GB2289545A

GB2289545A - Brightness measuring

Info

Publication number: GB2289545A
Application number: GB9509868A
Authority: GB
Inventors: Soon-Gil Seo
Original assignee: Samsung Aerospace Industries Ltd
Current assignee: Hanwha Aerospace Co Ltd
Priority date: 1994-05-16
Filing date: 1995-05-16
Publication date: 1995-11-22
Anticipated expiration: 2015-05-16
Also published as: CN1144914A; GB9509868D0; FR2719916A1; RU95107896A; FR2719916B1; JPH0850314A; GB2289545B; KR100236641B1; DE19517747A1; RU2134896C1; KR950033632A

Description

2289545

BACKGROUND OF THE INVENTION

Field Of The Invention

The present invention relates to an exposure control system for imaging. More particularly, the present invention relates to exposure value determination for imaging moving objects or objects in changing light conditions.

Description Of The Related Art

In imaging, the exposure value relates to the amount of light which reaches the imaging medium such as film. A brightness measuring circuit measures the light reflected off an object to determine the exposure value.

In a conventional still picture camera, when a user presses a shutter button to take a photograph, a first step release switch is operated and a second step release switch is operated. When the first step release switch is operated, an automatic distance measuring circuit measures the distance to the object, and the brightness measuring circuit measures the ambient brightness around the object. A micro-controller calculates a suitable exposure value in accordance with the brightness value measured by the brightness measuring circuit. When the second step release switch is operated, the microcontroller directs a shutter to open and sets an optional variable aperture in accordance with the exposure value to expose the film.

The conventional brightness measuring device only measures the light once per exposure, and the shutter speed is determined based upon this one measurement. Conditions can, however, change between the actuation of the fist and second step release switches. The object may move, the camera may move, or the light may change. The user cannot take a photograph having the correct exposure when the object moves during the time interval before the operation of the second step release switch because the exposure value was determined in accordance with the measured brightness value before the movement of the object.

Accordingly, with the conventional brightness measuring device, the user may not obtain a photograph having the correct exposure because the shutter is operated in accordance with the exposure value calculated using the previously measured brightness value and the ambient brightness around the object may change before the second step release switch is operated.

SUMMARY OF THE INVENTION

An object of the present invention is to provide a successive brightness measuring device for a camera and a related control method that overcomes the problems and disadvantages of the conventional devices.

The advantages and purpose of the invention will be sat forth in part in the description which follows, and in part will be obvious from the description, or may be learned by practice of the invention. The advantages and purpose of the invention will be realized and attained by means of the elements and combinations particularly pointed out in the appended claims.

To attain the advantages and in accordance with the purpose of the invention, as embodied and broadly described herein, the invention comprises a successive brightness measuring device for a camera.

1 9 A user operates first and second step release switches. An ambient brightness around an object is measured when the first step release switch is operated. Then, the ambient brightness is successively measured around the object at every predetermined time interval when the second step release switch is not operated for a predetermined time after the first stop release switch is operated. Then, an exposure value is calculated in accordance with the brightness amount measured finally when the second step release switch is operated.

A method for measuring an-ambient brightness successively for a camera includes measuring the ambient brightness around an object when the first step release switch is operated; determining whether a predetermined time has elapsed after the first step release switch,was operated while the second step release switch is not operated; successively measuring the ambient brightness around the object at every predetermined time interval based on the result of the determination; and calculating an exposure value of the camera in accordance with the brightness amount measured finally before the second step release switch is operated.

It is to be understood that both the foregoing general description and the following detailed description are exemplary and explanatory only and are not restrictive of the invention, as claimed.

BRIEF DESCRIPTION OF THE DRAWINGS The accompanying drawings, which are incorporated in and constitute a part of this specification, illustrate an embodiment - 3 of the invention and together with the description, serve to explain the principles of the invention. In the drawings,

FIG. 1 is a block diagram showing a successive brightness measuring device in accordance with a preferred embodiment of the present invention; FIG. 2 is a detailed circuit diagram showing a brightness measuring circuit of the successive brightness measuring device in accordance with the preferred embodiment of the present invention; FIG. 3 is a diagram showing the charging time of a capacitor of the brightness measuring circuit in accordance with the preferred embodiment of the present invention; FIG. 4 is a flowchart of the stens in a method for measuring successive brightness in accordance with the preferred embodiment of the present invention; and FIG. 5 is a timing chart showing operation of the successive brightness measuring device in accordance with the preferred embodiment of the mresent invention.

DETAILED DESCRIPTION OF A PREFERRED EMBODIMENT

An exposure value determination system measures the light reflected off of an object whose image is to be recorded when a first step release switch is activated. The image of the object is recorded at the calculated exposure value when a second step release switch is activated. If the time between the activation of the first step release switch and the second step release switch exceeds a predetermined time limit, the exposure value determination circuit measures the light a second time and 9 Q 11 calculates a new exposure value. If the predetermined time is again exceeded before the second step release switch is activated, the exposure value determination circuit will measure the light again and calculate a second new exposure value. Thus, if the object whose image is to be recorded moves between the activation of the first and second step release switches, a new exposure value will be used to record the image. Additionally, if the light conditions change between the activation of the first and second step release switches, the exposure value determination circuit will determine a new exposure value based upon the new light conditions.

As shown in FIG. 1, the successive brightness measuring device in accordance with an embodiment of the present invention is controlled by a microcontroller 40. The microcontroller 40 is connected to a first step release switch S1, a second step release switch S2, an automatic distance measuring circuit 10, a brightness measuring circuit 20, a film sensitivity sensor 30, and terminals of the switches S1 and S2.

The automatic distance measuring circuit 10 measures the distance between the camera and an object to be recorded. The brightness measuring circuit 20 measures the ambient brightness around the object. The film sensitivity sensor 30 measures the sensitivity of the film. The microcontroller also controls a shutter 50, a motor actuator 60, and an information display 70. The brightness measuring circuit may take several forms. For example, an incident light meter may be used or a reflected light meter such as a spot, average, or matrix meter may be used.

FIG. 2 shows a schematic diagram of an embodiment of a brightness measuring circuit which may be used in accordance with the present invention. The brightness measuring circuit includes a photoresistive light receiving element Cds. The resistance value of the light receiving element Cds changes in accordance with the amount of light on the light receiving element Cds. The microcontroller sends signals to the brightness measuring circuit on a terminal labeled OUT and receives signals on a terminal labeled IN.

The brightness measuring circuit includes a comparator IC1 and three bipolar transistors T1, T2, and T3. Each transistor T1, T2, and T3 has a base, a collector, and an emitter. A voltage source Vcc and a capacitor Cl are connected in parallel between a ground voltage and the emitter of transistor T1. The collector of transistor T2 connects to the base of transistor T1, and the emitter of transistor T2 connects to the ground voltage. The base of transistor T2 receives an input pulse from the microcontroller 40 on the OUT terminal.

The collector of transistor Tl is connected to a resistor Rl, the light receiving element Cds, a variable resistor VR1, and a resistor R4. The resistors RI and R2 form a voltage divider between the collector of transistor Tl and the ground voltage. The output of the voltage divider is connected to the inverting input terminal of the comparator IC1. The light receiving element Cds and the variable resistor VRI are connected in parallel between the collector of transistor Tl and a resistor R3. The resistor R3 connects the light receiving element Cds to - 6 the noninverting terminal of the comparator IC1 and to the ground voltage through a capacitor C2.

The collector of the bipolar transistor T3 is connected to the =inverting terminal of the comparator IC1, and the emitter of the transistor T3 is connected to ground. The base of transistor T3 is connected to the base of the transistor T1 and the collector of the transistor T2. The output of the comparator IC1 is connected to the resistor R4 and the microprocessor 40 through the IN terminal.

The operation of the camera in accordance with an embodiment of the present invention will be explained with reference to the accompanying drawings As shown in FIG. 4, electric power is applied at the start (STEP 100). The microcontroller 40 initializes all operation circuits, variables, and an inner timer (STEP 110) and then determines if the first step release switch S1 is operated (STEP 120). When a user presses the shutter release to take a photograph of an object, the first step release switch S1 is operated and a corresponding electric signal is inputted to the microcontroller 40.

The microcontroller 40 checks the voltage condition and the charging condition of a strobe, or flash unit, not shown (STEP 130) and measures the sensitivity of the film loaded in the camera. The film sensitivity sensor 30 senses the sensitivity of the film and sends an electric signal corresponding to the sensitivity of the film to the microcontroller 40 (STEP 140).

- 7 The microcontroller 40 produces (STEP 140) the driving signal OUT of high level to low level and drives the brightness measuring circuit 20 to measure the ambient brightness around the object after finishing the above step (STEP 150). Then, the microcontroller 40 counts the time until the high level signal is produced from the brightness measuring circuit 20 by operating the internal timer.

The high level driving signal OUT produced from the microcontroller 40 is applied to the base terminal of the transistor T2 of the brightness measuring circuit 20, and the transistor T2 turns ON. When the transistor T2 turns ON, the electric potential at the collector of transistor T2 goes low, and the low signal is applied to the bases of the transistors Tl and T3. The transistor T1 turns ON, and the transistor T3 turns OFF.

The brightness measuring circuit 20 measures the ambient brightness around the object when the transistor T1 turns ON and power is applied to the light receiving element Cds. The resistors R1 and R2 divide the voltage applied to the brightness measuring circuit 20 and, thus, determine a reference voltage applied to the inverting terminal of the comparator IC1.

The voltage applied through the transistor T1 is charged by the capacitor C2 in accordance with the resistance value of the light receiving element Cds. The resistance value of the light receiving element Cds varies in accordance with the ambient brightness around the object. The charging speed of the - a - capacitor C2 varies in accordance with the resistance value of the light receiving element Cds.

When the voltage applied to the noninverting terminal of the comparator IC1 is higher than the voltage applied to the inverting terminal of the comparator IC1 because of an increase in the charging voltage of the capacitor C2, the output of the comparator IC1 changes from a low level to a high level. This output is then sent to the microcontroller 40 (STEP 160).

The microcontroller 40 reads the count number of the internal timer and determines the brightness condition of the object when the high level signal appears on the IN terminal of the brightness measuring circuit 20. The microcontroller 40 determines that the brightness of the object is too high when the read count number is under a first predetermined value and is too low when the read count number is greater than a second predetermined value. The microcontroller 40 determines that the brightness is high when the count number is less than eight and low when the count number is more than eighty.

FIG. 3 shows the charging speed of the capacitor C2 under different light conditions A, B, and C. Curve A indicates the high brightness, while curve C indicates the low brightness in accordance with the charging speed of the capacitor as varied by the ambient brightness around the object. Curve B indicates a brightness between A and C.

If the brightness is too low (STEP 170), the microcontroller 40 warns the user by driving the information display 70 (STEP 180 to STEP 190). The microcontroller 40 also sets the 9 - 1 shutter speed to the minimum or slowest speed. If the brightness is too high (STEP 200), the microcontroller 40 sets the shutter speed to the maximum or fastest speed (STEP 210).

The microcontroller 40 determines the shutter speed (STEP 220) by driving the automatic exposure program in accordance with the measured count number when the measured count number is between the first and second predetermined values, and therefore, the brightness is neither too low nor too high.

The microcontroller 40 measures the distance between the camera and the object by driving the automatic distance measuring circuit 10 after determining the shutter speed in accordance with the brightness of the object. The microcontroller 40 then performs an automatic distance calculation (STEP 230 to STEP 240) in accordance with the measured distance.

After performing the automatic distance calculation, the microcontroller 40 determines (STEP 250) if the second step release switch 82 is operated and determines (STEP 260) when a predetermined time passes during which the second step release switch 52 is not operated. If the predetermined time passes, the microcontroller 40 returns to STEP 150. At STEP 150, the microcontroller 40 drives the brightness measuring circuit 20 to measure the brightness.

Thus, if the object changes position or the camera changes position, the microcontroller 40 calculates a new exmosure value. If the lighting changes between the first and second step release, a new exposure value is also calculated. The microcontroller 40 calculates exposure values on the basis of the - brightness value measured just before the second step release switch 82 is operated after measuring successively the ambient brightness around the object when the second step release switch S2 is not operated for the predetermined time.

The microcontroller 40 takes the photograph of the object when the second step release switch is operated (STEP 270). The microcontroller 40 controls the shutter 50 in accordance with the exposure value determined in STEP 220. After exposing a cut of film, the microcontroller 40 advances the film by driving the motor actuator 60 and finishes all the steps (STEP 280 to STEP 290).

The second step release switch is operated by pressing the shutter and measuring the ambient brightness around the object. The ambient brightness around the object is successively measured when the second step release switch is not operated for the predetermined time, thereby obtaining a photograph having a suitable exposure in accordance with the brightness change of the object due to changing the position of the object or the composition of the camera before the second step release switch S2 is operated.

The present invention has been described in terms of a still picture camera. However, the present invention may be used in other devices which measure the brightness around a moving object or in changing light conditions. For example, the present invention may be used in an optical measuring device. Further, the present invention has a low manufacturing price and a high reliability.

Although only a preferred embodiment and select modifications of the invention have been disclosed and described, it is apparent that other embodiments and modifications of the invention are possible within the scope of the appended claims.

12 - 9 C-LAIM5, 1. A successive brightness measuring device for a camera comprising: first and second step release switches operated by a user; means for successively measuring an ambient brightness around an object at every predetermined time interval when said second step release switch is not operated for a predetermined time after said first step release switch is operated; and means for calculating an exposure value in accordance with a brightness amount measured finally when said second step release switch is operated.

2. The device according to claim 1, further comprising: means for measuring a distance between the camera and the object; means for sensing the sensitivity of a film mounted on the camera; means for exposing the film mounted on the camera; means for transferring a photographed film; means for warning the user that said measured brightness amount is too low when the ambient brightness around the object is low.

3. The device according to claim 2, wherein said sensing means senses the film sensitivity; and said measuring means measures the distance when the first step release switch is operated, 13 - further, comprising means for setting a shutter speed to be the minimum when the ambient br..;ightness around the object is too low and the maximum when the ai-bient brightness around the object is too high, wherein said calculating means determines the exposure value according to a measured distance from the object and the measured brightness amount when the arbient brightness is neither too low nor too high, and further, comprising means for photographing the object by operating a shutter according to determined exposure value when the second step release switch is operated.

4. The device according to claim 3, wherein said means for successively measuring an ambient brightness includes means for measuring an elapsed time and determining if the ambient brightness around the object is too low or too high based on the elapsed time.

5. A method for successively measuring brightness for a camera having first and second step release switches, comprising the steps of: measuring an ambient brightness around an object when the first step release switch is operated; determining whether a predetermined time has elapsed after the first step release switch was operated while the second step release switch is not operated; - 14 successively measuring the ambient brightness around the object at every predetermined time interval based on the result of said determination; and calculating an exposure value in accordance with a brightness amount measured finally before the second step release switch is operated.

6. The method according to claim 5, further comprising the steps of: sensing the sensitivity of a film mounted on the camera and measuring a distance from the object when the first step release switch is operated; determining a shutter speed to be the minimum when the ambient brightness around the object is too low and the maximum when the brightness around the object is too high and the exposure value according to the measured brightness amount when the brightness is neither too low nor too high; and taking a photograph at the determined exposure value.

7. An exposure value determination device for an image recorder, comprising: means for recording an image of an object; a light meter for measuring light at the object; means for actuating the means for recording an image; and means for actuating the light meter; wherein the means for actuating the light meter actuates the light meter at set time intervals to measure the light at the object; and A wherein the light meter may be actuated a plurality of times between the time when the light meter is first actuated to measure the light at the object and when the means for recording an image is actuated to record the image of the object.

A i.

8. The device according to claim 7, wherein the means for recording an image is a light sensitive medium and the means for actuating the means for recording an image is a shutter.

9. The device according to claim 8, wherein the shutter speed is determined in accordance with the last light measurement made by the light meter before the shutter is actuated.

10. The device according to claim 8, wherein the shutter speed is determined in accordance with an average of the light measurements made between the time when the light meter is first actuated to record the image of the object and the time when the shutter is actuated.

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