JP3478649B2 - Imaging device - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image pickup apparatus such as a silver halide film camera, an electronic still camera, and a video camera.
In particular, the present invention relates to an imaging device having an automatic focus adjustment function. 2. Description of the Related Art Conventionally, in an automatic focusing apparatus used for an image pickup apparatus such as a silver halide film camera, an electronic still camera, and a video camera, when an object at a different distance exists in a photographing area, an accurate image is obtained. A method of limiting the range of the camera in accordance with the distance of the subject to be photographed so that the focusing operation is performed on the subject has been considered. More specifically, the subject distance is divided into a near area and other normal areas, and when photographing an object in the near area, the lens is controlled to move from the closest end to a predetermined position. On the other hand, when photographing a subject in the normal area, the lens is controlled to move from the infinity end to a predetermined position. [0004] However, in the image pickup apparatus having the above-described autofocus function, when the lens is controlled as described above, the photographer changes the photographing mode of the camera to the close-up photographing mode. There is a problem that focusing cannot be performed even if a subject in the normal region is erroneously photographed in the normal shooting mode. The same is true when a subject in a close region is photographed in the normal shooting mode. In addition, there is a problem that when the lens is moved over the entire distance measurement range regardless of the shooting mode, the focusing speed is significantly reduced. SUMMARY OF THE INVENTION The present invention has been made in view of the above problems, and can accurately focus an object outside an assumed distance measurement range without significantly lowering the focusing speed. It is an object to provide a possible imaging device. [0006] An image pickup apparatus according to the present invention is configured as follows. [0007] (1) a photoelectric conversion means for converting into an electrical signal an object image via the focusing lens, the focus
Driving means for driving the lens, wherein the focusable area is configured to include at least two areas, and the focus lens is located in a closest area of the area when the close-up shooting mode is set. Said when
A signal subjected to predetermined <br/> calculation of K times the signal output from the photoelectric conversion means obtained while moving Tokoro quantify the focus lens (K> 1), the near side of the area of the region Move the focus lens more than the predetermined amount when the focus lens is located in a region that is not
Comparing the signal and not subjected to the predetermined operation on the signal output from the photoelectric conversion means obtained while the drive
The focus lens is driven to the in-focus position by moving means
I did it. An embodiment of the present invention will be described below with reference to the drawings. FIG. 1 is a block diagram showing a configuration of an electronic camera to which the present invention is applied. In FIG. 1, 1 is a fixed lens, 2 is a light amount control member such as an aperture and a shutter, 3 is a drive motor for an aperture and a shutter, 4 is a mechanical drive circuit for driving an aperture and a shutter by a drive motor 3, Reference numeral 5 denotes a focus lens for focusing on an image pickup device, which will be described later, and performs focus adjustment on a subject image. Reference numeral 6 denotes a photo interrupter for detecting a reset position of the focus lens 5, and 7 denotes a focus lens 5
8 is a focus lens drive circuit (drive means) for driving the drive motor 7 to move the focus lens 5; 9 is the above-described image sensor for converting reflected light from a subject into an electric signal; It is provided as photoelectric conversion means for photoelectrically converting the formed subject image. Reference numeral 10 denotes a timing signal generating circuit (hereinafter referred to as TG) for generating a timing signal necessary for operating the image pickup device 9, and reference numeral 11 denotes a CDS circuit or an A / D (A / D) for removing output noise of the image pickup device 9. A pre-processing circuit (processing means) comprising a non-linear amplifier circuit performed before analog / digital conversion, 12 an A / D converter, 13 a buffer memory, 14 a read / write of a buffer memory 13 and a refresh operation of a DRAM (not shown) Is a microcontroller (control means) for controlling the entire system such as a photographing sequence;
It is composed of a CPU. Reference numeral 16 denotes an operation display unit for performing a display for assisting operation and indicating the state of the camera, 17 denotes an operation unit for operating the camera from outside, and 18 denotes an electrically rewritable nonvolatile memory (EEPROM). , 19 are interfaces (I / F) with an extension unit described later, 20
Is a detachable expansion unit that is connected to the camera body to perform various processes and operations, and 21 is an interface for connecting to a recording medium 22. A memory card, a hard disk, or the like is provided as the recording medium 22. . Reference numeral 23 denotes a main switch for turning on the power to the system, 24 denotes a switch (SW1) for performing a photographing standby operation such as AF or AE, and 25 denotes a switch (SW) for performing photographing after the photographing standby switch 24 is operated.
2) and 26 are mode switches for setting a shooting mode;
Reference numeral 7 denotes a strobe light, and reference numeral 28 denotes an auxiliary light source including an LED or the like. Here, in the above-mentioned electronic camera, the pre-processing circuit 11 is provided with an extracting means for extracting a signal representing a high-frequency component of the luminance of the subject from the output signal from the image pickup device 9. The moving range in the optical axis direction, that is, the in-focus region is configured to include at least two regions. When the focus lens 5 is located in any one of the regions, the microcontroller 15 performs a predetermined operation on the output from the extracting unit, and calculates the output of the extracting unit. The result is compared, and the focus lens driving circuit 8 is controlled according to the comparison result. Alternatively, the microcontroller 15 performs different control on the focus lens drive circuit 8 in each of the above-mentioned regions. Next, the operation of the electronic camera using the AF device of the present embodiment will be described with reference to the flowchart of FIG. Here, a case will be described where the lens position where the high-frequency component of the luminance signal obtained from the image sensor 9 is maximized is set as the focusing position as the AF method. First, in step S101, the state of the main switch 23 is checked, and if it is ON, the process proceeds to step S102. In step S102, the remaining capacity of the recording medium 22 is checked. If the remaining capacity is 0, the process proceeds to step S103; otherwise, the process proceeds to step S104. In step S103, a warning is issued that the remaining capacity of the recording medium 22 is 0, and the flow advances to step S101.
The warning may be displayed on the operation display unit 16, a warning sound may be output from an audio output unit (not shown), or both. In step S104, the focus lens 5 is reset and moves to the initial position. In step S105, the state of the switch 24 is checked. If the switch is ON, the process proceeds to step S107; otherwise, the process proceeds to step S106. In step S106, the state of the main switch 23 is checked. If it is ON, the process proceeds to step S105; otherwise, the process proceeds to step S101. In step S107, the subject brightness is calculated from the output signal of the image sensor 9. In step S108, the focus lens 5 is driven according to the flowchart of FIG. In step S109, the state of the photographing switch 25 is checked. If the switch is ON, the process proceeds to step S111; otherwise, the process proceeds to step S110. Step S11
If it is 0, the state of the switch 24 is checked. If it is ON, the process proceeds to step S109; otherwise, the process proceeds to step S105. In step S111, the photographing operation is performed according to the flowchart of FIG. In step S112, the remaining capacity of the recording medium 22 is checked. If the remaining capacity is 0, the process proceeds to step S103; otherwise, the process proceeds to step S113.
Proceed to. In step S113, the state of the photographing switch 25 is checked. If it is not ON, the process proceeds to step S110. FIG. 3 shows A in step S108 of FIG.
It is a flowchart which shows F (automatic focus adjustment) operation | movement.
In the following description, it is assumed that the distance measurement mode of the camera is set to a close-up shooting mode for shooting a subject in a close-up area. First, in step S201, the focus lens 5 is moved to a scan start position. Here, the scan start position is the closest end. Next, in step S202, the focus detection signal (focus evaluation value) obtained from the high frequency component of the luminance signal in the video signal obtained from the image sensor 9 and the current lens position are stored in the buffer memory 13. At this time, the focus evaluation value may be normalized by dividing the focus evaluation value by an average value or a peak value of the object luminance in order to prevent the fluctuation of the focus evaluation value due to the flicker of the light source or the change of the object luminance. When a stepping motor is used as the drive motor 7 of the focus lens 5, the lens position is calculated from the number of steps from the reset position and stored. When a DC motor is used, the position is stored as an absolute position using an encoder or the like. In the following description, a stepping motor is used, but a DC motor may be used. In step S203, the current position of the focus lens 5 stored in step S202 is compared with a predetermined position. If the current position is closest to the predetermined position, step S2 is executed.
04, otherwise to step S206. In step S204, the focus evaluation value corresponding to the current position of the focus lens 5 stored in step S202 is multiplied by K. Here, K is assumed to be K> 1. In step S205, the focus lens 5 is moved by m steps toward infinity,
Proceed to step S202. Here, m is a positive integer. In step S206, the current position of the focus lens 5 stored in step S202 is compared with a predetermined position.
Otherwise, the process proceeds to step S208. In step S207, the focus evaluation value corresponding to the current position of the focus lens 5 stored in step S202 is multiplied by K.
This K is K> 1 as in the case of step S204. In step S208, the current position of the focus lens 5 stored in step S202 is compared with the scan end position. If the position coincides with the scan end position, the flow advances to step S210; otherwise, the flow advances to step S209. In step S209, the focus lens 5 is moved n steps toward infinity, and the process proceeds to step S202.
Here, n is a positive integer and m <n. In step S210, the buffer memory 13
The maximum value and the position of the focus lens 5 corresponding to the maximum value are extracted from the focus evaluation values stored in. Step S2
In step 11, the focus lens 5 is moved to a position corresponding to the maximum value among the maximum values extracted in step S210. Next, how the focus position is detected when the camera is controlled according to the flowchart of FIG. 3 will be described below. In the following description, it is assumed that the camera is set to the close-up shooting mode as in the case described above. (1) In the case of photographing a subject in the close area When the distance of the subject in the close area is measured, the relationship between the focus lens 5 and the focus evaluation value is as shown in FIG. Focus lens 5 moves from the closest end toward infinity
As the pulse moves, the focus evaluation value gradually increases.
At this time, the focus evaluation value is multiplied by K because of the close-up shooting mode. At this time, K> 1. The maximum value is shown at a certain point P, and then gradually decreases, and the focus lens 5 reaches the boundary between the near area and the normal area. When the focus lens 5 enters the normal area beyond this boundary, the focus lens 5 moves toward the infinity side by n pulses, and the focus evaluation value is not multiplied by K. Here, the relationship between m and n is m <n. Thus, FIG.
Is obtained, and the peak position of this curve, that is, the point P is set as the focus position. (2) When the subject is present in both the close area and the normal area When the subject is present in both the close area and the normal area, the relationship between the focus lens 5 and the focus evaluation value is as shown in FIG. In the proximity region, m is set in the same manner as in the case (1) described above.
The focus evaluation value is obtained while moving each pulse, and is multiplied by K. At this time, K> 1 as in (1). When the focus lens 5 crosses the boundary between the proximity area and the normal area, the focus evaluation value is obtained while moving by n pulses. At this time, since the subject is also present in the normal area, a peak is formed at the position Q of the focus lens 5 corresponding to the subject distance. However, since the focus evaluation value of the normal area is not multiplied by K, the focus evaluation value of the peak point Q in the normal area is a value sufficiently smaller than the focus evaluation value of the peak point P in the adjacent area multiplied by K. . Therefore, the peak position as a whole, that is, the point P is set as the focus position. (3) When photographing a subject in the normal area When the subject is present only in the normal area, the relationship between the focus lens 5 and the focus evaluation value is as shown in FIG. First, the focus lens 5 obtains a focus evaluation value while moving by m pulses from the nearest end to the infinity end, and multiplies the focus evaluation value by K to reach the boundary between the close area and the normal area. However, since there is no subject in the close area, no peak appears in this area, and the focus evaluation value becomes a very small value even when multiplied by K. The focus evaluation value slightly increases near the boundary. Next, when the focus lens 5 enters the normal area,
A focus evaluation value is obtained while moving by n pulses. Since the focus evaluation value in the normal region is not multiplied by K, it decreases immediately after the boundary is exceeded. Therefore, a peak is formed at the boundary point P. Since the subject is present in the normal area, the focus evaluation value gradually increases as the focus lens 5 is further moved, and decreases beyond the point Q. As a result,
As a whole, there are two peaks, point P and point Q.
Comparing the focus evaluation values at the point P and the point Q, the value at the point P is sufficiently smaller than the value at the point Q, which is the original peak, though it is multiplied by K. Therefore, the peak position as a whole, that is, the point Q is set as the focus position. FIG. 4 is a subroutine showing the contents of the photographing operation in step S111 of FIG. First, in step S301, the subject brightness is measured. Step S3
In 02, exposure to the image sensor 9 is performed according to the subject luminance measured in step S301. In step S303, output noise removal of the image sensor 9 and non-linear processing performed before A / D conversion are performed. In step S304, the analog signal from the pre-processing circuit 11 is converted into a digital signal. In step S305, the output data from the A / D converter 12 is temporarily stored in the buffer memory 13 via the memory controller 14. Step S306
Then, the data in the buffer memory 13 is transferred to the recording medium 22 such as a memory card mounted on the camera body via the memory controller 14 and the interface 21. By controlling the camera in this manner, it is possible to accurately focus even when the camera is in the close-up shooting mode, even when shooting a subject in a normal area. In the close-up shooting mode, the number of movement pulses of the focus lens 5 in the normal area is set to be larger than that in the close-up area. Therefore, even if the entire distance measurement area is measured, the focusing speed does not significantly decrease. Therefore, even when the subject is located outside the subject distance range assumed from the distance measuring mode of the camera, an accurate and quick focusing operation can be realized. In the above-described embodiment, the focus evaluation value in the close area is multiplied by K in the close-up shooting mode, but the focus evaluation value in the normal area is multiplied by K instead of the focus evaluation value in the close area. Is also good. In this case, K <1. In the above description, the photographing mode of the camera is set to the close-up photographing mode. However, this may be performed in the normal photographing mode. In this case, it goes without saying that the focus evaluation value in the normal area is multiplied by K, and the number of steps of moving the focus lens 5 in the close area is made larger than the number of steps in the normal area. Further, in the above description, the AF method is used in which the lens position at which the high-frequency component of the luminance signal obtained from the image sensor 9 is maximized is set as the in-focus position. However, another method may be used. . As described above, according to the present invention,
There is an effect that it is possible to accurately focus on an object outside the assumed distance measurement range without significantly lowering the focusing speed.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a block diagram showing a configuration of an electronic camera according to the present invention. FIG. 2 is a flowchart showing a basic operation of the electronic camera of FIG. 1 FIG. FIG. 4 is a flowchart showing an automatic focus adjustment operation. FIG. 4 is a flowchart showing an image recording operation in the electronic camera of FIG. 1. FIG. 5 is an explanatory diagram showing a relationship between a focus lens and a focus evaluation value when a subject is present in a close area. FIG. 6 is an explanatory diagram showing a relationship between a focus lens and a focus evaluation value when a subject is present in both a proximity area and a normal area. FIG. 7 is a view showing a relationship between a focus lens and a focus evaluation value when a subject is present in a normal area. 5 Focus lens 7 Drive motor 8 Focus lens drive circuit (drive means) 9 Image sensor (photoelectric conversion means) 11 Pre-processing circuit (processing Means) 15 Microcontroller (Control means)

Claims (1)

(57) [Claim 1] A photoelectric conversion means for converting a subject image through a focus lens into an electric signal, and the focus lens
Driving means for driving the focus lens, wherein the focusable area is configured to include at least two areas, and the focus lens is positioned in an area on the closest side of the area when the close-up shooting mode is set. The four
A signal which has been subjected to a predetermined calculation for multiplying the signal output from the photoelectric conversion means obtained by moving the cas lens by a predetermined amount by K times (K> 1), and Forward when the focus lens is positioned
Move the focus lens more than the predetermined amount.
One Tokura is obtained by comparing the signal not subjected to the predetermined operation on the signal output from the photoelectric conversion means, said drive means
Imaging device comprising a this <br/> for driving the focus lens to the focusing position by.