JP4120703B2 - Camera with focus detection device - Google Patents

Description

  The present invention relates to a camera including a focus detection device that detects a focus adjustment state of a photographing lens.

A phase difference detection type focus detection apparatus is known. A phase difference detection type focus detection apparatus will be described with reference to FIG.
The light beam incident through the region 101 of the photographing lens 100 passes through the field mask 200, the field lens 300, the aperture opening 401, and the re-imaging lens 501, and forms an image on the A column of the image sensor array 600. The A column of the image sensor array 600 includes a plurality of photoelectric conversion pixels, and outputs a signal sequence corresponding to the light intensity distribution of the subject image. Similarly, the light beam incident through the region 102 of the photographing lens 100 passes through the field mask 200, the field lens 300, the aperture opening 402, and the re-imaging lens 502, and forms an image on the B row of the image sensor array 600. . The B column of the image sensor array 600 also includes a plurality of photoelectric conversion pixels, and outputs a signal column corresponding to the light intensity distribution of the subject image.

  A pair of subject images formed on the A and B rows of the image sensor array 600 are close to each other in a so-called front pin state in which the photographing lens 100 forms a sharp image of the subject before the planned focal plane, and conversely planned. In the so-called rear pin state, in which a sharp image of the subject is formed after the focal plane, they move away from each other. Further, at the time of so-called in-focus, in which a sharp image of a subject is formed on the planned focal plane, a pair of subject images on the A and B columns of the image sensor array 600 are positioned at a predetermined interval. Therefore, a pair of subject images on the image sensor array 600 are photoelectrically converted by the A and B columns of the image sensor array 600, and these signals are arithmetically processed to obtain a positional deviation amount of the pair of subject images. The focus adjustment state of the lens 100 with respect to the planned focal plane, here, the distance away from the focused state and its direction (hereinafter referred to as defocus amount) can be obtained.

  The field mask 200, the field lens 300, the aperture openings 401 and 402, the re-imaging lenses 501 and 502, and the image sensor array 600 are mounted on a housing molded using a plastic material. Built into the bottom of the. Hereinafter, the field mask 200, the field lens 300, the aperture openings 401 and 402, the re-imaging lenses 501 and 502, and the image sensor array 600 mounted on the housing are referred to as a focus detection module.

Each of the A column and the B column of the image sensor array 600 includes a plurality of photoelectric conversion pixels, and a pair of output signal columns a [1],. . . , A [n], b [1],. . . b [n] is output. Then, using this pair of output signal sequences, for example, the focus detection calculation disclosed in Patent Document 1 is executed to calculate the positional deviation amount Ls. Further, the defocus amount DF is calculated from the positional deviation amount Ls by the equation (1).
DF = Kf · (Ls−ZL) (1)
In the equation (1), Kf is a conversion coefficient from the positional shift amount Ls to the defocus amount DF, which is determined by the pitch width of the photoelectric conversion pixels of the optical system and the image sensor array 600 shown in FIG. ZL is the amount of displacement when the taking lens 100 is in focus, and is caused by a manufacturing error that occurs when the focus detection module is incorporated into the camera. Therefore, this positional deviation amount ZL differs for each focus detection device. Therefore, in the conventional focus detection apparatus, the positional deviation amount ZL at the time of in-focus is measured at the time of manufacture and stored in a storage medium such as an EEPROM, and is used during the focus detection calculation of equation (1).

Prior art documents related to the invention of this application include the following.
Japanese Patent Laid-Open No. 60-037513

By the way, the relationship between the defocus amount DF and the positional deviation amount is not actually linear but nonlinear as shown in FIG.
In FIG. 4, the horizontal axis represents the positional deviation amount Ls, and the vertical axis represents the defocus amount DF. Curve (A) shows the characteristics when the positional deviation amount ZL at the time of focusing is positive, curve (B) shows the characteristics when the positional deviation amount ZL at the time of focusing is 0, and curve (C) shows the characteristics when the positional deviation amount ZL is zero. The characteristic when the positional deviation amount ZL at the time of focusing is negative is shown.

Thus, since the relationship between the positional deviation amount Ls and the defocus amount DF is nonlinear, it is necessary to correct the defocus amount DF obtained by the equation (1) by the equation (2).
DF = DF / {1 + DF / Po} (2)
An arithmetic expression substantially the same as the expression (2) is disclosed in Japanese Patent Laid-Open No. 57-165806. In the equation (2), Po is the distance between the conjugate plane of the openings 401 and 402 by the field lens 300 and the planned focal plane, and is usually designed to be about 100 mm.

  The conversion coefficient Kf is the slope of the tangent line of the curve shown in FIG. 4, and the slope of the tangent line of the curve in the focused state (defocus amount DF = 0), that is, the characteristic curves (A) to (C) in FIG. The slope of the tangent at the intersection with the straight line with the amount DF = 0 is the optimum conversion coefficient Kf for accurately converting the positional deviation amount to the defocus amount in the vicinity of the focal point. FIG. 5 shows the relationship between the positional shift amount ZL at the time of focusing and the optimum conversion coefficient Kf.

As described above, the positional deviation amount ZL at the time of in-focus differs depending on the focus detection device. However, when the variation in the positional deviation amount ZL for each focus detection device is small, the conversion coefficient Kf may be a fixed value. On the contrary, when the variation of the positional deviation amount ZL is large, an appropriate conversion coefficient Kf must be set for each focus detection device.
An object of the present invention is to provide a focus detection apparatus in which an optimum conversion coefficient is set for each focus detection apparatus to improve focus detection accuracy.

(1) The invention according to claim 1 is a photoelectric conversion that receives at least a pair of light beams that have passed through different areas of the photographing optical system and outputs a pair of signal sequences according to the light intensity distribution of the pair of subject images by the light beams. A positional deviation amount detecting means for detecting a relative positional deviation amount of a pair of signal sequences output from the photoelectric conversion means, and a relative displacement amount using a predetermined conversion coefficient. A conversion coefficient calculating means for calculating a conversion coefficient for a reference deviation amount when the photographing optical system is in focus, and a conversion coefficient stored therein; Conversion coefficient storage means.
(2) In the camera provided with the focus detection device according to claim 2, the conversion coefficient calculation means is provided independently of the focus detection device.
(3) A camera including the focus detection apparatus according to claim 3 receives at least a pair of light beams that have passed through different regions of the photographing optical system via the re-imaging optical system by the photoelectric conversion unit.

According to the present invention, since the conversion coefficient based on the reference deviation amount at the time of focusing is obtained and stored, the optimum conversion coefficient can be set for each individual focus detection device, and the focus detection accuracy is improved. Can be made.
Further, according to the present invention, since the conversion coefficient calculation means is independent of the focus detection apparatus, it is not necessary to calculate the conversion coefficient in the focus detection apparatus, and the scale of calculation can be reduced.

-First embodiment of the invention-
A position shift amount ZL at the time of focusing measured during manufacture of the focus detection device is stored in a memory in the focus detection device, and an optimum conversion coefficient Kf is set based on the position shift amount ZL at the time of focusing. 1 is described.

FIG. 1 shows the configuration of the first embodiment.
The focus detection module 1 includes the field mask 200, the field lens 300, the aperture openings 401 and 402, the re-imaging lenses 501 and 502, and the image sensor array 600 shown in FIG. The focus detection calculation unit 2 detects the positional deviation amount Ls and calculates the defocus amount DF.

Here, for example, a method for detecting the positional deviation amount Ls disclosed in Japanese Patent Application Laid-Open No. 60-37513 will be described.
As shown in FIGS. 8A and 8B, the A and B columns of the image sensor array 600 mounted on the focus detection module 1 are a pair of signal columns a [1],. . . , A [n], b [1],. . . b [n] is output. Then, the correlation calculation is performed while the data in a predetermined range of the pair of output signal sequences is relatively shifted by L by predetermined data. When the maximum shift amount is lmax, the range of L is from −1max to lmax. Specifically, the correlation amount C [L] is calculated by the equation (3).
C [L] = Σ | a [i + L] −b [i] |,
L = -lmax, ...,-2, -1,0,1,2, ..., lmax (3)
In the equation (3), Σ indicates a summation operation of i = k to r, and L is an integer indicating the shift amount of the data string.

The first term k and the last term r in the equation (3) are changed depending on the shift amount L as shown in, for example, the equation (4).
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)
In equation (4), k0 and r0 are the first term and the last term when the shift amount L is zero.

  A combination for calculating the absolute value of the difference between the signals in columns A and B in equation (3) when the first term k and the final term r are changed by equation (4), and the operation for adding the absolute value of the difference The range is shown in FIG. Thus, as the shift amount L changes, the ranges used for the correlation calculation of the A column and the B column shift in opposite directions. There is also a method in which the initial term k and the final term r are made constant regardless of the shift amount L. In this case, the range used for correlation calculation of one column is always constant, and only the other column is shifted. Since the positional deviation amount is the shift amount L when the pair of data coincides, the shift amount that gives the minimum correlation amount is detected from the correlation amount C [L] thus obtained.

By the way, the correlation amount C [L] is a discrete value as shown in FIG. 8C, and the minimum unit of the detectable positional deviation amount is that of the photoelectric conversion pixels in the A and B columns of the image sensor array 600. It is limited by the pitch width. Therefore, the true local minimum value Cex is calculated by performing an interpolation operation based on the discrete correlation amount C [L], and fine focus detection is performed. As shown in FIG. 7, the true minimum value Cex is obtained by using the correlation amount C [Le] which is the minimum value and the correlation amounts C [Le + 1] and C [Le-1] at the shift amounts on both sides thereof. Is calculated by the equations (5) and (6).
DL = (C [Le-1] -C [Le + 1]) / 2
Cex = C [Le]-| DL |,
E = MAX {C [Le + 1] -C [Le], C [Le-1] -C [Le]} (5)
Ls = Le + DL / E (6)
In the formula (5), MAX {Ca, Cb} indicates that the larger one of Ca and Cb is selected.

It is necessary to determine whether the positional deviation amount Ls obtained in this way truly indicates the positional deviation amount or due to the fluctuation of the correlation amount due to noise or the like, and when the condition shown in the equation (7) is satisfied The positional deviation amount Ls is assumed to be reliable.
E> E1 & Cex / E <G1 (7)
E1 and G1 in equation (7) are predetermined threshold values. 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 region 101 and the region 102, a slight difference occurs between the pair of subject images, and the difference does not become zero. Since the influence of noise and the difference between the subject images 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. Naturally, the closer Cex / E is to 0, the higher the degree of coincidence of the pair of data and the higher the reliability.
In some cases, the contrast relating to one of the pair of data is calculated instead of the numerical value E, and the reliability is determined using this. When it is determined that there is reliability, the defocus amount DF is calculated by the above equations (1) and (2).

  The reference deviation amount storage unit 3 is a memory that stores a positional deviation amount ZL at the time of focusing measured at the time of manufacture. After the focus detection module 1 is incorporated into the camera, the positional deviation amount ZL at the time of focusing is measured and stored in the reference deviation amount storage unit 3. The in-focus position shift amount ZL is output to the focus detection calculation unit 2 and used for the focus detection calculation of equation (1).

In addition, when the variation in the positional deviation amount ZL at the time of focusing is within a relatively narrow range centered on the predetermined positional deviation amount zb, the change of the conversion coefficient Kf with respect to the positional deviation amount ZL is linear. In this case, the table is not necessary, and the conversion coefficient Kf is calculated by the equation (8).
Kf = kb + ak · (ZL−zb) (8)
Here, kb is the optimum conversion coefficient when the positional deviation amount is the predetermined value zb, and ak is the slope of the approximate line.
The conversion coefficient Kf set in this way is output to the focus detection calculation unit 2 and used for the focus detection calculation of equation (1).

Thus, even when there is a large variation in the positional deviation amount ZL at the time of focusing due to an error or the like when the focus detection module is mounted on the camera, an appropriate conversion coefficient Kf can be set.
Alternatively, the conversion coefficient Kf may be set as described above when the camera power is turned on, and the conversion coefficient Kf may be held until the camera power is turned off. , The conversion coefficient Kf may be set as described above immediately before each time the defocus amount DF is to be calculated. In these cases, the former only needs to hold the conversion coefficient Kf while the camera is turned on, and it is not always necessary to store the conversion coefficient Kf, and the conversion coefficient Kf is converted every time the defocus amount DF is to be calculated. There is no need to set the coefficient Kf, and the defocus amount DF can be calculated quickly. The latter does not need to store or hold the conversion coefficient Kf, and eliminates the need to increase the capacity of a storage medium such as an EEPROM.

-Second embodiment of the invention-
Second embodiment in which a correction amount Hc for a reference conversion coefficient kc at a predetermined positional deviation amount zc is stored, and the reference conversion coefficient kc is corrected using this correction amount Hc and set as a conversion coefficient Kf Will be explained.

FIG. 2 shows the configuration of the second embodiment. The focus detection module 1, the focus detection calculation unit 2, and the reference deviation amount storage unit 3 are the same as those in the first embodiment shown in FIG.
A correction amount Hc applied to the reference conversion coefficient kc is calculated at the time of manufacture based on the in-focus position shift amount ZL measured at the time of manufacture, and is stored in the correction amount storage unit 5.

A method of setting the correction amount Hc will be described with reference to FIG.
First, the conversion coefficient KL suitable for the positional shift amount ZL at the time of focusing is obtained from the curve of the conversion coefficient Kf with respect to the positional shift amount ZL at the time of focusing shown in FIG. Then, the correction amount Hc is calculated by the equation (9).
Hc = KL-kc (9)
Here, kc is a conversion coefficient at a predetermined displacement amount zc.

Based on the correction amount Hc stored in the correction amount storage unit 5, the conversion coefficient correction unit 6 calculates the conversion coefficient Kf used for the focus detection calculation of the equation (1) by the equation (10).
Kf = kc + Hc (10)
The conversion coefficient Kf set in this way is output to the focus detection calculation unit 2 and used for the focus detection calculation of equation (1).

  Further, the correction amount calculation means for calculating the correction amount Hc at the time of manufacture is not in the focus detection device, but may be in, for example, an adjustment device other than the focus detection device, and in this case, in the focus detection device. It is not necessary to store several points of a curve indicating the relationship between the positional deviation amount ZL and the conversion coefficient Kf at the time of focusing as a table, the scale of calculation related to focus detection, and the capacity of a storage medium such as an EEPROM in the focus detection device Can be reduced. Furthermore, by storing the correction amount Hc, the amount of information to be stored may be smaller than storing the conversion coefficient Kf itself.

  Furthermore, the conversion coefficient Kf may be calculated by the expression (10) when the camera is turned on, and the conversion coefficient Kf may be continuously held until the camera is turned off. Alternatively, the conversion coefficient Kf may be maintained by the expression (1). When calculating the amount DF, the conversion coefficient Kf may be calculated by the equation (10) immediately before every time the defocus amount DF is to be calculated. In these cases, the former only needs to hold the conversion coefficient Kf only while the camera is turned on, and it is not always necessary to store the conversion coefficient Kf, and whenever the conversion coefficient DF is to be calculated, the conversion coefficient Kf is stored. There is no need to calculate Kf, and the calculation of the defocus amount DF can be accelerated. The latter does not need to store or hold the conversion coefficient Kf, and eliminates the need to increase the capacity of a storage medium such as an EEPROM.

  In the second embodiment, the correction amount is calculated in the form of the difference and the correction is performed by addition. However, for example, the correction amount may be calculated in the form of a ratio and the correction may be performed by multiplication. .

  Since the curve showing the relationship between the amount of displacement and the conversion coefficient (curve in FIG. 5) cannot be expressed by a simple functional equation, it is not necessary to memorize many points of the curve by doing in this way. A large storage capacity is not required in the camera, and the calculation time for calculating the conversion coefficient Kf can be shortened.

-Third embodiment of the invention-
A third embodiment in which an appropriate conversion coefficient Kf is obtained based on the in-focus position shift amount ZL measured at the time of manufacturing the focus detection apparatus, and this conversion coefficient Kf is stored will be described.

FIG. 3 shows the configuration of the third embodiment. The focus detection module 1, the focus detection calculation unit 2, and the reference deviation amount storage unit 3 are the same as those in the first embodiment shown in FIG.
The conversion coefficient storage unit 7 obtains a conversion coefficient Kf suitable for the in-focus position shift amount ZL measured during manufacture from the curve of the conversion coefficient Kf with respect to the in-focus position shift amount ZL shown in FIG. Remember.

  Further, the conversion coefficient calculation means for calculating the conversion coefficient Kf at the time of manufacture is not in the focus detection device, but may be in an adjustment device, for example, different from the focus detection device. It is not necessary to store several points of a curve indicating the relationship between the positional deviation amount ZL and the conversion coefficient Kf at the time of focusing as a table, the scale of calculation related to focus detection, and the capacity of a storage medium such as an EEPROM in the focus detection device Can be reduced.

The figure which shows the structure of 1st Embodiment. The figure which shows the structure of 2nd Embodiment. The figure which shows the structure of 3rd Embodiment. The figure which shows the relationship of the defocusing amount DF with respect to the positional offset amount Ls of the to-be-photographed image on an image sensor array. The figure which shows the relationship between position shift amount ZL at the time of focusing, and conversion coefficient Kf Diagram showing focus detection optical system and image sensor array The figure which shows the relationship of the correlation amount C [L] with respect to the shift amount L The figure which shows the relationship between the output signal sequence of an image sensor array, and the correlation amount C [L] with respect to the shift amount L Diagram for explaining correlation calculation

Explanation of symbols

DESCRIPTION OF SYMBOLS 1; Focus detection module, 2; Focus detection calculating part, 3; Reference | standard deviation amount memory | storage part, 7; Conversion coefficient memory | storage part, 100; Shooting lens, 200; Field mask, 300; Field lens, 401, 402; 501, 502; Re-imaging lens 600; Image sensor array

Claims (3)

Photoelectric conversion means for receiving at least a pair of light beams that have passed through different areas of the photographing optical system and outputting a pair of signal sequences corresponding to the light intensity distribution of the pair of subject images by the light beams;
A positional deviation amount detecting means for detecting a relative positional deviation amount of a pair of signal sequences output from the photoelectric conversion means;
In a camera including a focus detection device including conversion means for converting the relative displacement amount into a defocus amount of the photographing optical system using a predetermined conversion coefficient,
Conversion coefficient calculation means for calculating the conversion coefficient with respect to a reference deviation amount when the photographing optical system is in focus;
A camera provided with a focus detection device, comprising conversion coefficient storage means for storing the conversion coefficient. In the camera provided with the focus detection apparatus according to claim 1,
The camera provided with a focus detection device, wherein the conversion coefficient calculation means is provided independently of the focus detection device. In the camera provided with the focus detection device according to claim 1 or 2,
The photoelectric conversion means receives at least a pair of light beams that have passed through different areas of the photographing optical system via a re-imaging optical system, and has a focus detection device.

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