JP2007024941A - Focus detecting apparatus, focusing apparatus and imaging apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a focusing apparatus capable of carrying out AF at high speed and with high accuracy using phase difference detection system AF and imaging surface AF, in focus detecting areas with a greater number than that of a conventional manner. <P>SOLUTION: In the focus detecting area 21, focus detection only by the phase difference detecting system can be carried out. In the focus detecting area 22, focus detection by the phase difference detecting system and the calculation of a contrast value by using an imaging signal can be carried out. In the focus detecting area 22 where the phase detecting system focus detection is unfeasible, an estimated operation is performed based on a defocus quantity detected for the focus detecting area 21 near the area 22, and the phase difference detection system AF is carried out by using the estimated defocus quantity. For example, in the case a focus detecting area 22C is selected as a focus detecting area to be AF, the mean value of the defocus quantities of the focus detecting areas 21c and 21d nearest to the area 22C is used as the estimated defocus quantity of the focus detecting area 22C. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a focus detection apparatus, a focus adjustment apparatus, and an imaging apparatus that perform focus detection using a phase difference detection method and focus detection using an imaging signal.

  As an AF system for a digital camera, a hybrid focus adjustment device using a phase difference detection AF and an imaging surface AF is known (for example, see Patent Document 1). In the conventional technique, after performing the phase difference detection method AF, the contrast value is calculated using the imaging signal in the same focus detection area as in the phase difference detection method AF, and the imaging surface AF is calculated based on the contrast value. Furthermore, by performing it, both high speed AF and high accuracy are achieved.

JP-A-9-274129

  However, in the case of the imaging surface AF, the focus evaluation value can be obtained in an arbitrary region of the imaging surface. However, in the case of the phase difference detection method AF, focus detection is performed only in the focus detection area where the AF sensor is provided. Can not. Therefore, conventionally, high-speed and high-precision AF using the phase difference detection AF and imaging surface AF can be performed only in a limited number of focus detection areas, and in order to perform high-speed and high-precision AF in a wider range. Increasing the number of AF sensors increases the cost and is difficult in terms of space.

According to a first aspect of the present invention, there is provided a focus detection apparatus comprising: a first detection unit configured to detect a focus adjustment state by a first detection method with respect to a first focus detection region set in a field image plane by a photographing optical system; The second detection means for detecting the focus adjustment state by the second detection method with respect to the second focus detection area set in the field image plane, and the first detection means with respect to the first focus detection area And determining means for determining a focus adjustment state according to the first detection method for the second focus detection area based on the detected focus adjustment state.
According to a second aspect of the present invention, in the focus detection apparatus according to the first aspect, the determination is made based on a focus adjustment state of a region set closest to the second focus detection region in the first focus detection region. Is to do.
According to a third aspect of the present invention, there is provided a focus adjusting apparatus according to the first or second aspect, and the focus adjustment of the photographing optical system based on the focus adjustment state determined by the determining means with respect to the second focus detection area. Control means for further performing a focus adjustment operation of the photographing optical system based on the focus adjustment state detected by the second detection means after the operation is performed.
According to a fourth aspect of the present invention, there is provided an imaging apparatus comprising: the focus adjustment apparatus according to the third aspect of the present invention; and an imaging element that captures a subject image. The image pickup signal relating to the focus detection region is extracted, and the contrast value that is the focus adjustment state by the second detection method is detected based on the high-frequency component of the extracted image pickup signal.

  According to the present invention, the focus adjustment state according to the first detection method can be obtained by the determination means even for the second focus detection region where the focus adjustment state cannot be detected by the first detection means. Therefore, the focus adjustment state according to the first detection method and the focus adjustment state according to the second detection method can be obtained also for the second focus detection region.

  Hereinafter, the best mode for carrying out the present invention will be described with reference to the drawings. FIG. 1 is a diagram showing a schematic configuration of a digital camera equipped with a focus adjusting apparatus according to the present invention. The digital camera shown in FIG. 1 is an interchangeable lens type digital camera, and a lens barrel 3 having a photographing lens 2 is attached to the camera body 1 in a replaceable manner. The photographic lens 2 is provided with a focus lens (not shown) for focus adjustment, and the focus lens is driven in the optical axis direction by the lens driving unit 4 to adjust the focus of the photographic lens 2.

  Reference numeral 5 denotes an image pickup device for picking up an image, and a CCD, a CMOS or the like is used. A quick return mirror 6 that reflects the subject light that has passed through the photographing lens 2 to the finder optical system is disposed between the photographing lens 2 and the image sensor 5. The quick return mirror 6 has a main mirror 6a and a sub mirror 6b provided behind the main mirror 6a. Part of the subject light passes through the semi-transmissive main mirror 6a, is reflected downward by the sub-mirror 6b, and then enters the focus detection module 7.

  On the other hand, the subject light reflected by the main mirror 6 a forms an image on the finder screen 8 provided at a position optically conjugate with the image sensor 5. The subject image formed on the finder screen 8 can be observed through the pentaprism 9 and the eyepiece 10. At the time of shooting, the quick return mirror 6 is moved from the optical path of the subject light to the outside of the optical path, and a subject image is formed on the image sensor 5.

  The focus detection module 7 performs focus detection by a known phase difference detection method, and includes a field mask, a field lens, a separator lens, an AF sensor, and the like. As this AF sensor, a charge accumulation type image sensor is generally used, and a signal corresponding to the light intensity distribution of a pair of subject images formed on the image sensor is output. The phase difference AF calculation unit 11 performs focus detection calculation based on the output signal of the focus detection module 7 and calculates the defocus amount of the subject image plane with respect to the planned focal plane of the photographing lens 2. In the present embodiment, as shown in FIG. 2A, phase difference focus detection can be performed with 11 focus detection areas 21 indicated by solid lines on the imaging screen 20.

  On the other hand, the imaging signal of the imaging device 5 is input to the imaging surface AF calculation unit 12. The imaging plane AF calculation unit 12 calculates a focus evaluation value obtained by extracting a high frequency component of the imaging signal. This focus evaluation value is data for evaluating the contrast of the subject image, and is maximized when a focused subject image is obtained. The imaging plane AF calculation unit 12 can calculate the focus evaluation value for an arbitrary area of the shooting screen 20, but in the present embodiment, as shown in FIG. The focus evaluation values are set so that a total of 41 focus detection areas 21 and 22 including the detection area 21 and 30 focus detection areas 22 indicated by broken lines can be calculated.

  The user can select at least one focus detection area from the 41 focus detection areas 21 and 22 by the area selection operation unit 13. The AF control unit 14 drives the lens driving unit 4 based on the calculation results of the phase difference AF calculation unit 11 and the imaging plane AF calculation unit 12 and the focus detection area selected by the area selection operation unit 13 to photograph. The focus of the lens 2 is adjusted. SW1 is a half-push switch that is turned on in conjunction with the half-pressing operation (AF operation) of the release button of the camera, and SW2 is a full-push switch that is turned on in conjunction with the full-pressing operation (shooting operation) of the release button.

<< Explanation of AF operation >>
FIG. 3 is a flowchart for explaining the AF operation in the present embodiment, and shows processing from AF to photographing. Before half-pressing the release button of the camera, the user operates the area selection operation unit 13 to select a desired focus detection area from the 41 focus detection areas 21 and 22 shown in FIG. In the flowchart of FIG. 3, a case where a focus detection area where phase difference focus detection is not possible and indicated by reference numeral 22C in FIG. 2B is selected will be described as an example.

  In step S1, the focus detection area 22C selected by the area selection operation unit 13 is set as a focus detection area for performing the AF operation. In step S2, it is determined whether or not the half-press switch SW1 in FIG. 1 is turned on, that is, whether or not AF is instructed. When the half-press switch SW1 is turned on, the process proceeds from step S2 to step S3. In step S3, the phase difference AF calculation unit 11 calculates a defocus amount for each of the 11 focus detection areas 21 shown in FIG.

  In step S4, the selected focus detection area, that is, the focus detection area 22C set in step S1, is the focus detection area 21 in which focus detection can be performed by both the phase difference AF calculation unit 11 and the imaging plane AF calculation unit 12. It is determined whether or not. Here, since the focus detection area 22C that can be detected only by the imaging surface AF calculation unit 12 is selected, it is determined as NO in Step S4, and the process proceeds to Step S5. On the other hand, if any of the eleven focus detection areas 21 is selected in step S1, YES is determined in step S4, and the process proceeds to step S6.

  In step S5, the defocus amount of the selected focus detection area 22C is determined based on the defocus amount of each focus detection area 21 calculated in step S3. There are various determination methods, and several examples will be described later. In step S6, a lens driving amount up to the focal point is calculated based on the defocus amount detected in step S3 or the defocus amount determined in step S5, and the focus lens is driven based on the calculated lens driving amount. To do.

  In step S7, it is determined whether or not the release button is fully pressed and the full-press switch SW2 of FIG. 1 is turned on. If it is determined in step S7 that the button is fully pressed, the process proceeds to step S9. If it is determined that the button is not fully pressed, the process proceeds to step S8. In step S8, it is determined whether or not the half-pressed state has been released, that is, whether or not the half-press switch SW1 has changed from on to off. If it is determined in step S8 that it is turned off (released), the process returns to step S2, and if it is determined that the on-state is continued (not released), the process returns to step S7.

  When the release button is fully pressed and the process proceeds from step S7 to step S9, the quick return mirror 6 is retracted (mirror up) to a position outside the subject optical path in step S9. In step S10, a contrast value is calculated based on the imaging signal in the focus detection area 22C set in step S1, and a focus adjustment operation using a known imaging surface AF is performed on the basis of the contrast value to finally determine the photographing lens 2. Adjust the focus. In step S11, a photographing operation is performed.

<Estimation calculation method>
Here, the estimation calculation method will be briefly described. In the first estimation calculation method, the focus detection area 21 that is closest to the selected focus detection area is selected, and when there are a plurality of closest areas, the average of their defocus amounts is calculated, and the closest proximity area is equal to one. In the case where the number is one, the defocus amount is set as the estimated defocus amount of the selected focus detection area. For example, when the focus detection area 22C shown in FIG. 2B is selected, the average defocus amount of the focus detection areas 21c and 21d located on the left and right is set as the estimated defocus amount of the focus detection area 22C.

  FIG. 4 shows the defocus amounts detected in the focus detection areas 21a, 21b, 21c, 21d, and 21e arranged in a horizontal row shown in FIG. 2B. A curve L indicates the defocus amount in the area where the focus detection areas 21a to 21e in FIG. For each focus detection area 21a to 21e, defocus amounts D (a) to D (e) in the black square marks shown on the curve L are detected.

  Then, the defocus amount of the focus detection area 22C is estimated and calculated as (D (c) + D (d)) / 2. 4 indicate the estimated defocus amounts calculated for the focus detection areas 22A to 22D. When the focus detection area 22F is selected, the closest focus detection area 21 is the four focus detection areas 21b, 21c, 21f, and 21g, and therefore the estimated defocus amount of the focus detection area 22F is (D ( b) + D (c) + D (f) + D (g)) / 4.

  Furthermore, instead of simply taking the average, weighting may be performed according to the reliability of the defocus amount detected for the focus detection area 21. As described above, the AF sensor of the focus detection module 7 outputs a signal corresponding to the light intensity distribution of the subject image, but the reliability of the calculated defocus amount greatly depends on the contrast that is the luminance distribution of the subject. To do. In the case of a subject with low contrast, the defocus amount is calculated based on an output signal sequence with a low S / N ratio, and the reliability is low. Therefore, a reliability evaluation value corresponding to the subject luminance is obtained for each focus detection area 21, and an average is calculated by assigning more weight to the defocus amount of the focus detection area 21 with higher reliability. By performing such estimation calculation, the calculation accuracy of the estimated defocus amount for the focus detection area 22C is improved.

  In addition, for example, when shooting is performed at a very short time interval as in continuous shooting, the calculation may be performed in consideration of a temporal change in the defocus amount. In FIG. 5, a curve L1 represents the distribution of the defocus amount at the time of shooting the first image, and a curve L2 represents the distribution of the defocus amount at the time of shooting the second image. That is, the defocus amount changed from the curve L1 to the curve L2 due to the movement of the subject. As a result, the defocus amount detected in the focus detection area 21d changes from D (d) to D (d) + ΔD.

  Therefore, it is considered that the defocus amount in the focus detection area 22C is also larger by ΔD than the defocus amount estimated for the first sheet (for example, (D (c) + D (d)) / 2). When such an estimation calculation is performed and an AF operation using the phase difference detection method is performed, the subsequent imaging surface AF operation can be greatly shortened, and the imaging surface AF operation can be omitted.

  As described above, in the present embodiment, for the focus detection area 22 where the focus detection by the phase detection method cannot be performed, an estimation calculation is performed based on the defocus amount detected for the focus detection area 21 around the focus detection area 22. Thus, the phase difference detection method AF is performed using the estimated defocus amount. Therefore, even in the focus detection area 22 where only the imaging surface AF can be conventionally performed, high-speed and high-precision AF using both the phase difference detection method AF and the imaging surface AF can be performed.

  In the above-described embodiment, the digital camera has been described as an example. However, the present invention is not limited to the digital camera and can be applied to any imaging apparatus having two types of focus detection methods. In addition, the present invention is not limited to the above embodiment as long as the characteristics of the present invention are not impaired. For example, instead of performing the imaging surface AF using an imaging element for photographing, an AF imaging element may be separately provided at a position optically equivalent to the imaging element in the observation optical system or the like. In this case, both the phase difference AF and the imaging surface AF can be performed without mirror-up.

It is a figure which shows schematic structure of the digital camera carrying the focus adjustment apparatus by this invention. It is a figure which shows arrangement | positioning of the focus detection areas 21 and 22, (a) shows only the focus detection area 21, (b) shows both the focus detection areas 21 and 22. FIG. It is a flowchart explaining AF operation | movement. It is a figure which shows the defocus amount detected in the focus detection areas 21a-21e. It is a figure explaining an estimation calculation method, and shows a defocus amount L1 at the time of first image shooting and a defocus amount L2 at the time of second image shooting.

Explanation of symbols

2: Shooting lens 4: Lens drive unit 5: Image sensor 7: Focus detection module 11: Phase difference AF calculation unit 12 Imaging surface AF calculation unit 13: Area selection operation unit 14: AF control unit 20: Shooting screen 21, 22: Focus detection area

Claims (4)

First detection means for detecting a focus adjustment state by a first detection method with respect to a first focus detection region set in the field image plane by the photographing optical system;
Second detection means for detecting a focus adjustment state by a second detection method with respect to a second focus detection region set in the object scene image plane;
Determining means for determining a focus adjustment state according to the first detection method for the second focus detection region based on a focus adjustment state detected by the first detection unit with respect to the first focus detection region; A focus detection apparatus comprising the focus detection apparatus. The focus detection apparatus according to claim 1,
The determination means performs the determination based on a focus adjustment state of an area set in a position closest to the second focus detection area in the first focus detection area. . The focus detection apparatus according to claim 1 or 2,
Based on the focus adjustment state detected by the second detection means after performing the focus adjustment operation of the photographing optical system based on the focus adjustment state determined by the determination means with respect to the second focus detection area. And a control means for further performing a focus adjustment operation of the photographing optical system. A focusing device according to claim 3;
An image sensor that captures a subject image;
The second detection means extracts an imaging signal related to the first and second focus detection areas from an imaging signal of the imaging element, and uses the second detection method based on a high frequency component of the extracted imaging signal. An image pickup apparatus that detects a contrast value in a focus adjustment state.

Images