JP2014215475A5 - - Google Patents

Description

The present invention relates to an imaging apparatus and a control method therefor, and more particularly to a focus detection technique based on imaging plane phase difference AF.

There are a phase difference detection method and a contrast detection method as main automatic focus detection (autofocus: AF) methods of the imaging apparatus.
In the phase difference detection method, the defocus amount of the imaging optical system is determined from the phase difference between a pair of image signals obtained by imaging light beams from a subject that has passed through different exit pupil regions in the imaging optical system on a pair of line sensors. Ask. When the focus lens is moved by an amount corresponding to the defocus amount, the imaging optical system is in focus on the subject (see Patent Document 1). However, when a light beam is imaged on the phase difference detection line sensor, a general configuration in which the optical path to the image sensor is blocked cannot perform focus detection by the phase difference detection method while performing LV imaging.

On the other hand, in the contrast detection method, an in-focus state is obtained by searching for a focus lens position where a contrast evaluation value generated from an image pickup signal obtained using an image pickup element is maximized (see Patent Document 2). The contrast detection method is suitable for AF at the time of LV photographing because focus detection is performed based on the imaging signal, and is the most mainstream AF method at the time of LV photographing in recent years. However, the contrast detection method cannot easily determine the position and direction in which the focus lens is moved to focus on the subject. For this reason, the contrast detection method may require time for focusing, may cause the focus lens to move in the wrong direction, or may pass through the focus position. In particular, at the time of moving image shooting, an image shot while the focus lens is moving is also recorded. Therefore, the moving time and moving operation of the focus lens up to the in-focus state affect the image quality of the recorded moving image.

Therefore, in AF control during moving image shooting, a high-quality focus detection operation that has a small influence on a recorded image is required rather than a speed (responsiveness) until a focused state is reached. For this reason, an imaging plane phase difference detection method has been proposed as a method capable of high-quality focus detection operation even during LV shooting. The imaging surface phase difference detection method is a method for obtaining a defocus amount based on a phase difference between a pair of signals obtained from an imaging element.

As a method for realizing the imaging surface phase difference detection method, a method has been proposed in which the imaging pixel of the imaging element is pupil-divided by a microlens and light is received by a plurality of focus detection pixels to detect the defocus amount simultaneously with imaging. Yes. In Patent Document 3, each photodiode is configured to receive light from a different pupil plane of an imaging lens by dividing photodiodes collected by one microlens in one pixel. Has been. This makes it possible to detect the focus by the imaging plane phase difference detection method from the outputs of the two photodiodes. By using the imaging surface phase difference detection method, it is possible to obtain the defocus amount and know the moving direction and the moving amount of the focus lens even during LV shooting, so that the focus lens can be moved at high speed and with high quality. . One of the advantages of performing LV shooting with the imaging plane phase difference detection method is that the defocus amount can always be detected, so even in scenes where the subject distance changes continuously, such as when the subject approaches or moves away, It is excellent in the followability of the focused state with respect to the movement.

In Patent Document 4, if the difference between a plurality of image shift amounts detected simultaneously is small, it is determined that the reliability of the image shift amount is high, and focus detection is performed based on these image shift amounts, thereby improving the stability of focus detection control. Can be increased. On the other hand, if it is determined that there is a large difference between the plurality of increase deviation amounts and the reliability of the image deviation amount is low, focus detection is performed in consideration of the image deviation amounts detected in the past, for example, a continuous distance change. Focus detection control can be performed with emphasis on the ability to follow a certain subject.

An object of the present invention is to improve the quality of a focus detection operation using an imaging surface phase difference detection method in view of such problems of the conventional technology.

The foregoing objects, an acquisition unit for acquiring an image signal to be used for focus point detection of the phase difference detection method from an imaging element, based on the image signal, and detecting means for detecting the defocus amount of the photographing optical system, the photographing optical Control means for controlling the driving of the focus lens included in the system, and the control means detects a defocus amount not more than a predetermined amount in advance by detecting the defocus amount a plurality of times by the detecting means. This is achieved by an imaging device that controls the drive of the focus lens so as to stop the drive of the focus lens when it is detected more than a predetermined number of times more than a predetermined number of times.

With such a configuration, according to the present invention, it is possible to improve the quality of the focus detection operation using the imaging plane phase difference detection method.

The imaging device 201 of the present embodiment includes two photodiodes in one pixel, and generates an image signal used for automatic focus detection (hereinafter referred to as imaging plane phase difference AF) using an imaging plane phase difference detection method. Is possible. 2A schematically illustrates an example of a pixel configuration that does not correspond to the imaging surface phase difference AF, and FIG. 2B schematically illustrates an example of a pixel configuration that corresponds to the imaging surface phase difference AF. Here, in any case, it is assumed that a Bayer array primary color filter is provided. In the pixel configuration of FIG. 2B corresponding to the imaging surface phase difference AF, one pixel in FIG. 2A is divided into two in the horizontal direction, and AB two photodiodes (light receiving regions) are provided. Note that the division method illustrated in FIG. 2B is an example, and other methods may be used, or different division methods may be applied depending on the pixels.

Therefore, in this embodiment, in order to realize a focus detection operation that smoothly follows the change in the subject distance during moving image shooting, the focus stop determination unit 213 determines not only whether the subject is in focus but also the current subject. Judgment is made as to whether or not the tracking is continued. Then, if the subject is continuously being tracked, control is performed so that the focus lens continues to be driven without stopping even if it is determined to be in focus. Details regarding the operation of the in-focus stop determination unit 213 will be described later with reference to a flowchart describing the control of the camera body 20.

As described above, in the present embodiment, when the defocus amount within the depth of focus is detected, it is determined that the focus is in focus immediately, and driving of the focus lens is not stopped, but the defocus amount within the depth of focus is determined. When it is continuously detected a predetermined number of times or more, the driving of the focus lens is stopped. As a result, even when shooting a subject whose distance is gradually changing, focus detection that smoothly follows the subject distance without changing the focus state of the captured image greatly, that is, quality A good focus lens can be driven.

As described above, in the present embodiment, when the defocus amount within the depth of focus is detected, it is determined that the focus is in focus immediately, and driving of the focus lens is not stopped, but the defocus amount within the depth of focus is determined. When the predetermined ratio or more is detected, the driving of the focus lens is stopped. Even with this method, even when shooting a subject whose distance is gradually changing, focus detection that smoothly follows the subject distance without greatly changing the focus state of the captured image, that is, It is possible to drive a focus lens of good quality. In particular, the method of the first embodiment is more suitable for the effect of suppressing the occurrence of hunting under the condition that the defocus detection accuracy is lowered.

Claims (9)

Obtaining means for obtaining an image signal used for focus point detection of the phase difference detection method from an imaging element,
Detecting means for detecting a defocus amount of the photographing optical system based on the image signal;
Control means for controlling driving of a focus lens included in the photographing optical system,
The control means, when a defocus amount equal to or smaller than a predetermined amount is detected by a plurality of predetermined defocus amounts detected by the detection means, when the defocus amount equal to or smaller than the predetermined amount is detected more than once. An imaging apparatus that controls driving of the focus lens so as to stop driving of the focus lens.   The control means controls the drive of the focus lens so as to stop the drive of the focus lens when a defocus amount equal to or less than the predetermined amount is detected continuously a plurality of times in advance. The imaging apparatus according to claim 1. A determination unit for determining whether or not the photographing condition matches a predetermined condition for reducing the detection accuracy of the defocus amount;
When it is determined that the shooting condition matches the condition, the control means, when a defocus amount equal to or less than the predetermined amount is detected a predetermined number of times less than the predetermined multiple times, The imaging apparatus according to claim 1, wherein the driving of the focus lens is controlled so as to stop the driving of the focus lens.   The imaging apparatus according to claim 3, wherein the condition includes at least one of an image height of a focus detection area being a predetermined value or more and an aperture value being a predetermined value or more. . The focal length of the photographing optical system is variable,
The control means, when the focal length is less than or equal to a predetermined value, when a defocus amount equal to or less than the predetermined amount is detected a predetermined number of times less than the predetermined multiple times, 5. The image pickup apparatus according to claim 1, wherein the driving of the focus lens is controlled so as to stop the driving of the focus lens. 6. The detection means further determines the reliability of the detected defocus amount;
6. The control unit according to claim 1, wherein the control unit performs the control based on a number of times that a defocus amount equal to or less than the predetermined amount and having a reliability higher than a predetermined value is detected. The imaging apparatus according to item 1.   The imaging apparatus according to claim 1, wherein the control unit performs the control during moving image shooting. An acquisition step of acquiring from an imaging element of the image signal used for the focus point detection of the phase difference detection method,
Based on the prior Kizo signal, a detection step of detecting a defocus amount of the photographing optical system,
The pre-Symbol detection step predetermined plurality of defocus amounts detected by, when the following defocus amount predetermined quantity was detected following a predetermined or more times wherein the plurality of times, the imaging optical system And a control step of controlling the drive of the focus lens so as to stop the drive of the focus lens included in the image pickup apparatus.   The program for functioning the computer which an imaging device has as each means of the imaging device of any one of Claims 1-7.