JP2005128293A - Focus detector - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To improve precision in an amount of deviation computed by a focus detector in which width of a region detected by one focus detecting optical system is wide and a diaphragm conjugate plane where diaphragm openings are inversely projected is set further than an exit pupil. <P>SOLUTION: Inversely projected images of a pair of diaphragm openings 410a and 410b are projected onto a conjugate plane CP which is set further (an object to be photographed side) than the exit pupil of a photographic lens. A photographic luminous flux, which is made incident from the photographic lens and passes a focus detection region set by a visual field opening 210, passes a condenser lens 3 and is pupil divided by the pair of diaphragm openings 410a and 410b. This pair of luminous fluxes is image reformed on a pair of light receiving sensor arrays 610a and 610b by image reforming lens sections 510a and 510b. Lens intrinsic correction coefficients are stored in the photographic lens. These correction coefficients are read into a camera main body for focus detection computations, location of a focus detection computation region with respect to the center of the focus detecting region and the amount of correction corresponding to the arrangement direction of the pair of diaphragm openings with respect to the region are computed to obtain the true amount of deviation. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to a focus detection device that detects a focus adjustment state of a photographing optical system.

  As a phase difference detection type focus detection apparatus, those disclosed in Patent Document 1 and Patent Document 2 are known. As shown in FIG. 6 (a), the focus detection apparatus of Patent Document 1 uses an aperture conjugate conjugate plane CP at a position farther away from the back projection image RI of the aperture opening of the focus detection optical system than in the vicinity of the exit pupil EP of the interchangeable lens. To project. Thereby, even when the focus shift amount (defocus amount) is large, the shift amount can be calculated.

  The focus detection apparatus disclosed in Patent Document 2 improves the accuracy of the amount of deviation calculated in a focus detection region set off-axis. The photographing lens has a field curvature aberration from the optical axis to the off-axis, and the deviation amount calculated in the focus detection region set off-axis includes an error due to the field curvature aberration. Therefore, in the focus detection apparatus disclosed in Patent Document 2, correction data for curvature of field unique to the photographing lens is stored in the lens ROM, and when the focus detection calculation is performed in the off-axis focus detection region, the amount of deviation is determined by the correction data. Is to correct.

JP-A-7-234356 JP-A-6-130283

  Here, in the focus detection apparatus described in Patent Document 1, for example, when focus detection is performed using a single focus detection optical system in a wide region including the optical axis, the region away from the optical axis, in other words, the image height. In a high focus detection region, there is a case where the shift amount cannot be corrected appropriately with correction data based on curvature of field as in Patent Document 2.

  For example, as shown in FIG. 6A, the principal ray M0 ′ of the image indicated by the image height y2 passes through a point away from the optical axis of the exit pupil EP, and the principal ray of the image indicated by the image height y1 is the exit pupil EP. It passes through a point close to the optical axis. When the correction method shown in Patent Document 2 is used, qualitatively, the deviation amount calculated for the image height y2 includes an unacceptable error, and the error of the deviation amount calculated for the image height y1 is It can be said that it is acceptable. This error is because the correction data of Patent Document 2 is for a light beam passing through a region near the optical axis of the exit pupil EP.

  Incidentally, as shown in FIG. 6B, when the back projection image RI of the aperture opening of the focus detection optical system is designed to be projected in the vicinity of the exit pupil EP of the interchangeable lens, focus detection with a high image height indicated by y2 is performed. Even the focus detection light beam corresponding to the region passes through the region in the vicinity of the optical axis at the exit pupil EP of the interchangeable lens, so that the deviation amount error due to the field curvature aberration is small. As shown in FIG. 6B, the principal ray MO having the same image height y2 as in FIG. 6A passes through the optical axis on the exit pupil EP.

(1) According to the first aspect of the present invention, the light beam passing through the position corresponding to the focus detection area among the subject light beam from the photographing lens is divided into pupils by a diaphragm mask having a pair of aperture openings via a condenser lens. A focus detection optical system that re-images each of the pair of divided light beams on the pair of light receiving elements, an image surface of the photographing lens and a predetermined image forming surface based on a subject image signal detected by the pair of light receiving elements Calculating means for calculating the amount of deviation of the aperture, the position of the aperture conjugate plane where the aperture opening is back-projected by the condenser lens is set closer to the subject side than the exit pupil position of the photographic lens, and the calculating means In a focus detection apparatus that calculates a shift amount based on a subject image signal corresponding to at least a part of a region (hereinafter referred to as a focus detection calculation region), the calculation means is configured to calculate the center of the focus detection region Position of point detection calculation region, and, and obtaining by correcting the deviation amount based on the correction amount corresponding to the arrangement direction of the pair of the aperture stop.
(2) The invention according to claim 2 is the focus detection device according to claim 1, wherein the focus detection area is separated from the first detection area whose center is located on the optical axis of the photographing lens and the optical axis of the photographing lens. And a second detection region located at a position.
(3) The invention according to claim 3 is characterized in that, in the focus detection apparatus according to claim 1, the correction amount is obtained by a calculation means based on information unique to the photographing lens stored on the photographing lens side. .
(4) A fourth aspect of the present invention is the photographic lens used in the camera having the focus detection device according to the first aspect, wherein the pupil position of the focus detection optical system and the position of the focus detection calculation area with respect to the optical axis of the photographic lens. The image processing apparatus includes an acquisition unit that acquires information on the camera from a camera, a lens-side calculation unit that calculates a correction amount based on the information, and an output unit that outputs the calculated correction amount to the calculation unit of the camera.

  According to the present invention, in a focus detection device that performs focus detection in a region with a high image height such that the focus detection light beam passes through a region away from the optical axis at the exit pupil position of the interchangeable lens, focus detection with respect to the center of the focus detection region is performed. A correction amount corresponding to the position of the target region and the direction in which the pair of aperture stops is arranged, and the calculated shift amount is corrected with the correction amount. Therefore, it is possible to calculate a focus adjustment state with high accuracy even when focus detection within a wide focus detection region is performed by one focus detection optical system, while the shift amount can be calculated even when the focus shift amount is large.

An embodiment in which the focus detection apparatus of the present invention is applied to a single-lens reflex camera will be described.
FIG. 1 is a schematic configuration diagram of a single-lens reflex camera equipped with a focus detection apparatus according to the present invention. The light beam from the subject is guided into the camera body CB through the photographing lens (interchangeable lens) LE in the lens barrel LB. A part of the light beam guided to the camera body CB passes through the semi-transmissive main mirror 51, is reflected downward by the sub mirror 52, and then enters the focus detection module 10. The CPU 56 that is a focus detection calculation circuit drives the lens drive motor 57 based on the focus detection signal that is the output of the focus detection module 10 to adjust the focus of the photographic lens LE. On the other hand, the light beam reflected by the main mirror 51 is observed by the eyepiece lens 55 via the pentaprism 54. IM is a photographing and recording means such as a film or a CCD.

  FIG. 2 shows a focus detection area of the focus detection apparatus according to this embodiment. In FIG. 2, M is a photographing screen showing the photographing range of the subject image by the photographing optical system, and is a rectangle that is long in the horizontal direction as shown in the figure. In this focus detection apparatus, a focus detection area 100 extending in the horizontal direction in the center of the shooting screen M and focus detection areas 200 and 250 extending in the vertical direction in the left and right peripheral portions of the shooting screen M are set. ing. Lx indicates the center of the screen corresponding to the optical axis of the photographing lens.

  In FIG. 2, the focus detection area 100 is divided into three divided areas 101 to 103. Similarly, the focus detection areas 200 and 250 are also divided into three divided areas 201 to 203 and 251 to 253. These divided regions can be selected by a predetermined algorithm based on the subject image on the light receiving sensor of the focus detection module 10.

  The focus detection method by the focus detection module 10 is called a known phase difference detection method or pupil division type re-imaging method. This method detects the focus adjustment state of the photographic optical system based on a relative positional shift between a pair of images formed by a pair of light beams that have passed through different portions on the exit pupil plane of the photographic optical system. It is a method.

  As shown in FIG. 3, the focus detection module 10 includes a field mask 2, a condenser lens 3, a diaphragm mask 4, a re-imaging lens 5, and an image sensor 6. Reference numerals 100a and 100b denote pupil regions corresponding to the focus detection region 100 shown in FIG. 2, and are back-projected images of stop apertures 410a and 410b of the stop mask 4 described later. Reference numerals 200a and 200b denote pupil areas corresponding to the focus detection areas 200 and 250 shown in FIG. 2, and are back-projected images of stop openings 420a and 420b and 425a and 425b of the stop mask 4 described later. Accordingly, the plane CP on which these pupil regions are formed is a plane conjugate with the stop mask 4. As can be seen from FIG. 3, the conjugate plane CP is set at a position (subject side) farther than the exit pupil EP. This is because, like Patent Document 1, focus detection is possible even when the amount of focus deviation is large.

  The focus detection module 10 will be further described. The focus detection light beam that travels along the photographing optical axis of the photographing lens LE and is reflected by the sub mirror 52 forms an image on a planned focal plane that is a primary imaging plane of the photographing light beam. The field mask 2 is provided in the vicinity of the primary imaging plane. The field mask 2 is provided with a field opening 210 corresponding to the focus detection area 100, a field opening 220 for the focus detection area 200, and a field opening 225 for the focus detection area 250.

  A condenser lens 3 is disposed behind the field mask 2. The condenser lens 3 includes a lens unit 310 corresponding to the focus detection region 100, a lens unit 320 for the focus detection region 200, and a lens unit 325 for the focus detection region 250. Behind the condenser lens 3, an aperture mask 4 having three pairs of aperture openings 410a and 410b, 420a and 420b, and 425a and 425b is disposed. Behind the diaphragm mask 4, the re-imaging lens 5 having three pairs of lens portions 510a and 510b, 520a and 520b, and 525a and 525b corresponding to each of the pair of diaphragm apertures is disposed. Behind the re-imaging lens 5, an image sensor 6 having three pairs of light receiving sensor arrays 610a and 610b, 620a and 620b, and 625a and 625b is arranged. The light receiving sensor arrays 610a and 610b, 620a and 620b, and 625a and 625b are each configured by a photoelectric conversion element array.

  As described above, the focus detection module in this embodiment includes the focus detection optical system 100AF in the focus detection area 100, the focus detection optical system 200AF in the focus detection area 200, and the focus detection optical system 250AF in the focus detection area 250. It has. The focus detection optical system 100AF includes a field opening 210, a condenser lens unit 310, a pair of aperture openings 410a and 410b, and a pair of re-imaging lens units 510a and 510b. The focus detection optical system 200AF includes a field opening 220, a condenser lens unit 320, a pair of aperture openings 420a and 420b, and a pair of re-imaging lens units 520a and 520b. The focus detection optical system 250AF includes a field opening 225, a condenser lens unit 325, a pair of aperture openings 425a and 425b, and a pair of re-imaging lens units 525a and 525b.

  The focus detection light beam forms an image on the image sensor 6 by such a focus detection optical system. The focus detection region 100 will be described. An image formed on the primary image formation plane is divided into a pair of images from the condenser lens 3 through the openings 410a and 410b. The pair of divided images are re-imaged on the light receiving sensor arrays 610a and 610b by the re-imaging lens portions 510a and 510b. Based on the correlation between the pair of re-imaged images, the focus adjustment state (defocus amount) of the photographic lens LE is calculated. The focus adjustment state is similarly calculated for the focus detection areas 200 and 250.

  FIG. 4 is a control block diagram related to focus detection of a single-lens reflex camera equipped with a focus detection apparatus according to the present invention. The CPU 56 receives detection signal strings from the three pairs of light receiving sensor arrays 610a and 610b, 620a and 620b, and 625a and 625b. Connected to the CPU 56 is an area selection switch 58 for selecting one of the focus detection areas 100, 200, 250 shown in FIG. Further, a memory 59 for temporarily storing correction data read from the lens ROM in the interchangeable lens 1 is connected. The photographic lens LE stores correction data specific to the lens, which will be described later.

  The CPU 56 performs focus detection calculation for each divided area of the focus detection area 100. That is, from the detection signal sequence of the light receiving sensor array 610a and the detection signal sequence of the light receiving sensor array 610b, the detection signal sequence from the photoelectric conversion element corresponding to the divided region used for the focus detection calculation is extracted, and the correlation calculation is performed. Calculate the adjustment state. The same applies to the focus detection areas 200 and 250. That is, in this embodiment, correlation calculation is performed for each photoelectric conversion element group corresponding to the divided regions 101 to 103, 201 to 203, and 251 to 253 shown in FIG. The focus adjustment state calculated by the correlation calculation is calculated as an image shift amount between the imaging surface of the subject image by the photographing lens LE and the film surface or the CCD light receiving surface (conjugated with the planned imaging surface). This amount of image shift is converted into the amount of movement of the focusing lens to the in-focus position, and this amount of movement is output to the AF motor 57.

  In the present invention, the image shift amount is corrected by the shift correction amount corresponding to the divided area where the focus detection calculation is performed. Here, the deviation correction amount is to correct a deviation amount calculation error generated based on the field curvature aberration of the photographing lens LE, and includes a so-called tangential direction correction amount and a radial direction correction amount. . In the present invention, different correction amounts are used for the focus detection area 100 and the focus detection areas 200 and 250.

  As described above, this embodiment includes the focus detection optical system 100AF, the focus detection optical system 200AF, and the focus detection optical system 250AF. The influence of the photographic lens LE on the focus detection calculation due to the field curvature aberration differs between the focus detection optical system 100AF and the focus detection optical system 200AF. This is also different between the focus detection optical system 100AF and the focus detection optical system 250AF. The influence appears equally between the focus detection optical systems 200AF and 250AF.

In the off-axis divided regions 102 and 103 of the focus detection region 100, the arrangement direction of the corresponding aperture openings is a tangential direction with respect to the optical axis, so that the tangential corresponding to the image height from the photographing optical axis Lx. A direction correction amount HT ₁₀₀ is required. The correction amount HT ₁₀₀ is calculated according to the positions of the divided areas 102 and 103 with respect to the center of the focus detection area 100. In the divided area 201 of the focus detection area 200, the arrangement direction of the aperture stops corresponding to this is the radial direction with respect to the optical axis, so the correction amount HR _{200 in} the radial direction corresponding to the image height from the photographing optical axis Lx is is necessary. The divided areas 202 and 203 of the focus detection area 200 require a radial correction amount HR ₁₀₀ in addition to the radial correction amount HR ₂₀₀ . The correction amount HR _{100 is} also calculated according to the positions of the divided areas 202 and 203 with respect to the center of the focus detection area 200.

In summary, the correction amount H can be expressed as follows for each divided region of each focus detection region.
(A) Correction is not performed for the divided area 101 on the axis of the focus detection area 100.
(B) The correction amount H of the divided areas 102 and 103 of the focus detection area 100 is expressed by the following equation (1).
H = Tangential correction amount HT ₁₀₀ (1)
The correction amount _{HT 100,} for the focus detection area 102 and 103 of FIG. 2, a correction amount in the tangential direction to eliminate the influence of FIG 6 (a).

(C) The correction amount H of the divided area 201 of the focus detection area 200 is expressed by the following equation (2).
H = Radial correction amount HR ₂₀₀ (2)
(D) The correction amount H of the divided areas 202 and 203 of the focus detection area 200 is expressed by the following equation (3).
H = radial correction amount HR ₂₀₀ + radial correction amount HR ₁₀₀ (3)
The correction amount HR ₁₀₀ is a radial correction amount that eliminates the influence of FIG. 6A on the focus detection areas 202 and 203 in FIG.

Hereinafter, this correction calculation will be described in detail.
As described in JP-A-6-130283, the CPU 56 detects a detection signal sequence corresponding to a selected divided region from among the detection signal sequence of the light receiving sensor array 610a and the detection signal sequence of the light receiving sensor array 610b. Is used to calculate the focus adjustment state. When this calculation result is represented by a deviation amount P and the correction amount is represented by H, the true deviation amount D can be expressed by the following equation (4).
D = P−H (4)

(A) Focus detection area 100
Since the divided area 101 is a focus detection area on the optical axis and the correction amount H is zero, the true shift amount D is expressed by the following equation (5).
D = P (5)

The divided areas 102 and 103 are off-axis focus detection areas deviating from the optical axis in the X direction, and the correction amount H is expressed by the following equation (6).
H = HT ₁₀₀ = kt _100-2 × y ² + kt _100-0 (6)

(B) Focus detection area 200
The focus detection area 200 is a focus detection area extending in the Y direction at a position away from the optical axis in the X direction. The divided area 201 is a focus detection area extending in the Y-axis direction at a position separated in the X direction, and the correction amount H is expressed by the following equation (7).
_{H = HR 200 = kr 200-4 ×} y 4 + kr 200-2 × y 2 + kr 200-0 ...... (7)

The divided areas 202 and 203 are areas shifted further in the Y direction with respect to the off-axis focus detection area 200, and the correction amount H is expressed by the following equation (8).
H = HR ₂₀₀ + HR ₁₀₀
= (Kr _200-4 xy ⁴ + kr _200-2 xy ² + kr _200-0 ) +
(Kr _100-2 × y ² + kr _100-0 ) (8)

The above correction amount H includes the fourth-order correction coefficient kr _200-4 , the second-order correction coefficient kr _200-2 , kt _100-2 , kr _100-2 , the zero-order correction coefficient kt _200-0 , kt _{100- 0} and kr _100-0 are shown as polynomials. These coefficients are data specific to the interchangeable lens and correspond to the image height in the focus detection optical system in which the position of the stop conjugate plane is farther from the exit pupil position. These correction coefficients will be described at the image height y2 in FIG.

  As shown in FIG. 6A, the stop conjugate plane CP is at a position away from the exit pupil EP, and the image is formed by the light beam of the principal ray MO ′ passing through the center of the stop conjugate plane CP. ), The aperture conjugate plane CP is at the exit pupil EP, and the difference from the position formed by the light beam of the principal ray MO passing through the center of the aperture conjugate plane CP is expressed as a function of the image height. It is a coefficient. Therefore, as shown in FIG. 1, these lens-specific correction coefficients are stored in advance in the lens ROM of the interchangeable lens LE. When the interchangeable lens LE is attached to the camera body CB, the correction coefficient is read from the lens ROM into the memory 59 of the camera body CB.

A procedure for focus detection calculation in the camera system configured as described above will be briefly described.
When the main power supply is turned on, the focus adjustment process is performed under the control of the CPU 56 as follows. The above-described coefficients are read into the memory 59 from the lens ROM of the photographic lens LE. Of the detection signal sequences of the pair of light receiving sensor arrays, the signal sequence corresponding to the divided region used for the focus detection calculation is extracted to calculate the shift amount P. Further, the correction amount H corresponding to the divided area used for the focus detection calculation is calculated using any one of the above formulas (6) to (8). It should be noted that the image height y in the equations (6) to (8) is set to a predetermined value for each divided area. Then, the true deviation amount D is calculated by the equation (4).

The focus detecting apparatus configured as described above can provide the following operational effects.
(1) When focus detection is performed in a region having a high image height such that the focus detection light beam passes through a region away from the optical axis at the exit pupil position of the interchangeable lens, the position of the focus detection calculation region with respect to the center of the focus detection region, and A correction amount corresponding to the direction in which the pair of aperture openings are arranged is used. Therefore, even when focus detection in a wide focus detection region is performed by one focus detection optical system, a highly accurate focus adjustment state can be calculated.

  Even when the focus detection areas 300 and 350 are set as shown in FIG. 5, the image shift amount may be calculated by the same correction calculation as the focus detection areas 200 and 250.

  In the above embodiment, the correction lens specific to the interchangeable lens is stored in the lens ROM of the interchangeable lens, and the correction correction calculation is performed by reading these coefficients into the camera body. However, the following configuration is also possible. Good.

  In the lens ROM in the interchangeable lens, for each focus detection module used in the camera body to which the interchangeable lens is mounted, its pupil position (aperture conjugate plane position) and the position of the focus detection calculation area with respect to the optical axis of the mounted lens Is stored as a coefficient. These correction formulas are the same as the correction formulas described above.

  When the interchangeable lens is attached to the camera body, the interchangeable lens reads the pupil position of the mounted focus detection module and the position information of the divided area used for the focus detection calculation from the camera body and uses them as the coefficients of the correction formula. Then, the correction amount H is calculated using these correction coefficients and transmitted to the camera body.

  The camera body stores these shift correction amounts H in the memory 59. The camera body calculates a deviation amount P by a known correlation calculation, and corrects the deviation amount P with a deviation correction amount H to calculate a deviation amount D. The difference from the above embodiment is whether the correction amount is obtained on the camera side or the lens side.

  The present invention is not limited to the embodiment described above, and can be realized in various forms. For example, the main object in the wide focus detection area is extracted by the extraction means, the predetermined area including the main object is specified by the image height y, and the correction amount is calculated by the equations (6) to (8). Good. The focus detection optical system, the arrangement of the focus detection areas, and the division method within one focus detection area are not limited to the embodiments. The present invention is not limited to a lens-interchangeable silver salt single-lens reflex camera, and may be a camera in which lenses cannot be exchanged. Furthermore, the present invention can be used for a digital camera. In the case of a digital camera, an image sensor for photographing may be used for focus detection.

It is sectional drawing of the automatic focus adjustment single-lens reflex camera incorporating the focus detection apparatus of embodiment. It is a figure which shows three focus detection areas set in the imaging | photography screen. It is a figure which shows the structure of a focus detection optical system. It is a control block diagram of a focus detection apparatus. It is a figure which shows five focus detection areas set in the imaging | photography screen. It is a figure explaining the error of the focus detection calculation by image height.

Explanation of symbols

1: photographing lens 2: field mask 3: condenser lens 4: aperture mask 5: re-imaging lens 6: image sensor 56: CPU 58: selection switch CP: conjugate plane EP: exit pupil

Claims (4)

Of the subject luminous flux from the photographic lens, the luminous flux that passes through the position corresponding to the focus detection region is pupil-divided by a diaphragm mask having a pair of aperture openings via a condenser lens, and each of the pair of pupil-divided luminous fluxes is paired A focus detection optical system for re-imaging on the light receiving element;
Computation means for computing the amount of deviation between the image plane of the photographing lens and the planned imaging plane based on subject image signals detected by the pair of light receiving elements,
The position of the diaphragm conjugate plane obtained by projecting back the aperture aperture by the condenser lens is set closer to the subject side than the exit pupil position of the photographing lens, and the calculation means is at least a part of the focus detection area (hereinafter referred to as the focus detection area). In the focus detection device that calculates the shift amount based on the subject image signal corresponding to the focus detection calculation area),
The calculating means calculates and calculates the shift amount based on a correction amount according to a position of the focus detection calculation area with respect to a center of the focus detection area and an arrangement direction of the pair of aperture openings. Focus detection device. The focus detection apparatus according to claim 1.
The focus detection area includes a first detection area whose center is located on the optical axis of the photographing lens and a second detection area located at a position away from the optical axis of the photographing lens. Focus detection device. The focus detection apparatus according to claim 1.
The focus detection apparatus characterized in that the correction amount is obtained by the calculation means based on information unique to the photographing lens stored on the photographing lens side. In a photographic lens used for a camera provided with the focus detection device according to claim 1,
Acquisition means for acquiring information about the position of the pupil of the focus detection optical system and the position of the focus detection calculation region relative to the optical axis of the photographing lens from the camera;
Lens-side computing means for obtaining the correction amount based on the information;
An imaging lens, comprising: an output unit that outputs the obtained correction amount to an arithmetic unit of the camera.

Images