and a mismatch between the lightsensitive member and the photo-sensitive material in the case of making color prints. In this case it is possible that different blackening exponents apply 'to the different layers or" the color print material sensitive to light of different basic colors. Also the character and degree of a mismatch between the light-sensitive member and the color print material may differ for different basic colors so that in the production of color prints notonly wrong densities but also wrong colors may result if the blackening exponent and a mismatch are not taken into account.

Inorder to avoid such undesirable results it is adaccording to the invention it is possible to take intoaccount the blackening exponent for each differently color-sensitive layer of the color print material and-to take into account the character and degree of a mismatch of the photocell. with the color-sensitivity of each layer of the material.

The time switch arrangement according to the invention-can also be applied advantageously to color printing apparatus in which, e.g. in accordance with the French Patent 1,173,295, the individual component color exposures are carriedout in sequence with the use of additive filters and with a single exposure control device used repeatedly during a complete color printing operation. In this case the arrangement as described and illustrated may be modified in such a manner that the potentiometer taps 46, 47, 52 are moved automatically into predetermined positions before the start of each indi vidual component exposure.

Of course, the arrangement as described and illustrated may be modified in various respects. For instance, the two RC-

circuits

32, 33 and 34, 35 in the adjustment i) circuit 9 may be supplemented by additional RC-circuits having time constants diilering from the time constants of the other RC-circuits. In such case it is advisable to connect also the capacitors of the additional RC-circuits in series with the

capacitors

32, 34.

Each of the

potentiometers

36, 37 having fixed center taps 42, 43 and

movable taps

46, 47, respectively, is Well suited for reversing the polarity of the means influencing the cathode potential of the tube 22 also if only one capacitor is used instead of a plurality of

capacitors

32, 34, Generally it is advisable to use one single device for producing, by polarity reversal, an increase as Well as a decrease of the potential of the cathode 49 of the tube 22.

The start and termination of an exposure may be effected, instead of switching on and off the light source 1, also in such a manner that the light source 1 is left witched on continuously while a shutter arranged across the path of the radiating energy furnished by the source 1 is opened and closed by means of electromagnetic means controlled by the relay coil 23.

The capacitor 32 or" the adjustment circuit 9 may be connected, instead of to the cathode 49 of tube 22, also to another electrode of the tube, e.g. to a screen grid not shown in the drawing but existing in a ditierent type of'a control tube in which case of course a corresponding change of poential at the

capacitors

32, 34 is to be providcd.

Finally, it is to be borne in mind that the time switch arrangement according to the invention is applicable not only to photographic printing apparatus but also to other devices, e.g., X-ray picture apparatus.

It will be understood that each of the elements described above, or two or more together, may also find a useful application in other types of an electric time switch arrangement differing from the types described above.

While the invention has been illustrated and described as embodied in an electric time switch arrangement for controlling the duration of exposures of photo-senstitive material to radiating energy, it is not intended to be limited to the details shown, since various modifications and structural changes may be made without departing in any way from the spirit of the present invention.

Without further analysis, the foregoing will so fully reveal the gist of the present invention that others can by applying current knowledge readily adapt it for various applications Without omitting features that, from the standpoint of prior art, fairly constitute essential characteristics of the generic or specific aspects of this invention and, therefore, such adaptations should and are intended to be comprehended within the meaning and range of equivalence of the following claims.

What is claimed as new and desired to be secured by Letters Patent is:

1. In an electric tirru'ng arrangement for controlling the duration of exposures of photo-sensitive material to radiating energy, in combination, means for interrupting the exposure of said material to said radiating energy, an electron tube controlling said exposure interrupting means in dependence of a conductive condition of said tube whereby said conductive condition itself depends upon a predetermined potential. relation between two electrodes of said tube, a first condenser connected to one of said electrodes of said tube, means for varying the electric charge of said first condenser during the exposure :of said material, means for applying a first predetermined potential to the other one of said electrodes, and correction means for modifying the time limiting action of said timing arrangement, said correction means including at least two RC-circuit means including second capacitors, respectively, means which at the beginning of the exposure period commence the bringing about of the charging of each of said second capacitors to respective predetermined charge potential condition, and means for varying the electric charge of each of said second capacitors during the exposure of said material, each or" said RC-circuit means having a predetermined charging time constant different from that of the other one and said second capacitors being connected in series with each other and in circuit with said other one of said electrodes for changin said first potential applied to said other electrode in accordance with the change of charge potentials of said second capacitors during the exposure of said material.

2. In an electric time switch arrangement for controlling the duration of exposures of photo-sensitive material to radiating energy furnished by a source of such radiating energy, in combination, control means for limiting the exposure time in accordance with the amount of radiating energy impinging during an exposure on said photosensitive material, said control means including an electron tube controlling, upon being rendered non-conductive, the start, and upon being returned to conductive condition, the end of the exposure, the conductive condition of said tube depending upon a predetermined potential relation between two electrodes of said tube, and photoelectric means exposed to said radiating energy and furnishing to one of said electrodes a potential gradually varying depending upon said radiating energy impinging on said photo-electric means and thereby changing the potential at said one of said electrodes; and correction means for modifying the time limiting action of said control means, said correction means including means for applying a first predetermined potential to the other one of said electrodes, at least two chargeable RC-circuit means including capacitors, respectively, connected in series with each other, each of said RC-circuit means having a predetermined charging time constant different from that of the other one and being connected in circuit with said other one electrode for changing said first potential at said other electrode depending upon the charge potentials of said RC-circuit means, means which at the beginning of the lighting period commence the bringing about of the charging of each of said capacitors to a respective predetermined charge potential condition, and adjustment means for varying said charge potentials in accordance with the blackening exponent of the photosensitive material being used, the superposition of said charge potentials on said first potential applied to said other electrode by said correction means modifying the time period required for establishing said predetermined potential relation between said two electrodes and thus determining the duration of said conductive condition of said electron tube and thereby the duration of the exposure.

3. In an electric time switch arrangement for controlling the duration of exposures of photosensitive material to radiating energy furnished by a source of such radiating energy, in combination, control means for limiting the exposure time in accordance with the amount of radiating energy impinging during an exposure on said photo-sensitive material, said control means including an electron tube controlling, upon being rendered non-conductive, the start and, upon being returned to conductive condition, the end of the exposure, the conductive condition of said tube depending upon a predetermined potential relation between the cathode and at least one of the electrodes of said tube, and photo-electric means exposed to said radiating energy, and capacitor means constituting .a series-combination with said photo-electric means, said series-combination furnishing to one of said electrodes a potential gradually varying depending upon said radiating energy impinging on said photoelectric means and thereby changing the potential at said one of said electrodes; and correction means for modifying the time limiting action of said control means, said correction means including potentiometer means for applying a first predetermined. potential to said cathode, at least two chargeable RC-circuit means including second capacitor means, respectively, connected in series with each other, each of said RC-circuit means having a predetermined charging time constant difierent from that of the other one and one of said second capacitor means being connected in circuit with said cathode, and the other one of said second capacitor means being connected with the movable tap of said potentiometer means for changing said first potential at said cathode depending upon the charge potentials-of said RC-circuit means, means which at the beginning of the lighting period commence the bringing about of the charging of each of said capacitors to a respective predetermined charge potential condition, and adjustment means for varying said charge potentials in accordance with the blackening exponent of the photosensitive material being used, the superposition of said charge potentials on said firstpotential applied to said cathode by said correction means modifying the time period required for establishing said predetermined potential relation between the cathode and at least one of the electrodes and thus determining the duration of said conductive condition of said electron tube and thereby the duration of the exposure.

4. An arrangement according to claim 3, comprising a control circuit including a first power supply unit, said electron tube and relay means controlled by said electron tube and controlling the source of radiating energy, further comprising a time control circuit including a second power supply unit, said photo-electric means, said first capacitor means and said potentiometer means, and further comprising an adjustment circuit including a third power supply unit and said RC-circuit means.

5. An arrangement according to claim 4, wherein said potentiometer means are connected in parallel with said series-combination of photo-electric means and first capacitor means.

v 6. An arrangement according to claim 5, wherein said correction means include means for reversing the polarity of said first predetermined potential with respect to an intermediate potential value. 7. An arrangement according to claim 6, wherein said adjustment means include a first and a second control potentiometer connected in parallel with each other and in circuit with said second power supply unit, one of said RC-circuit means being connected between a fixed intermediate tapping point and the movable tap of said first control potentiometer, the other one of said RC-circuit means being connected between a fixed intermediate tapping point and the movable tap of said second control potentiometer.

8. An arrangement according to claim 7, wherein said movable taps of said first and second control potentiometers are mechanically coupled with each other and jointly controllable.

9. An arrangement according to claim 8, wherein said first and second control potentiometers and their respective movable taps are so arranged that joint movement of said movable taps has opposite adjustment effect on the respective control potentiometers.

10. An arrangement according to claim 8, wherein said movable taps of said first and second control potentiometers and the movable tap of said potentiometer means controlling said photo-electric means are all mechanically coupled with one another and jointly controllable.

11. An arrangement according to claim 10, including control means for controlling all of said movable taps and including indexing means for determining the adjustment of said taps.

12. In an electric timing arrangement for controlling the duration of exposures of photo-sensitive material to radiating energy, in combination, means for interrupting the exposure of said material to said radiating energy, an electron tube controlling said exposure interrupting means in dependence of a conductive condition of said tube whereby said conductive condition itself depends upon a predetermined potential relation between two electrodes of said tube, a first condenser connected to one of said electrodes of said tube, means for varying the electric charge of said first condenser during the exposure of said material, potentiometer means for applying a first predetermined potential to the other one of said electrodes, said potentiometer means including a resistance connected with a power supply circuit and a tap movable along said resistance and connected with said other one of said electrodes, and correction means for modifying the time limiting action of said timing arrangement, said correction means including at least two RC- circuit means including second capacitors, respectively, means which at the beginning of the exposure period commence the bringing about of the charging of each of said second capacitors to a respective predetermined charge potential condition, and means for varying the electric charge of each or said second capacitors during the exposure of said material, each of said RC-circuit means having a predetermined charging time constant different from that of the other one and said second capacitors being connected in series with each other and in circuit between said movable tap of said potentiometer means and said other one of said electrodes for changing said first potential applied to said other electrode in accordance with the change of charge potentials of said second capacitors during the exposure of said material.

13. An arrangement according to claim 12, comprising a relay arranged in the circuit of said electron tube, and switches each of them shunting one of said first and second condensers, respectively, said switches and said exposure interrupting means being controlled by said relay.

14. An arrangement according to claim 3, wherein said adjustment means for varying said charge potentials are constructed for simultaneously changing, when desired, also the polarity of said charge potentials.

15. An arrangement according to claim 7, wherein each of said first and second control potentiometers has two portions extending in opposite direction from the respective fixed intermediate tapping point thereof, the outer ends of said first and second control otentiometers being connected with the terminals, respectively, of said third power supply unit so that also the polarity of said variable charging potentials of said RC-circuit means is changeable depending upon whether said movable taps of said control potentiometers are moved from said intermediate tapping point in one or the other direction over said portions thereof.

References Cited by the Examiner UNITED STATES PATENTS 2,078,677 4/37 Long 250-217 X 2,472,815 6/49 Fleming 250-205 2,749,799 6/56 Strem 250-217 2,885,563 5/59 Batina et a1 250-405 2,929,000 3/60 Arrison 250 2,993,124 7/61 Graves et al. 25095 3,033,988 5/62 Edgerton 250205 I FOREIGN PATENTS 564,500 9/ 44 Great Britain. 7 06,671 3 54 Great Britain.

RALPH G. NILSON, Primary Examiner.

Claims

1. IN AN ELECTRIC TIMING ARRANGEMENT FOR CONTROLLING THE DURATION OF EXPOSURES OF PHOTO-SENSITIVE MATERIAL TO RADIATING ENERGY, IN COMBINATION, MEANS FOR INTERRUPTING THE EXPOSURE OF SAID MATERIAL TO SAID RADIATING ENERGY, AN ELECTRON TUBE CONTROLLING SAID EXPOSURE INTERRUPTING MEANS INDEPENDENCE OF A CONDUCTIVE CONDITION OF SAID TUBE WHEREBY SAID CONDUCTIVE CONDITION ITSELF DEPENDS UPON A PREDETERMINED POTENTIAL RELATION BETWEEN TWO ELECTRODES OF SAID TUBE, A FIRST CONDENSER CONNECTED TO ONE OF SAID ELECTRODES OF SAID TUBE, MEANS FOR VARYING THE ELECTRIC CHARGE OF SAID FIRST CONDENSER DURING THE EXPOSURE OF SAID MATERIAL, MEANS FOR APPLYING A FIRST PREDETERMINED POTENTIAL TO THE OTHER ONE OF SAID ELECTRODES, AND CORRECTION MEANS FOR MODIFYING THE TIME LIMITING ACTION OF SAID TIMING ARRANGEMENT, SAID CORRECTION MEANS INCLUDING AT LEAST TWO RC-CIRCUIT MEANS INCLUDING SECOND CAPACITORS, RESPECTIVELY, MEANS WHICH AT THE BEGINNING OF THE EXPOSURE PERIOD COMMENCE THE BRINGING ABOUT OF THE CHARGING OF EACH OF SAID SECOND CAPACITORS TO A RESPECTIVE PREDETERMINED CHARGE POTENTIAL CONDITION, AND MEANS FOR VARYING THE ELECTRIC CHARGE OF EACH OF SAID SECOND CAPACITORS DURING THE EXPOSURE OF SAID MATERIAL, EACH OF SAID RC-CIRCUIT MEANS HAVING A PREDETERMINED CHARGING TIME CONSTANT DIFFERENT FROM THAT OF THE OTHER ONE AND SAID SECOND CAPACITORS BEING CONNECTED IN SERIES WITH EACH OTHER AND IN CIRCUIT WITH SAID OTHER ONE OF SAID ELECTRODES FOR CHANGING SAID FIRST POTENTIAL APPLIED TO SAID OTHER ELECTRODE IN ACCORDANCE WITH THE CHANGE OF CHARGE POTENTIALS OF SAID SECOND CAPACITORS DURING THE EXPOSURE OF SAID MATERIAL.