JP2952899B2 - Focus detection device - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a focus detection device mounted on a single-lens reflex camera or the like.

[Conventional technology]

As a focus detection method in a single-lens reflex camera, there is a phase difference detection method. The outline of this method will be described with reference to FIG. The light beam incident through the region 101 of the objective lens 100 passes through the field mask 200, the field lens 300, the aperture opening 401, and the re-imaging lens 501 to form an image on the image sensor array A. Similarly, the light beam incident through the area 102 of the objective lens 100 is reflected by the field mask 200 and the field lens 3.
The image passes through the aperture opening 402 and the re-imaging lens 502 to form an image on the image sensor array B. The pair of subject images formed on the image sensor arrays A and B are separated from each other in a so-called front focus state in which the objective lens 100 forms a sharp image of the subject before the predetermined focal plane. Conversely, they approach each other in a so-called back focus state in which a sharp image of the subject behind the predetermined focal plane is formed. The subject image just formed on the predetermined focal plane relatively matches on each image sensor array. Therefore, this pair of subject images is referred to as an image sensor array A,
The signals are photoelectrically converted at B, converted into electric signals, and these signals are arithmetically processed to obtain the relative positions of the pair of subject images. The direction (hereinafter abbreviated as defocus amount) can be understood. In general, a pair of image sensor arrays A and B are arranged in a horizontal direction with respect to a shooting screen, and focus detection is performed based on horizontal contrast. This is based on the fact that there is a high probability that the contrast in the horizontal direction is higher than the contrast in the vertical direction as a subject for normal photography.

When the focus is detected using an image sensor composed of a plurality of light receiving pixels arranged only in one direction horizontally or vertically as shown in FIG. 8, two problems occur.

The first problem occurs when, for example, the subject is a thin thread-like object. This problem is related to the fact that a thread-like object extending in the vertical direction (that is, the vertical direction) of the screen or the horizontal direction of the screen is often focused on as a subject. FIG. 6A is a diagram for explaining such a problem, and is an enlarged view of the light receiving pixels A1 to A9 constituting the image sensor array A shown in FIG. The light receiving pixels A1 to A9 are arranged so as to extend in a direction perpendicular to the arrangement direction of the image sensor array A (that is, the boundary between the light receiving pixels is perpendicular to the arrangement direction of the image sensor). . Assuming that there is only a thin thread-like subject image extending in the vertical direction within the focus detection area in the screen, the images incident on the image sensor arrays A1 to A9 are:
As shown in the luminance distribution of FIG. 6 (2), the width may be smaller than the width of one pixel. Even if the image shown in FIG. 6 (2) moves to the image shown in FIG. 6 (4), the output itself from the image sensor array will be the same as that shown in FIGS. 6 (3) and (5).
It becomes the same as shown in. Therefore, a correct relative position cannot be calculated accurately.

In view of this, the present applicant has disclosed in Japanese Patent Application Laid-Open No. 55-29731 that the light receiving pixels are inclined with respect to the arrangement direction of the image sensor array (or the direction perpendicular thereto) as shown in FIG. . That is, the direction in which the light receiving pixels extend does not match the direction perpendicular to the direction in which the image sensor arrays are arranged. In this way, even when a very narrow image extending in the vertical direction enters as shown in the luminance distribution of FIGS. 7 (2) and (4), the image is formed over a plurality of pixels. The output of the image sensor array A changes as shown in FIG. 7 (3) for the image of FIG. 7 (2) and as shown in FIG. 7 (5) for the image of FIG. 7 (4). Therefore, a correct relative position can be calculated.

The problem shown in FIG. 2 occurs when the subject in the focus detection area has no luminance change, that is, no contrast in one direction. That is, in the focus detection method described above, focus detection cannot be performed when the arrangement direction of the image sensor arrays A and B matches the direction in which no contrast exists. Therefore, the arrangement direction of the pair of image sensor arrays A and B must be a direction in which contrast is easily generated. However, an actual subject may have a low contrast in the horizontal direction or a low change in contrast in the vertical direction, and may further use the camera in a vertical position or a horizontal position.

In order to cope with such various cases, a focus detection method as shown in FIG. 9 has been considered. As shown in FIG. 9, a pair of image sensor arrays A and B and a pair of image sensor arrays C and D are arranged in the horizontal direction and the vertical direction, respectively, to focus on the contrast in either the horizontal or vertical direction. The detection is made possible.
The image sensor arrays A, B, C and D have the same form as that shown in FIG. In an optical system of this type, a field mask 2, a field lens 3, an aperture 4, a re-imaging lens 5, and an image sensor chip 6 are arranged in this order on the optical axis of an objective lens 1. The field mask 2 has a cross-shaped opening, and is arranged near a predetermined focal plane of the objective lens 1 to regulate an aerial image of a subject formed by the objective lens 1. Aperture 4 is 4
It has three openings 41,2,43,44. These openings are
Areas 11 and 1 on the objective lens by the field lens 3
2, 13, and 14 can be projected. The re-imaging lens 5 is ninth
As shown in FIG. 2B, the image sensor 4 includes four lenses 51, 52, 53, and 54 corresponding to the openings 41, 42, 43, and 44 of the stop 4, and forms an image of the field mask 2 on the image sensor chip 6. . Therefore, the light beam incident from the area 11 of the lens 1 passes through the field mask 2, the field lens 3, the aperture 41 of the stop 4, and the lens 51 of the re-imaging lens to form an image on the image sensor array A. Similarly, light beams incident from the regions 12, 13, and 14 of the objective lens 1 are image sensor arrays B, C, and D, respectively.
Image on top. Then, the image sensor arrays A and B
When the objective lens 1 is in front focus, it moves away from each other, when the objective lens 1 is in rear focus, approaches each other, and are aligned at a certain interval when focused. Therefore, by performing arithmetic processing on the signals of the image sensor arrays A and B, the focus adjustment state of the objective lens in the horizontal direction can be detected. Similarly, the subject images formed on the image sensor arrays C and D move away from each other when the objective lens 1 is in the front focus, approach each other when the objective lens 1 is in the back focus, and are arranged at a predetermined interval when the objective lens 1 is in focus. Therefore, by performing arithmetic processing on the signals of the image sensor arrays C and D, the focus adjustment state of the objective lens in the vertical direction can be detected.

The direction in which the lens is driven based on the focus adjustment state based on the contrast in which direction can be determined, for example, by (1) selecting a direction with high contrast from both directions, and (2) preferentially using one direction. One way is to perform focus detection in the other direction. (3) Average the calculation results in both directions.

However, in the above-described focus detection device that performs focus detection in both the vertical direction and the horizontal direction, nothing has been considered about the configuration of the pixels themselves of the image sensor array arranged in each direction. As a result, there still remains a problem that it is difficult to detect a focus on a system-like subject extending vertically or horizontally as described in the first problem.

SUMMARY OF THE INVENTION An object of the present invention is to provide a focus detection device including an image sensor array that is hardly affected by a state distribution such as contrast of a subject, and the like.

[Means for solving the problem]

In order to achieve the above object, a focus detection device according to the present invention includes a first image sensor array (1A, B1) including a plurality of light receiving pixels (pc1) arranged in a predetermined direction on a predetermined focal plane of an objective lens. And a second image sensor array (C1, D1) arranged in a direction orthogonal to the predetermined direction on the predetermined focal plane, and the photoelectric conversion signals detected by the first and second image sensor arrays. The focus detection state is calculated based on. Further, in the focus detection device according to the present invention, the boundary line (b1) between adjacent light receiving pixels included in each of the first image sensor arrays (A1, B1) is aligned with the arrangement direction of the light receiving pixels (that is, the first image). The second image sensor array (C1, D2) is formed to be inclined from a vertical line with respect to a predetermined direction in which the sensor array extends.
1) the boundary line (b
1) is formed to be inclined from a vertical line with respect to the arrangement direction of the light receiving pixels (that is, a direction perpendicular to the predetermined direction). Here, if the light receiving pixels of the two image sensor arrays that are orthogonal to each other are simply tilted, a problem (which will be clarified later) occurs, and therefore, the inclination direction of the boundary between the light receiving pixels of the first image sensor array. Are in the same direction as the inclination direction of the boundary line of the light receiving pixels of the second image sensor array.

[Action]

With the above configuration, focus detection can be performed with predetermined accuracy regardless of the contrast state of the subject image detected in the focus detection area corresponding to the light receiving area of the image sensor array (A1, B1, C1, D1). I can do it. In other words, the structure projected onto the plurality of light receiving pixels (pc1) is of a type in which the conventional focus detection method using the image sensor array is inadequate (horizontal or vertical linear, or various inclinations). Edge-shaped image), a high-contrast portion can be captured by a plurality of light-receiving pixels for a linear image, and the edge direction and light-receiving pixel for an edge-shaped image. Can be ensured to be equal to or smaller than a predetermined value, so that focus detection accuracy is improved.

〔Example〕

FIG. 1 shows an image sensor array used in a focus detection device according to the present invention.

Explaining the structure of the image sensor array in FIG. 1, image sensor arrays A1 and B1 are arranged in the horizontal direction, and image sensor arrays C1 and D1 are arranged in the vertical direction as shown in FIG. Each image sensor array A1, B1,
Both C1 and D1 are arranged such that the light receiving pixel pc1 is inclined clockwise from a line perpendicular to the arrangement direction of the light receiving pixel pc1 itself. (That is, the boundary line b1 of the light receiving pixel pc1 is all tilted clockwise with respect to the vertical line.) The optical system that guides the subject image to the image sensor arrays A1, B1, C1, and D1 is the Since it is the same as that shown in FIG. 9, detailed description will be omitted. The photoelectric conversion outputs of the image sensor arrays A1, B1, C1, and D1 are
Ninth conventional technology (a TTL of the type that performs focus detection by processing photoelectric conversion signals from two sets of image sensor arrays)
Phase difference detection method),
Since the technique is a known technique as described above, the details are omitted.

Second, the image sensor array (A2, A2,
B2, C2, D2). The image sensor array shown here is an imaginary one taken up to explain the difference between the image sensor array merely combining the prior art and the image sensor array according to the present application. As shown in FIG. 2, image sensor arrays A2 and B2 are arranged in the horizontal direction, and image sensor arrays C2 and D2 are arranged in the vertical direction as shown in FIG. The light receiving pixels pc2 of the image sensor arrays A2 and B2 are arranged to be inclined in the clockwise direction from a vertical line with respect to the pixel arrangement direction (that is, the light receiving pcc extending in the horizontal direction).
The second boundary line b2 is inclined clockwise with respect to the vertical line. ), The light receiving pixels pc2 of the image sensor arrays C2 and D2 are arranged to be inclined in the left rotation direction from the vertical line to the pixel arrangement direction (that is, the boundary line b2 of the light receiving pixels pc2 extending in the vertical direction is the vertical line). To the left.

Hereinafter, focus detection in the case where a two-color pattern of white and black is inclined by 45 ° on the image sensor array will be considered.

If the light receiving pixel is not tilted in both the vertical and horizontal directions, the relative angle is 45 ° in both sensor rows, and the focus detection calculation accuracy is the same. The smaller the angle between the edge of the pattern and the direction of the boundary between the plurality of light-receiving pixels of the sensor (hereinafter, abbreviated as relative angle), the higher the output with high contrast can be obtained, and the accuracy of the focus detection calculation is improved. However, focus detection may not be performed on a subject having a linear contrast in the vertical direction or the horizontal direction, which has already been described.

The case where the light receiving pixels are inclined by a certain angle α (that is, the arrangement of the light receiving pixels as shown in FIGS. 1 and 2) will be described with reference to FIG. Each of the horizontal image sensor arrays A1, A2, B1, and B2 shown in FIGS.
The image sensor arrays in FIGS. (1) and (3) correspond. The image sensor array C1 in the vertical direction shown in FIG.
The image sensor arrays of FIGS. 3 (2) and (4) correspond to each of D1. Image sensor arrays C2 and D2 in FIG.
Correspond to the image sensor arrays of FIGS. 3 (5) and (6). First, the black and white pattern is on the right
The case of tilting by 45 ° (this direction is assumed to be +) will be considered with reference to FIGS. 3 (1), (2) and (5). In the horizontal direction, as shown in FIG. 3 (1), the relative angle is R1 = 45 ° −
given as α. In the vertical direction, as shown in FIG. 3 (2), the relative angle is given as R2 = 45 ° + α in the image sensor arrays C1 and D1 according to the present invention, and the relative angle is given as R2 = 45 ° + α in the image sensor arrays C2 and D2 not according to the present invention. 3. As shown in FIG. 3 (5), the relative angle is given as R5 = 45 ° −α. Therefore, the image sensor array C according to the present invention
1.When D1 is used, the relative angle is reduced by tilting the light receiving pixels in the horizontal direction, and the focus detection accuracy is increased.
In the vertical direction, the relative angle becomes larger, so that the accuracy is reduced. On the other hand, a sensor A not according to the present invention
In 2,2, C2, D2, the relative angle is reduced in both the vertical and horizontal directions, and the accuracy is improved.

Next, the case where the black and white pattern is inclined 45 ° to the left as viewed in the figure will be considered with reference to FIGS. 3 (3), (4) and (6). In the horizontal direction, the relative angle is given as R3 = 45 ° + α, as shown in FIG. With respect to the vertical direction, in the image sensor arrays C1 and D1 according to the present invention, as shown in FIG. 3 (4), the relative angle is given as R4 = 45 ° −α, and in the image sensor arrays C2 and D2 not according to the present invention. As shown in FIG. 3 (6), the relative angle R =
Given as 45 ° + α. Therefore, when the image sensor array according to the present invention is used, the relative angle increases in the horizontal direction due to the tilting of the pixels, and the pixel portion for detecting the edge of the black-and-white pattern is widened. Accuracy is reduced and the relative angle in the vertical direction is made smaller, so that the pixel output corresponding to the edge becomes acute and the accuracy is increased. On the other hand, in the image sensor array not according to the present invention, the relative angle becomes large in both the vertical and horizontal directions, and the accuracy is lowered.

As is evident from the comparison of the focus detection of the two types of edge patterns inclined at 45 °, when the image sensor array according to the present invention is used, either the vertical or the horizontal can perform the focus detection calculation with high accuracy, so that as a whole, Will reduce the number of poor patterns. On the other hand, when an image sensor array not according to the present invention is used, there is an unfavorable pattern in which the accuracy of the focus detection calculation is reduced both vertically and horizontally.

FIG. 4 shows the relationship between the inclination of the pattern projected on the image sensor array and the relative angle when the inclination of the pixel is 10 °. FIG. 4 (1) shows the case of the image sensor array according to the present invention, and FIG. 4 (2) shows the case of the image sensor array of FIG. 2 not according to the present invention. The solid line corresponds to the horizontal image sensor array, and the dotted line corresponds to the vertical image sensor array. As is clear from the figure, in the image sensor array according to the present invention, the pattern angle is −35 ° and 55 °, and the relative angle is 45 ° both vertically and horizontally.
゜ is the worst condition in a sense. On the other hand, in the image sensor array not according to the present invention, the relative angle becomes 55 ° in both the vertical and horizontal directions at the pattern angle of −45 °. Even worse than the worst conditions in.

The method of tilting the pixel will be described in detail with reference to FIG.

The reason why the pixels are tilted is to prevent the thin pattern from completely entering one pixel as described above. Therefore, the minimum pixel inclination is a problem below the horizontal positions of the upper and lower bases of the pixels (hereinafter abbreviated as the inclination width) caused by the inclination (P1 in FIG. 5 (1)).
Length). For example, as shown in FIG.
In contrast, when the inclination width P2 is P2 ≦ P0, it is not convenient because a thin pattern may completely enter one pixel. However, if the inclination width is very large with respect to the width of the pixel, the relative angle to the normal pattern (the edge is perpendicular to the arrangement direction of the pixels) becomes large, and the contrast of the sensor output becomes low. As a result, the focus detection calculation accuracy is reduced. Therefore, there is a limit to the tilt of the pixel, and empirically, the limit of the tilt width seems to be about twice the pixel width as shown in FIG. 5 (3). Therefore, it is appropriate that the inclination width is about 1.5 times the pixel width.

If the pixel height (width of the light receiving pixel in the direction perpendicular to the light receiving pixel arrangement direction) is different between the horizontal image sensor array and the vertical image sensor array, It is desirable to make the inclination width of the light receiving pixels the same. This is because it is desirable that the vertical and horizontal image sensor arrays have the same focus detection characteristics. Therefore, the light receiving pixels of one image sensor array have a height W1 as shown in FIG. 5 (1), and the light receiving pixels of the other image sensor array have a height W4 as shown in FIG. 5 (4). This value W4
Is larger than the value W1, the inclination widths P1 and P4 of both may be the same. As a result, the inclination angles G1 and G4 of the light receiving pixels
(See FIGS. 5 (1) and (4).)

〔The invention's effect〕

As described above, by using the image sensor array according to the present invention, it is possible to accurately perform focus detection even on a thin pattern or a slanted pattern, and reduce unsatisfactory patterns.

[Brief description of the drawings]

FIG. 1 is a diagram showing an image sensor array according to the present invention, FIG. 2 is a diagram showing an image sensor array not according to the present invention, and FIGS. FIGS. 4 (1) and 4 (2) show the relationship between the pattern inclination angle and the angle between the height direction of the image sensor array and FIGS. 5 (1) and 5 (1). 6) to (4) are diagrams for explaining how to tilt the pixels constituting the image sensor array, and FIGS. 6 (1) to (5) are for explaining the case where a thin pattern is formed on the image sensor array in which the pixels are not tilted. FIGS. 7 (1) to 7 (5) are diagrams for explaining a case where a fine pattern is formed on an image sensor array in which pixels are inclined, FIG. 8 is a conventional focus detection optical system, and FIG. It is a conventional technology, It is a diagram illustrating a focus detection optical system for focus detection. [Explanation of Signs of Main Parts] A1, B1, C1, D1 ... Image sensor array pc1 ... Light receiving pixel b1 ... Boundary line between plural light receiving pixels

──────────────────────────────────────────────────続 き Continuation of the front page (56) References JP-A-55-29731 (JP, A) JP-A-64-78207 (JP, A) (58) Fields investigated (Int. Cl. ⁶ , DB name) G02B 7/28-7/40

Claims (2)

(57) [Claims] 1. A first image sensor array comprising a plurality of light receiving pixels arranged in a predetermined direction on a predetermined focal plane of an objective lens, and arranged in a direction substantially orthogonal to the predetermined direction on the predetermined focal plane. A second image sensor array,
A focus detection device for calculating a focus detection state based on the photoelectric conversion signals detected by the first and second image sensor arrays, wherein each of the first and second image sensor arrays includes an adjacent focus detection device. A boundary line between the light receiving pixels is formed to be inclined from a vertical line with respect to a direction in which the light receiving pixels are arranged, and the inclination direction of the boundary line of the light receiving pixels of the first image sensor array is the same as the light receiving direction of the second image sensor array. A focus detection device, wherein the direction is the same as the direction of inclination of a boundary line between pixels. 2. Each of the light receiving pixels of the first and second image sensor arrays is surrounded by upper and lower bases extending in the arrangement direction and having a predetermined length and adjacent to the boundary line. And the upper bottom of each light receiving pixel is arranged in the arrangement direction with respect to the lower bottom of the light receiving pixel by a length of 1 to 2 times the predetermined length. The focus detection device according to claim 1, wherein