JP2011085690A - Focus detector and camera - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To properly focus a camera even when a main object exists in the neighborhood of a boundary of blocks obtained by dividing a plurality of focus detection areas. <P>SOLUTION: A focus detector includes: focus detection means 4, 6 for detecting focus adjusting states of imaging optical systems 1 in three or more focus detection areas provided in an image face of the imaging system 1; a classifying means 6 for classifying the three or more focus detection areas into a plurality of the blocks; a block selecting means 6 for selecting a predetermined block in the plurality of the classified blocks; and a control means 6 for determining the amount of focus adjustment control of the imaging optical system 1, on the basis of the focus adjustment state detected for the focus detection area included in the selected block. The classifying means 6 classifies the blocks so that at least one of the focus detection areas included in the block overlaps the focus detection area included in the adjacent blocks. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to a focus detection apparatus and a camera.

  A plurality of focus detection areas set in the shooting screen are divided into a plurality of blocks, and the blocks are grouped based on the defocus amount for each of the plurality of blocks, and the main subject is captured from these groups. A focus detection apparatus that selects a block having a defocus amount corresponding to an area that is expected to be used is known (see Patent Document 1).

JP 2008-197210 A

  In the prior art, when a main subject is present near the boundary between a plurality of blocks, there is a problem in that the selected block is different even if the camera angle is slightly shifted. If the selected block is different, the main subject cannot be correctly focused.

  A focus detection apparatus according to the present invention includes a focus detection unit that detects a focus adjustment state of a photographing optical system in each of three or more focus detection areas provided in an image plane of the photographing optical system, and three or more focus detections. Classification means for classifying an area into a plurality of blocks, block selection means for selecting a predetermined block among the plurality of classified blocks, and focus adjustment detected for a focus detection area included in the selected block Control means for determining a focus adjustment control amount of the photographing optical system based on the state, and the classification means so that at least one of the focus detection areas included in the block overlaps with the focus detection area included in the adjacent block. It is characterized by classifying blocks.

  According to the present invention, it is possible to properly focus even when a main subject exists near the boundary of a block into which a plurality of focus detection areas are divided.

It is a figure which shows the structure of one embodiment. FIG. 6 is a layout diagram of focus detection areas set in an image plane. It is a figure which shows a focus detection optical system. It is a figure which shows the example which classified the arrangement position of the focus detection area into the some block. It is a figure which illustrates the position and range of a block. It is a figure which illustrates the position and range of a block. It is a figure which illustrates the position and range of a block. It is a figure which illustrates the position and range of a block. It is a figure explaining the focus detection area and weight contained in a block. It is a figure explaining the focus detection area and weight for determining an employment area. It is a figure explaining the reliability of a focus detection result. It is a figure explaining the reliability of a focus detection result. It is a flowchart explaining the flow of a focus adjustment operation | movement.

  Hereinafter, embodiments for carrying out the present invention will be described with reference to the drawings. FIG. 1 is a diagram illustrating a single-lens reflex camera equipped with a focus adjustment apparatus according to an embodiment of the present invention. In FIG. 1, the light from the subject that has passed through the photographing lens 1 passes through the half mirror portion of the main mirror 2, is reflected by the sub mirror 3, and is guided to the focus detection device 4. The light from the subject that has passed through the photographing lens 1 is reflected by the main mirror 2 and guided to the finder 5 at the top of the camera. The main mirror 2 and the sub mirror 3 are placed in the photographing optical path before photographing as shown in the figure, and are flipped upward and retracted from the photographing optical path during photographing. The control device 6 includes a microcomputer (not shown) and peripheral components such as a memory, and obtains the focus adjustment state (defocus amount) of the photographing lens 1 based on the focus detection signal output from the focus detection device 4. Further, the lens driving device 7 is driven and controlled based on the obtained focus adjustment state, and the focus of the photographing lens 1 is adjusted.

  In the focus detection device 4, 51 focus detection areas are set in the image plane of the photographing optical system as shown in FIG. 2. The focus detection areas are represented as a1 to a51 as shown in FIG. Each focus detection area is provided with a focus detection optical system as indicated by 200 to 600 in FIG. In FIG. 3, a light beam incident through the region 101 of the photographing optical system 100 corresponding to the photographing lens 1 of FIG. 1 passes through the field mask 200, the field lens 300, the aperture opening 401, and the re-imaging lens 501. An image is formed on the A column of the sensor array 600. The A column of the image sensor array 600 is a one-dimensional array of a plurality of photoelectric conversion pixels that generate an output corresponding to the incident intensity. Similarly, the light beam incident through the region 102 of the photographing optical system 100 passes through the field mask 200, the field lens 300, the aperture opening 402, and the re-imaging lens 502 and is coupled onto the B row of the image sensor array 600. Image. The B column of the image sensor array 600 is a one-dimensional array of a plurality of photoelectric conversion pixels that generate an output corresponding to the incident intensity.

  A pair of subject images formed on the A and B columns of the image sensor array 600 are separated from each other in a so-called front pin state in which the photographing optical system 100 forms a sharp image of the subject before the planned focal plane, and conversely In the so-called rear pin state in which the sharp image of the subject is connected after the planned focal plane, the images approach each other, and the subject images on the A and B columns of the image sensor array 600 are predetermined at the time of the so-called in-focus state where the sharp image of the subject is just connected to the planned focal plane. It becomes the interval of. Accordingly, the pair of subject images are photoelectrically converted into electric signals by the A and B columns of the image sensor array 600 and converted into electric signals, and these signals are subjected to arithmetic processing by the control device 6 to calculate the relative positional deviation amount of the pair of subject images. By determining, the focus adjustment state of the photographic optical system 100, here, the distance away from the in-focus state and its direction (hereinafter referred to as defocus amount) can be known.

  Next, a method for adjusting the focus of the taking lens 1 from the defocus amount obtained in each focus detection area will be described. In the camera of the present embodiment, the control device 6 classifies the positions where the focus detection areas a1 to a51 set in the shooting screen in the focus detection device 4 are arranged into a plurality of blocks, and the plurality of blocks are classified into a plurality of blocks. Classify into groups. Then, one of the plurality of groups is selected, and the driving amount (focal point) of the photographing lens 1 is selected based on the defocus amount detected for the focus detection area located in the block belonging to the selected group. (Adjustment control amount) is determined. The control device 6 performs focus adjustment of the photographic lens 1 by driving and controlling the lens driving device 7 in accordance with the focus adjustment control amount thus determined. In this way, even if 51 points and a large number of focus detection areas are set in the shooting screen, the focus adjustment state for adjusting the focus of the shooting lens 1 can be changed regardless of the number of focus detection areas. Decide correctly and focus can be adjusted.

  An example in which 51 focus detection areas a1 to a51 are classified into a plurality of blocks is shown in FIG. In this classification example, the focus detection areas a1 to a51 are classified into a total of 17 blocks. Particularly in the present embodiment, the blocks are divided so as to include a common focus detection area between adjacent blocks (that is, adjacent blocks overlap).

  The 17 blocks described above are denoted as b1 to b17, and which of the focus detection areas a1 to a51 is included in each block will be described with reference to FIGS. FIG. 5 is a diagram illustrating positions and ranges of the block b7, the block b1, and the block b14. The block b7 includes six focus detection areas a39, a40, a42, a44, a45, and a47. The block b1 includes nine focus detection areas a1, a2, a4, a6, a7, a9, a11, a12, and a14. The block b14 includes six focus detection areas a21, a22, a24, a26, a27, and a29.

  FIG. 6 is a diagram illustrating positions and ranges of the block b10, the block b4, the block b11, and the block b17. The block b10 includes six focus detection areas a44, a45, a47, a49, a50, and a51. The block b4 includes nine focus detection areas a11, a12, a14, a34, a35, a37, a39, a40, and a42. The block b11 includes nine focus detection areas a6, a7, a9, a16, a17, a19, a21, a22, and a24. The block b17 includes six focus detection areas a26, a27, a29, a31, a32, and a33.

  FIG. 7 is a diagram illustrating positions and ranges of the block b5, the block b6, the block b12, and the block b13. The block b5 includes six focus detection areas a12, a13, a35, a36, a40, and a41. The block b6 includes six focus detection areas a14, a15, a37, a38, a42, and a43. The block b12 includes six focus detection areas a7, a8, a17, a18, a22, and a23. The block b13 includes six focus detection areas a9, a10, a19, a20, a24, and a25.

  FIG. 8 is a diagram illustrating positions and ranges of the block b8, the block b9, the block b2, the block b3, the block b15, and the block b16. The block b8 includes four focus detection areas a40, a41, a45, and a46. The block b9 includes four focus detection areas a42, a43, a47, and a48. The block b2 includes six focus detection areas a2, a3, a7, a8, a12, and a13. The block b3 includes six focus detection areas a4, a5, a9, a10, a14, and a15. The block b15 includes four focus detection areas a22, a23, a27, and a28. The block b16 includes four focus detection areas a24, a25, a29, and a30.

  Since the block classification method described above is an example, the present invention is not limited to this content. Arbitrary focus detection areas can be classified for inclusion in arbitrarily shaped blocks.

  When the control device 6 classifies into 17 blocks b1 to b17 based on the 51 focus detection areas a1 to a51 as described above, based on the defocus amount detected in the focus detection area belonging to each block. The defocus amount is calculated for each block. The calculation of the defocus amount for each block will be described later.

  After calculating the defocus amount for each block, the control device 6 next executes a grouping process for classifying the blocks b1 to b17 into a plurality of groups based on the calculated defocus amount for each block. For example, blocks having defocus amounts within a predetermined range are grouped into the same group, and blocks b1 to b17 are grouped. The grouping process can be performed by various other methods. In this way, the control device 6 classifies the blocks b1 to b17 into a plurality of groups.

  After the blocks b1 to b17 are classified into a plurality of groups, the control device 6 next selects an optimal block expected to capture the main subject from the group. For example, the block indicating the closest defocus amount is selected as the optimum block (for example, block b14). The optimum block can be selected by various other methods.

  When the optimum block (block b14 in this example) is selected in this way, the control device 6 next starts from the block based on the defocus amount detected in the focus detection area belonging to the optimum block (block b14 in this example). An adoption area (for example, focus detection area a26) is selected. A method for selecting the adoption area will be described later.

  The control device 6 determines the driving amount of the photographing lens 1, that is, the focus adjustment control amount, based on the defocus amount (d26 in this example) detected in the adopted area (in this example, the focus detection area a26). The driving amount of the photographing lens 1 can be determined based on the defocus amount detected in the focus detection area belonging to the optimum block by various other methods.

<Calculation of defocus amount for each block>
The calculation of the defocus amount for each block will be described. FIG. 9 is a diagram for explaining focus detection areas and weights included in a block. In FIG. 9, B [1] to B [17] correspond to blocks b1 to b17, respectively. i indicates a focus detection area included in the block among the focus detection areas a1 to a55. For example, the block b1 indicates that nine focus detection areas a1, a2, a4, a6, a7, a9, a11, a12, and a14 are included as illustrated in FIGS. W [i] represents the weights for the nine focus detection areas a1, a2, a4, a6, a7, a9, a11, a12, and a14. For example, in the case of the block b1, the weights for the nine focus detection areas a1, a2, a4, a6, a11, a7, a9, a12, and a14 are 10, 4, 4, 4, 4, 2, 2, respectively. , 2 and 2. The focus detection areas and weight values exemplified in FIG. 9 are determined in advance and tabulated, and stored in a memory in the control device 6. The value of the weight is as large as the one corresponding to the focus detection area that does not overlap with the adjacent block and the one corresponding to the focus detection area located near the center in the own block.

The control device 6 uses the defocus amount detected in the focus detection area included in each block and its weight to calculate the defocus amount Dj representing the block bj (j = 1 to 17) by the following equation (1). Calculate sequentially.
Dj = Σdi × Wi / ΣWi (1)
However, j = 1 to 17, i = a code indicating the focus detection area ai included in the block bj, and any value of 1 to 51, di = defocus amount detected in the focus detection area ai, Wi = Weight for focus detection area ai.

  For example, taking the case where the defocus amount D1 representing the block b1 is calculated as an example, from the above equation (1), D1 = (d1 · 10 + d2 · 4 + d4 · 4 + d6 · 4 + d7 · 2 + d9 ・ 2 + d11 ・ 4 + d12 ・ 2 + d14 ・ 2) / (10 + 4 + 4 + 4 + 2 + 2 + 4 + 2 + 2). Similarly, the control device 6 calculates defocus amounts D1 to D17 representing each block for the 17 blocks.

<Selection of employment area>
A method for selecting the above-described employment area will be described. FIG. 10 is a diagram for explaining the focus detection area and the weight for determining the adoption area. In FIG. 10, B [1] to B [17] correspond to blocks b1 to b17, respectively. i indicates a focus detection area included in the selected block among the focus detection areas a1 to a55. For example, in the case of the selection block b14, as illustrated in FIG. 4 and FIG. 5, it indicates that six focus detection areas a21, a22, a24, a26, a27, and a29 are included. W [i] represents the weights for the six focus detection areas a21, a22, a24, a26, a27, and a29. For example, in the case of the block b14, the weights for the six focus detection areas a21, a26, a22, a27, a24, and a29 are 0.00, 0.00, 0.07, 0.07, and 0.07, respectively. , 0.07. The focus detection areas and the weight values exemplified in FIG. 10 are determined in advance as a table and stored in a memory in the control device 6. The value of the weight is as large as the one corresponding to the focus detection area that does not overlap with the adjacent block and the one corresponding to the focus detection area located near the center in the own block.

The control device 6 uses the defocus amount detected in the focus detection area included in the selected block and its weight to sequentially calculate the weighted defocus amount Xi according to the following equation (2).
Xi = di + Wi (2)
However, i = a code indicating the focus detection area ai included in the selected block, and any value from 1 to 51, di = defocus amount detected in the focus detection area ai, Wi = focus detection area ai It is a weight.

  For example, taking the case where the selected block is b14 as an example, there are six focus detection areas a21, a26, a22, a27, a24, and a29 included in the selected block. For example, in the case of the focus detection area a21, X21 = d21 + 0.00 from the above equation (2). Similarly, the control device 6 calculates weighted defocus amounts X21, X26, X22, X27, X24, and X29 for the focus detection areas in the selected block.

  And the control apparatus 6 determines the focus detection area (for example, a26) corresponding to the minimum value among the defocus amounts X21, X26, X22, X27, X24, and X29 after the weighting as the adopted area.

<Focus detection calculation>
Here, focus detection calculation for calculating the defocus amount will be described. The A column and B column of the image sensor array 600 shown in FIG. 3 are each composed of a plurality of photoelectric conversion pixels, and a plurality of output signal sequences α [1],. . . , Α [n], β [1],. . . β [n] is output (FIGS. 11A and 11B). The control device 6 performs correlation calculation while relatively shifting the predetermined range of data by L by a predetermined amount of data in the pair of output signal sequences. If the maximum shift number is lmax, the range of L is from −1max to + 1max. Specifically, the correlation amount C [L] is calculated by the following equation (3).
C [L] = Σ | a [i + L] −b [i] | (3)
However, (SIGMA) shows the sum total of i = k-r, and the first term k and the last term r are changed depending on shift amount L like following Formula (4), for example. L is an integer corresponding to the shift amount of the data string described above, and L = −lmax,. . . , -2, -1, 0, 1, 2,. . . , Lmax.
When L ≧ 0;
k = k0 + INT {−L / 2},
r = r0 + INT {−L / 2},
When L <0;
k = k0 + INT {(− L + 1) / 2},
r = r0 + INT {(−L + 1) / 2} (4)
However, k0 and r0 are the first term and the last term when the shift amount L is zero.

  Since the relative positional deviation amount is the shift amount L when the pair of data coincides, the shift amount giving the minimum correlation amount is detected from the correlation amount C [L] thus obtained. 3 is multiplied by a constant determined by the pitch width of the photoelectric conversion pixels of the image sensor array 600 and the optical system shown in FIG. Therefore, a larger defocus amount can be detected as the maximum shift number lmax is larger.

By the way, the correlation amount C [L] is a discrete value as shown in FIG. 11C, and the minimum unit of the defocus amount that can be detected is the photoelectric conversion pixels of the A column and B column of the image sensor array 600. It is limited by the pitch width. Therefore, a method of performing a precise focus detection by newly calculating a true minimum value Cex by performing an interpolation operation based on the discrete correlation amount C [L] will be described. As shown in FIG. 12, this method uses a correlation amount C [Le], which is a minimum value, and correlation amounts C [Le + 1], C [Le-1] in the shift amounts on both sides of the correlation amount C [Le-1]. The value Cex and the shift amount Ls that gives it are calculated by the following equation (5).
DL = (C [Le-1] -C [Le + 1]) / 2
Cex = C [Le]-| DL |,
E = MAX {C [Le + 1] -C [Le], C [Le-1] -C [Le]},
Ls = Le + DL / E (5)
In the above formula (5), MAX {Ca, Cb} means that the larger one of Ca and Cb is selected. The defocus amount DF is calculated by the following equation (6) from the shift amount Ls.
DF = Kf · Ls (6)
Kf is a constant determined by the pitch width of the photoelectric conversion pixels of the optical system and the image sensor array 600 shown in FIG.

It is necessary to determine whether the defocus amount obtained in this way truly indicates the defocus amount or due to the fluctuation of the correlation amount due to noise or the like. The control device 6 determines that the defocus amount is reliable when the conditions shown in the following equations (7) and (8) are satisfied.
E> E1 (7)
Cex / E <G1 (8)
In the above formulas (7) and (8), E1 and G1 are threshold values for reliability determination criteria. The numerical value E indicates how the correlation amount changes, and is a value that depends on the contrast of the subject. The larger the value, the higher the contrast and the higher the reliability. Cex is a difference when a pair of data most closely matches and is originally 0. However, due to the influence of noise and further, parallax is generated between the area 101 and the area 102, a subtle difference occurs between the pair of subject images and does not become zero. Since the effect of the difference between the noise and the subject image is smaller as the subject contrast is higher, Cex / E is used as a numerical value representing the degree of coincidence between a pair of data. Of course, the closer Cex / E is to 0, the higher the degree of matching between a pair of data and the higher the reliability.

  In the present embodiment, the defocus amount obtained in the 51 focus detection areas a1 to a51 illustrated in FIG. 2 is defined as Def (i) (i = 1 to 51). Further, the reliability of each defocus amount is a value E (i) depending on the contrast of the subject shown in the above equation (7), or a numerical value Cex / E representing the degree of coincidence between a pair of data shown in the above equation (8). (i).

  As described above, when the contrast of the subject image in the focus detection area is low, a highly reliable defocus amount cannot be obtained. Therefore, when calculating the defocus amount Dj for each block and when selecting an adopted area in the selected block, the control device 6 excludes a focus detection area with a defocus amount with low reliability.

  FIG. 13 is a flowchart illustrating the flow of the focus adjustment operation described above. When the main switch of the camera is turned on, the control device 6 starts the process shown in FIG. In step S10 of FIG. 13, the control device 6 confirms whether or not a shutter button (not shown) is half-pressed, and proceeds to step S20 if the shutter button is half-pressed. If the shutter button is not half-pressed, the determination process is repeated.

  In step S20, the control device 6 calculates the defocus amount di in the 51 focus detection areas ai, and proceeds to step S30. In step S30, the control device 6 calculates the defocus amount Dj for each block using the defocus amount di and the weight (FIG. 9) in step S20, and proceeds to step S40.

  In step S40, the control device 6 performs block grouping based on the defocus amount Dj. In step S50, the control device 6 selects one of the plurality of groups divided in step S40 as the optimum group, and proceeds to step S60. In step S60, the control device 6 selects any of the blocks belonging to the optimum group selected in step S50 as an adopted block, and proceeds to step S70.

  In step S70, the control device 6 calculates the weighted defocus amount Xi using the defocus amount di and the weight (FIG. 10) in the focus detection area ai included in the selected block, and proceeds to step S80. In step S80, the control device 6 selects an adopted area from the focus detection area ai in the selected block, and proceeds to step S90.

  In step S90, the control device 6 performs focus adjustment on the photographing lens 1 based on the defocus amount of the adopted area, and ends the processing in FIG.

According to the embodiment described above, the following operational effects can be obtained.
(1) The single-lens reflex camera includes three or more focus detection devices 4 for detecting the defocus amount di of the photographing lens 1 in three or more focus detection areas ai provided in the image plane of the photographing lens 1. The focus detection area ai is classified into a plurality of blocks bi, a predetermined block is selected from the classified blocks bi, and the defocus amount detected for the focus detection area included in the selected block And a control device 6 for determining the focus adjustment control amount of the photographic lens 1 based on the above, and at the time of the classification, at least one of the focus detection areas included in the block overlaps with the focus detection area included in the adjacent block. did. As a result, the same block is selected even if the camera angle is slightly deviated, so that even if a main subject exists in the vicinity of the block boundary, appropriate focusing can be performed on the main subject.

(2) The single-lens reflex camera further includes a defocus amount di detected for each of the plurality of focus detection areas ai included in each of the plurality of blocks bi and each block bi in advance for each of the plurality of focus detection areas ai. The defocus amount Xi representing the block bi is calculated for each block bi based on the weight information Wi (FIG. 9) determined for each block, and a plurality of blocks are calculated based on the defocus amount Xi representing the calculated block. One block was selected from bi. Accordingly, it is possible to perform appropriate focusing as compared with the case where the defocus amount Xi representing the block is not calculated.

(3) The single-lens reflex camera further includes a defocus amount di detected for each of the plurality of focus detection areas ai included in the selected block and a plurality of focus detection areas ai included in the selected block. On the other hand, a focus detection area representing the selected block is selected based on weight information Wi (FIG. 10) determined in advance, and the defocus amount di detected for the selected focus detection area is set. Based on this, the focus adjustment control amount of the taking lens 1 is determined. As a result, appropriate focusing can be performed in consideration of the defocus amounts di of the plurality of focus detection areas ai included in the selected block.

(4) The weight information Wi has a larger value as it does not overlap with other blocks among the plurality of focus detection areas ai included in the block bi and closer to the center position of the block. As a result, the influence of the defocus amount di obtained in the focus detection area overlapping with other blocks can be suppressed, and appropriate focusing can be performed.

(Modification 1)
In the example described above, one adopted area is selected in the selected block. However, not only one but also a plurality of focus detection areas may be selected as adopted areas. In this case, the average value or median value of the defocus amounts in a plurality of adoption areas can be obtained, and the focus adjustment of the photographing lens 1 can be performed using the calculation result.

(Modification 2)
Although the example in which the focus adjustment device is mounted on the single-lens reflex camera has been described, the focus adjustment device may be mounted on a camera other than the single-lens reflex camera.

  The above description is merely an example, and is not limited to the configuration of the above embodiment.

DESCRIPTION OF SYMBOLS 1 ... Shooting lens 4 ... Focus detection apparatus 6 ... Control apparatus 7 ... Lens drive device
a1 to a51 ... Focus detection area
b1-b17 ... Block

Claims (5)

Focus detection means for detecting a focus adjustment state of the imaging optical system in each of three or more focus detection areas provided in an image plane of the imaging optical system;
Classification means for classifying the three or more focus detection areas into a plurality of blocks;
Block selecting means for selecting a predetermined block among the plurality of classified blocks;
Control means for determining a focus adjustment control amount of the photographing optical system based on the focus adjustment state detected for a focus detection area included in the selected block;
The said classification | category means classifies the said block so that at least 1 of the focus detection area contained in the said block may overlap with the focus detection area contained in an adjacent block, The focus detection apparatus characterized by the above-mentioned. The focus detection apparatus according to claim 1,
Based on the focus adjustment state detected for each of the plurality of focus detection areas included in each of the plurality of blocks, and weight information determined for each of the blocks in advance for the plurality of focus detection areas, A calculation unit that calculates a focus adjustment state representing the block for each block;
The focus selection apparatus, wherein the block selection unit selects one block from the plurality of blocks based on the calculated focus adjustment state representing the block. The focus detection apparatus according to claim 2,
The focus adjustment state detected for each of the plurality of focus detection areas included in the selected block, and weight information predetermined for the plurality of focus detection areas included in the selected block. Further comprising area selection means for selecting a focus detection area representative of the selected block,
The focus detection apparatus characterized in that the control means determines a focus adjustment control amount of the photographing optical system based on a focus adjustment state detected for the selected focus detection area. The focus detection apparatus according to claim 2 or 3,
The focus detection is characterized in that the weight information has a larger value as it does not overlap with other blocks among a plurality of focus detection areas included in the block and closer to the center position of the block. apparatus. The focus detection apparatus according to any one of claims 1 to 4,
Adjusting means for performing focus adjustment of the photographing optical system based on a focus adjustment control amount determined by the control means;
A camera comprising:

Images