JP2009111743A - Exposure control device and imaging apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an exposure control device and imaging apparatus capable of suppressing a hunching phenomenon of brightness in live view display. <P>SOLUTION: An exposure control device includes: an imaging device 136 for receiving luminous flux passed through an optical system 210; a detection means 173 for detecting the quantity of light received by the imaging device; an calculation means 174 which iteratively obtains an exposure value for the imaging device; and a control means 175 which determines an exposure control value for the imaging device based on a latest exposure value EVn obtained by the calculation means, and determines the exposure control value based on an exposure value EVn-1 obtained in the past when an absolute value of a difference between the latest exposure value EVn and the exposure value EVn-1 obtained in the past is equal to or less than a predetermined value K. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

The present invention relates to an exposure control device and an imaging device.

  A single-lens reflex camera having a live view display function (also referred to as a through image display function or an electronic viewfinder function) is known (see Patent Document 1).

JP 2007-189481 A

  However, since the exposure value of the conventional live view display is repeatedly calculated based on the amount of light received by the image sensor, there is a problem that a brightness hunting phenomenon occurs.

  The problem to be solved by the present invention is to provide an exposure control device and an imaging device capable of suppressing the brightness hunting phenomenon in live view display.

  The present invention solves the above problems by the following means. In addition, although the code | symbol corresponding to drawing which shows embodiment of this invention is attached | subjected and demonstrated, this code | symbol is only for making an understanding of this invention easy, and is not the meaning which limits this invention.

  [1] An exposure control apparatus according to the present invention includes an image sensor (136) that receives a light beam that has passed through an optical system (210), a detection means (173) that detects the amount of light received by the image sensor, and a detection means. Based on the amount of received light detected by the calculation means (174) for repeatedly calculating the exposure value for the image sensor, and determining the exposure control value for the image sensor based on the latest exposure value (EVn) obtained by the calculation means. When the absolute value of the difference between the latest exposure value (EVn) and the exposure value (EVn-1) obtained in the past is equal to or smaller than the predetermined value (K), the exposure value (EVn-1) obtained in the past is set. And a control means (175) for determining an exposure control value on the basis thereof.

  In the exposure control apparatus according to the above invention, the control means (175) controls at least one of the aperture stop (AV) of the optical system and the exposure time (TV) of the image sensor based on the exposure control value. The calculation resolution by the means (174) can be configured to be finer than the control resolution of the aperture stop or exposure time by the control means (175).

  In this case, the aperture stop and the exposure time control resolution can be made equal.

  In the exposure control apparatus according to the above invention, the predetermined value (K) can be set as the control resolution.

  [2] An imaging apparatus according to the present invention includes the exposure control apparatus according to the above invention.

  In this case, it can comprise so that the display means (140) which displays the image imaged by the image pick-up element (136) may be provided.

  Further, the calculating means (174) can be configured to obtain the exposure value (EV) based on the distribution of received light amount by the detecting means (173).

  According to the present invention, it is possible to suppress the brightness hunting phenomenon in live view display.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings.

  FIG. 1 is a block diagram showing a camera according to an embodiment of the present invention.

  The camera 1 according to this embodiment includes a camera body 100 and a lens barrel 200 that is detachably attached to the camera body 100.

  The lens barrel 200 includes a lens group 210 including a focus lens 211 that can move along the optical axis L1, a diaphragm mechanism 220 that restricts the light beam, and a lens drive motor that moves the focus lens 211 along the optical axis L1. 230 and a diaphragm driving unit 240 that controls the aperture diaphragm of the diaphragm mechanism 220 are provided.

  Although the specific configuration of the moving mechanism along the optical axis L1 of the focus lens 211 is not particularly limited, as an example, a rotating cylinder is rotatably inserted into a fixed cylinder fixed to the lens barrel 200, and the inner periphery of the rotating cylinder A helicoid groove (spiral groove) is formed on the surface, and an end of a lens frame for fixing the focus lens 211 is fitted into the helicoid groove. Then, by rotating the rotating cylinder by the lens driving motor 230, the focus lens fixed to the lens frame moves linearly along the optical axis L1.

  The focus lens 211 fixed to the lens frame by rotating the rotating cylinder with respect to the lens barrel 200 moves straight in the direction of the optical axis L1, and a lens driving motor (actuator) 230 as a driving source thereof is used. The lens barrel 200 is provided. The lens driving motor 230 and the rotating cylinder are connected by a transmission composed of a plurality of gears, for example, and when the driving shaft of the lens driving motor 230 is driven to rotate in any one direction, it is transmitted to the rotating cylinder at a predetermined gear ratio, and When the rotating cylinder rotates in any one direction, the focus lens 211 fixed to the lens frame moves straight in any direction of the optical axis L1. When the drive shaft of the lens drive motor 230 is rotationally driven in the reverse direction, the plurality of gears constituting the transmission also rotate in the reverse direction, and the focus lens 211 moves straight in the reverse direction of the optical axis L1.

  The focus lens 211 moves in the direction of the optical axis L1 from the end portion (also referred to as the closest end) on the camera body 100 side to the end portion (also referred to as the infinite end) on the subject side by the rotation of the rotating cylinder described above. This movement is controlled by a command from the lens drive control unit of the camera body 100.

  The diaphragm mechanism 220 restricts the light flux that passes through the lens group 210 and reaches the image sensor 110, the in-finder image sensor 136, and the finder 134 of the camera body 100. The diaphragm driver 240 adjusts the aperture diaphragm. The aperture driving unit 240 is driven by a control signal from a control device 170 of the camera body 100 described later.

  The camera body 100 is provided with an image sensor 110 composed of a two-dimensional CCD image sensor, MOS sensor, CID, or the like, and an electric image signal photoelectrically converted by the image sensor 110 is stored in a memory (not shown).

  On the front surface of the image sensor 110, a half mirror 121 that can rotate by a predetermined angle and a total reflection mirror 122 that rotates together with the half mirror 121 are provided. The half mirror 121 and the total reflection mirror 122 are in a position shown by a solid line in an autofocus mode in which an automatic focusing operation is performed. Then, the subject image is formed on the imaging device 110 and exposure is performed.

  The camera body 100 is provided with an autofocus module 161 (hereinafter also referred to as an AF module) for performing automatic focusing adjustment. In the autofocus mode, the half mirror 121 and the total reflection mirror 122 are positioned at the positions indicated by solid lines in the figure, so that the light flux from the subject is guided to the half mirror 121 through the focus lens 211, and one of them. The part passes through the half mirror 121 and is input to the AF module 161 along the optical axis L4 by the total reflection mirror 122. In the AF module 161, automatic focusing control by a phase difference detection method using subject light is executed.

  The AF-CCD control unit 162 controls the gain and accumulation time of the line sensor of the AF module 161 in the autofocus mode. The AF-CCD control unit 162 receives information on the focus detection area selected as the focus detection position from the control device 170. A pair of output patterns detected by the pair of line sensors corresponding to the focus detection area are read and output to the defocus calculation unit 162.

  The defocus calculation unit 162 calculates a deviation amount (defocus amount) of the output pattern from the pair of output patterns sent from the AF-CCD control unit 162, and outputs this to the lens drive amount calculation unit 164.

  Based on the defocus amount sent from the defocus calculation unit 163, the lens drive amount calculation unit 164 calculates a lens drive amount for making the defocus amount zero, and supplies this to the lens drive control unit 165. Output.

  The lens drive control unit 165 sends a drive command to the lens drive motor 230 while taking in the lens drive amount sent from the lens drive amount calculation unit 164, and moves the focus lens 211 by the lens drive amount.

  On the other hand, part of the subject light reflected by the half mirror 121 is guided to the pentaprism 132 through the finder screen 131 disposed on a surface optically equivalent to the image sensor 110, and bent by the pentaprism 132. After that, it passes through the eyepiece 133 along the optical axis L2 and is guided to the photographer's eyeball. As a result, the subject and its background can be observed through the finder 134 in a state where the release is not performed.

  In addition, a lens 135 and an in-finder image pickup device 136 are provided in the vicinity of the eyepiece 133, and part of the subject light reflected by the half mirror 121 is imaged on the finder screen 131 and then guided to the pentaprism 132. After being bent by the pentaprism 132, the light is guided to the in-finder image pickup device 136 along the optical axis L3.

  The in-finder image pickup device 136 is constituted by a two-dimensional color CCD image sensor, a MOS sensor, a CID, or the like, and detects a light amount such as a subject luminance value when calculating an exposure value of a photographed image, and also displays a live view in this example Get image information for. Image information detected by the in-viewfinder image sensor 136 is output to a control device 170 described later, and is used for automatic exposure control and live view display control.

  The viewfinder screen 131, the pentaprism 132, the eyepiece 133, the lens 135, and the in-finder image pickup device 136 are also referred to as an observation optical system 130.

  The operation unit 150 is a switch for the user to perform auto focus mode and other shooting mode settings, area selection in each mode, and the like. Selection of the live view display of this example is also performed by operating the operation unit 150.

  On the back surface of the camera body 100, a display unit 140 including a liquid crystal display and a driving circuit thereof is provided. In addition to the live view display by the above-described in-finder image pickup device 136, an input screen by the operation unit 150 is also displayed. The

  FIG. 2 is a block diagram showing an exposure control apparatus according to the present embodiment.

  The exposure control device of this example is included as a part of the control device 170 shown in FIG. 1, and power supply to the in-finder image pickup device 136 is turned on / off, image pickup timing control, gain adjustment of AD conversion signal, AD conversion, etc. And an image processing unit 172 that performs color correction, contrast correction, and other processing on the image information captured by the in-finder image sensor 136 and outputs the processed information to the display unit 140.

  Further, the exposure control apparatus of this example includes a received light amount detection unit 173, an exposure value calculation unit 174, and a control unit 175.

  The received light amount detection unit 173 detects the received light amount of the light beam received by the in-finder image sensor 136 at predetermined time intervals, divides the light receiving area of the in-finder image sensor 136 into several areas, The distribution of the amount of received light is detected. The amount of received light detected here is output to the exposure calculation unit 174 as a luminance value.

  The exposure calculation unit 174 repeatedly calculates an exposure value at predetermined time intervals based on the luminance value distribution of each region sent from the received light amount detection unit 173, and outputs this to the control unit 175.

  In this example, when calculating the exposure value, an appropriate exposure value is calculated based on the distribution of luminance values of each divided area of the in-finder image sensor 136, distance information to the subject, and other shooting information. To do.

  The control unit 175 determines an exposure control value for the in-finder image sensor 136 based on the exposure value obtained by the exposure value calculation unit 174.

  Here, the exposure value EV correlates with the exposure time TV (shutter speed) of the in-viewfinder image pickup device 136 and the aperture stop AV of the aperture mechanism 220, and the relationship EV = TV + AV is generally established. If the brightness value BV of the light beam and the sensitivity SV of the in-finder image pickup device 136 are assumed, the relationship EV = BV + SV is also established.

  Therefore, based on the exposure value EV calculated by the exposure value calculation unit 174, the exposure time TV of the in-viewfinder image sensor 136 and the aperture stop AV of the stop mechanism 220 are determined. Since the exposure time TV of the in-viewfinder image pickup device 136 is controlled by the image pickup device driving unit 171, the exposure time TV is converted into a control value in the image pickup device driving unit 171. Since the aperture stop AV of the aperture mechanism 220 is controlled by the aperture drive unit 240, the aperture stop AV is converted into a control value of the aperture drive unit 240. These exposure time and aperture stop control values are collectively referred to as exposure control values.

  The exposure time control value is output to the image sensor driving unit 171 and the aperture stop control value is output to the aperture driving unit 240.

  Note that one of the exposure time TV of the in-viewfinder image pickup device 136 and the aperture stop AV of the stop mechanism 220 can be determined based on the exposure value EV.

  The control unit 175 of this example temporarily stores the exposure value that is repeatedly calculated and sent, and when determining the exposure control value based on the latest exposure value, the latest exposure value and the past, for example, the previous time When the absolute value of the difference is equal to or less than the predetermined value K, the exposure control value is determined based on the previous exposure value instead of the latest exposure value. On the other hand, when the absolute value of the difference between the latest exposure value and the previous exposure value exceeds a predetermined value K, the exposure control value is determined based on the latest exposure value.

  FIG. 3 is a diagram showing the relationship between the exposure value calculation resolution and the aperture stop control resolution according to this example, the left shows the exposure value calculation resolution calculated by the exposure value calculation unit 174, and the right shows the aperture The control resolution of the aperture stop in the mechanism 220 is shown.

  In the example shown in the figure, the aperture stop control resolution in the stop mechanism 220 is 1/6 step, whereas the exposure value calculation resolution obtained based on the brightness value detected by the received light amount detection unit 173. Is a 1/24 step increment. Although not shown, the exposure resolution control resolution of the in-finder image sensor 136 is also larger (rougher) than the 1/24 step increment, which is the exposure value calculation resolution.

  As described above, when the calculation resolution of the exposure value is smaller than the control resolution of the aperture stop or the control resolution of the exposure time, the following problem occurs. That is, as shown in the figure, if the exposure value calculated last time (past) is M9 and the exposure value calculated this time (latest) is M8, the change amount of the exposure value itself is only M1 ( Despite being 1 / 24th), the aperture stop control value changes from F3 to F2 by 1 / 6th. When the next exposure value becomes M9 again, the aperture stop control value returns to F3 again, and when this is repeated, a hunting phenomenon occurs in the brightness of the live view image displayed on the display unit 140.

  Further, as shown in the figure, the aperture stop control value remains F3 even when the exposure value changes by 3/24 steps (1/8 step) from M9 to M12, and the exposure value changes from M9 to M8. Compared with the case, the change of the aperture stop becomes smaller, which is unnatural.

  Therefore, in the present embodiment, when the calculation resolution of the exposure value is finer than the control resolution of the exposure control value, the latest control value is determined when determining the exposure control value based on the latest exposure value as described above. When the absolute value of the difference is equal to or less than a predetermined value, the exposure control value is determined based on the previous exposure value instead of the latest exposure value.

  Here, the predetermined value K that is a threshold value of the absolute value of the difference between the latest exposure value and the previous exposure value is not particularly limited, but is preferably a resolution of the exposure control value. If the predetermined value K is the resolution of the exposure control value, the occurrence of the hunting phenomenon can be suppressed, and the change rate of the exposure control value with respect to the change rate of the exposure value becomes equal, so that the live view display becomes natural. However, the predetermined value K may be smaller than the exposure control value resolution and larger than the exposure value calculation resolution.

  Although not particularly limited, it is desirable that the control resolution of the aperture stop is equal to the control resolution of the exposure time. By making the control resolution of the aperture stop equal to the control resolution of the exposure time, the control in the control unit 175 and the like is simplified. Further, as described above, it is desirable that the predetermined value K, which is the threshold value of the absolute value of the difference between the latest exposure value and the previous exposure value, be the control resolution of the exposure control value. By setting the time control resolutions equal to each other and setting them to a predetermined value K, the effect of suppressing the occurrence of the hunting phenomenon and the naturalness of the live view display become more effective.

  Next, the operation of the exposure control apparatus according to this embodiment will be described.

  FIG. 4 is a flowchart showing a control flow of the exposure control apparatus according to the present embodiment. Here, exposure control in the case where the live view display mode is selected and an image captured by the in-finder image sensor 136 is displayed on the display unit 140 will be described.

  First, in steps S <b> 101 and S <b> 102, split light metering (multi-pattern metering) of the in-finder image sensor 136 is performed by the received light amount detection unit 173. As described above, the in-finder image sensor 136 is divided into several areas, the distribution of luminance values in each area is detected and output to the exposure value calculator 174.

  In step S <b> 103, the latest exposure value EVn is calculated by the exposure value calculation unit 174 and output to the control unit 175.

  In step S104, the absolute value of the difference between the latest exposure value EVn calculated in step S103 and the exposure value EVn-1 calculated in the previous routine is calculated, and it is determined whether this is equal to or less than a predetermined value K.

  If the absolute value of the difference between the latest exposure value EVn and the previous exposure value EVn-1 exceeds the predetermined value K as a result of the determination in step S104, the process proceeds to step S105, and exposure control is performed based on the latest exposure value EVn. Determine the value. On the other hand, if the absolute value of the difference between the latest exposure value EVn and the previous exposure value EVn-1 is equal to or smaller than the predetermined value K, the process proceeds to step S106, and the exposure control value is set based on the previous exposure value EVn. decide.

  In step S107, the aperture stop control value determined in step S105 or S106 is output to the aperture drive unit 240, and the exposure time control value is output to the image sensor drive unit 171.

  As a result, the aperture stop of the aperture mechanism 240 is controlled by the control value of the aperture stop, and the exposure time of the in-finder image pickup device 136 is controlled by the control value of the exposure time.

  By executing the above processing at predetermined time intervals, a live view display with a natural brightness and no hunting phenomenon can be obtained.

  In the above-described embodiment, the absolute value of the difference between the latest exposure value and the previous exposure value is compared with the predetermined value K in step S104 of FIG. 4, but the exposure before the previous time is used instead of the previous exposure value. The absolute value of the difference from the value can also be used as a comparison target.

It is a block diagram which shows the camera which concerns on embodiment of this invention. It is a block diagram which shows the exposure control apparatus which concerns on embodiment of this invention. It is a figure which shows the relationship between the calculation resolution of the exposure value which concerns on embodiment of this invention, and the control resolution of an aperture stop. It is a flowchart which shows the control flow of the exposure control apparatus which concerns on embodiment of this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 100 ... Camera body 110 ... Image sensor 121 ... Half mirror 130 ... Observation optical system 131 ... Viewfinder screen 136 ... Image sensor in finder 140 ... Display part 170 ... Control apparatus 171 ... Image sensor drive part 172 ... Image processing part 173 ... Light reception amount Detection unit 174 ... Exposure value calculation unit 175 ... Control unit 200 ... Lens barrel 220 ... Aperture stop 240 ... Aperture drive unit

Claims (7)

An image sensor that receives the light beam that has passed through the optical system;
Detecting means for detecting the amount of light received by the image sensor;
An arithmetic means for repeatedly obtaining an exposure value for the image sensor based on the amount of received light detected by the detection means;
When an exposure control value for the image sensor is determined based on the latest exposure value obtained by the computing means, and the absolute value of the difference between the latest exposure value and the exposure value obtained in the past is less than or equal to a predetermined value Comprises a control means for determining the exposure control value based on the exposure value obtained in the past. The exposure control device according to claim 1,
The control means controls at least one of an aperture stop of the optical system and an exposure time of the image sensor based on the exposure control value,
An exposure control apparatus characterized in that a calculation resolution by the calculation means is finer than a control resolution of the aperture stop or exposure time by the control means. The exposure control device according to claim 2, wherein
An exposure control apparatus characterized in that the aperture diaphragm and the exposure time have the same control resolution. In the exposure control device according to any one of claims 1 to 3,
The exposure control apparatus, wherein the predetermined value is the control resolution. An imaging apparatus comprising the exposure control apparatus according to claim 1. The imaging apparatus according to claim 5,
An image pickup apparatus comprising: a display unit that displays an image picked up by the image pickup element. In the imaging device according to claim 5 or 6,
The imaging device is characterized in that the calculation means obtains the exposure value based on a distribution of the amount of received light by the detection means.

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