JP2005300795A - Automatic focusing device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To shorten range-finding time by using past range-finding information even at the time of zooming operation. <P>SOLUTION: An imaging apparatus comprises a first range-finding means for measuring a prescribed subject distance range, a second range-finding means for measuring a range narrower than the subject distance range, a storage means for storing a photographing condition at the time of range-finding, a zooming operation means for changing a field angle, an automatic focusing means interlocking with zooming operation which automatically changes a focusing position on a focused position after zooming variation, and a control means for selecting the second range-finding means when scenes are regarded as same scene by a preceding photographing condition and a present photographing condition, and selecting the first range-finding means when these scenes are not regarded as the same scene. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to an autofocus device that changes a distance measurement method for the next shooting based on shooting information obtained at the previous distance measurement.

  Digital cameras and the like often adopt an autofocus (hereinafter referred to as AF) method called a TV-AF method. In this method, the focus lens is moved to acquire image data at each point, an AF evaluation value that increases as the focus state is approached from each image is calculated, and the AF evaluation value becomes larger. An in-focus state is obtained by driving the focus lens. For example, when the distance measurement range is from infinity to 50 cm, an AF evaluation signal as shown in FIG. 6 is obtained, and the in-focus state is obtained by controlling the focus lens to a distance A at which the AF evaluation signal has the largest value. . Also, the AF evaluation value is obtained by sampling at intervals corresponding to the normal depth of field.

  When performing the above-described control, particularly in the case of a camera having an optical system with a shallow depth of field or a camera with a wide distance measurement range, AF evaluation values for the entire distance measurement range are acquired. There is a problem that it takes a long time.

  In order to avoid this problem, the following method has been proposed. If the shooting conditions and focus position at the previous distance measurement are stored, the current shooting conditions and the shooting conditions at the previous distance measurement are compared to determine whether they can be regarded as the same scene. If it is determined, only a narrow range is measured with the focus position at the time of the previous distance measurement as the center, and if it is determined that the scene cannot be regarded as the same scene, normal distance measurement is controlled. .

According to the above method, the focusing speed can be increased more than usual when the shooting conditions of the previous distance measurement and this time can be regarded as the same scene.
JP 05-188277 A

  However, the scenes where the effect can be obtained are limited, and in particular, when the zoom lens is driven and the angle of view is changed, it is not effective because it cannot be regarded as the same scene.

  An object of the present invention is to provide an autofocus device that can increase the focusing speed even when the angle of view changes.

  In order to achieve the above object, the autofocus device of the present invention has the following configuration.

  A first distance measuring means for measuring a predetermined subject distance range; a second distance measuring means for measuring a range narrower than the subject distance range; a storage means for storing shooting conditions at the time of distance measurement; The zoom operation means that changes the angle of view, the zoom operation-linked automatic focusing means that automatically changes the focus position to the in-focus position after zooming, and the same scene from the previous shooting condition and the current shooting condition at the time of shooting The second distance measuring means is selected when it can be regarded as the same scene, and the control means for controlling the first selection means when it cannot be regarded as the same scene. If is not changed, the distance measuring unit is selected based on the previous shooting conditions and the current shooting conditions.If the zoom is changed, the shooting conditions for the distance measurement after the zoom operation and the current shooting conditions are selected. Based on this, the distance measuring means is selected.

  According to the above-described embodiment, even when there is a zooming operation and there is a change in the angle of view, it is possible to increase the focusing speed without degrading accuracy when it can be regarded as the same scene by using past shooting information. It is.

  Embodiments of the present invention will be described below with reference to the drawings.

(First embodiment)
FIG. 1 is a schematic diagram of a digital camera according to an embodiment of the present invention.

  The digital camera in the present embodiment has an optical system 01 and a focus lens 02 that can perform zoom operation, and a CDS circuit that photoelectrically converts light imaged by these using the image pickup device 03 and removes output noise or before A / D conversion. Signals digitized through a pre-processing circuit 04 having a non-linear amplifier circuit and an A / D converter 05 are stored in the memory 07 via the memory controller 06 and converted into an image by a signal processing circuit (not shown). Then, an image is recorded on the recording medium 08.

  A zoom operation and a focus operation accompanying the zoom operation will be described. Any control is performed via the control unit 19. The zoom operation is controlled so that the optical system 01 is driven by the zoom lens driving circuit 17 by operating the Zoom1 switch 11 and the Zoom1 switch 12, and the focal length becomes longer and shorter, respectively. It is possible to obtain a desired focal length by controlling the optical system to be stopped when the Zoom switch is pressed and to be stopped when the Zoom switch is pressed.

  In addition, the focus operation is automatically performed after the zoom operation. In the focus operation, the focus lens 02 is driven by the focus lens driving circuit 18, the image signal picked up at each position is calculated by the AF evaluation value calculation circuit 15, and a position where the maximum value is found is detected, and then the focus lens is driven to that position. Is done.

  This will be described with reference to the flow of FIG. When either the Zoom1 switch or the Zoom2 switch is operated in step S1, the angle of view is changed according to the switch in step S2. After the zoom operation, control is performed so that the distance measurement operation is automatically performed and the focus lens is driven to the in-focus position in step S3. In step S4, the photographing condition storage means 16 sets the photographing conditions for distance measurement for the purpose described later. Remember.

  Note that the AF evaluation value is calculated by, for example, adding the maximum absolute value of the signal obtained through a filter that extracts a high frequency component in the horizontal direction for each line in the vertical direction for the target area of the captured image. do it.

  Next, the AF operation when the SW 109 is pressed will be described. When the SW 109 is pressed, the shooting condition analysis unit 13 determines whether the previous distance measurement and the current distance can be regarded as the same scene. Next, when it is determined by the scanning position / range setting means 14 that the above result can be regarded as the same scene, a narrow range is set for shortening the distance measurement time, and when it is not determined that the scene can be regarded as the same scene. Is set to measure a predetermined normal ranging area. Next, an in-focus state is obtained by driving the focus lens for the set distance measurement area and controlling the AF evaluation value to be maximized.

  This will be described in more detail with reference to the flow of FIG. If SW1 is pressed, the shooting conditions are analyzed in step S01. Specifically, the current shooting conditions are acquired and compared with the previous shooting conditions at the time of distance measurement. For example, it is determined that the scenes are the same when the change in the brightness of the subject is small or the time difference from the previous shooting is not so much satisfied. In step S02, if the determination result can be regarded as the same scene, the process proceeds to step S03, where a narrow range including the focus position at the previous distance measurement is set as the distance measurement range. If they cannot be regarded as the same scene, a predetermined all ranging area is set in step S04. Next, in step S05, the set area is measured, and in step S06, the focus lens is driven to the in-focus position to obtain an in-focus state. In step S07, the in-focus position and shooting conditions are stored.

Note that the above-described shooting condition analysis means may determine whether the previous scene and the current scene can be regarded as the same scene by combining at least one of the following conditions. That is,
1. [Current shooting time]-[Last shooting time] <(30 seconds)
2. [Previous macro setting] = [Current macro setting]
3. [Previous AF frame setting] = [Current AF frame setting]
4). | [Brightness this time]-[Brightness last time] | <1 (Ev)
5). | [Current AF evaluation value]-[Previous AF evaluation value] | <(predetermined value)
Only when the above conditions are satisfied, it is regarded as shooting under the same conditions.

  By configuring as described above, even when zooming is performed, the distance is automatically measured and controlled in focus, and the shooting conditions are also stored. Since the number of cases that can be regarded as the same scene increases stochastically, it is only necessary to measure the distance in the vicinity of the previous in-focus position, and an imaging apparatus capable of reducing the distance measurement time without reducing accuracy can be realized.

(Second embodiment)
In this embodiment, an example in which the focus operation after the zoom operation in the first embodiment is changed in accordance with the zoom change amount will be described.

  If the distance measurement is always performed automatically after the zoom operation as in the first embodiment, the waiting time of the user may increase and become troublesome. Therefore, in the present embodiment, when it is not necessary to automatically measure the distance, the distance is not changed.

  Specifically, assuming that the angle of view is fine-tuned to shoot the same subject, automatic ranging after zooming is performed if the amount of zoom change from the zoom position at the previous distance measurement is small Do not. However, correction of the shift of the focus position due to the change in the angle of view described later is performed. Further, when the zoom change amount is large, it is assumed that the scene has changed, and automatic ranging after zooming is performed.

  This will be specifically described with reference to the flow of FIG. If the Zoom1 or Zoom2 switch is pressed in step S001, the angle of view is changed in step S002. Next, in step S003, it is determined whether or not the zoom change amount from the zoom position at the previous distance measurement is larger than a predetermined amount. If so, the process proceeds to step S004, and the AF operation is performed as in the first embodiment. Do. In step S006, the in-focus position and shooting conditions are stored. When the zoom change amount is smaller than the predetermined amount, the AF operation is not performed, and control is performed so as to correct only the focus position shift accompanying the zoom change in S005. The focus position shift is caused by a change in the focus position of the focus lens with respect to the same subject when the zoom position is changed. For example, as shown in FIG. 5, the focus position for the same subject varies depending on the zoom position. By correcting this deviation, it is possible to always maintain the in-focus state for the same subject even when the angle of view changes.

  By configuring as described above, when the zoom change amount is large, the AF operation is automatically performed and the shooting conditions are also updated, so that the distance measurement time can be shortened at the next shooting, When the amount of zoom change is small, only the focus position shift due to the zoom position change is corrected and no distance measurement is performed.Therefore, the waiting time after zoom operation is eliminated, and the angle of view changes little. It is possible to reduce the distance measurement time in a situation where the scene can be regarded as the same scene.

1 is a schematic diagram of a digital camera to which an autofocus device according to an embodiment of the present invention is applied. 4 is a flow of a zoom operation and a focus operation after the zoom operation according to the first embodiment. It is a flow of a focus operation when SW1 is pressed. 10 is a flow of a zoom operation and a focus operation after the zoom operation according to the second embodiment. It is a figure which shows the relationship between the zoom position with respect to the same subject, and a focusing focus lens position. An example of the relationship between the subject distance and the AF evaluation value is illustrated.

Explanation of symbols

DESCRIPTION OF SYMBOLS 01 Optical system 02 Focus lens 03 Image pick-up element 04 Pre-processing circuit 05 A / D converter 06 Memory controller 07 Memory 08 Recording medium 09 SW1 switch 10 SW2 switch 11 Zoom1 switch 12 Zoom2 switch 13 Imaging condition analysis means 14 Scanning position / range Setting means 15 AF evaluation value calculation circuit 16 Imaging condition storage means 17 Focus lens drive circuit 18 Zoom lens drive circuit 19 Control unit

Claims (3)

First distance measuring means for measuring a predetermined subject distance range;
A second distance measuring means for measuring a range narrower than the subject distance range;
Storage means for storing shooting conditions during distance measurement;
Zoom operation means for changing the angle of view;
Zoom operation-linked automatic focusing means that automatically changes the focus position to the in-focus position after zooming,
At the time of shooting, the second distance measuring means is selected when the same scene can be regarded as the same scene from the previous shooting conditions and the current shooting condition, and the first selection means is selected when the same scene cannot be regarded as the same scene. Control means to control, and
If the zoom position has not been changed since the last shooting, the distance measuring unit is selected based on the previous shooting and current shooting conditions. If the zoom has been changed, the shooting conditions for the distance measurement after the zoom operation are selected. And a distance measuring means is selected based on the current shooting conditions. A first distance measuring means for measuring a predetermined subject distance range; a second distance measuring means for measuring a range narrower than the subject distance range;
Storage means for storing shooting conditions during distance measurement;
Zoom operation means for changing the angle of view;
Focus correction means for correcting movement of the focus position due to zoom fluctuation;
Zoom operation-linked automatic focusing means that automatically changes the focus position to the in-focus position after zooming,
When the zoom change amount from the previous distance measurement is small after the zoom operation, the focus correction unit is executed, and when the zoom change amount is large, the zoom operation-linked automatic focusing unit is executed to record the shooting condition. First control means to:
At the time of shooting, the second distance measuring means is selected when the same scene can be regarded as the same scene from the previous shooting conditions and the current shooting condition, and the first selection means is selected when the same scene cannot be regarded as the same scene. Second control means for controlling as follows,
If the zoom position has not changed since the previous shooting, or if it is very small, select the distance measurement method based on the shooting conditions for the previous shooting and the current shooting. A distance measuring means is selected based on the imaging conditions and the current imaging conditions.   The imaging apparatus according to claim 1, wherein the second distance measuring unit measures a distance so as to include a focus position at the time of the previous distance measurement.

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