Search Images Maps Play YouTube News Gmail Drive More »
Sign in
Screen reader users: click this link for accessible mode. Accessible mode has the same essential features but works better with your reader.

Patents

  1. Advanced Patent Search
Publication numberUS3769887 A
Publication typeGrant
Publication dateNov 6, 1973
Filing dateMay 19, 1972
Priority dateMay 31, 1971
Also published asDE2226592A1, DE2226592B2, DE2226592C3
Publication numberUS 3769887 A, US 3769887A, US-A-3769887, US3769887 A, US3769887A
InventorsT Nobusawa
Original AssigneeAsahi Optical Co Ltd
Export CitationBiBTeX, EndNote, RefMan
External Links: USPTO, USPTO Assignment, Espacenet
Electrical shutter-control systems for cameras
US 3769887 A
Abstract
An electrical shutter-control system to be used in a camera. The system includes a solenoid which responds to a signal for initiating shutter-closing operations. A signal-transmitting circuit transmits the signal to the solenoid and receives one of a plurality of timing signals from a timing circuit which is automatically operated to select a timing signal which will provide the best exposure. A signal-altering circuit detects when the conditions require a change in the selected timing signal for improving the exposure, and this signal-altering circuit measures the extent to which the selected timing signal should be changed and alters the timing signal accordingly so that the altered timing signal is transmitted to the solenoid for improving the exposure. The alteration in the timing signal is determined in accordance with a fractional interval of time between the time increments corresponding to the timing signals, so as to achieve a continuous exposure time adjustment, or according to non-linear film characteristics to compensate for the latter characteristics, or in accordance with both of these factors.
Images(10)
Previous page
Next page
Claims  available in
Description  (OCR text may contain errors)

United States Patent 9 1 Nobusawa.

[ ELECTRICAL SHUTTER-CONTROL SYSTEMS FOR CAMERAS [75] Inventor: Tsukumo Nobusawa, Tokyo, Japan [73] Assignee: Asahi Kogaku Kogyo Kabushiki Kaisha, Tokyo-to, Japan [22] Filed: May 19, 1972 [21] Appl. No.: 255,217

[30] Foreign Application Priority Data May 31, 1971 Japan 46/36921 June 16, 1971 Japan... 46/42500 June 16, 1971 Japan 46/42501 June 24, 1971 Japan 46/45265 July 5, 1971 Japan... 46/48790 July 7, 1971 Japan 46/49611 [52] 11.8. C1. 95/10 CT [51] Int. Cl G03b 7/08, G03b 9/58, H03k 17/00 [58] Field of Search 95/10 CT [56] References Cited UNITED STATES PATENTS 3,603,799 9/1971 Nobusawa 95/10 CT 3,703,130 11/1972 Watanabe.... 95/10 CT 3,602,717

8/1971 Konig 95/10 CT Nov. 6, 1973 [57] ABSTRACT An electrical shutter-control system to be used in a camera. The system includes a solenoid which responds to a signal for initiating shutter-closing operations. A signal-transmitting circuit transmits the signal to the solenoid andreceives one of a plurality of timing signals from a timing circuit which is automatically operated to select a timing signal which will provide the best exposure. A signal-altering circuit detects when the conditions require a change in the selected timing signal for improving the exposure, and this signal-altering circuit measures the extent to which the selected timing signal should be changed and alters the timing signal accordingly so that the altered timing signal is transmitted to the solenoid for improving the exposure. The alteration in the timing signal is determined in accordance with a fractional interval of time between the time increments corresponding to the timing signals, so as to achieve a continuous exposure time adjustment, or according to non-linear film characteristics to compensate for the latter characteristics, or in accordance with both of these factors.

16 Claims, 29 Drawing Figures li 7 a],

SELECTING 4 4b CIRCUIT zz-f PAIENIEUNHY 6 ms SHEET UlUF 10 SELECTING CIRCUIT swirchmg osihon of fhc ICSISTOF clemenf PATENTEU NOV 6 I975 SHEET 0.20F 1O PAIENTEDNUY sum 3.769.887 SHEET 030F10 fr'lqger volfage conTral vzlve when file fimllg reslsf or 4; i5 .seleded Trigger vol rage PATENTEDNUV 6 Ian SHEET 07 0F 10 a 8 a 8 z 8 BACKGROUND OF THE INVENTION The present invention relates to cameras.

In particular, the present invention relates to shuttercontrol circuits for cameras.

There are known exposure-time controlling circuits of the digital type, in that these known circuits select a given timing resistor. With such known shutter controls an external exposure adjusting value is determined by the time constant which, in turn, is determined by a timing resistor selected in accordance with light received from the object to be photographed. The circuit includes a timing capacitor which has a constant capacity and which is connected in series with the timing resistors. The resistances of these timing resistors are preselected in such a way that they vary according to a multiple proportion, corresponding to the intensity of the light received from the object which is to be phot graphed, so that these timing resistors together with the timing capacitor develop exposure-time adjusting values which vary in accordance with a multiple proportion. As a consequence, with this type of shuttercontrol circuit it is only possible to achieve a discontinuous or stepping type of adjustment of exposure time. One of the important features of a timing resistor selecting type of electric shutter control circuit resides in the fact that it is well-suited for cameras which utilize internal light-receiving systems. However, such electrical shutter control circuits do not permit a continuous adjustment of the exposure time to be achieved so that they are limited to the extent that it is only possible to provide from such circuits certain preselected exposure times which vary from one to the next by given time intervals.

A further problem encountered with cameras resides in the characteristics of the film exposed therein. Thus,

it is well known that filmhas a characteristic curve which does not vary linearly throughout the entire range of light intensity in which exposures are made. For example it is well known that at a lower range of light intensity the film characteristic is non-linear so that due to the nature of the film itself there are inherent inaccuracies when making exposures with a relatively small amountof light.

Thus, with conventional electrical shutter control systems the exposure time which is determined is always with respect to a limited range of light which represents only part of the entire range over which the film is exposed. There is a degree of disagreement between the exposure time which is automatically determined and the actual optimum exposure time for the film both at higher and lower ranges of light intensity. Thus, it is commonly known that the film characteristic is determined by the light-sensitive material used for the film, and it is impossible to achieve linearity in the film characteristic curve at both higher and lower ranges of light intensity where the film is likely to be over-exposed or under-exposed, even if the film has a constant 7 value. Thus, the proportional relationship between the light intensity and the density of the image which is formed in the film is lost at certain ranges of light intensity. In addition the proportional relationship may vary depending upon the developing solution which is used for the film as well as the developing time.

SUMMARY OF THE INVENTION It is accordingly a primary object of the present invention to provide an electrical shutter-control system which is capable of operating circuits of the above type in such a way that the selected signals are altered to give the same effect as a continuous adjustment of exposure time.

Furthermore, it is an object of the present invention to provide for an electrical circuit of the above type a compensation which will automatically compensate for the non-linear characteristics of the film at certain ranges of light intensity.

It is furthermore an object of the present invention to provide circuitry of the above type which is relatively simple and inexpensive and which operates very reliably.

In accordance with the invention the electrical shutter control system includes an electrical means for responding to a signal for initiating shutter-closing operations. A signal-transmitting means is electrically connected with the electrical means for transmitting a signal thereto. A timing circuit means is electrically connected with the signal-transmitting means for delivering to the latter, to form at least part of the signal transmitted thereby to the electrical means, one of a plurality of timing signals which differ from each other by increments corresponding to different time intervals. An electrical selecting means is electrically connected with the timing circuit means for selecting from the latter, to be delivered to the signal-transmitting means, that one of the plurality of timing signals which will provide the best exposure. An electrical operating means is electrically connected with the selecting means for operating the latter to select this particular timing signal which will provide the best exposure. An electrical signal-altering means is provided for automatically detecting when the photographing conditions require a change in the selected timing signal so as to improve the exposure as well as for determining the extent to which this selected time signal should be changed in order to improve the exposure. This signal-altering means is electrically connected with the signaltransmitting means for altering the selected timing signal received thereby to the extent determined by the signal-altering means before a signal is transmitted to the electrical means which initiates the shutter-closing operations. In this way this latter electrical means will receive a timing signal which, if necessary, is altered to improve the exposure.

BRIEF DESCRIPTION OF DRAWINGS The invention is illustrated by way of example in the accompanying drawings which form part of this application and in which:

FIG. 1 illustrates an electrical circuit forming one embodiment of the invention; r

FIG. 2 is a graph illustrating the configuration of an altering signal generated with the circuitry of FIG. 1;

FIGS. 3a-3c respectively illustrate variations of that part of the circuitry of FIG. 1 which generates the signal illustrated in FIG. 2;

FIGS. 40 and 4b respectively show fragmentary circuits which explain the operation of embodiments such as those shown in FIGS. 3b and 30;

FIG. 5 is a wiring diagram of a further embodiment of the invention;

FIG. 6 is a graph illustrating an altering signal generated with the circuitry of FIG.

FIG. 7a is a wiring diagram of a further embodiment of circuitry according to the invention;

FIGS. 7b and 70 respectively illustrate graphically signals generated with the circuitry of FIG. 7a;

FIG. 8 is a fragmentary illustration of a different embodiment of an oscillating circuit capable of being used in place of the oscillating circuit of FIG. 711;

FIG. 9 is a wiring diagram of a further embodiment of a shutter-controlling circuit of the invention;

FIG. 10 shows a variation of that part of the circuitry of FIG 9 which compensates for film characteristics;

FIGS. 11 and 12 respectively illustrate graphically the manner in which the embodiments of FIGS. 9 and 10 compensate for film characteristics;

FIG. 13 is a wiring diagram of a further variation of the circuitry of FIG. 9',

FIG. 14 is a graph illustrating the configuration of a signal generated with the circuitry of FIG. 13;

FIG. 15 is a wiring diagram of a further embodiment of electrical circuitry according to theinvention;

FIGS. l6a-l6d respectively illustrate the configurations of different signals generated with the circuitry of FIG. 15;

FIG. 17 is a wiring diagram of yet another embodiment of a shutter-controlling circuit according to the invention;

FIG. 18 is'a graph illustrating the configuration of a signal generated with the circuitry of FIG. 17; and

FIGS. 19-21 respectively illustrate variations of parts of a signal-altering circuit of FIG. 17.

DESCRIPTION OF PREFERRED EMBODIMENTS If an electrical shutter-control device operates in such a way that it obtains an exposure value as determined by where, c

E exposure value, I

t I energy of the light, and

t =-exposure time given by'the shutter device, then the appropriate exposure will not be obtained in the lower light intensity region, because the film characteristic curve itself is not proportional to the light intensity in such a region. Thus, no matter how the electrical shuttercontrol circuitry'may operate to determine exposure time in accordance with equation (1), there will be an unsatisfactorily exposed film both in the higher and in the lower light intensity regions.

In accordance with the present invention, the exposure value in the lower light intensity region is expressed as and the light sensitivity efficiency of the light energy is compensated with the exposure time given by the shutter-control circuit'so as to avoid this disadvantage.

Thus, when the exposure time determined by the shutter-control system is t at an intermediate light intensity region and [/3 in the lower light intensity region, then the exposure time will meet the film characteristics. In order to satisfy this requirement the exposure time given by the shutter-control system should be increased to some extent in the' lower light intensity region.

As is well known, a timing resistor selecting type of electrical shutter-control circuit adjusts the exposure time in a stepwise manner. With the present invention it is possible to provide an improved circuitry to be accommodated to such an electrical shutter-control device for adjusting the exposure time continuously. In addition, with the circuitry of the invention there is provided an automatic means which will compensate for the exposure time in such a way as to enable the exposure time to be adjusted with the electrical shuttercontrol system of the invention so as to meet the particular characteristics of the film in the camera.

For this purpose it is proposed with the present in vention to make use of a timing resistor selecting type of electrical shutter-control circuit provided with a timing circuit which is made up of a plurality of timing resistors to be selectively inserted into the circuit depending upon the intensity of the light received from the object to be photographed, this circuit including a timing capacitor which is connected in series to the timing resistors and aswitching circuit which receives the adjusted information from the timing circuit so as to detennine the adjusting values in a stepwise manner. Thus, the switching circuit and the capacitor form a signal-transmitting means for transmitting a signal to an electrical means which will initiate shutter-closing operations.- A signal-altering means of the invention develops a control voltage to achieve altering signals the levels of which are determined within the minimum range of the adjusting value with the variation of the altering signal depending upon the intensity of the light received from the object to be photographed, and the operation of the signal-transmitting means is controlled by these altering signals so that a continuous adjustment of the exposure time is made possible even when using such a timing resistor selecting type of electrical shutter-control system.

It is'furthermore proposed with the invention to provide a signal-altering means where when exposures are made at relatively low light intensity, corrections are automatically carried out in such a way that the altering signal has an increasingly larger amplitude. toward the lower light intensity region in the event that photographs are made with a relatively small amount of light. Also, in the case where the altering signal is maintained at a constant amplitude it is possible to change the voltage level at which the altering signals are generated so as to compensate for the film characteristics. In this way it is possible to achieve a continuous adjustment of exposure time with a timing resistor selecting type of electrical shutter-control system while at the same time it is also possible to adjust the exposure time in order to compensate for exposures made at a region of low light intensity.

In the embodiment of the invention which is illustrated in FIG. 1, the electrical shutter-control system is constructed in such a way as to determine a timing signal in a stepwise manner by operation of a switching circuit which receives adjusting information from a timing circuit made up of a plurality oftimingr'esistors which are selectively inserted in the circuit depending upon the intensity of the light received from the object to be photographed. These resistors are electrically connected on the one hand with a timing capacitor and on the other hand with a transistor, the latter components forming a signal-transmitting means. The electrical shutter-control system of FIG. 1 includes a signalaltering circuit itself made up of a composite resistor means which includes a plurality of separate resistor elements as well as a light-responsive component connected in series with the composite resistor means. Each of the several separate resistor elements respectively form pairs with each of the timing resistors and are supplied with current when an associated timing resistor has been selected. The variation range of the terminal voltage across the composite resistor means of the signal-altering circuit is determined by the common ratio of the multiple proportion preselected in association with the resistor elements which are sequentially supplied with current simultaneously with the selection of the associated timing resistors, and the trigger voltage of the switching circuit which forms the signaltransmitting means is controlled according to the voltage level determined by the intensity of the light received from the object to be photographed, so that a continuous adjustment of the exposure time is made possible with a timing resistor selecting type of electrical shutter-control system.

Thus, referring to FIG. 1, there is illustrated therein a wiring diagram of a timing resistor selecting type of electrical shutter-control system which includes a signal-altering means of the invention. There are illustrated in FIG. elements 1-4 which respectively form components of a circuit for selecting a given exposure time from among a plurality of different exposure times which differ from each other by increments corresponding to different time intervals. Thus, the circuit includes the photosensitive means 1 which responds to the light received from the object to be photographed in a well known manner. This light-responsive component 1 is connected in series with a bleeder resistor 2, and a selecting means 3 is electrically connected to a junction between the components 1 and 2. This electrical selecting means 3 is thus operated by the light responsive means 1, 2 and serves to select from a timing circuit 4 a timing resistor circuit which will ,correspond to a given light intensity. Thus, the timing circuit means'4 includes a plurality of timing resistors 4a, 4b, and 4c adapted to condition the light from the object to be photographed in accordance with a multiple proportion. These resistors are connected in parallel with each other. The several resistors 4a, 4b, and 4c, are respectively connected in series with switching transistors 4a, 4b, and 4c. The bases of the latter transistors are all connected to the electrical selecting means 3, so that each of the transistors becomes conductive in response to a timing resistor selecting signal received from the selecting means 3. The selected timing signal is transmitted to a signal-transmitting means which includes a timing capacitor 5 connected in series with the timing circuit means 4, so as to form therewith a structure for participating in the transmission of a suitable timing signal to the electrical means 7 in the form of a solenoid for responding to the transmitted signal in ,order to initiate the shutter-closing operations in a well known manner. The signal-transmitting means includes in addition to the capacitor 5 a switching transistor 6 electrically connected directly with the electromagnet 7.

The signal-altering means of the invention is electrically connected in the embodiment of FIG. 1 with the transistor 6 and includes a transistor 8 which operates to control the trigger level of the switching transistor 6. The emitter terminals of the transistor 6 and 8 are both coupled with a trigger resistor 9. The circuitry includes a shutter-releasing switch 10 constructed so as to operate in synchronism with depression of a shutter button. The switch 10 is normally closed so as to bypass the timing capacitor 5.

The signal-altering means of the embodiment of FIG. 1 includes the signal-altering circuit 11 which develops the signal-altering signal to be applied by way of the transistor 8 to the transistor 6 so as to alter the signal transmitted to the electrical means 7. The signalaltering means 11 includes the resistor-transistor composite 12 connected in series with a light-responsive means formed by the light-sensitive component 13. The resistor-transistor composite 12 consists of a plurality of resistors 12a, 12b, and 120 connected in parallel with each other. These resistors are respectively connected in series with switching transistors 12a, 12b, and 12c. The terminal voltage across the resistor-transistor composite 12 is applied to the base of a transistor 14 of the signal-altering means. A resistor 15 is connected in the emitter circuit of transistor 14, and the signal-altering means includes a memory capacitor 16 capable of being connected in parallel with the resistor 15 by way of a change-over switch 17. The bases of the several transistors 12a, 12b, and 120 are respectively connected to the selecting means 3 in the same way as the bases of the transistors 4a, 4b and 4c, respectively, so that a signal selecting a given timing resistor will be simultaneously transmitted to the bases of a given pair of transistors 40' and 12a, 4b and 12b, or 40' and 120'.

FIG. 1 illustrates a power source switch 18 as well as a power source 19. The signal-altering means further includes the normally closed contact 1711 and the normally open contact 17b of the switch 17, the common terminal of which is connected to the capacitor 16 as illustrated. The normally open terminal 17b of the switch 17 is electrically connected to the base of the signal-altering transistor 8.

The embodiment of FIG. 1 illustrates a timing resistor selecting type of shutter-control system in which the timing resistors are sequentially selected with only one timing resistor being selected at any given time so that in accordance with the light intensity one timing resistor is selected, then the latter becomes unenergized and the next timing resistor is selected, and so on, until a selection is made of a timing resistor which will correspond most closely to the lighting conditions. For example, when the timing resistor 4b is to be selected after the timing resistor 4a has been inserted into the delay circuit, the timing resistor 4a will be disconnected from the delay circuit upon insertion of the subsequent timing resistor 4b. The same is true of the connection of the timing resistor 40 after the timing resistor 4b has been selected. These timing resistors have resistances varying in accordance with a multiple proportion. Thus, if it is assumed that the time constant of the timing resistor 4a and the timing capacitor 5 is set to correspond to an exposure time of H50 sec., then the time constant of the timing resistor 4b and the capacitor is set to give an exposure time of U100 sec., and the time constant of the resistor 40 and capacitor 5 is set to given an exposure time of 1/200 sec. Thus, the resistances of the resistors 4a, 4b, and 4c are'preselected so that they reduce in magnitude in a stepwise manner. In the illustrated embodiment the timing circuit 4 includes only three timing resistors, but in practice any number of timing resistors may be used so as to spread the adjustable range of exposure time.

Assuming now that the switch 18 is closed prior to releasing the shutter, a certain photoelectrically converted information corresponding to light from the object will be applied by a divided voltage developed by the light-sensitive element 1' and the bleeder resistor 2 to the selecting means 3, so that the selecting means 3 will develop a selecting signal which will select any one of the resistors 4a, 4b, 4c. Assuming that the timing resistor 4a is selected, then an exposure time of 1/50 sec. will be provided, in accordance with the above example. It is to be noted that this exposure time will be provided even if the lighting conditions are such as to require a somewhat shorter exposure time. For example if it is assumed that actual lighting conditions are such as to require more precisely an exposure time between the H50 sec. provided by resistor 4a and the 11100 sec. provided by resistor 4b, then the circuitry will operate to select the resistor 4a in the event that the error is smaller by selection of this particular resistor. Thus, the circuitry operates so as to select an exposure time which will provide the best exposure within the limitations inherent in the stepwise selection of timing signals which respectively correspond to increments without the possibility of choosing the values between these increments. I

This latter factor is one of the great drawbacks of conventional timing resistor types of exposure-time selecting circuits, .and with the present invention this drawback-is avoided.

Thus, simultaneously with selection of the timing resistor 4a, in the above example, the switching transistor 12a in the signal-altering'circuit will turn on'so as to supply current to the timing resistor 12a as well as to the light-responsive means '13. As a consequence, the terminal voltage across thetiming resistor 12a will be applied to ;the base of the transistor 14 so as to render. the latter conductive for accumulating a charge in the capacitor 16, this charge corresponding to the resistance of the timing resistor 12a. At the instant when the change-over switch 17 is actuated to engage the normally open contact 17b, the charge accumulated at the capacitor 16 will be transmitted through the transistor 8 to the transistor 6 for altering the signal received thereby from the timing circuit means 4. Under these conditions, when the shutter-releasing switch is opened by depression of the shutter operating button tomatically corrected. I

As is apparent from the above description, the trigger voltage should be controlled continuously to cover and meet the entire range of light sensitivity with a level corresponding to the gap between the timing resistors 4a and 4b. This requires a signal-altering circuit which has a special construction. Thus, the timing resistors 4a, 4b, and 4c have resistance values varying in accordance with a multiple proportion, and the difference between the light values of the light conditioned by the timing resistor 4a and by the timing resistor 4b as well as the difference in the light values of the light conditioned by the timing resistor 4b and the timing resistor 40 will be constant and equal with each other. So long as the resistances of the timing resistors are determined in accordance with a multiple proportion irrespective of the number of timing resistors, such differences in light values'will be constant and equal and will form a common ratio therebetween.

The photoelectrically converted information of the light from the object, or the light corresponding tothe common ratio, will be constant. Therefore, by setting the resistances of the timing resistors 12a, 12b and 120 in such amanner that the divided voltage Vrn derived from the photoelectrically converted information is developed at the junction point A of the signal-altering circuit 11, this divided voltage Vm will vary with the change in the internal resistance of the light-sensitive component 13, and the upper limit of the voltage Vm will be'determined within the voltage range Vm- V0 of the photoelectrically converted information.

Assuming that the timing resistor 12a is selected, then the voltage V at the junction point A will be where, R is the internal voltage of the light-responsive component 13 when the timing resistor 12a is selected, r is the resistance of the timing resistor 12a, and

E is the voltage of the power source 19.

This equation shows that the voltage V, at the junction A varies with the change in the internal resistance of the light-responsive means 13. This variation may be plotted to form a graph as shown in FIG. 2; As is apparent from the graph of FIG. 2, the voltage at the junction point rises along a steep slope between the internal resistance r up to the resistance r of component 13 until the voltage Vm is reached. In this manner the voltage at the junction point A reaches Vm but never exceeds 'Vm, and when it does reach Vm, the timing resistor 12b (having a resistance of r will be selected.

At the instant when the timing resistor 12b is selected, the voltage V at the junction point A will be where, R is the internal resistance of the light-sensitive component 13 when the timing resistor 12b is selected,

and x Y I r is the resistance of the timing resistor 12b.

Thus, the voltage Vm at the junction point A will be lowered rapidly to V, due to the newly inserted resistances R and r In order to satisfy the above relation, the voltages Vm, V and V should be set depending upon the common ratio between the resistances of the timing resistors as Vm V V Therefore, the relation between the resistors 12a and 12b will be expressed as & R,"

This means that the resistance r of resistor 12b should be selected as [R /R,] r,.

In the same way, the resistance r of timing resistor 12c should be where, R is the internal resistance of the light sensitive element 13 when the resistor 120 is selected.

The voltage Vm determined by the common ratio of the resistances of the timing resistors will in turn be determined by Thus, the common ratio will be constant as long as the time constants are set in accordance with a multiple proportion. From equations (3) and (4) By selecting the timing resistors 12a, 12b, and 120 in this way, the continuous adjustment of the exposure time corresponding to the interval or gap between any two adjacent timing resistors will be made possible under continuous control of the trigger voltage.

As has been pointed out above, with the circuitry of FIG. 1 selection is sequentially made from one timing resistor to the next. These circuits also can be constructed so as to have the timing resistors accumulatively selected with the circuit operating in such a way that after the timing resistor 4a, for example, has been inserted in the delay circuit, the timing resistor 4b which is to be inserted subsequently in the delay circuit will form a parallel-connected composite resistor with the resistor 4a, and then both of these parallelconnected resistors are electrically connected to the capacitor 5.

FIGS. 3a, 3b, and represent three different forms of signal-altering circuits 11 to be used with a timing resistor type of circuit where the timing resistors are accumulatively connected into the circuit. In FIGS. 3a-3c the various components are designated by the same reference characters as in FIG. 1.

In the embodiment illustrated in FIG 3a, the resistors 12a, 12b, and 120 of the illustrated signal-altering means'are selected accumulatively and form a composite resistor so as to determine the voltage at junction point A. For example, if the timing resistors 4a and 4b are selected, the switching transistors 12a and 12b will be turned on to thereby combine the resistor elements 12a and 12b in parallel for connecting them to the light-sensitive element 13. Therefore, the resistances of the resistor elements is set in such a way that the voltage developed at junction point A by the composite resistor consisting of the newly added resistor element 12x and the resistor element 12a becomes equal to the voltage V, at the junction point A of the preceding embodiment. In the same way, the voltage developed at the junction point A by the composite resistor consisting of resistor elements 12x, 12a, and 12b is set equal to the voltage V at junction point A of FIG. 1. By setting the resistance of each resistor element, it becomes possible to develop an inclined, sawtooth voltage curve as illustrated in FIG. 2.

In the embodiment illustrated in FIG. 3b, the signalaltering means is provided, not with resistors, but instead with diodes 20a, 20b, and 20x. In this case the number of diodes used cannot be determined according to a definite rule, but the voltage at junction point A will theoretically form a slope as illustrated in FIG. 2 if the number of diodes employed corresponds to the square of the L.V. and the diodes employed have en equal and constant characteristic with respect to each other.

This relationship is described mathematically below: Referring to FIG. 40, part of the circuitry of FIG. 3b is illustrated. Utilizing symbols as shown in FIG. 411, V, will be expressed as VI l m! Since i1 is nearly equal to E/R,,

, (in the above equation it is assumed that the possible voltage drop developed in the diode D, by means of 1'] is negligible compared with V,, and that the proportional ratio is unity for convenience of explanation.)

Assuming that the resistances of timing resistors 4a, 4b, and 4c are preselected at an interval corresponding to l L.V., then the voltage V, will rise up in an inclined slope in accordance with the equation (6) until a level corresponding to the increase of l L.V. is reached in the light from the object, and at this instant the subsequentstage timing resistor will be selected. If the internal resistance ofthe light sensitive element 13 is expressed as R the current i, will become i As a result, the terminal voltage of diode D, will be changed from V, to

2 n (E/R2) Assuming that the internal resistance R, of the photosensitive element 13 corresponds to the rising point of the terminal voltage V,, the terminal voltage V will be the voltage at the point where the intensity of light from the object has been increased by l L.V.

If the internal resistances R, and R are assumed to be and V z 1,, (E/R 2" where,

R z resistance of photosensitive element 13 when it receives no light,

E z power source voltage,

h z L.V. -equivalent value, and

'y -y -value of photosensitive element 13. Therefore In order to develop the repeated inclined voltage providing the sawtooth curve as shown in FIG. 2, the condition V V is required. When a diode D which is equal to the diode D is added as illustrated in FIG. 4b, the current i will be divided into two currents, respectively flowing through the diodes D D which have equal characteristics. Each half of the divided current will be expressed as i /2, so that the terminal voltage V will be 'z n 2/ 2) o1) 7 In the above equation if 'y l z n ol) Equation (9 is equal to equation (7), if 'y is unity..

Therefore, the voltage at junction point A drops to zero at any time when the light value increases by l L.V.

The relationship according to which equations (7) and FIG. 3c illustrates an arrangement where each branch has a plurality of series-connected diodes coupled together for varying the resistances of the branches. According to this embodiment, since the res'istance of each branch can be preset at an optional value, it is possible also with this embodiment to develop an inclined voltage at the junction point A in the same manner as illustrated in FIG. 3a.

It is to be noted, therefore, that the electrical shuttercontrol system of the invention while accommodating a timing circuit means 4 having timing resistors which are used accumulatively can also provide a continuous adjustment of the exposure time within any interval'between any two adjacent-timing resistances as a result of the signal-altering means 11 as illustrated in FIGS.

3a-3c. I

Thus, according to the above embodiments a photosensitive element and a composite resistor means consisting of a plurality of resistors or .diodes associated with each branch are connected in series so that the terminal voltage of the composite resistor means always corresponds to the trigger control voltage for adjusting the exposure time within the interval between any two adjacent timing resistors. Therefore, even if the intensity of light from the object has a value within the interval between the light values corresponding to the timing resistors and a subsequent timing resistor, the trigger voltage can be controlled continuously in accordance with the added portion of light intensity which is required and which cannot be covered by the first timing resistor. In this way an accurate and contin uous adjustment of the exposure time may be made by using the time constant determined by the selected timing resistor and the capacitor of the signal-transmitting means, and then by altering the signal with the signalaltering means of the invention to achieve a controlled trigger voltage. In this way a timing resistor selecting type of electrical shutter-control system can be operated to provide a continuous adjustment of the exposure time.

In the above embodiments, electromagnetic relays or the like may be used instead of the switching transistors 4a, 4b, and 4c in the timing circuit means 4 as well as instead of the switching transistors 12a, 12b, and 120' in the signal-altering means 11. In addition, any desired number of timing resistors and resistor elements or diodes may be employed in the timing circuit means 4 and the signal-altering means 11.

FIG. 5 illustrates another embodiment of a shuttercontrol system of the invention. This embodiment is also capable of altering the timing signal so as to achieve a continuous exposure time control rather than a stepwise control. In addition, with the embodiment of FIG. 5 it is possible to alter the signal so as to compensate for the film characteristic in a range of low light intensity. The illustrated system is constructed so as to determine the exposure time in a stepwise manner by operation of the conventional timing circuit which has sity received from the object to be photographed, the

inserted resistor or resistors being electrically connected with a signal-transmitting means which includes a timing capacitor connected in series to the timing resistors. The shutter-control system of the invention includes a signal-altering means which in the embodiment of FIG. 5 also is made up of a composite resistor assembly including'a plurality of separate resistor elements-and these elements are electrically connected with a photosensitive element connected in series with the composite resistor assembly. Each of the plurality of separate resistor elements forms a pair with a corresponding timing resistor and is supplied with current when the associated timing resistor has been selected by the selecting means. The variation range of the terminal voltage across the composite resistor means is determined according to a common ratio of the multiple proportion preselected in association with the resistor elements which are sequentially supplied with current simultaneously with the selection of the associated timing resistors. The voltage level determined in accordance with the light received from the object is raised in a lower light intensity region so that it corresponds with the characteristic curve of the film, and this latter rise in the voltage is provided by the signal-altering means of the invention which alters in a corresponding manner the signal transmitted to the solenoid which forms the means which responds to initiate the shutterclosing operations, so that in this way with the embodiment of FIG. the exposure time is increased when photographing under low light intensity conditions.

Referring now to FIG. 5, the electrical system illustrated therein is a timing resistor selecting type of electrical shutter-control system which accommodates an automatic means in order to compensate for the stepwise selection of exposure time. In the wiring diagram of FIG. 5 there are illustrated a photosensitive means 21 which senses the light from the object to be photographed, this photosensitive means 21 being connected in series with a bleeder resistor 22 so as to form therewith an electrical operating means which is electrically connected with the electrical selecting means 23 which selects a given timing signal from the timing circuit means 24 of FIG. 5. The timing circuit means 24 includes the plurality of timing resistors 24a, 24b, 24c, 24d, and 24e, connected in parallel with each other and adapted to condition the light from the object in accordance with a multiple proportion. The several timing resistors are respectively connected electrically with the switching transistors 24a, 24b, 24c, 24d, and 242' which are electrically connected to the electrical selecting means 23 so that each of the switching transistors turns on in response to a selecting signal intermittently developed at the circuit of the selecting means 23. The signal-transmitting means to which a timing signal is delivered from the timing circuit means 24 includes the capacitor 25 and the transistor 26. Thus, the circuit means 24 is connected in serieswith the capacitor 25. The switching transistors 26 of the signaltransmitting means is arranged so as to become conductive in response to the time constant determined by the selected timing resistor and capacitor 25 so that in this way a signal will be transmitted to the solenoid 27 which is inserted in the collector circuit of the switching transistor 26 and which forms the electrical means for responding to the transmitted signal in order to initiate the shutter-closing operations. A shutter release switch 30 is operated in synchronism' with depression of the-shutter button. The switch 30 is normally closed and bypasses the capacitor 25.

The embodiment of FIG. 5 is 'provided with'a signalalteri'ng means 31 for developing a control voltage, the altering circuit 31 including a plurality of resistors 32a, 32b, 32c, 32d and 32e which are connected in-parallel with each other. The several resistors 32a-32c are respectively connected in series with the switching transistors 32a, 32b, 32c, 32d, and 32e' in order to form a resistor-transistor combination, to which in turn there are connected in series the photosensitive element 33 and a transistor 34 to receive the terminal voltage of the resistor-transistor combination 32 at the base thereof. A resistor 35 is coupled to the emitter of transistor 34, and a memory capacitor 36 is connected in parallel with the resistor 35 when the switch 37 is in its normal position shown in FIG. 5 engaging the switch contact 37a. The bases of the several transistors 32a32e' are coupled with the selecting means 23 in the same way as the bases of the transistors 24a'24e, respectively, so that the selection signals are transmitted simultaneously to a pair of base terminals of a pair of associated transistors 24a and 32a, 24b and 32b,

24c and 32c, 24d and 32d, or 24c and 32e', these selection signals being transmitted at equal and constant intervals. I

FIG. 5 also illustrates the power source switch 38 and the power source 39. The switch 37 has a normally open contact 37b which can be closed when the switch 37 is changed over from contact 37a to contact 37b. This contact 37b is electrically connected to the base of transistor 28 of the signal-altering means, so that through the latter the signal received by the transistor 26 from the timing circuit means 24 is altered as required before being transmitted to the electrical means 27.

The embodiment illustrated in FIG. 5 has a timing circuit means 24 in which the resistors are sequentially selected so that specific timing resistors are selected separately one from the other in order to provide the exposure time selected by the selecting means 23. Thus, if the timing resistor 24b is to be selected after the timing resistor 24a has been inserted into the delay circuit, this timing resistor 24a will be disconnected from the delay circuit simultaneously with the connect ing of the resistor 24b into the circuit. The same is true in connection with any pair of successive timing resistors 24b and 24c, or 24d and 24s. The resistances of the timing resistors 24a, 24b, 24c, 24d, and 24e are preselected in accordance with a multiple proportion. Therefore, if the time constant of the timing resistor 24a and the capacitor 25 is set to correspond to an exposure time of one-eighth sec., the time constant determined by the timing resistor 24b and capacitor 25 will give an exposure time of one-fifteenth sec., and the timing resistor 24c, 24d, and 242 will respectively provide exposure times of one-thirtieth sec., one-sixtieth sec., and one one hundred twenty-fifth sec. In the illustrated embodiment the timing circuit means 24 includes for purposes of illustration only five timing resistors, but in a practical device any number of timing resistors may be employed to provide a wider range of adjustment of the exposure time.

Thus, it will be understood that the embodiment of FIG. 5 is similar to that of FIG. 1 and permits a continuous adjustment of exposure time to be achieved because of the altering of the signal from the timing circuit means 24 by way of the altering signal received through thetransistor 28 from the signal altering means 31 which includes the transistor 28. Thus, the continuous control of exposure time is achieved with a sawtooth shaped voltage curve as described above in connection with FIG. 2.

However, in the embodiment of FIG. 5 the resistors 32a and 32b, which are supplied with current in a lower light intensity region, have their resistance values set in such a way that they develop an inclined voltage as described above but with a change as illustrated in FIG. 6 and as described below. 7

In this way it will be possible for the signal-altering means of FIG. 5 not only to achieve a continuous exposure time adjustment but also to compensate for the film characteristic which is non-linear in the low light intensity region.

Thus, with the embodiment of FIG. 5 the values of the resistances of resistors 32a and 32b are set in accordance with the non-linear portion of the film characteristic curve (i.e. the lower light intensity region). Thus, when it is determined that the resistor elements 32a and 32b are to be supplied with current, the inclined voltages will have higher upper limit values, as indicated at a and b in FIG. 6. In other words, with the embodiment of FIG. 5 the construction is such that the signal transmitted by the signal-transmitting means 25, 26

to the electrical means 27 is altered by the 'signalaltering means 31 so that the trigger voltage is increased in the non-linear portion where there is a lower intensity of light received from the object to be photographed, so that in this way it is possible to extend the exposure time when making an exposure with a relatively low light intensity.

Thus, with the above structure a timing resistor selecting type of electrical shutter-control system is provided in order to insure that the exposure time is consistent with the film characteristic even in a lower light intensity region so that unsatisfactorily exposed negatives will be avoided, so as to overcome this latter problem which has been considered inevitable when making photographs under conditions of low light intensity.

The automatic means for compensating the exposure time according to the present invention provides the same photographing conditions in the lower light intensity region as in the higher light intensity region. With the provision of such an automatic means, the electrical shutter-control system of the invention operates advantageously when making photographs in theatres or the like, where the available light is at a low range of intensity and where flash photography is prohibited. In

addition, the automatic exposure time compensating circuitry of the invention can be incorporated into a continuous exposure time adjusting circuit arrangement having a timing resistor selecting type of electrical shutter-control device as pointed out above. This is advantageous in that automatic exposure time compensating means can be constructed relatively simply and can be accommodated in a camera housing which offers only a limited amount of space.

In the lower light intensity region the embodiment of FIG. Swill provide the extended exposure time in accordance with the light intensity. However, when the embodiment of FIG. 5 is used to control exposure time in an inexpensive camera, this embodiment may be constructed in such a manner that it provides an extended exposure time in a lower light intensity region below the predetermined low light intensity value.

By selecting the resistances of the resistor elements which are to be supplied with current in the higher light intensity region in such a way that they follow the non linearity of the film characteristic at the higher intensity region, it is possible also to construct the automatic means so that it will compensate the exposure time in the higher light intensity region in accordance with the teachings of the present invention.

FIGS. 7a and 8 respectively illustrate different embodiments of an electrical signal-altering means according to the invention. In each of these embodiments there is an oscillation circuit which forms the electrical altering means of this embodiment has a memory capacitor which is charged and discharged each time a sawtooth signal changes. These embodiments include a time determining circuit in the form of a lightresponsive circuit means electrically connected with the operating means for determining the duration of operation thereof. This light-responsive circuit means is also connected with the signal-altering means so as to actuate the latter to transmit to the signaltransmitting means any quantities stored at the memory capacitor of the signal-altering means when the operation of the operating means is terminated. The lightresponsive circuit means which determines the duration of operation receives light from the object to be photographed and uses this information to provide equal and constant intervals corresponding to the period of the sawtooth signals and the pulse signals. Under the operation of this light-responsive circuit the memory means has its operation stopped so as to transfer the memorized electrical quantity to the signaltransmitting means to form the altering signal. Thus, with these operations the oscillation which provides the pulses is interrupted and the number of timing resistors to be selected is determined by the number of pulses which are developed, so that an exposure time adjusting value is obtained which corresponds to the preselected interval between the timing resistors of the timing circuit means. In this manner the trigger section of the switching circuit can be controlled depending upon the actual light intensity within the interval between the timing resistors, so that a continuous adjustment of exposure time is achieved in proportion to the intensity of light received from the object which is to be photographed.

Referring to FIG. 7a, the electrical selecting means 41 and the timing circuit means 42 are electrically connected to each other in a manner similar to the abovedescribed embodiments. The timing circuit means 42 is made up of the plurality of timing resistors 42a, 42b, and 420 which are connected in parallel with each other. These resistors are respectively connected in series with the switching transistors 42a, 42b and 420' which respectively turnon when receiving at the bases thereof a selecting signal from the electrical selecting means 41 so as to thereby supply current to the selected timing resistor 42a, 42b, or 420. The selected timing resistor will, by its series connection with the capacitor 43 of the signal-transmitting means, form a timing circuit- THE timingr'esistors 42if42bfand 42care arranged in either of two different ways. In one arrangement they are sequentially selected one after the other, while in the second. arrangement they are accumulatively selected so as to be connected in parallel into a single composite resistor. The switching transistor 44 forms with the capacitor 43 thesignal-transmitting means of this embodiment and is arranged so that it receives at its base the terminal voltage across the capacitor 43. The collector terminal of the transistor 44 is electrically connected to the electrical means formed by the solenoid 45 for initiating the shutter-closing operations in response to the signal received from the signaltransmitting means. A normally closed shutter releasing switch=46 serves to bypass the capacitor 43, this switch 46 being opened 'upon depression of the shutterreleasing button of the camera. 7

The above-described structure of FIG. 7a operates in the manner described above in connection with the above embodiments. This embodiment of FIG. 7a includes the electrical operating means 47 in the form of an oscillating circuit which is electrically connected to the selecting means 41 to operate the latter with operating pulses, and this embodiment also includes the light-responsive circuit means 48 for determining the duration of operation.

The oscillating circuit 47 includes a timing circuit made up of a variable resistor 49 and a capacitor 50 which are connected in series to a power source 51. This circuit includes a unijunction transistor 52 having its emitter electrically connected to a junction between the resistor 49 and capacitor 50.

The signal-altering means includes an amplifying transistor 53 having its base electrically connected to the junction between the variable resistor 49 and capacitor 50. In addition the signal-altering means includes the memory capacitor 54 connected electrically to the output terminal b of the amplifying transistor 53. The output terminal or first base a of UJT 52 is electrically connected to the electrical selecting means 41 for transmitting thereto the operating pulses developed at the terminal or junction a, and in response to these operating pulses the selecting means 41 will operate to select an appropriate timing resistor 42a, 42b, or 420 depending upon the received operating pulses. The memory capacitor 54 which is connected to the output terminal b of the amplifying transistor 53 is electrically connected to the common terminal 55c of a changeover switch 55 so that it normally is electrically connected to the terminal b through the normally closed switch contact 55a. The switch 55 includes a normally open contact 55b which is electrically connected to the base of transistor 56 of the signal-altering means so as to provide the altering signal to be combined with the signal from the timing circuit means 42 in order to provide the signal which is transmitted to the electrical means 45. Thus, the trigger level of the switching transistor 44 is controlled depending upon the electrical quantity stored in the memory capacitor 54. On the other hand, a trigger resistor 57 is electrically connected to the emitter terminals of the transistors 44 and 56 so that these transistors will cooperate electrically with each other.

It is to be noted that the oscillating frequency of the oscillating circuit 47 need not be set at a fixed value but may be set at any optional value as long as it maintains a constant relation with the light received from the object to be photographed. Thus, the logarithmically converted information of the light received from the object is to be conditioned at the same period as those of the oscillation pulses which continue to be generated-at equal and constant intervals. As long as this condition is satisfied the oscillation frequency may be determined in such a way, for example, that the period of 1 sec. corresponds, for example, to 1 L.V.

The intensity of the light received from the object to be photographed can be conditioned at equal and constant intervals by converting it logarithmically. In order to further convert the logarithmically converted infor- .mation into time-limiting information, the lightresponsive circuit 48 is provided, this circuit 48 including a buffer transistor 60 connected at its base to a junction between the series-connected photosensitive element 58 and logarithmic conversion diode 59. A transistor 62 is connected through a variable resistor 61 to the emitter of the buffer transistor 61). A transistor 63 has its internal resistance adjusted under the control of the transistor 62. A timing capacitor 64 is electrically connected to the collector of the transistor 63. The transistor 63 forms a timing circuit together with the capacitor 64. A switching transistor 65 is arranged in such a way that it operates under the action of the timing circuit. In the collector circuit of the switching transistor 65 are inserted relay coils 66 and 67. The relay coil 67 is positioned so as to actuate the changeover switch 55 while the relay coil 66 serves to open the normally closed switch 66a which is connected to the terminal a of UJT 52 and to the selecting means 41. A power source switch 68 is provided so as to close dur ing an initial increment of movement of the shutterreleasing plunger of the camera.

With the embodiment of FIG. 7a, when the power source switch 68 is closed prior to actual release of the shutter, the oscillating circuit 47 starts oscillating in accordance with the time constant of the variable resistor 49 and the capacitor 50. At this time UJT 52 oscillates at a preset constant frequency irrespective of the light received from the object to be photographed. As a consequence a series of operating pulses with a relatively small pulse width will appear at the terminal a of UJT 52 as a result of the characteristics thereof. Therefore, the selecting means 41 will be operated in response to these pulses so as to select timing resistors 42a, 42b, and 42c in the manner illustrated in FIG. 7b where the pulses are graphically shown. 7

Assuming now for purposes of explanation that the oscillating period of UJT 52 is set so as to be 1 sec., the signals appearing at the output terminal b will have the sawtooth configuration illustrated in FIG. 70 and having a period of 1 sec. The shape of the signal is determined by the emitter voltage of UJT 52.

On the other hand, inasmuch as the internal resistance of the light-responsive circuit 48 drops in response to the light received by the photosensitive element 58, the diode 59 will develop a logarithmically converted signal in accordance with the light from the object. Upon receipt of this signal all of the transistors 60, 62, and 63 will become conductive and will therefore supply current to the timing circuit formed by the transistor 63 and capacitor 64. As the internal resistance of transistor 63 varies in accordance with the logarithmically converted signal, which can be conditioned at an equal and constant interval, a transistor 65 which is rendered operative depending upon the time constant of the timing circuit will be turned on in accordance with the logarithmically converted signal. Therefore, by equalizing the value for conditioning the logarithmically converted signal at an equal and constant interval with the oscillation frequency of the oscillating circuit 47, the oscillating operation of the oscillating circuit 47 may be terminated in response to the light receivedfrom the object to be photographed. Assuming now that the transistor 65 is preset so as to turn on in 1 sec. at 1 L.V., in 2 sec. at 2 L.V., and so on, if the intensity of the light received from the object corresponds to 4 L.V., the transistor 65 will be rendered conductive in 4 sec. to thereby convert the light from the object into a time signal conditioned at an equal and constant interval. Accordingly, the opening of the switch 66a in the oscillating circuit 47 will be accompanied by the changeover of the switch 55 and thus the contact 55a will open while the contact 55b will close. In this case, assuming that the oscillating circuit 47 os-

Patent Citations
Cited PatentFiling datePublication dateApplicantTitle
US3602717 *Feb 26, 1969Aug 31, 1971Zeiss Ikon AgAutomatic photoelectric shutter control circuit for single lens mirror reflex cameras
US3603799 *Mar 26, 1969Sep 7, 1971Asahi Optical Co LtdLight measuring device comprising a plurality of binary circuits for providing a digital representation of photocell output
US3703130 *Mar 23, 1971Nov 21, 1972Nippon Kogaku KkElectronic shutter control device
Referenced by
Citing PatentFiling datePublication dateApplicantTitle
US3961341 *Dec 11, 1974Jun 1, 1976Fuji Photo Optical Co., Ltd.Automatic shutter speed control means for a camera
US4006484 *May 27, 1975Feb 1, 1977Asahi Kogaku Kogyo Kabushiki KaishaCamera systems for providing precise exposures with digital light measurement
US4032932 *May 9, 1975Jun 28, 1977Asahi Kogaku Kogyo Kabushiki KaishaAutomatic shutter controls for cameras
US4200371 *Oct 12, 1977Apr 29, 1980Canon Kabushiki KaishaPhotographic camera with film speed setting system
Classifications
U.S. Classification396/250, 396/254
International ClassificationG03B9/58, G03B7/083
Cooperative ClassificationG03B9/58, G03B7/083
European ClassificationG03B9/58, G03B7/083