JP2008158028A - Electronic still camera - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To shorten a focusing time, regarding an electronic still camera. <P>SOLUTION: In the electronic still camera configured to drive a focusing lens and detect a focal position in response to an operation to start up focusing operation by the focusing lens, and then, to move the focusing lens up to the detected focal position, when the operation is released (7) after the focusing lens is moved up to the focal position (4), the focusing lens is moved by a prescribed amount (d) toward the moving end located close to the focal position (8). <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to an electronic still camera.

  In an electronic still camera that performs focus adjustment by scanning the focusing lens from the closest end to the infinite end when the release button is pressed halfway to detect the in-focus position (hereinafter referred to as lens in-focus position scanning). If the first half-press operation is followed by the second half-press operation, if the condition that the focusing lens exists within the focusing range (for example, within the depth of field) is satisfied, There is known an electronic still camera in which the release time lag is shortened without performing in-focus position scanning (see, for example, Patent Document 1).

Prior art documents related to the invention of this application include the following.
Japanese Patent Laid-Open No. 2004-354581

  However, the above-described conventional electronic still camera has a problem that it takes time to adjust the focus because the above-described lens in-focus position scanning is performed in the same manner as the first time when the subject distance changes.

  When there is an operation to start the focusing operation by the focusing lens, the focusing lens is detected by driving the focusing lens and moving the focusing lens to the detected focusing position. When the operation is released after the movement, the focusing lens is moved by a predetermined amount toward the moving end closer to the in-focus position.

  According to the present invention, the time required for the focus adjustment operation can be shortened.

  FIG. 1 shows a configuration of an electronic still camera according to an embodiment. In FIG. 1, illustration and description of camera devices and circuits not directly related to the present invention are omitted. The photographing lens 1 includes an objective lens 1a, a zooming lens 1b, a diaphragm 1c, and a focusing lens 1d, and forms a subject image on the light receiving surface of the image sensor 2. The image pickup device 2 is composed of a CCD, a CMOS, or the like, and receives a subject image and outputs an image signal. The signal processing circuit 3 performs processing such as sampling, noise removal, sensitivity correction, and A / D conversion on the image signal output from the image sensor 2. The image processing circuit 4 performs processing such as pixel interpolation, resolution conversion, white balance control, gamma correction, matrix calculation, and image compression on the image data processed by the signal processing circuit 3.

  The image memory 5 is a memory that temporarily stores image data before or after processing by the image processing circuit 4. The recording medium 6 is controlled by a driver 7 and records subject image data. Various memory cards can be used for the recording medium 6. The monitor 8 is controlled by a driver 9 and displays a subject image and various types of shooting information. The driver 10 drives the zooming lens 1b and changes the focal length of the photographing lens 1 according to the operation of a zoom button (not shown). The driver 11 drives the aperture 1c and adjusts the aperture value automatically selected by the camera based on the exposure calculation result or the aperture value set by the photographer using the aperture setting switch (not shown). The driver 12 drives the focusing lens 1d to adjust the focus of the photographing lens 1. The timing generator 13 controls the timing of image capturing and signal readout of the image sensor 2.

  The controller 14 includes a microcomputer 14a and a memory 14b, and performs various calculations such as exposure calculation and various sequence controls such as focus adjustment control. The operation member 15 is various switches for operating the camera. The operation member 15 includes a power switch, a half-press switch and a full-press switch that operate in conjunction with a release button, a zoom switch that operates in conjunction with a zoom button, an aperture setting switch, and the like. The reset sensor 16 is a sensor for determining the lens position after the power is turned on.

  Prior to describing the focus adjustment operation of one embodiment, the focus adjustment operation of a conventional camera will be described. FIG. 2 is a timing chart showing the focus adjustment operation of the conventional camera. In the figure, black circles indicate the position of the focusing lens for each operation. When the half-push switch is turned on when the release button is half-pressed (1), from the initial lens position to the moving end that is closer to the closest moving end (closest end) or the infinite moving end (infinite end) The focusing lens is moved (to the closest end in this example) (2) and the live view display on the monitor is started. Next, while moving the focusing lens toward the opposite moving end by a predetermined step amount X, the image output of the image sensor is read, the contrast is detected by image processing, and the focus evaluation value is calculated based on the contrast. (3). That is, the position with the maximum focus evaluation value, that is, the in-focus position is scanned. The in-focus position is calculated by interpolation calculation processing based on each moving position of the focusing lens at the time of in-focus position scanning (the position of the black circle in the figure) and the focus evaluation value at that position.

  After scanning the focus position, the focusing lens is moved to the detected focus position (4), and the focus adjustment of the photographing lens is finished. Next, when the full-press switch is turned on in response to the full-press operation of the release button (5), after adjusting the aperture value of the exposure calculation result, the subject image formed by the taking lens is picked up by the image pickup device. Then, the captured image is recorded on the recording medium (6). Here, when the release button is released and the half-press switch and the full-press switch are turned off (7), the focusing lens continues to stop at the position at the time of imaging.

  When the half-press switch is turned on again in response to the half-press operation of the release button in this state (1 ′), the initial lens position (here, the first focus position) is the same as the first movement (2). The focusing lens is driven (2 ′) from the close end to the moving end that is closer to the infinite end (in this example, to the infinite end). Let L be the amount of movement at this time. Next, while moving the focusing lens toward the opposite moving end by a predetermined amount, the image output of the image sensor is read, the contrast is detected by image processing, and the focus evaluation value is calculated based on the contrast (3 ′ ), That is, the position where the focus evaluation value is maximum, that is, the focus position is scanned. After scanning the focus position, the focusing lens is moved to the detected focus position (4 ').

  In such a conventional camera focus adjustment operation, when the second half-pressing operation is performed after the first half-pressing operation, the first focus position is changed to the closest end as in the first time. After moving the focusing lens to the moving end that is closer to the infinite end, the focus position is scanned toward the moving end on the opposite side, resulting in focusing of the photographic lens from the second halfway release. It takes as much time as the first time.

  Therefore, in one embodiment of the present invention, the focus adjustment operation of the photographing lens 1 is performed according to the procedure shown in the timing chart of FIG. The focus adjustment operation of the embodiment shown in FIG. 3 will be described with a focus on operations different from the focus adjustment operation of the conventional camera shown in FIG. The first focus adjustment operation from release half-press ON (1) to release half-press after imaging and full press OFF (7) is the same as the operation of the conventional camera shown in FIG. After driving the focusing lens 1d to the in-focus position A by half-pressing the release button, when the release button is released, the focusing lens 1d in the in-focus position A is moved to the moving end close to the in-focus position A (in this example) (8). This predetermined amount d will be described later.

  When the half-press switch (15) is turned on in response to the second half-pressing operation of the release button (1 ′), the initial lens position (here, the first focusing is performed) as in the first movement (2). The focusing lens 1d is moved from the position) to the moving end closer to the closest end or the infinite end (in this example, to the infinite end) (2 '). The amount of movement at this time is (Ld). Next, while moving the focusing lens 1d by a predetermined amount toward the moving end on the opposite side, the image output of the image sensor 2 is read out, the contrast is detected by image processing, and the focus evaluation value is calculated based on the contrast ( 3 ′), that is, the position where the focus evaluation value is maximum, that is, the in-focus position is scanned. After scanning the focus position, the focusing lens 1d is moved to the detected focus position A (4 ').

  In the conventional camera, the focusing lens is driven by the movement amount L toward the moving end after the second half-press of the release as shown in FIG. 2, but in this embodiment, as shown in FIG. It is only necessary to drive the focusing lens by the amount of movement (Ld) toward the moving end after the half-press of the second release. That is, when the lens driving amount is reduced by a predetermined amount d and the moving speed of the focusing lens is S (m / s), the time required for lens movement (2 ′) after the second half-press of the release (L−d) ) / S, and the time required for the second focus adjustment operation (1 ′) to (4 ′) can be shortened by d / S seconds.

  Next, a method for shortening the time required for the first focus adjustment operation after the camera is turned on will be described with reference to FIG. Here, the description will focus on an operation different from the focus adjustment operation of the camera described in FIGS. When the power of the camera is turned on (10), after driving the focusing lens 1d from the initial lens position to the position where the reset sensor 16 operates (11), as described above, either the closest end or the infinite end is close. The focusing lens 1d is moved to the far moving end (to the closest end in this example) (2), and the live view display on the monitor 8 is started.

  Further, while moving the focusing lens 1d by a predetermined amount toward the moving end on the opposite side, the image output of the image sensor 2 is read, the contrast is detected by image processing, and the focus evaluation value is calculated based on the contrast (3 ). That is, the position with the maximum focus evaluation value, that is, the in-focus position is scanned. In the above-described embodiment, the lens is driven to the in-focus position by performing the in-focus position scan after half-pressing the release, but here, the release half-press operation is not performed and the lens is driven to the in-focus position. There is no need. Therefore, in preparation for the first release half-press operation after the power is turned on, the focusing lens 1d is moved in advance from the in-focus position to a position C in front of the predetermined amount d.

  When the first release half-press operation is performed after the power is turned on (1 ′), the focusing lens 1d stopped at a position C in front of the in-focus position by a predetermined amount d is moved infinitely from the position C to the nearest end. It moves to the moving end that is closer to either end (in this example, to the infinite end) (2 '). Since the moving amount at this time is (Ld), the lens driving amount is reduced by a predetermined amount d from the distance L to the moving end. If the moving speed of the focusing lens is S (m / s), the time required for the lens movement (2 ′) after the first half-press of the release is (Ld) / S, and the second focus adjustment operation (1 The time required for ') to (4') can be shortened by d / S seconds.

  Next, a method for determining the predetermined amount d for moving the focusing lens 1d from the in-focus position after shooting or after power-on will be described. Since the through image is displayed on the monitor 8 after shooting and after the power is turned on, if the focusing lens 1d is largely moved from the in-focus position, the subject image displayed on the monitor 8 will be blurred, and the photographer Will give a sense of incongruity. Accordingly, it is desirable that the amount of movement (predetermined amount d) from the in-focus position after shooting or after power-on is at least to the extent that the photographer does not feel blur (image change) of the subject image on the monitor 8.

In this embodiment, the predetermined amount d is determined by the following equation.
d = D / (2 · k · R · NA) (1)
In equation (1), D is the minimum circle of confusion on the monitor 8, NA is the image-side numerical aperture of the taking lens 1 (where the refractive index of the image-side space is n = 1), and k is the focusing lens. An image plane movement coefficient of 1d, R is a screen size ratio between the monitor 8 and the image sensor 2. The predetermined amount d may be determined based on one or a plurality of parameters among the minimum circle of confusion D, the image-side numerical aperture NA, the image plane movement coefficient k, and the screen size ratio R. For example, the closer the NA is to the open F value, the easier it is for the human eye to recognize the change in the image due to lens movement (lens position change). It is also possible to perform a calculation process that reduces. Further, when the predetermined amount d obtained in this way is larger than the distance L from the in-focus position to the moving end on the near side, the moving amount is set to L. That is, the focusing lens 1d is moved to the moving end.
if (d> L), THEN (d = L) (2)

  Next, in general, the driving system of the focusing lens 1d has a backlash, and when adjusting the focus prior to photographing, so-called “backlash” in which the lens is once driven past the in-focus position and then driven in the reverse direction to be positioned in the in-focus position. Operation is performed. In the present embodiment, assuming that the lens driving mechanism requires a backlash removal operation when driving the lens in the direction from the infinite end side to the closest end side, in FIG. When moving to the in-focus position A by scanning, the in-focus position scan (3) drives the lens in the direction from the closest side to the infinite side to scan the in-focus position. In the movement (4) to the focal position, the lens is driven in the direction from the infinity side to the closest side. At this time, the focusing lens 1d is positioned at a position deviated from the correct in-focus position by the backlash Z of the focusing lens drive mechanism.

  Therefore, when moving to the in-focus position A in (4), the in-focus position A passes once by the backlash Z, the driving direction is reversed, and the focusing lens 1d is positioned at the in-focus position A. In this way, the lens driving direction in the in-focus position scanning (3) and the lens driving direction in the movement to the in-focus position (4) are the same direction, and the deviation of the backlash Z of the lens driving mechanism is eliminated. Thus, the focusing lens 1d can be positioned at the correct in-focus position. As shown by “A” in FIGS. 3 and 4, this “backlash” operation of the lens is always performed during the movement to the in-focus position (4) after the in-focus position scan (3).

By the way, as shown in FIG. 4, when the focusing lens 1d is moved to the position C before the focus position by a predetermined amount d after the focus position scan (3) after the power is turned on (12), the infinite side is also the closest side. The lens is driven in the direction toward, but the lens is driven to the moving end by the subsequent half-pressing of the release (1 ′). Does not perform rattling. Thus, even if the lens is originally driven in the direction in which the backlash is removed, if the backlash removal is wasted due to the subsequent operation (the operation in (1 ′)), the backlash removal is performed. Since no processing is performed, the time required for the lens movement processing after the power is turned on can be shortened.
On the other hand, as shown in FIG. 3, when the focusing lens 1d is driven by a predetermined amount d after moving to move to the position B (7), from the closest end side, which does not originally require backlash, toward the infinite end side. Since there is a case where the lens is driven, the backlash removal operation is not performed. In addition, since the lens is driven to the moving end by a half-press of the release (2 ′), it is not necessary to perform the above-described rattling at the position B from this point. Not performed.

  Note that the focus adjustment operation described with reference to FIG. 3 and the focus adjustment operation described with reference to FIG. 4 can be used together to reduce the time required for the focus adjustment each time a release half-press operation is performed after the camera is turned on. Can do.

  Thus, according to one embodiment, when the shutter button is pressed halfway, the focusing lens 1d is driven to detect the in-focus position, and the focusing lens 1d is moved to the detected in-focus position. When the shutter button is released after moving the focusing lens 1d to the in-focus position, the focusing lens 1d is moved by a predetermined amount d toward the moving end closer to the in-focus position. The time required for the focus adjustment operation when the half-pressing operation is performed can be shortened.

  Further, according to the embodiment, the predetermined amount d is set so that the subject image displayed on the monitor 8 is not blurred. Therefore, even if the focusing lens 1d is moved from the in-focus position by the predetermined amount d, the subject image is not blurred. It is possible to prevent the photographer from feeling uncomfortable.

  According to one embodiment, the predetermined amount d is the minimum circle of confusion D on the monitor 8, the NA value of the photographing lens, the image plane movement coefficient k of the focusing lens 1d, and the screen size ratio between the monitor 8 and the image sensor 4. It is determined by one or more of R, and can be adapted to all specifications of the photographing lens 1 such as focal length, open aperture value, and angle of view, and what kind of photographing lens 1 is a camera. Even if it is attached to the camera, the time required for focus adjustment can be shortened without causing the photographer to feel uncomfortable.

  According to one embodiment, after the camera is turned on, the focusing lens 1d is driven to detect the in-focus position, and the focusing lens 1d is moved to a position before the predetermined amount d of the detected in-focus position. The focus adjustment time can be shortened even when the release button is pressed halfway for the first time after the power is turned on.

  In the above-described embodiment, the focus position is detected by half-pressing the release button, the focusing lens 1d is moved to the focus position, and then the release button is released, the position is close to the focus position. Although the example in which the focusing lens 1d is moved by a predetermined amount d toward the moving end on the side has been shown, the timing for starting these operations is not limited to the shutter button operation, and any operation for starting the focusing operation by the focusing lens 1d. It may be the timing when

The figure which shows the structure of one embodiment Timing chart showing focus adjustment operation of a conventional camera Timing chart showing focus adjustment operation of one embodiment Timing chart showing focus adjustment operation of one embodiment

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Shooting lens 1d Focusing lens 2 Image sensor 4 Image processing circuit 8 Monitor 14 Controller 15 Operation member

Claims (6)

Imaging means for imaging a subject image formed by the taking lens;
A lens driving means for moving the focusing lens of the photographing lens between a close side moving end and an infinite side moving end;
Control means for detecting a focus position by driving the focusing lens by the lens driving means and moving the focusing lens to the detected focus position when there is an operation to start a focusing operation by the focusing lens; In an electronic still camera equipped with
When the operation is released after moving the focusing lens to the in-focus position by the lens driving unit, the control unit has a predetermined amount toward the moving end closer to the in-focus position by the lens driving unit. An electronic still camera characterized by moving the focusing lens only. The electronic still camera according to claim 1.
A display unit for displaying a subject image captured by the imaging unit;
The electronic still camera according to claim 1, wherein the predetermined amount is an amount that does not blur a subject image displayed on the display means. The electronic still camera according to claim 2,
The predetermined amount depends on one or more of a minimum circle of confusion on the display means, an NA value of the photographing lens, an image plane movement coefficient of the focusing lens, and a screen size ratio of the display means and the imaging means. An electronic still camera characterized by determining. The electronic still camera according to any one of claims 1 to 3,
The control means detects the in-focus position by driving the focusing lens by the lens driving means after the power of the camera is turned on, and reaches the position just before the predetermined amount of the detected in-focus position. An electronic still camera characterized by moving a focusing lens. In the electronic still camera according to any one of claims 1 to 4,
An electronic still camera, wherein when the distance from the in-focus position to the moving end closer to the in-focus position is shorter than the predetermined amount, the predetermined amount is set as the distance. In the electronic still camera of any one of Claims 1-5,
The control means moves the focusing lens to a position away from the in-focus position by the predetermined amount even when the focusing lens drive mechanism performs a backlash operation when moving the focusing lens in a predetermined direction. The electronic still camera is characterized in that when the focusing lens is driven to a position that is a predetermined amount before the in-focus position, the backlashing operation of the focusing lens is not performed.

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