JP2003029137A - Automatic focusing detector - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an automatic focusing detector which secures a focus detection accuracy to enable acquisition of an object image, in optimal focusing state at all times. SOLUTION: The automatic focusing detector is provided with a focal length detection means 34 which detects the focal length of a photographic optical system 11, a photometric means 40 which detects the luminance of an object, a distance measurement region setting means (system controller 38) which sets the size of a distance measurement region in a photographic image on the basis of the output of the focal length detection means and the output of the photometric means, and a focusing state detection means 23 which detects the focusing state, on the basis of an image signal corresponding to the range of the range of the distance measurement area.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an automatic focus detection device, and more particularly to automatically detecting the focus state of a subject image in order to optimally form the subject image desired to be photographed on a predetermined image pickup surface. The present invention relates to an automatic focus detection device.

[0002]

2. Description of the Related Art Conventionally, an image pickup apparatus having an automatic focus detection device for automatically detecting a focus state of a subject image in order to form a desired subject image on a predetermined image pickup surface in an optimum state. Thus, for example, so-called electronic cameras and the like configured to acquire and record electronic images are widely used.

In such a conventional image pickup apparatus, as a photographing optical system for forming a desired subject image on a predetermined image pickup surface, the focal length can be freely set continuously or stepwise within a predetermined range. A variable power optical system provided with a variable power mechanism for enabling change, that is, a so-called zoom lens system is generally used.

When performing a photographing operation using the conventional image pickup device having the automatic focus detection device and the variable power optical system, a desired subject image is first formed in an optimum state on a predetermined image pickup surface. The causing operation, that is, the automatic focus detection operation is usually performed by the automatic focus detection device.

In this case, the automatic focus detection device is
CCD (C as means for detecting the focus state of the subject image
The image pickup device includes a harge coupled device) type image pickup device and the like, and is configured to detect the focus state of the subject image based on the output signal of the image pickup device.

Specifically, for example, a so-called hill-climbing method for extracting the high-frequency component of the output signal in a predetermined area of the output signal of the image pickup device, that is, the distance measurement area and detecting the position where the optimum focus state is achieved. Means for performing a passive focus detection operation have been generally put into practical use.

An image pickup apparatus having a variable power optical system as a photographing optical system is provided with a focal length detecting means such as an encoder for detecting the focal length of the photographing optical system, and based on the detection result of this focal length detecting means. Various means for changing the size of the distance measuring area in the photographing screen have been proposed and generally put into practical use.

For example, an automatic focus detection device disclosed in Japanese Patent Laid-Open No. 63-66519 detects a distance to a subject or a focus state of a subject image and a focal length of a variable power optical system. And a detection unit, and after setting a distance measuring area of a predetermined size based on the focal length of the variable power optical system detected by the latter detection unit, the focus detection operation is performed using the former detection unit. It is configured to include a display unit that displays the size of the set distance measurement area while performing the operation.

Further, the automatic focus detection device disclosed in Japanese Patent No. 2575607 discloses a detection means for detecting a focus state of a subject image, a detection means for detecting a focal length of a photographing optical system, and a distance measuring area. And a range-finding area control unit for changing the size in a plurality of steps, and the range-finding area control unit is operated in response to an instruction signal for instructing the start of the focus detection operation, and the detected focal length of the variable magnification optical system is set. A predetermined changing process is performed to make the corresponding distance measurement area have an appropriate size.

[0010]

By the way, in a variable power optical system, in general, the longer the focal length, the larger the numerical aperture of the optical system (F value; f-number). is there. That is, the longer the focal length, the darker the brightness of the optical system tends to be.

Therefore, the magnified image formed when the variable power optical system is set to the long focal length side is an unnecessary signal as compared with the subject image of the same brightness when it is set to the short focal length side. There is a tendency that many noise components are generated.

Generally, in a passive type automatic focus detection device, if a noise component is mixed in when a high frequency component is detected, there is a problem that the probability of erroneous detection increases.

Also, regardless of the focal length of the photographic optical system, even when the subject brightness is low, the noise component tends to increase, and the same erroneous detection problem occurs.

However, the above-mentioned Japanese Laid-Open Patent Publication No. 63-66519.
The means disclosed in Japanese Patent Publication No. 2575607 and the like only change the size of the distance measurement area based on the focal length of the variable power optical system, and the subject brightness is low. In such cases, the erroneous detection of the focus detection operation caused by the noise component included in the acquired signal is not considered.

The present invention has been made in view of the above-mentioned points, and an object thereof is to set focus detection by setting the size of the distance measuring area in consideration of the brightness of the subject to be photographed. An object of the present invention is to provide an automatic focus detection device capable of further improving focus detection accuracy by performing an operation and always obtaining a subject image in an optimum focus state.

[0016]

In order to achieve the above object, an automatic focus detection device according to a first aspect of the present invention comprises a focal length detection means for detecting the focal length of a photographing optical system and photometry for detecting the brightness of an object. Means, distance measuring area setting means for setting the size of the distance measuring area in the photographing screen based on the output of the focal length detecting means and the output of the photometric means, and corresponding to the range of the distance measuring area. And a focus state detecting means for detecting the focus state based on the image signal.

According to a second aspect of the present invention, in the automatic focus detection device according to the first aspect of the present invention, the distance measuring area setting means sets a distance measuring area wider when the subject brightness is low than when it is high brightness. Is characterized by.

A third invention is characterized in that the automatic focus detection device according to any one of the first invention and the second invention further comprises display means for displaying a distance measuring area. To do.

A fourth aspect of the invention is the automatic focus detection device according to any one of the first, second, or third aspects of the invention, in which a read-only memory in which a plurality of distance measuring area information is stored in advance. Further, the distance measuring area setting means reads the distance measuring area information according to the output of the focal length detecting means and the output of the photometric means from the read-only memory and sets the distance measuring area information.

[0020]

BEST MODE FOR CARRYING OUT THE INVENTION The present invention will be described below with reference to the illustrated embodiments. The automatic focus detection device of the present invention is, for example, a so-called electronic camera or other image pickup device (hereinafter referred to as an electronic camera) capable of acquiring and recording an electronic image, or a photograph for recording an optical image on a film for photography. It is applied to devices and the like. In the following embodiments, a case where the automatic focus detection device of the present invention is applied to an electronic camera will be described as an example.

FIG. 1 is a block diagram showing the outline of the internal arrangement of an electronic camera to which an automatic focus detection device according to an embodiment of the present invention is applied.

As shown in FIG. 1, the electronic camera 1 includes a plurality of lenses for forming an optical image of an object, such as a zoom lens 11a contributing to a zooming operation and a focus lens 11b contributing to a focus adjusting operation. , A various types of members that contribute to the exposure operation, such as a photographing optical system including a plurality of lenses, a diaphragm unit (not shown) that adjusts the amount of light flux from a subject, and a lens mirror that holds these members. A photographing lens unit 11 formed of a cylinder and a zoom lens moving means for moving the zoom lens 11a of a plurality of lenses constituting the photographing lens unit 11 in a direction along the optical axis O to perform a zooming operation. A zoom motor 33 which is a part, a zoom motor drive circuit 32 which is a part of a zoom lens moving means for driving and controlling the zoom motor 33, and a photographing lens. By detecting the position of the zoom lens 11a in's unit 11, a zoom lens position sensor 34 which constitutes a part of the focal length detection means for detecting the focal length of the imaging optical system that is set at that time,
Of the plurality of lenses of the photographing lens unit 11, the focus motor 36 that constitutes a part of the focus lens moving unit that moves the focus lens 11b in the direction along the optical axis O to perform the focus adjustment operation, and the focus motor 36. With a focus motor drive circuit 35 forming a part of the focus lens moving means for drive control, a focus lens position sensor 37 for detecting the position of the focus lens 11b in the taking lens unit 11, and a plurality of lenses of the taking lens unit 11. An image pickup element 12 such as a CCD, which is a part of an image pickup means for converting an imaged optical object image into an electric signal to generate an image signal of a predetermined form, and an image acquired by the image pickup element 12. An electric circuit that performs predetermined signal processing on a signal And an A / D conversion circuit 14 (simply abbreviated as A / D in FIG. 1) that receives an output signal (analog signal) from the imaging circuit 13 and converts it into a digital signal. An automatic exposure processing circuit 40 (AE processing circuit), which is a part of photometric means for receiving a signal output from the A / D conversion circuit 14 and performing a predetermined calculation that contributes to automatic exposure control to calculate a predetermined AE evaluation value. 1 is simply abbreviated as AE), and the A / D conversion circuit 14
Focus evaluation value calculation means for calculating a predetermined focus evaluation value (for example, a contrast value indicating the contrast of a subject image) by performing a predetermined calculation that contributes to the automatic focus adjustment operation by receiving the output signal from the And an automatic focus detection processing circuit 23 (AF processing circuit; simply abbreviated as AF in FIG. 1), which is a focus state detection means, and an A / D conversion circuit 14.
A built-in memory 15 which is a buffer memory such as a non-volatile memory for temporarily storing the image signal converted into a digital signal by the above, and a recording medium for recording the digital image signal stored in the built-in memory 15 as a predetermined image data file A removable memory 39, which is a nonvolatile memory or a magnetic recording medium that forms a part of the recording means, a card slot 17 in which the removable memory 39 is mounted at a predetermined position of the electronic camera 1, and the card slot 17 When the removable memory 39 is loaded in the card, the card interface section 16 (in FIG. 1, which is a part of the recording means is composed of an electric circuit such as a controller that secures an electrical connection between them and controls data). (Simply abbreviated as I / F)
And an external input / output terminal 19 to which a cable (not shown) for electrically connecting the electronic camera 1 to an external information device or the like (not shown) can be detachably arranged, and an external input / output terminal 19 The external information device includes an electric circuit or the like that secures an electrical connection between the output terminal 19 and the electronic camera 1, and outputs predetermined image data including a predetermined image signal and various image information accompanying the predetermined image signal. And an external interface (I / F) unit 18 for performing data control so as to receive an input signal from an external information device or the like connected to the external input / output terminal 19 and stored in the built-in memory 15. CRT (Cathod Ray Tube) type display device or liquid crystal display (LCD; Liquid Crystal Displa)
y) A signal in a form optimal for displaying as a video image on a display device such as a device, for example, a standard television signal (NTSC (National Television System).
(Committee) type image signal) or the like, or by reading out the image data or the like recorded in the removable memory 39 and converting it into an image signal of an optimum form for reproduction and display. A video output circuit 20 for executing various kinds of image processing and the like required when displaying an image signal as an image, and an image signal for display which is controlled by the video output circuit 20 and is generated by the video output circuit 20. A liquid crystal display (L) which is a display means for displaying an image based on the image and various image information accompanying the image data representing the image, that is, an information display means and an image display means.
Image display LCD 21 such as CD) and this image display LCD
A connection cable (not shown) for electrically connecting an external display device (not shown) different from 21 to the electronic camera 1 is detachably provided to the external display device. A video output terminal 22 capable of outputting a display image signal or the like generated by the video output circuit 20, and a power supply 26 such as a battery for supplying a predetermined electric power to various electric circuits and the like constituting the electronic camera 1. A connection cable (not shown) for electrically connecting the electronic camera 1 to another external power supply device (not shown) different from the power supply 26 is detachably arranged. External power supply input terminal 27 capable of receiving power to be input from a power supply device (not shown)
And a power supply unit 25 serving as a power supply control means for controlling the electric power input from the power supply 26 or the external power supply input terminal 27, and strobe light emission for illuminating a desired subject with auxiliary illumination light when performing a shooting operation. The unit 31 and the operation unit 28 including various operation members for performing desired operations of the electronic camera 1, and a small size capable of displaying various information within the range of the field of view observable by the optical finder unit. L
LCD 24 for displaying information in the optical viewfinder including a CD
An image processing unit 38a (hereinafter, referred to as an information display LCD 24) for controlling the entire electronic camera 1 and performing a predetermined image processing on a predetermined area inside itself.
And compressing image data at a predetermined compression ratio and outputting,
A compression / decompression unit 3 that receives the compressed image data and decompresses the image data into a form suitable for processing the image data.
8b or a read memory (ROM; R; R which stores a plurality of distance measuring area data relating to a predetermined distance measuring area size and the like).
A system controller 38 such as a central processing unit (CPU) having an OM) 38c and the like.

Although not shown in the figure, the electronic camera 1 optically images a subject or the like that the user desires to photograph, and before the photographing process is executed, the desired subject is photographed. An optical finder unit (not shown) including an observation optical system and the like for observing the included image is arranged.

The optical finder unit is constructed so that an optical image in a range substantially equivalent to an image to be obtained by executing the photographing process by the electronic camera 1 can be observed.

A display portion of the information display LCD 24 is arranged inside the optical finder unit. The display part of the information display LCD 24 is, for example, a part outside the image formation area of the optical image formed by the unit, and is arranged at a predetermined position of the upper edge and / or the lower edge of the screen frame. Has been done. Accordingly, various kinds of information regarding the photographing process, that is, information regarding the distance to the subject and the exposure state of the subject can be viewed at the same time as the optical image desired to be photographed.

Further, in the optical finder unit, a screen frame display serving as an index indicating a photographing range, a distance measuring area display indicating a target range for performing focus detection processing, and the like are displayed in a form superimposed on the optical image. Has become. Therefore, it is possible to visually check the screen frame and the index of the distance measurement area at the same time as the optical image desired to be photographed. In addition, as display means such as screen frame display and distance measurement area display,
For example, the information display LCD 24 is used.

To this end, the information display LCD 24 is provided with a display section for displaying various kinds of information at a position deviated from the optical image forming area as described above, and, for example, in the optical image forming area, A display unit such as a transmissive liquid crystal panel is provided.

On the other hand, a specific example of the above-mentioned operation unit 28 is as follows. That is, (1) a switch for generating an instruction signal for starting execution of a photometry operation, a distance measurement operation, and a focus adjustment operation and an operation member interlocked with the switch, that is, a first release switch (1ST-S).
W) and first release operating member (1S
T release operation member), (2) switch for generating an instruction signal (release signal) for starting an exposure operation and an operation member interlocked with the switch, that is, a second release switch (abbreviated as 2ND-SW) and a second release. Operation member (abbreviated as 2ND release operation member),
(3) A zoom switch for generating a scaling instruction signal for moving the zoom lens 11a in the direction along the optical axis O to instruct execution of the scaling operation, and an operation member (magnification instruction operation member) interlocked with the zoom switch. (4) A switch as an operation mode switching means for switching the operation mode of the electronic camera 1 and an operation member (operation mode switching member) interlocked with the switch,
(5) A switch as a power source switching unit for switching the power source state of the electronic camera 1 and an operation member (power source switching member) interlocked with the switch.

The operation of the electronic camera provided with the automatic focus detection device of this embodiment having the above-described structure will be described in detail below.

FIG. 2 shows a range of an image forming area of an optical image that can be observed in the viewfinder unit of the electronic camera according to the present embodiment and a size of the distance measuring area displayed within the range of the image forming area. FIG. 6 is a diagram conceptually illustrating a state in which the brightness changes according to the brightness of a subject.

In a normal state in which power is supplied to the electronic camera 1, an image forming area 24x (x = a.b.multidot.b) in the observation field of view of a finder unit (not shown).
c / d) is set. A distance measuring area 41x (x = a.b.c.d .; a hatched area in FIG. 2) is located at a predetermined position in a substantially central portion of the image forming area 24x. Has been set. Then, an index indicating the distance measuring area 41x is displayed so as to be visible in a form superimposed on the optical image observed by the finder unit.

For example, immediately after the electronic camera 1 is started, the distance measuring area 41a is set. The size of the distance measuring area 41a is, for example, the size when the subject brightness (AE evaluation value) is sufficiently high and the focal length of the zoom lens 11a is set to the widest angle end. In the electronic camera 1, the size of the distance measuring area 41a is preset as a reference size (size).

In this state, when the user arbitrarily operates the zooming instruction operating member of the operating portion 28, the zooming operation is executed and the zoom lens 11a moves in the direction along the optical axis O, A desired focal length will be set.
Such an operation is called a zoom operation.

When this zoom operation (see reference numeral Z1 in FIG. 2) is performed, the focal length of the zoom lens 11a is displaced from the wide angle side to the telephoto side. Along with this, the imaging region 24a
At the same time as the optical image displayed inside is enlarged, the distance measuring area 41a displayed in the substantially central portion of the image forming area 24a.
Changes to the state shown by the distance measuring area 41b shown in the image forming area 24b (see the alternate long and short dash line A1 in FIG. 2).

Further, as described above, in a state where the distance measuring area 41a is set as in the state immediately after the electronic camera 1 is activated, as a result of the photometric processing by the predetermined means, the area is within the image forming area 24a. When the brightness (AE evaluation value) of the formed subject image is lower than a predetermined reference value, that is, when the environment including the subject is dark, it is displayed in the substantially central portion of the image forming area 24a. The distance measuring area 41a is the image forming area 24.
The state changes to the state shown by the distance measuring area 41c shown in c (see the chain line B1 in FIG. 2).

Further, in this state, that is, the brightness of the subject image (A
When the zoom operation (see reference numeral Z2) is performed in a state where the environment including the subject is dark, the distance measurement area 41c displayed in the substantially central portion of the image formation area 24c is Distance measuring area 41 shown in the imaging area 24d
The state changes to d (see the alternate long and short dash line A2 in FIG. 2).

Further, as described above, in the state where the subject brightness (AE evaluation value) is sufficiently high and the focal length of the zoom lens 11a is set to the telephoto side,
As a result of the predetermined photometric processing, when the subject brightness (AE evaluation value) within the range of the image formation region 24b is lower than the predetermined reference value and the environment including the subject is dark, the image formation region 24b is substantially centered. The distance measurement area 41b displayed in the part is the image formation area 2
4d changes to the state shown by the distance measuring area 41d (see the chain line B2 in FIG. 2).

As described above, in the electronic camera 1 equipped with the automatic focus detection device of the present embodiment, the size of the distance measuring area 41x to be set corresponds to the set focal length or the brightness of the object. , Are automatically changed based on predetermined conditions.

The predetermined condition in this case is
For example, it is as shown in FIG.

FIG. 3 shows information stored in advance in the internal ROM 38c of the system controller 38 in the electronic camera 1 of the distance measuring area preset according to the focal length of the photographing optical system and the AE evaluation value. It is a distance measurement area change table showing the relationship of size.

In FIG. 3, the values indicated by the symbols F1 to F4 indicate the focal length region of the photographing optical system (zoom lens), and the symbols E1 and E2 indicate that the AE evaluation value is brighter than a predetermined reference value. And the case of darkness, respectively. Then, each column of the table conceptually shows the size of the distance measurement area according to each condition of the set value of the focal length (focal length area) and the lightness / darkness of the AE evaluation value.

In this case, the size of the distance measuring area is set to increase stepwise as the focal length increases, and at the same focal length, A
The size of the distance measurement area is set to be larger when the E evaluation value is darker than when it is bright.

Incidentally, as shown in FIG. 3, in addition to the means for stepwise displacing the size of the distance measuring area according to the area of the focal length, an appropriate predetermined calculation is performed based on the detected focal length value, for example. Alternatively, the size of the corresponding distance measurement area may be set.

Next, the main flow of the operation of the electronic camera equipped with the automatic focus detection device of this embodiment will be described below with reference to the main flow chart of FIG.

When a desired photographing operation is started by the electronic camera 1, the user of the electronic camera 1 first operates a predetermined operation member (power source switching member) of the operation unit 28 to operate the electronic camera. The power state of the camera 1 is shifted to the open state.

Specifically, when the power supply state of the electronic camera 1 is in the closed state, the user operates the power supply switching member (not shown) of the operation unit 28. Then, the power source switching member of the operation unit 28 generates an instruction signal for turning on the power source. This power-on instruction signal is
It is transmitted to the system controller 38. In response to this, the system controller 38 controls the power source 26 or an external power source device (not shown) connected to the external power source input terminal 27 via the power source unit 25, and the power source state of each circuit in the electronic camera 1 is controlled. Executes switching control to open the switch. As a result, in each electric circuit of the electronic camera 1,
Electric power is supplied from an external power supply device or the like connected to the power supply 26 or the external power supply input terminal 27 via a cable or the like. In this way, the electronic camera 1 is activated.

When the electronic camera 1 is in the activated state, the zoom setting process is first executed in step S1. This zoom setting process is executed in the following procedure.

A user of the electronic camera 1 operates a magnification changing operation section (not shown) of the operation section 28 to form a desired image by a finder unit (not shown) of the electronic camera 1. The observation image is set so that it can be observed at a desired magnification. By carrying out this operation, the scaling operation section of the operation section 28 generates a predetermined instruction signal for instructing the scaling operation, and this scaling instruction signal is transmitted to the system controller 38. In response to this, the system controller 38 controls the zoom motor 33 via the zoom motor drive circuit 32 to drive the zoom lens 11a. As a result, the zoom lens 11a moves in the direction along the optical axis O, and a desired photographing magnification according to the operation is set.

In this case, the system controller 3
8 constantly monitors the zoom lens position sensor 34. That is, when the variable power operation section of the operation section 28 is operated as described above, the zoom lens 11a is set to a predetermined position according to the operation of the variable power operation section. The position of the zoom lens 11a is determined by the zoom lens position sensor 3
4, each time it is detected. Then, the system controller 38 always grasps the position information of the zoom lens 11a.

Based on the result of the position detecting operation by the zoom lens position sensor 34, the system controller 38
Is capable of acquiring focal length information of the taking lens unit 11 set by the position of the zoom lens 11a (details will be described later. See step S11 in FIG. 5).

Next, in step S2, the system controller 38 operates the 1ST-SW of the operation unit 28.
Check if (not shown) is in the ON state.
Here, when it is confirmed that the 1ST-SW is in the off state, the process returns to the above-mentioned step S1 and the subsequent processes are repeated. If it is confirmed that the 1ST-SW is in the ON state, the process proceeds to the next step S3.

In step S3, the system controller 38 controls the AE processing circuit 40 to execute a predetermined exposure processing (also called AE processing; simply abbreviated as AE in FIG. 4). This exposure processing is signal processing performed based on the output signal from the A / D conversion circuit 14 as described above.

That is, the AE processing circuit 40 includes the image pickup device 1
After being taken out by 2, the image data is output through the image pickup circuit 13 and the A / D conversion circuit 14 for one frame (one screen)
Image signals (output signals) are sequentially input. Upon receiving this image signal, the AE processing circuit 40 sequentially performs a predetermined exposure processing.

This exposure processing is, for example, a part of an image signal for one frame, that is, a part of an image signal representing an image of one photographic screen. The processing is performed based on the image signal corresponding to the range of the set distance measurement area, and signal processing such as cumulative addition of brightness values is performed. As a result, the AE evaluation value according to the brightness of the subject in the distance measurement area is calculated, and the calculation result is output to the system controller 38.

Subsequently, in step S4, the system controller 38 executes a ranging area setting process. This distance measurement area setting process is performed based on the AE evaluation value calculated in step S3 and the zoom position of the photographing lens unit 11 set in step S1, that is, the information on the focal distance, which is an appropriate distance measurement area. Is a process for setting. Details of the distance measurement area setting processing will be described later (see the subroutine of FIG. 5 and FIGS. 2 and 3).

Next, in step S5, the system controller 38 controls the AF processing circuit 23 to execute the AF processing. This AF processing is a focus detection and adjustment operation performed for the distance measurement area set in the processing of step S5 described above, and is a normal AF processing performed in a conventional general electronic camera or the like. It is the same process. Therefore, detailed description is omitted. Then, the process proceeds to the next step S6.

In step S6, as a result of the AF process in step S5, the system controller 38 brings the focus state of the optical image formed by the taking lens unit 11 into a focused state on the image pickup surface of the image pickup device 12. Check if it is imaged. If it is confirmed that the optical image is not in focus, the AF area is narrow because the distance measurement area is narrower than the subject brightness.
It is determined that the process has failed, and the process proceeds to step S7.

In step S7, the system controller 38 executes the ranging area changing process. The distance measuring area changing process executed here is a process of changing the setting of the distance measuring area so that the in-focus state can be reliably ensured in the next AF processing to be executed next. Specifically, the distance measurement area to be set is reset to a wider distance measurement area. After that, the process returns to the above step S5, and the subsequent processes are repeated.

On the other hand, in step S6, when the system controller 38 confirms that the in-focus state is achieved, the process proceeds to the next step S8.

In step S8, the system controller 38 reconfirms the status of the 1ST-SW in the operation unit 28. Here, if it is confirmed that the 1ST-SW is in the off state, it is determined that the predetermined 1ST release operation by the user has been canceled, the process returns to the above-mentioned step S1, and the subsequent processes are repeated. . Also,
If it is confirmed that the 1ST-SW is in the on state, the process proceeds to the next step S9.

The process in step S8 is similar to the process in step S2,
1ST-confirmed in the process of step S2 described above
This is a processing step for confirming whether the ON state of the SW is still continued after reaching the processing of step S8.

Subsequently, in step S9, the system controller 38 confirms whether or not the state of the 2ND-SW in the operation unit 28 is the ON state. Here, when it is confirmed that the 2ND-SW is in the off state, the process returns to the above step S8, and the subsequent processes are repeated. If it is confirmed that the 2ND-SW is in the ON state, the process proceeds to the next step S10.

In step S10, the system controller 38 drives and controls the image pickup device 12 to execute a predetermined photographing process. The photographing process performed here is a process of acquiring a predetermined image signal using the image sensor 12 as in the normal electronic camera 1. Therefore, detailed description is omitted. After that, the series of sequences is completed after waiting for the photographing process to end, and the electronic camera 1
A predetermined shooting preparation state is set.

Next, the details of the distance measuring area setting processing in step S4 will be described below.

FIG. 5 is a flow chart showing the details of the flow of the processing of step S4 of the flow chart shown in FIG. 4, that is, the distance measuring area setting processing.

As described above, after the predetermined exposure processing is executed in step S3 of FIG. 4, the processing shifts to the processing of step S4, that is, the distance measuring area setting processing of FIG.

As shown in FIG. 5, in step S11, the system controller 38 first executes a focal length detection process. This focal length detection processing is performed by the zoom lens position sensor 3 monitored by the system controller 38.
It is performed based on the detection result of 4. That is, the system controller 38 receives the output of the zoom lens position sensor 34, and the system controller 38 (the zoom lens 1 of the taking lens unit 11).
The focal length information of 1a) is acquired. After that, step S
Then, the process proceeds to 12.

Subsequently, in step S12, the system controller 38 sets a distance measuring area according to the set focal length based on the focal length information acquired in step S11. In this case, the information on the distance measuring area is, for example, the distance measuring area information corresponding to the focal length information acquired in the process of step S11 among the information prepared in advance in the ROM 38c of the system controller 38. Read out. The distance measurement area information read here is information as shown in the table of FIG. 3, for example. Since FIG. 3 has already been described in detail, description thereof will not be repeated. Then, step S1
Proceed to the process of 3.

Next, in step S13, the system controller 38 determines whether or not the subject brightness is lower than a predetermined value based on the AE evaluation value calculated in step S3 of FIG. Confirm whether it is darker than a predetermined brightness. Here, if it is confirmed that the subject brightness is lower than the predetermined value (the subject environment is dark), the process proceeds to the next step S14. If it is confirmed that the subject is brighter than the predetermined value, step S1
Proceed to the process of 5.

Here, the predetermined value of the subject brightness which is the reference here means the brightness necessary for surely executing the AF process even if the size of the distance measuring area set at this time is used. Say.

Next, when it is confirmed that the subject brightness is lower than the predetermined value in the above-mentioned step S13, and the process proceeds to the next step S14, the system controller 3
8 executes the ranging area changing process in step S14. The ranging area changing process performed here is the following process.

At this point, step S1 described above is performed.
In the process of 1 / S12, the distance measurement area corresponding to the focal length of the taking lens unit 11 is set (see FIG. 3). Then, in the above-described processing of step S13, it is determined that the subject brightness is dark. That is, in this state, it is determined that a reliable AF processing result cannot be obtained with the size of the distance measurement area that has already been set. Therefore, in the process of step S14, the setting is changed so that the distance measuring region is wider than the distance measuring region set in the process of step S12. For this setting change, for example, the distance measurement area change information shown in FIG. 3 is referred to so that the distance measurement area information is one step or two steps larger than the size of the distance measurement area set at this point. This is the setting change processing to be performed.

Then, in step S15, the system controller 38 executes a ranging area display process for displaying a predetermined index so that the ranging area set in step S12 or step S14 can be clearly indicated. To do. This distance measurement area display processing is a display operation for superimposing on the optical image observed by the finder unit to clearly indicate the range of the distance measurement area set in step S12 or step S14.

As the display means in this case, as described above, for example, the LCD 2 for displaying information in the optical viewfinder is used.
4 etc. are used. The operation at this time is as follows.
That is, information about the distance measurement area is displayed by the system controller 3
The data is output to the LCD 24 for displaying information in the optical viewfinder via 8. Then, an index indicating the distance measuring area is displayed by being superimposed on the optical image observed by the finder unit.

In this way, the system controller 38 executes the ranging area setting process. Therefore, the system controller 38 also serves as a distance measurement area setting means.

As the display means for clearly indicating the range of the distance measuring area, the above-mentioned L for displaying information in the optical finder is used.
The image display LCD 21 may be used separately or simultaneously with the CD 24.

The image display LCD 21 is a display means for displaying an image based on the image signal obtained by the image pickup device 12. In order to clearly indicate the range of the distance measurement area on the display unit of the image display LCD 21, the following processing may be performed, for example.

That is, in the distance measuring area display processing in step S15 described above, the system controller 38 generates data capable of displaying an index for indicating the range of the distance measuring area (referred to as distance measuring area index data). To the video output circuit 20. In response to this, the video output circuit 20
Performs the predetermined signal processing by combining the distance measurement area index data and the image signal from the A / D conversion circuit 14.

Then, the signal-processed image data is output to the image display LCD 21. In response to this, the image display LCD 21 displays the image sensor 12 on its own display section.
An image in a form in which the image acquired by and the index indicating the range of the set ranging area are superimposed is displayed.

When the execution of the distance measuring area display processing in step S15 is completed in this way, the series of distance measuring area setting processing shown in FIG. 5 is completed with the display state as the processing result maintained. To do. Then, the process returns to the main sequence shown in FIG. 4 (proceeding to step S5 of FIG. 4).

As described above, according to the first embodiment, not only is the distance measuring area set according to the focal length, but also the photometric processing is performed within the range of the distance measuring area, Since the range-finding area is set in consideration of the subject brightness (AE evaluation value) obtained as a result, the accuracy of the AF process can be ensured more reliably.

That is, the automatic focus detection apparatus of the present embodiment resets the range-finding area in the direction of enlarging the range-finding area when it is confirmed by the photometric processing that the subject brightness is lower than the predetermined value. Therefore, AF processing is performed after increasing the amount of information for AF processing. As a result, a reliable focus detection result can always be obtained.

In the above-described embodiment, the series of distance measuring area setting processing according to the focal length and the distance measuring area changing processing according to the photometric result are executed only once. Considering the case where an appropriate AF processing result could not be obtained even in the result of performing AF processing based on the distance measuring area set by this, a series of similar distance measuring area setting sequences is performed. It may be repeated twice.

In this case, if the proper AF processing result cannot be obtained even after executing the second series of sequences, a warning indicating that focus detection is impossible is issued. To do.

In this case, if the series of sequences for setting the distance measurement area is repeatedly executed, the operation of the image pickup apparatus 1 itself may become unstable. In consideration of this, it is desirable that the sequence is repeated only twice.

By the way, in an ordinary electronic camera,
For example, an AGC (auto gain control) circuit is usually provided so that the output level of an image signal that is output after being photoelectrically converted by an image sensor can be adjusted. In an electronic camera equipped with such an AGC circuit, if the subject brightness (AE evaluation value) obtained by the photometric means is lower than a predetermined value,
There is a system controller that executes a gain-up process using an AGC circuit, that is, a control process for correcting a gain value of an image signal acquired by an image sensor so as to be larger than usual. The AGC circuit is arranged, for example, inside the image pickup circuit 13.

When this gain-up process is executed, the noise component also tends to increase in the image signal acquired thereby. Therefore, erroneous detection may occur in the focus detection operation executed on the basis of the image signal containing such a noise component.

Therefore, the electronic camera as described above, that is, A
In the case of an electronic camera equipped with a GC circuit, in order to apply the present invention, for example, the range changing area setting changing process is performed so that the size of the range measuring region is wide even when the gain-up process is executed. You may do it. With this configuration, it is possible to obtain substantially the same effect as that of the above-described embodiment.

On the other hand, the above-described one embodiment exemplifies the case where the present invention is applied to the electronic camera 1 as described above. As described above, the photometric means in the electronic camera 1 calculates the predetermined AE evaluation value by the AE processing circuit 40 receiving the output (image signal) of the image sensor 12 and executing the predetermined exposure processing. There is.

However, the present invention is not limited to this, and can be easily applied to, for example, a so-called film camera for taking a picture using a photo film.
In this case, a photometric means suitable for receiving the light flux from the subject and performing the photometric processing may be provided, and the AE evaluation value may be calculated based on the output from the photometric means.

In the above embodiment, an electronic camera provided with an optical finder unit for observing an optical image is described as an example. However, the present invention is not limited to this, and is similarly applied to an electronic camera including an electronic viewfinder unit (electric viewfinder unit) configured to observe an electronic image acquired by the image pickup device 12. In this case, the same effect as that of the above-described embodiment can be obtained.

[0092]

As described above, according to the present invention, the focus detection accuracy is further improved by setting the size of the distance measurement area in consideration of the brightness of the object to be photographed and executing the focus detection operation. It is possible to provide an automatic focus detection device which can improve and always obtain a subject image in an optimal focus state.

[Brief description of drawings]

FIG. 1 is a block diagram of a main part showing an outline of an internal configuration of an electronic camera to which an automatic focus detection device according to an embodiment of the present invention is applied.

2 is a range of an image forming area of an optical image observable in the viewfinder unit of the electronic camera of FIG. 1 and a size of a distance measuring area displayed in the range of the image forming area is a focal length or a brightness of an object; FIG. 3 is a conceptual diagram showing a simplified state when changing according to.

3 is information stored in advance in a ROM in a system controller of the electronic camera of FIG. 1, which is information of a size of a distance measuring area preset according to a focal length of a photographing optical system and an AE evaluation value. Distance measurement area change table showing the relationship.

FIG. 4 is a main flowchart showing a main flow of the operation of the electronic camera provided with the automatic focus detection device of the present embodiment.

5 is a flowchart showing the details of the flow of distance measurement area setting processing in the flowchart shown in FIG.

[Explanation of symbols]

1 ... Electronic camera 11 ... Shooting lens unit (shooting optical system) 11a ... Zoom lens (shooting optical system) 11b ... Focus lens (shooting optical system) 23 ... Automatic focus adjustment processing circuit (AF processing circuit; focus) State detecting means) 24 ... LCD for displaying information in the optical viewfinder (display means) 24a, 24b, 24c, 24d ... Imaging area 28 Operation section 32 ... Zoom motor drive circuit 33 ... Zoom motor 34 ... Zoom lens Position sensor (focal length detecting means) 38 ... System controller 38c ... Read-out memory (ROM) 40 Automatic exposure processing circuit (AE processing circuit; photometric means) 41a, 41b, 41c, 41d ... Distance measuring area

Claims (4)

[Claims] 1. A focal length detecting means for detecting a focal length of a photographing optical system, a photometric means for detecting the brightness of an object, and a photographing screen based on an output of the focal length detecting means and an output of the photometric means. And a focus state detecting means for detecting a focus state based on an image signal corresponding to the range of the range-finding area. And automatic focus detection device. 2. The automatic focus detection device according to claim 1, wherein the distance measuring area setting means sets a distance measuring area wider when the subject brightness is low than when the subject brightness is high. 3. The automatic focus detection device according to claim 1 or 2, further comprising display means for displaying the distance measurement area. 4. A read-only memory that stores a plurality of distance measuring area information in advance, wherein the distance measuring area setting means is a distance measuring area according to the output of the focal length detecting means and the output of the photometric means. The automatic focus detection device according to claim 1, 2 or 3, wherein information is read from the read-only memory and set.