JP4923587B2 - Focus detection apparatus, method and camera - Google Patents

Description

  The present invention relates to a focus detection apparatus and method for detecting a focus adjustment state of a photographic lens, and a camera including the focus detection apparatus.

  The focus adjustment state of the photographic lens, that is, the defocus amount is detected in a plurality of focus detection areas set in the shooting screen, and the defocus amounts that fall within a predetermined defocus amount range (width) are set as the same group. There is known a focus detection device that is divided into groups and selects an optimum group that is expected to capture a main subject from these groups (see, for example, Patent Document 1).

Prior art documents related to the invention of this application include the following.
Japanese Patent Laid-Open No. 02-178641

  However, in the conventional focus detection apparatus described above, a plurality of defocus amounts are grouped using a predetermined defocus width. Therefore, when the shooting distance is long, the difference in the defocus amount is small, and the group is originally different. Defocus amounts that should belong to the same group.

In a focus detection device that detects a plurality of defocus amounts with respect to a plurality of focus detection areas set in a photographing screen by a photographing lens , the invention of claim 1 obtains variations in the plurality of defocus amounts, and A variation width obtained by multiplying variation by a predetermined coefficient is set, the plurality of defocus amounts are arranged in numerical order, and if the difference between adjacent defocus amounts arranged in the numerical order exceeds the variation width, it is set as a separate group. And a control means for selecting a group for adjusting the focus of the photographing lens from the plurality of groups.
A focus detection method for detecting a plurality of defocus amounts with respect to a plurality of focus detection areas set in a photographing screen by a photographing lens, and obtaining a variation in the plurality of defocus amounts, A variation width obtained by multiplying variation by a predetermined coefficient is set, the plurality of defocus amounts are arranged in numerical order, and if the difference between adjacent defocus amounts arranged in the numerical order exceeds the variation width, it is set as a separate group. And a group for adjusting the focus of the photographing lens is selected from the plurality of groups.

  According to the present invention, it is possible to appropriately group a plurality of focus adjustment states so that focus detection areas capturing different subjects are not included in the same group even if shooting conditions such as a shooting distance change. Can do.

  An embodiment in which the focus detection apparatus of the present invention is applied to a single-lens reflex digital still camera will be described. The focus detection apparatus of the present invention is not limited to a single-lens reflex digital still camera, and can be applied to various cameras including a silver salt film camera and a video camera.

  FIG. 1 is a cross-sectional view of a single-lens reflex digital still camera provided with a focus detection apparatus according to an embodiment. Note that illustration and description of camera members not directly related to the present invention are omitted. An interchangeable lens 3 is attached to the body 2 of the camera 1. The camera body 2 includes a main mirror 4, a sub mirror 5, an image sensor 6, a focus detection device 7, a finder screen 8, a penta roof prism 9, an eyepiece lens 10, a control device 11, and the like. The interchangeable lens 3 includes a photographing lens 12 and the like.

  A part of the light from the subject that has passed through the photographing lens 12 is reflected by the main mirror 4 and guided to the finder screen 8, and part of the light is transmitted to the sub-mirror 5. A subject image is formed on the finder screen 8 by subject light guided to the finder screen 8, and the subject image is visually recognized by the photographer via the penta roof prism 9 and the eyepiece 10. On the other hand, the subject light guided to the sub mirror 5 is reflected by the sub mirror 5 and guided to the focus detection device 7, and the focus detection device 7 detects the defocus amount indicating the focus adjustment state of the photographing lens 12.

  A light beam that has passed through a pair of different areas of the photographic lens 12 is incident on the image sensor 76 via the field mask 71, condenser lens 72, bending mirror 73, aperture mask 74, and re-imaging lens 75. Form. In this embodiment, as shown in FIG. 2, eleven focus detection areas a to k are set on the shooting screen 21 set on the planned imaging plane of the shooting lens 12, and shooting is performed in each focus detection area. The focus adjustment state of the lens 12, that is, the defocus amount is detected. In other words, the defocus amount of the photographing lens 12 is detected in a plurality of focus detection areas of the object scene.

  In this embodiment, a plurality of defocus amounts detected in 11 focus detection areas a to k are grouped, an optimum group predicted to capture the main subject is selected, and the group is selected. The final defocus amount is obtained based on the defocus amount belonging to, and the focus of the photographic lens 12 is adjusted.

  Here, a method for grouping a plurality of defocus amounts detected in a plurality of focus detection areas a to k in the photographing screen 21 will be described. The shooting screen 21 includes various subjects in addition to the main subject intended by the photographer. When a plurality of defocus amounts are grouped, they are detected in a focus detection area that captures the same subject. It is necessary to ensure that the defocus amount thus set is included in the same group.

  For example, consider a shooting scene in which a person is standing in front of a background. In this shooting scene, the defocus amount of the focus detection area capturing the person must be grouped into the same group, and the defocus amount of the focus detection area capturing the background must be grouped into another same group. However, the difference in the defocus amount between the person and the background varies depending on the shooting distance. Generally, when the shooting distance is long, the difference in the defocus amount is small, and when the shooting distance is close, the difference in the defocus amount is large.

  Therefore, when grouping is performed using a predetermined defocus width that is set in advance as in the conventional focus detection device, when the shooting distance is short, the difference in defocus amount is large, so the defocus amount between the person and the background Can be accurately divided into separate groups, but when the shooting distance is long, the difference in defocus amount is small, making it difficult to accurately separate the defocus amounts of the person and the background into separate groups. Therefore, the background defocus amount may be mixed into the person defocus amount. In such a case, an appropriate defocus amount cannot be obtained, and the focus detection accuracy decreases.

  The above grouping problem also occurs due to the difference in the focal length of the photographing lens. In general, even if the photographing distance is the same, the difference in defocus amount for different subjects is small when the focal length of the photographing lens is short, and the difference in defocus amount for different subjects is large when the focal length is long. Therefore, when grouping is performed using a fixed defocus width that is set in advance as in the conventional focus detection device, the difference between the defocus amounts is large in a photographic lens with a long focal length. However, it is difficult to accurately divide the defocus amount between the person and the background into separate groups because the difference in the defocus amount is small with a photographic lens with a short focal length. Therefore, the background defocus amount may be mixed into the person defocus amount. In such a case, as described above, an appropriate defocus amount cannot be obtained, and the focus detection accuracy decreases.

  Therefore, in this embodiment, only the defocus amount detected in the focus detection area that captures the same subject is precisely the same group regardless of the shooting conditions such as the shooting distance and the focal length of the shooting lens 12. Group so that it is included in The grouping method will be described below.

  A defocus amount obtained from 11 focus detection areas a to k in the photographing screen 21 shown in FIG. 2 is assumed to be Xi (i = 1 to N). Here, N represents the number of valid data. The defocus amount is not always detected in all eleven focus detection areas a to k, and there is an area where the focus cannot be detected, or even if the defocus amount is obtained, the reliability is determined to be unreliable. Sometimes it is done.

First, a variance v of a set of N valid data, that is, N reliable defocus amounts is obtained by the following equation.
v = Σ (Xi−Xave) ² / N (1)
In Equation (1), Xave is an average value of N defocus amounts, and Σ represents a sum of i = 1 to N. Next, a standard deviation σ is obtained by the following equation as an amount representing the degree of variation in the set of N defocus amounts.
σ = √ (v) (2)
A defocus width H for grouping N defocus amounts Xi (i = 1 to N) is determined by the following equation using the standard deviation σ representing the variation degree of the set.
H = α · σ (3)
In the equation (3), α is a coefficient, and usually about 0.4 to 0.6 is appropriate.

一実施の形態の焦点検出装置は、被写体がカメラ１に近いほど小さいデフォーカス量を検出するので、デフォーカス量を小さい順に並べるということは焦点検出エリアａ〜ｋで捕捉されている複数の被写体をカメラ１に近い順に並べることになる。
The grouping is performed by the following procedure using the grouping defocus width H. First, N (11 in this example) defocus amounts Xi (i = 1 to N) shown in Table 1 are arranged in order of increasing values, and an array Y j ( j = 1 to N) as shown in Table 2 is arranged. Ask for.

Since the focus detection apparatus according to the embodiment detects a smaller defocus amount as the subject is closer to the camera 1, arranging the defocus amounts in ascending order indicates a plurality of subjects captured in the focus detection areas a to k. Are arranged in the order closest to the camera 1.

Next, when the difference between two adjacent defocus amounts in the array Y j is larger than the grouping defocus width H, it is assumed that there is a grouping boundary between the two defocus amounts. . That is,
| Y j + 1−Y j |> H (4)
Is true, the defocus amount Y j and Y j +1 is set as a grouping boundary. Note that there may be a plurality of grouping boundaries among the N defocus amounts Y j . Further, when the difference between two adjacent defocus amount of N defocus amount Y j is less than all defocus width H, N or all of the defocus amount Y j is the fact that in the same group .

The grouping procedure will be described in detail with reference to Tables 1 and 2. The standard deviation σ of the N defocus amounts Xi is σ = 0.148 from the above equations (1) and (2). When the coefficient α is 0.5, the grouping defocus width H is H = 0.074 from the above equation (3). In the array Y j (Table 2) in which N defocus amounts Xi are arranged in ascending order, when the boundary of grouping is examined by the above-described determination formula (4), the difference between adjacent defocus amounts is larger than the defocus width H. It is assumed that the increase is between Y1 and Y2, between Y3 and Y4, and between Y7 and Y8, and there is a grouping boundary between these adjacent defocus amounts. As a result, the N defocus amounts of the array Y j (Table 2) are 4 in (Y1), (Y2, Y3), (Y4, Y5, Y6, Y7), (Y8, Y9, Y10, Y11). Divided into groups. When the defocus amount is represented by Xi, there are four groups (X3), (X6, X10), (X1, X4, X8, X7), (X11, X5, X9, X2).

  FIG. 3 is a flowchart showing the operation of the embodiment. The microcomputer of the control device 11 repeatedly executes this operation while the camera 1 is powered on. In step 1, it is confirmed whether or not a release button (not shown) has been half-pressed. In step 2, the defocus amount is detected in the eleven focus detection areas a to k by the focus detection device 7, and photometry is performed by a photometry device (not shown).

  In step 3, the grouped defocus width H is determined by the above-described procedure based on the N defocus amounts Xi (the number of valid data) of the detection results, and in step 4, N defocus amounts are determined by the defocus width H Group Xi. In step 5, an optimum group is selected from a plurality of defocus amount groups. A well-known method can be applied to this optimal group selection method, but in this embodiment, the closest defocus amount group that is likely to capture the main subject is selected as the optimal group. .

  In step 6, the final defocus amount is determined based on the defocus amount belonging to the optimum group. As a method for determining the final defocus amount, a known method can be applied. In this embodiment, however, an average value of a plurality of defocus amounts belonging to the optimum group is determined as the final defocus amount. To do. In step 8, the photographic lens 12 is driven based on the final defocus amount to adjust the focus.

  In step 8, it is confirmed whether or not a release button (not shown) is fully pressed. If there is a release full press, the process proceeds to step 9. If there is no release full press, the process returns to step 1. If the release has been fully pressed, after the image is picked up by the image pickup device 6 in step 9, an image is recorded in an image recording device (not shown) in step 10.

  The result of grouping by the method of the embodiment will be described. FIG. 4 and FIG. 5 are images when a person who is a main subject is photographed at different photographing distances. In these drawings, the area numbers of the eleven focus detection areas a to k shown in FIG. 2 are not shown. In the image shown in FIG. 4 in which the person of the main subject is photographed at a far photographing distance, the defocus width H = 0.02 is obtained based on the detected N defocus amounts Xi (i = 1 to N). As a result of the grouping, the focus detection areas a and b capturing the person of the main subject are divided into the same group, and the focus detection areas c to k capturing the background are divided into the same group. . As described above, since the difference in the defocus amounts detected in the plurality of focus detection areas becomes smaller as the shooting distance is longer, the grouped defocus width H needs to be reduced. According to the grouping method of this embodiment, when the shooting distance is long, the defocus width H is set to a small value, and the defocus amount of the focus detection area capturing the same subject (person and background) Can be accurately grouped so that they are in the same group.

  On the other hand, in the image shown in FIG. 5 in which the person of the main subject is photographed at a close photographing distance, the defocus width H = 0.08 is obtained based on the detected N defocus amounts Xi (i = 1 to N). As a result of grouping, the focus detection areas a and b capturing the person of the main subject are in the same group, and the focus detection areas c to k capturing the background are in the same group. Divided. As described above, since the difference between the defocus amounts detected in the plurality of focus detection areas increases as the shooting distance is shorter, the grouped defocus width H needs to be increased. According to the grouping method of this embodiment, a large value is set for the defocus width H when the shooting distance is short, and the defocus amount of the focus detection area capturing the same subject (person and background). Can be accurately grouped so that they are in the same group.

  That is, even if the shooting distance changes, the N focus detection areas are accurately divided into a group capturing a person and a group capturing a background, and the grouping method according to the embodiment is appropriate. It shows that there is. From this, by determining the final defocus amount (for example, an average value) based on the defocus amounts of the focus detection areas a and b of the same group capturing the person, and performing the focus adjustment of the photographing lens, You can take a photo that is accurately focused on the person who is the main subject.

  In FIG. 4, when the person of the main subject is photographed at a far distance, the grouping is performed with the defocus width H = 0.02. However, if the defocus width H is 0.08, N defocus amounts are assumed. The difference between adjacent defocus amounts of Xi (i = 1 to N) is less than the defocus width H = 0.08, and it is determined that all the defocus amounts Xi belong to the same group. That is, although the shooting distance is long, the defocus width H is too large, so that grouping cannot be performed properly. As a result, the final defocus amount is determined based on all N defocus amounts Xi, and the focus of the photographic lens is adjusted, so that the person who is the main subject is accurately focused as shown in FIG. You will not be able to take the photos you had.

  Similarly, in FIG. 5, when the person of the main subject is photographed at a close photographing distance, the grouping is performed with the defocus width H = 0.08. However, if the defocus width H is 0.02, N pieces are assumed. The number of boundaries where the difference between adjacent defocus amounts of the defocus amount Xi (i = 1 to N) is greater than or equal to the defocus width H = 0.02 is increased, and the N defocus amounts Xi are divided into a number of groups. It is done. That is, although the shooting distance is short, the defocus width H is too small, so that grouping cannot be performed properly. As a result, only the focus detection area that captures the person who is the main subject intended by the photographer cannot be accurately extracted, and the focus detection area that captures the background is included in the focus detection area that captures the person. As a result, it becomes impossible to obtain an accurate defocus amount for the person who is the main subject. Therefore, since the focus adjustment of the taking lens is performed based on an inappropriate defocus amount, it is not possible to take a photograph that is accurately focused on the person who is the main subject as shown in FIG.

<< Modification of Embodiment >>
In the above-described embodiment, an example in which the standard deviation σ of the set is used as an amount representing the degree of variation of a plurality of defocus amounts detected in a plurality of focus detection areas has been described. It is good also as a quantity showing the variation degree of a quantity set. For example, an average value σ ′ of absolute values of deviations from the average value Xave of the defocus amount set shown in the following equation may be used as an amount representing the degree of variation in the defocus amount set.
σ ′ = Σ | Xi−Xave | / N (5)
In equation (5), N represents the number of valid data described above, and Σ represents the sum of i = 1 to N.

  According to an embodiment, in a focus detection device that detects a plurality of focus adjustment states of a photographic lens in a plurality of focus detection areas of an object scene, a plurality of focus adjustment state variations are obtained, and a plurality of focus adjustment states are determined based on the variation. The focus adjustment state is divided into a plurality of groups, a group is selected from the plurality of groups, and the final focus adjustment state is determined based on the focus adjustment state belonging to the selected group. A plurality of focus adjustment states can be appropriately grouped so that focus detection areas capturing different subjects are not included in the same group even if shooting conditions such as distance change.

  According to one embodiment, the variation range for dividing the plurality of focus adjustment states into a plurality of groups based on the variation is determined, and the plurality of focus adjustment states are grouped using the variation range. Even if shooting conditions such as shooting distance and focal length change, multiple focus adjustment states can be more appropriately grouped so that focus detection areas that capture different subjects are not included in the same group. .

It is a figure which shows the structure of the camera of one Embodiment. It is a figure which shows the example of arrangement | positioning of a focus detection area. It is a flowchart which shows operation | movement of one Embodiment. It is a figure for demonstrating the imaging result by grouping of one Embodiment. It is a figure for demonstrating the imaging result by grouping of one Embodiment. It is a figure for demonstrating the imaging result by grouping of one Embodiment. It is a figure for demonstrating the imaging result by grouping of one Embodiment.

Explanation of symbols

7 Focus Detection Device 11 Control Device 12 Shooting Lens

Claims (6)

In a focus detection device that detects a plurality of defocus amounts with respect to a plurality of focus detection areas set in a shooting screen by a shooting lens ,
Obtaining a variation in the plurality of defocus amounts, setting a variation width obtained by multiplying the variation by a predetermined coefficient, arranging the plurality of defocus amounts in numerical order, and determining a difference between adjacent defocus amounts arranged in the numerical order. when exceeding the variation width is divided into a plurality of groups by another group, characterized in that Ru comprising a control means for selecting a group for performing focus adjustment of the taking lens from the plurality of groups Focus detection device. The focus detection apparatus according to claim 1,
The focus detection apparatus characterized in that the control means changes the variation width according to an imaging distance . The focus detection apparatus according to claim 1 or 2,
The focus detection apparatus characterized in that the control means obtains a standard deviation of the plurality of defocus amounts and uses this as the variation. The focus detection apparatus according to claim 1 or 2 ,
The focus detection apparatus, wherein the control unit obtains an average value of absolute values of deviations from an average value of the plurality of defocus amounts, and uses the average value as the variation. The focus detection apparatus according to any one of claims 1 to 4,
  A camera comprising: focus adjusting means for adjusting the focus of the photographing lens based on a defocus amount belonging to the group selected by the control means. In a focus detection method for detecting a plurality of defocus amounts for a plurality of focus detection areas set in a shooting screen by a shooting lens,
  Obtaining a variation in the plurality of defocus amounts, setting a variation width obtained by multiplying the variation by a predetermined coefficient, arranging the plurality of defocus amounts in numerical order, and determining a difference between adjacent defocus amounts arranged in the numerical order. A focus detection method characterized in that when the variation width is exceeded, the group is divided into a plurality of groups, and a group for performing focus adjustment of the photographing lens is selected from the plurality of groups.

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