GB2280028A

GB2280028A - Camera light meter

Info

Publication number: GB2280028A
Application number: GB9413174A
Authority: GB
Inventors: Soon-Gil Seo
Original assignee: Samsung Aerospace Industries Ltd
Current assignee: Hanwha Aerospace Co Ltd
Priority date: 1993-07-01
Filing date: 1994-06-30
Publication date: 1995-01-18
Anticipated expiration: 2014-06-30
Also published as: DE4423000A1; GB2280028B; CA2127076A1; MY130087A; CN1103721A; GB9413174D0

Description

2280028 BACKGROUND 01P TEE INVENTION is irield of The Invention The

present invention relates generally to a brightness measuring device. and more particularlyr to a brightness measuring device for a camera and related control method. DescriRtion of Related Art Conventional brightness measuring devices measure an ambient brightness of an object and determine a suitable exposure amount. A conventional device includes a microcontroller to determine the suitable exposure amount in accordance with the ambient brightness of an object. An element for measuring the brightness produces a voltage which is converted by an analog/digital converter (A/D converter) to a digital signal that is recognizable by the microcontroller. The microcontroller provides a voltage level corresponding to the voltage from the brightness measuring element to determine the ambient brightness. The microcontroller compares each of the voltage levels which are output from a plurality of comparators, measures the ambient brightness of the object, and determines the suitable exposure amount in accordance with the measured brightness.

- However, the conventional brightness measuring device has a disadvantage in that because the ambient brightness is measured using a microcontroller and an A/D converter or a plurality of comparators, the price of a product is dri.Ven 2_ is high. Moreover# the microcontroller in the conventional brightness measuring device measures the ambient brightness of the object only once and controls the shutter exposure when a first step release switch is operated. Accordingly, the conventional brightness measuring device cannot obtain a suitable exposure when the object has moved during a time interval up to the operation of a second step release switch since the exposure amount was determined in accordance with the measured brightness value before the movement of the object.

SUMRARY OF THE INVENTION An object of the present invention is to provide a brightness measuring device for a camera that overcomes the problems and disadvantages of the conventional devices.

The features and advantages of the invention will. be set forth in the description which follows, and in part will be apparent from the description, or may be learned by practice of the invention. The objectives and other advantages of the invention will be realized and attained by the apparatus and method particularly pointed out in the written description and claims hereof as well as the appended drawings.

To achieve this and other objects and in accordance with the purpose of the invention, as embodied and broadly described herein, a brightness measuring device for a camera includes means for activating the brightness measuring, device; means -for accumulating electrical energy representing the level of a detected ambient brightness of 3 an object; =cans for measuring time between when the activating means activates the brightness measuring device and when the accumulating means accumulates electrical energy to a reference level; and means, coupled to the time measuring means# for determining a proper exposure value based on measured time.

According to another aspect of the present invention, a brightness measuring device for a camera includes a first switch for initiating brightness measurement; a second switch for initiating a photographing operation of the camera; means for detecting an ambient brightness of an object when the first switch is operated and for producing a brightness signal having a voltage level corresponding to a level of the detected ambient brightness; means for measuring time between when the first switch is operated and when the level of the brightness signal exceeds a reference level; means for determining a suitable exposure value based on a measured time; and means for controlling the photographing operation of the camera based on the suitable exposure value when the second switch is operated.

According to yet another aspect of the present invention, a method for measuring an ambient brightness of an object for a camera having a release switch to activate brightness measurement includes detecting an ambient brightness of an object when the release switch is oper.ated; accumulating electrical energy with a voltage corresponding to the detected ambient brightness when the release switch is operated; measuring time between when the release switch It is operated and when the electrical energy is accumulated to a reference value; and determining a suitable exposure -falue based on the measured time.

The objects and advantages of the invention will be set forth in part in the description which followsi and In part will be obvious from the description# or may be learned by practice of the invention. The objects and advantages of the invention will be realized and attained by means of the elements and combinations particularly pointed out in the appended claims.

The accompanying drawings, which are incorporated in and constitute a part of this specification# illustrate one embodiment of the invention and together with the description, serve to explain the principles of the invention.

BRIEP DESCRIPTION OP THE DRAWINGS rig. 1 is a block diagram of a camera with a brightness measuring device according to a preferred embodiment of the present invention.

Pig. 2 is a detailed circuit diagram of the brightness measuring device for a camera according to a preferred embodiment of the present invention.

Fig. 3 is a flowchart showing the operation of the brightness measuring device for a camera according to the preferred embodiment of the present invention.

rig. 4 is a timing diagram of the operation of the brightness measuring device for a camera according to the preferred embodiment of the present invention.

rig. 5 is a graph showing a charge state of a capacitor of the brightness measuring device for a camera according to the preferred embodiment of the present invention.

DESCRIPTION OF TEE PREFERRED EMBODIMENT is Reference will now be made in detail to the preferred embodiment of the invention, an example of which is illustrated in the accompanying drawings.

Referring to rig. 1# a brightness measuring device for a camera includes a switch block 10 having a first step release switch 51 and a second step release switch 52r a microcontroller 20 connected to output terminals of the switch block 10. a motor actuator 30 connected to an output of the microcontroller 20: an alarm 40, a shutter actuator 50. an automatic distance measuring circuit 60, a brightness measuring circuit 70, a film sensitivity sensor 80, and a strobe 90.

Referring to Pig. 2, the brightness measuring circuit 70 includes an actuator 71 for applying power to the camera after receiving a signal for measuring an ambient brightness of an object from the microcontroller 20. A brightness detector 73 produces a voltage corresponaing to the ambient brightness of the object after measuring the ambient brightness of the object when the actuator 71 is operated. A brightness signal producer 75 provides a brightness signal after receiving a signal from the actuator 71 and the brightness detector 73.

The actuator 71 includes a first capacitor Cl having one terminal connected to a power terminal and the oth er 4 is terminal connected to earth. a first transistor TI having an emitter terminal connected to the power terminal, a first resistor Rl having one terminal connected to the emitter terminal of the first transistor Tl and the other terminal connected to a base terminal of the first transistor TI, a second resistor IR2 with one terminal connected to the base terminal of the first transistor T1, and a third resistor R3 having one terminal connected to an output terminal of the microcontroller 20. The actuator 71 includes a second transistor T2 having a base terminal connected to the other terminal of the third resistor R3, a collector terminal connected to the other terminal of the second resistor R2 and an emitter terminal connected to the earth, and a fourth resistor R4 having one terminal connected to the base terminal of the second transistor T2 and the other terminal connected to the earth.

The brightness detector 73 includes a light receiving element, for example, a cadmium sulphic cell CDS, connected to the collector terminal of the first transistor Tit a variable resistor VR1 having terminals respectively connected to the terminals of the light receiving element CDS, and a seventh resistor R7 having one terminal connected to a terminal of the light receiving element CDS.

The brightness signal producer 75 includes a fifth resistor RS having one terminal connected to the collector terminal of the first transistor Tli and a sixth resistor R6 having terminals respectively connected to the fifth resistor R5 and the earth. The brightness signal producer 7 is includes a comparator Il having a non-inverting terminal connected to the seventh resistor R7, an inverting terminal connected to the sixth resistor R6 and the output terminal connected to an input terminal of the microcantroller 20. The signal producer 75 includes a second capacitor C2 having one terminal connected to the seventh resistor R7 and the other terminal connected to the earth# and a third transistor T3 having a collector terminal connected to the non-inverting terminal of the comparator 11 and an emitter terminal connected to the earth. -The signal producer 75 includes an eighth resistor R8 having one terminal connected to the base terminal of the third transistor T3 and the other terminal connected to the earth, a ninth resistor R9 having one terminal connected to the base terminal of the third transistor T3 and the other terminal connected to the collector terminal of the second transistor T2, and a tenth resistor R10 having one terminal connected to the variable resistor VR1 and the other terminal connected to the output terminal of the comparator 11.

The operation of the camera in accordance with the embodiment of the present invention will be explained with reference to the accompanying drawings.

Referring to Figs. 1 and 3, when power is applied to the camera and a user presses the first step release switch Sl in a standby mode to carry out the photographing operation, the switch block 10 produces a signal corresponding to the operation to the microcontroller 20 (Step 110).

9 is The microcontroller 20 receives the signal corresponding to the operation of the first step release switch and checks the camera battery (Step 120). The microcontroller 20 checks the charge state of the strobe 90 and senses the sensitivity of the film mounted in the camera through a film sensitivity sensor 80 (Step 130 - Step 140). After sensing the sensitivity of the film, the microcontroller 20 activates a control output signal OUT and transmits the signal to the brightness measuring circuit 70 to measure the ambient brightness"of the object (Step 150).

Referring to Fig. 2, the microcontroller 20 produces the Output Signal OUT of high level, which is transmitted to the base terminal of the transistor T2 of the actuator 71 of the brightness measuring circuit 70. Subsequently, transistor T2 becomes turned ON. When the transistor T2 is turned ON, the voltage level of the collector terminal of the transistor T2 becomes low. Referring to Fig. 4, since low level signal is applied to the base terminal of the first transistor T1 and to the base terminal of the third transistor T3, the transistor T1 becomes turned ON and the transistor T3 of the brightness signal producer 75 becomes turned OFF.

The first transistor TI of the actuator 71 is turned ON and power is applied to the light receiving element CDS of the brightness detector 73. Accordingly, the charge corresponding to the brightness of the received light starts to be charged at the second capacitor C2.

a 1 is In the light receiving element CDS, the resistance value changes In accordance with the brightness. When the brightness is high,the charge speed of the second capacitor C2 becomes high since the resistance value decreases. When the brightness is weak, however, the charge speed of the second capacitor C2 becomes low since the resistance value increases.

When the first capacitor Cl starts to be charged. the microcontroller 20 activates an internal counter (not shown) and starts to count the charge time of the first capacitor Cl.

When the charge amount of the second capacitor C2 is increased, such that the charge voltage is divided by the fifth resistor RS and the sixth resistor R6, and becomes greater than a reference voltage inputted to the inverting terminal in the comparator Il, the output from the comparator 11 transitions from a low state to a high state (as shown in Fig. 4). The comparator output is transmitted to the microcontroller 20.

The microcontroller 20 counts the time from when the second capacitor C2 starts to charge to when the charge voltage of the second capacitor C2 becomes the reference voltage of the comparator Il, that is. the time until a high level signal is output from the comparator Il. The microcontroller 20 determines the brightness value of the object corresponding to the measured count value. After determining the count value. the microcontroller 20 is determines whether the measured brightness value indicates a low brightness or a high brightness (Step 160 - Step 170).

Referring to rig. 5, the microcontroller 20 determines that the measured brightness value indicates a high brightness when the charge time of the second capacitor c2 is T1 (a), a low brightness when the charge time of th6 second capacitor C2 is T3 (c), and a brightness of a suitable exposure when the charge time of the second capacitor C2 is T2 (b). ACcordingly, the microcontroller 20 determines a relationship between the count value corresponding to the charge time of the second capacitor C2 in the brightness measuring circuit 70 and an established value for determining the brightness, and also determines whether the present brightness of the object is low or high.

The microcontroller 20 counts the charge time of the second capacitor C2 measured through the brightness measuring circuit 70, determines a relationship between the count value and a first established value corresponding to the low brightness (Step 160), and determines a relationship between the count value and a second established value corresponding to the high brightness when the count value is less than the first established value (Step 170).

The first established value according to the preferred embodiment of the present invention is 80. and for the second established value is 8. llowever, the present invention is not limited to such values, and the first and second established values can be adjusted according to desired design conditions.

11 is When the comt value measured in the above is greater j than the first established value# the microcontroller 20 determines that the present brightness is too low, activates the alarm 40, and informs the user that the present brightness is low (Step 180). The microcontroller 20 reduces the shutter speed, increases the exposure valuet and obtains a photograph having a suitable exposure (Step 190).

When the measured count value is less than the second established value, the microcontroller 20 determines that the present brightness is too high, -increases the shutter speed, reduces the exposure value such that the amount of incident light is reduced, and obtains a photograph having a suitable exposure (Step 200).

When the measured count value is less than the first established value and greater than the second established value, the microcontroller 20 determines that the ambient brightness of the object is suitable. The microcontroller 20 subsequently activates the shutter when the second step release switch is operated in accordance with the set speed of the shutter.

The microcontroller 20 sets a suitable exposure amount corresponding to the measured ambient brightness of the object (Step 210), activates the automatic distance measuring circuit 60, measures the distance from the object (Step 220), and carries out the auto-focusing (AF) calculation (Step 230). After carrying out the AF calculation, the microcontroller 20 determines whether-the second step release switch is operated (Step 240). When the )2_ is second step release switch is not operated (Step 250), the microcontroller 20 determines whether a predetermined time passes. When the predetermined time has passed without the operation of the second step release switch,, the microcontroller 20 again provides the signal for activating the brightness measuring circuit 70 to measure the current brightness corresponding to any change in the position of the object and the camera setting (Step 150).

Accordinglye when the second step release switch 32 is not operated during the predetermined- time, the microcontroller 20 measures the ambient brightness of the object successively, as explained above. and calculates the exposure amount an the basis of the brightness measured right before the second step release switch S2 is operated.

The microcontroller 20 carries out lens-focusing when the second step release switch 52 is operated (Step 260), concurrently activates the shutter actuator 50 according to the exposure amount and the speed of the shutter set as in the above, and carries out the photographing of the object (Step 270). The microcontroller 20 activates the motor actuator 30 after photographing one cut of the film, transfers the photographed film, and ends the operation (Step 280 - Step 300).

As described above, the brightness measuring device for a camera and related control method of the present invention has advantages in that the basic price for a product is, reduced and a common area of the circuits is reduced by measuring the ambient brightness of the object through the 13 is brightness measuring circuit using only one comparator. in addition, a photograph have a suitable exposure according to a brightness change around an object can be obtained even when the position of the object and the setting of the camera have changed before the activation of the second step release switch. This is because the ambient brightness of the object is successively measured when the second step release switch has not been operated during a predetermined time after measuring the ambient brightness of the object by the operation of the first step release switch. moreover, a suitable exposure for a picture can be obtained since the ambient brightness of a moving object can be accurately measured when the device is used for an optical measuring device.

Other embodiments of the invention will be apparent to those skilled in the art from consideration of the specification and practice of the invention disclosed herein. it is intended that the specification and examples can be considered as exemplary only, with a true scope and spirit of the invention being indicated by the following claims.

Claims

1 It 1. A brightness measuring device for a camera, comprising:

means for activating said brightness measuring device; means for accumulating electrical energy representing the level of a detected ambient brightness of an object; means for measuring time between when said activating =cans activates said brightness measuring device and when said accumulating means accumulates electrical energy to a reference level; and means, coupled to said time measuring means, for determining a proper exposure value based on measured time.

2. The brightness measuring device of claim 1, wherein said time measuring means includes means for repeatedly meas.uring said time periodically until the photographing operation of the camera is activated and means for determining said proper exposure value based on the measured time when the photographing operation is activated.

3. The brightness measuring device of claim 1, wherein said time measuring means include means for stopping the measuring of said time when said accumulating means accumulates electrical energy to a reference level.

4. The brightness measuring device of claim lt wherein said time measuring means includes means for comparing between a voltage corresponding to the level of accumulated electrical energy and a reference voltage and means for stopping the measuring of said time based on the result of the comparison.

5. The brightness measuring device of claim 1, further comprising means for indicating to a user of the camera whether 15, the detected ambient brightness is greater than or equal to or less than a reference value.

6. The brightness measuring device of claim 1, wherein said time measuring means includes a counter for counting time.

7. A brightness measuring device for a camera, comprising; a first switch for initiating brightness measurement; a second switch for initiating a photographing operation of the camera; means for detecting an ambient brightness of an object when said first switch is operated and for producing a brightness signal having a voltage level corresponding to a level of the detected ambient brightness, means for measuring time between when said first switch is operated and when the level of said brightness signal exceeds a reference level; means for determining a suitable exposure value based on a measured time; and means for controlling the photographing operation of the camera based on said suitable exposure value when said second switch is operated.

8. The brightness measuring device of claim 7, further comprising means for indicating to a user of the camera whether or not the.detected ambient brightness is sufficient.

9. The brightness measuring device of claim 7 wherein said brightness detecting means includes a light receiving element for producing said brightness signal having a voltage level based on the change in resistance thereof in response to the detected brightness; and J6 means for charging a capacitor to said voltage level.

10. The brightness measuring device of claim 7. wherein said time measuring means includes:

means for repeatedly measuring said time periodically until the second switch is operated; and means for determining the suitable exposure value based on the measured time when the second switch is operated.

11. The brightness measuring device for a camera of claim 8e wherein said time measuring means includes means for measuring the time that the capacitor is charged to a reference voltage level.

12. A method for measuring an ambient brightness of an object for a camera having a release switch to activate brightness measurementi comprising the steps of:

detecting an ambient brightness of an object when the release switch is operated; accumulating electrical energy with a voltage corresponding to said detected ambient brightness when the release switch is operated; measuring time between when the release switch is operated and when the electrical energy is accumulated to a reference value; and determining a suitable exposure value based on said measured time.

13. The method of claim 12, further comprising informing a user of the camera whether or not the detected ambient brightness of the object is sufficient.

17

14. The method of claim 12. wherein said time measuring step includes determining that the detected ambient brightness is low when the measured time is greater than a first established valuef determining that it is proper when the measured time is less than the first established value and greater than a second established valuet and determining that it is high when the measured time is less than the second established value.

15. The method of claim 12, wherein said time measuring step includes repeatedly measuring said time periodically until the photographing operation of the camera is activated, and measuring the suitable exposure value based on the measured time when the photographing operation of the camera is activated.