JP5380782B2 - Imaging device - Google Patents

Description

  The present invention relates to a light detection device, a focus detection device, and an imaging device.

  2. Description of the Related Art A focus detection device is known in which a microlens array is disposed on a planned focal plane of a photographing lens and a light receiving element array is disposed behind the microlens array to detect the focus of the photographing lens. (For example, refer to Patent Document 1).

Prior art documents related to the invention of this application include the following.
JP 54-159259 A

  However, the above-described conventional focus detection apparatus has a problem that a dead zone is generated at a boundary position between microlenses when an object image is present near the position of the microlens array. Since the object image is in the vicinity of the microlens array, if there is an edge of the object image between the microlenses, that is, a contrast change band, the image at this position is optically invalid between the microlenses. The projected light is projected onto the area, and an effective light beam is not projected onto the light receiving element, so that the focus detection performance is deteriorated.

An image pickup apparatus according to a first aspect of the present invention receives a plurality of microlenses arranged two-dimensionally in the vicinity of a predetermined imaging plane of a photographing optical system and a light beam transmitted through each of the plurality of microlenses. A plurality of light-receiving elements arranged two-dimensionally behind each microlens and each of the microlenses arranged in a predetermined direction are symmetrical in the predetermined direction about the optical axis of the microlens Selecting means for selecting a pair of light receiving element groups located at different positions, adding the output signals of the respective light receiving element groups, and calculating a pair of added output signals, and a pair of addition outputs calculated by the selecting means Focus detection means for detecting a focus based on a signal, and the selection means has a small number of light receiving elements in the light receiving element group and a small number of light receiving element groups when the amount of light incident on the light receiving element is large. When the amount of light incident on the light receiving element is small so that the number of light receiving elements is equal, the number of light receiving elements in the light receiving element group is large and the number of light receiving elements in the pair of light receiving element groups is equal. In addition, the number of light receiving elements of the light receiving element group is changed in accordance with the amount of light incident on the light receiving element, and the base line length of the pair of light receiving element groups in which the number of light receiving elements is changed is selected for each light receiving element group. The base line length corresponding to each method is read from a stored table, and the read base line length is used for focus detection by the focus detection means .

  According to the present invention, it is possible to improve the focus detection performance by eliminating the influence of the dead zone at the boundary position between the microlenses.

  FIG. 1 is a cross-sectional view of a camera as an imaging apparatus including a light detection device and a focus detection device according to an embodiment. Illustration and description of camera devices and circuits not directly related to the light detection device and the focus detection device of the present invention are omitted. In addition, the light detection device and the focus detection device of the present invention can be applied to all types of cameras such as a single-lens reflex camera and a compact camera. Furthermore, the light detection device of the present invention is not limited to the focus detection device, and can be applied to, for example, an image composition device.

  The light beam from the subject that has passed through the photographing lens (photographing optical system) 2 of the camera 1 forms a subject image on the scheduled imaging plane 3. Usually, an imaging element and a film are disposed on the planned imaging plane 3. Before photographing, the mirror 4 is placed in the photographing optical path of the photographing lens 2, and the light flux from the subject reflected by the mirror 4 is guided to the microlens array 5 and the light receiving element array 6. The microlens array 5 is disposed on a surface that is optically equivalent to the planned imaging plane 3, and the light receiving element array 6 is disposed behind the microlens array 5.

  FIG. 2 is an enlarged view of the microlens array 5 and the light receiving element array 6. The microlens array 5 is configured by arranging a plurality of microlenses 5a in a two-dimensional manner, and the light receiving element array 6 is configured by arranging a plurality of light receiving devices (photoelectric conversion elements) 6a in a two-dimensional manner.

  If a subject image is projected onto the light receiving element 6a in the optical axis direction by a certain micro lens 5a, a group of light receiving elements 6a in a certain range corresponds to the micro lens 5a. From this point, a group of light receiving elements 6a may be arranged for each microlens 5a. In this embodiment, however, a plurality of light receiving elements 6a are continuously arranged in a two-dimensional manner on a uniform plane. The element 6 will be described as an example.

  For example, in the example shown in FIG. 3, the light receiving element 6 a in a region (range shown by a thick line in FIG. 3) in which the square corners composed of 11 horizontal and 11 vertical light receiving elements 6 a are omitted with respect to one microlens 5 a. It corresponds. In the microlens 5a shown in the upper side of FIG. 3, the light-receiving element 6a filled in black at the center of the area of the corresponding light-receiving element 6a is located at the center of the optical axis of the microlens 5a, and the area of the light-receiving element corresponding to the microlens Has a spread of 5 elements vertically and horizontally. That is, one light receiving element 6a among the plurality of light receiving elements 6a on the light receiving element array 6 corresponding to each micro lens 5a on the micro lens array 5 is arranged on the optical axis of each micro lens 5a. The microlens array and the light receiving element array are relatively positioned.

  FIG. 4 shows the relationship between the plurality of microlenses 5a and the light receiving element 6a. In this example, the diameter of the microlens 5a is exactly an integral multiple of the length of one side of the light receiving element 6a, and light reception used for focus detection among the plurality of light receiving elements 6a in the light receiving element region corresponding to the microlens 5a. When the element 6a is selected, it can be selected in a balanced manner from within the region. Thereby, it is possible to prevent the fluctuation of each microlens 5a from occurring in the focus detection result.

  Here, the arrangement of the microlenses 5a will be considered. In the arrangement example of the microlenses 5a shown in FIG. 5, a plurality of microlenses 5a are arranged in a close-packed square (closest), and two rows of microlenses are arranged adjacent to each other in the horizontal direction (for example, row A in the figure). And B rows), the microlenses 5a are arranged alternately. Then, the horizontal center position of a certain microlens 5a is on the horizontal boundary line of the upper or lower microlens array. Note that the arrangement is similar in the vertical microlens array.

  As apparent from FIGS. 4 and 5, in this embodiment, the arrangement direction of the microlenses 5 a on the microlens array 5 is 45 degrees with respect to the arrangement direction of the light receiving elements 6 a on the light receiving element array 6. The microlenses 5a on the microlens array 5 are arranged so that In other words, two adjacent microlens rows (row A and row B shown in FIG. 5) arranged on the microlens array 5 are arranged with their phases shifted from each other by the radius of the microlens 5a.

  The distance between the centers of the microlenses 5a adjacent in the horizontal and vertical directions is an integral multiple of the length of one side of the light receiving element 6a as shown in FIG. The center distance is desirably an odd multiple of the length of one side of the light receiving element 6a. The reason is that the light receiving element 6a can be arranged at the center of the microlens 5a, and the relative relationship between the microlens 5a and the light receiving element 6a is the same for any microlens 5a. When selecting the light receiving element 6a used for focus detection from the light receiving element region corresponding to each micro lens 5a, the same selection pattern can be used for all the micro lenses 5a. In other words, the focus detection light-receiving element can be selected in a well-balanced manner from within the light-receiving element region corresponding to each microlens 5a, and the focus detection performance is prevented by causing fluctuation for each microlens 5a in the focus detection result. Can be made.

  Next, the arrangement of the microlens array 5 and the light receiving element array 6 in the optical axis direction of the photographing lens 2 will be considered. As described above, the microlens array 5 is disposed on a surface that is optically equivalent to the planned imaging surface 3 of the photographing lens 2, and the subject image formed by the photographing lens 2 is placed on the light receiving element 6a by the microlens 5a. Projected. The light-receiving surface of the microlens array 5 that is optically equivalent to the planned imaging surface 3 is at a position substantially conjugate with the pupil plane of the photographing lens 2, and the selection of the light-receiving element 6a of the light-receiving element array 6 is the focus detection optical. Equivalent to choosing a pupil opening in the system.

  Therefore, the light receiving element 6a on the optical axis of each micro lens 5a shown in FIG. 3, that is, the center light receiving element 6a in the light receiving element region corresponding to each micro lens 5a is selected to synthesize the image of the micro lens array 5. In other words, it is the same as that in which the photographing lens 2 is provided with a small aperture, and a deep focus, that is, a pan-focus image can be obtained. By disposing the light receiving element 6a at the center of each microlens 5a, a subject image that does not depend on the focal position can be obtained.

  More specifically, in the microlens 5a shown in the lower side of FIG. 3, the row (group) of the left and right light receiving elements 6a painted black is the subject that has similarly passed through the left and right strip-shaped apertures in the photographing lens 2. Synthesize the image. From the parallax between the left and right composite images, the focus adjustment state of the photographic lens 2 can be calculated.

  In this embodiment, the following focus adjustment state detection method is employed. Here, an example in which the focus adjustment state is detected from the horizontal column of the microlens array 5 shown in FIG. In this case, the focus adjustment state of the photographing lens 2 is detected based on the output signal of the light receiving element 6a corresponding to the micro lens 5a in the A row and the B row shown in FIG.

  Among a plurality of light receiving elements 6a corresponding to each of the microlenses 5a in the A row and the B row, a pair of light receiving elements 6a each including three right and left like the microlens 5a shown in the lower side of FIG. The light receiving element groups I and D are formed. First, the output signals of the three light receiving elements 6a included in the light receiving element group I are added, and this is used as the left data Aij of the jth microlens 5a in the A column. Similarly, the output signals of the three light receiving elements 6a included in the light receiving element group D are added to obtain the right data Adj of the jth microlens 5a in the A column.

The method of obtaining focus adjustment information based on the parallax of the pair of left and right data strings {Aij} and {Adj}, that is, the image shift, is basically the same as a conventional TCL (Through Camera Lens) type focus detection device. . First, consider Tak in which one of a pair of columns is shifted by a certain amount k.
Tak = Σ | Aij + k−Adj | (1)
In the equation (1), Σ represents the total sum of j = 1 to n in the A column (n is the number of light receiving elements used for focus detection). Find k that minimizes Tak expressed by equation (1). Since the image is essentially continuous and the shift amount also changes continuously, the shift amount HA is obtained by interpolating the discrete data Tak sequence obtained from the discrete calculation in this way.

As described above, this column includes a dead zone, and if the subject image plane is in the vicinity of the microlens array 5, the reliability of the calculation result decreases. Therefore, data corresponding to the microlenses 5a in the B row, which are adjacent to the microlenses 5a in the A row and whose positions are shifted by the lens half pitch, is used. Tbk is obtained in the same manner as the column A data is calculated.
Tbk = Σ | Bij + k−Bdj | (2)
In the equation (2), Σ represents an operation of j = 1 to n (n is the number of light receiving elements used for focus detection) in the B row. The B column data Tbk is interpolated to obtain a shift amount HB, and an arithmetic average or a geometric average of the shift amount HB and the shift amount HA of the A column can be obtained as focus adjustment information.

  In this way, the two rows, A row and B row, which are complementarily positioned complement each other's dead band, and a stable focus detection result can be obtained even if the subject image is in the vicinity of the light receiving surface of the microlens array 5. Can be obtained.

In this calculation, a new data string {Cdj} in which a pair of data strings {Adj} and {Bdj} are alternately arranged, and a new data in which a pair of data strings {Aij} and {Bij} are alternately arranged. Considering the sequence {Cij}, the same effect can be obtained by calculating the shift amount between these data sequences {Cdj} and {Cij}. At this time, the data strings {Cdj} and {Cij}
{Cdj} = ・ ・, Adj, Bdj, Adj + 1, Bdj + 1, Adj + 2, Bdj + 2, ...
{Cij} = ..., Aij, Bij, Aij + 1, Bij + 1, Aij + 2, Bij + 2, ... (3)
Thus, the sequence is a number sequence having a combined length of the A column and the B column. The deviation amount HC may be calculated from this sequence by a conventional method.

In order to reduce the amount of calculation, the following calculation method may be employed. In this case, instead of the above-described data string synthesis, the calculation values are synthesized. First, the shift amount HA is calculated from the data strings {Adj} and {Aij}, and similarly, the shift amount HB is calculated from the data strings {Bdj} and {Bij}. Since this value is complementary on the sequence, the deviation H is
H = √ (HA / HB) (4)
Or
H = (HA + HB) / 2 (5)
Asking. Thereby, it is possible to obtain focus adjustment information in which the influence of the dead zone is reduced.

  In this square arrangement, since the horizontal direction and the vertical direction are rotationally symmetric, the same applies to the vertical direction. When it is not necessary to consider the dead zone when the subject is in focus, it is possible to perform focus detection using a microlens array in the 45 degree direction. In this case, since the arrangement is not complementary even if adjacent columns are used, increasing the amount of data only has the meaning of stabilizing fluctuations, and processing in one column is sufficient. When the light receiving element group corresponding to each microlens 5a is, for example, a pair of light receiving element groups corresponding to the microlens 5a shown in FIG. 6, data suitable for this calculation can be prepared.

  When selecting a pair of focus detection light receiving element groups from the light receiving element regions corresponding to each micro lens 5a, it is necessary to change the selection method according to the arrangement of the micro lenses 5a and the direction of the base line. Since a pupil larger than the aperture of the photographing lens 2 cannot be provided, it is necessary to change the selection of the light receiving element group according to the aperture value of the photographing lens 2. Further, the amount of light incident on the light receiving element 6a or the amount of photons entering the light receiving element group affects the accumulation time or sampling time of the light receiving element 6a. 3 and the lower microlens 5a in FIG. 7), the area of the light receiving element group needs to be a small area close to the ideal (see the lower microlens 5a in FIG. 7). . When the direction of the base line rotates, of course, it is necessary to change the selected position of the light receiving element group accordingly.

  Since the ideal pupil position is a combination of several finite number of light receiving element groups according to various situations, a certain error occurs in the baseline length. Since the defocus value is linear with respect to the baseline length, this error is directly applied to the defocus value. Therefore, a baseline length table corresponding to each method of selecting each light receiving element group is prepared, and when selecting a light receiving element group, a necessary baseline length is read from the table and used as an effective value.

1 is a cross-sectional view of a camera including a focus detection device according to an embodiment. Enlarged view of micro lens array and light receiving element array The figure which shows the selection method of the light receiving element group for light detection element array on a light receiving element array corresponding to each micro lens on a micro lens array, and a pair of light receiving element group for focus detection The figure which shows the arrangement | sequence of the light receiving element on the light receiving element array corresponding to each micro lens on a micro lens array The figure which shows the arrangement of the micro lens on the micro lens array The figure which shows the selection method of the light receiving element group for light detection element array on a light receiving element array corresponding to each micro lens on a micro lens array, and a pair of light receiving element group for focus detection The figure which shows the selection method of the light receiving element group for light detection element array on a light receiving element array corresponding to each micro lens on a micro lens array, and a pair of light receiving element group for focus detection

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Camera 2 Shooting lens 5 Micro lens array 5a Micro lens 6 Light receiving element array 6a Light receiving element

Claims (3)

A plurality of microlenses arranged two-dimensionally in the vicinity of the planned imaging plane of the photographing optical system;
A plurality of light receiving elements arranged two-dimensionally behind each micro lens so as to receive a light beam transmitted through each of the plurality of micro lenses;
For each of the microlenses arranged in a predetermined direction, a pair of light receiving element groups positioned at positions symmetrical to the predetermined direction with the optical axis of the microlens as the center is selected, and each light receiving element group Selecting means for adding a pair of output signals to calculate a pair of added output signals;
A focus detection means for detecting a focus based on a pair of added output signals calculated by the selection means,
When the amount of light incident on the light receiving element is large, the selection unit applies the light to the light receiving element so that the number of light receiving elements in the light receiving element group is small and the number of light receiving elements in the pair of light receiving element groups is equal. When the amount of incident light is small, the number of light receiving elements in the light receiving element group is large and the number of light receiving elements in the pair of light receiving element groups is equal to each other. Change the number of light receiving elements ,
The base line length of the pair of light receiving element groups in which the number of light receiving elements is changed is read from a table in which base line lengths corresponding to the selection methods of the respective light receiving element groups are stored, and the read base line length is read from the focal point. An imaging apparatus used for focus detection by a detection means . The imaging device according to claim 1,
Each of the plurality of microlenses further includes image generation means for generating an image based on an output signal of the light receiving element disposed on the optical axis of the microlens. The imaging device according to claim 1 or 2,
The light receiving element of the light receiving element group is adjacent to each other.

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