JP2006047814A - Focus detector, and camera system having the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a focus detector which can detect focuses of various subjects, can suppress the light receiving area in a light receiving means from being increased while increasing the precision of detecting the focus of a bright objective lens, and can be efficiently arranged. <P>SOLUTION: The focus detector includes: a diaphragm having two pairs of apertures through which two pairs of luminous fluxes of different heights from an optical axis on the pupil of the objective lens pass; a secondary image forming system having two pairs of secondary image forming lenses corresponding to the two pairs of apertures; and a light receiving means having two pairs of light receiving elements on which two pairs of light quantity distributions corresponding to a subject are formed by the two pairs of secondary image forming lenses. The focus detector detects the position of the focal point of the objective lens by the use of signals from the light receiving means. Of the two pairs of light receiving elements of the light receiving means, the gravity interval of the one pair of light receiving elements that receive the pair of luminous fluxes whose height from the optical axis on the pupil of the objective lens is greater is defined as D1. The gravity interval of the other pair of light receiving elements that receive the other pair of luminous fluxes whose height from the optical axis on the pupil of the objective lens is less is defined as D2. In this case, the condition of 2≤D1/D2 is satisfied. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a focus detection apparatus, and is suitable for an imaging apparatus such as a single-lens reflex camera using a silver salt film or a digital single-lens reflex camera using a solid-state imaging device.

  Recently, many silver halide cameras or digital cameras have built-in automatic focus adjustment functions that automatically adjust the focus of an objective lens (photographing lens).

  In particular, in a single-lens reflex camera that requires strict focus accuracy, the imaging light flux from the objective lens is guided to a pair of aperture stops as a focus detection device, and the subject is formed by a re-imaging lens placed near these aperture stops. A pair of light quantity distributions relating to an image is formed on a light receiving element array (pixel array, sensor) of a photoelectric conversion element (light receiving means), and the focus of the objective lens is adjusted by the photoelectric conversion element based on the relative positional relationship between the pair of light quantity distributions. A so-called image shift method focus detection apparatus that detects a state is used (Patent Documents 1 and 2).

  In this method, in order to detect the focus, in principle, it is necessary to detect the light amount distribution of a subject having a pattern (density pattern) in the direction of the light receiving element array of the photoelectric conversion element. However, when there is no light quantity distribution, the focus detection cannot be performed.

  In order to solve this problem, a focus detection apparatus has been proposed and put into practical use that enables focus detection regardless of the direction of the light amount distribution of a subject using two pairs of light receiving element arrays in which the light receiving element arrays are orthogonal. ing.

  In the image shift type focus detection device, the detection performance of the focus detection device is determined by the opening interval of the pair of aperture stops. In general, in order to enable focus detection even with a (dark) objective lens having a large F value (F number), the aperture distance between the aperture stops is limited. For this reason, when a small (bright) objective lens having a small F-number is attached, the focus detection accuracy cannot be increased despite the fact that the aperture distance between the aperture stops can be increased.

  If the focus detection accuracy of an objective lens with a small F value can be increased, the focus detection accuracy increases when viewed as a whole lens (camera system), even if the detection accuracy when an objective lens with a large F value is attached is low. It leads to. It can also meet the demands of high amateurs who often use bright objective lenses.

In order to solve this, a focus detection system in which the aperture interval of the aperture stop used for focus detection of an objective lens having a large F value is narrowed with respect to a substantially same focus detection region in the imaging range, and a small F value A focus detection apparatus including two focus detection systems with a wide aperture interval of an aperture stop used for focus detection of an objective lens has been proposed and put into practical use.
JP-A-7-159684 JP-A-6-201976

  In order to improve focus detection accuracy even when focus detection is possible for various subjects that do not depend on the direction of the light amount distribution of the subject image, or when a bright objective lens having a small F value is attached, A large number of detection systems may be installed.

  However, this method causes an increase in the focus detection device. In particular, the expansion of the area of the sensor chip forming the photoelectric conversion element array is difficult to manufacture and increases the cost.

  In addition, installing multiple focus detection systems means projecting multiple subject images on the sensor chip. Light that is not necessary for focus detection is incident on the sensitivity range of the sensor, resulting in ghosting and focus detection accuracy. Will fall. Also, a means for preventing incidence on the sensitivity range must be provided, and the apparatus becomes complicated.

  The present invention provides a focus detection apparatus that can detect the focus of various subjects, increase the focus detection accuracy of a bright objective lens, and reduce the increase in the light receiving area of the light receiving means and improve the arrangement efficiency. With the goal.

The focus detection apparatus of the present invention is
A diaphragm provided with two pairs of apertures through which two pairs of light beams with different heights from the optical axis pass on the pupil of the objective lens, and two pairs of secondary imaging lenses corresponding to the two pairs of apertures Including a secondary image forming system and a light receiving means including two pairs of light receiving elements in which two pairs of light quantity distributions corresponding to a subject image are formed by the two pairs of secondary image forming lenses. A focus detection device that detects the focal position of the objective lens using the signal of the two of the pair of light receiving elements of the light receiving means, the one whose height from the optical axis is higher on the pupil of the objective lens The center-of-gravity interval between a pair of light-receiving elements that receive a pair of light beams is D1, and the center-of-gravity distance between a pair of light-receiving elements that receive a pair of light beams having a lower height from the optical axis on the pupil of the objective lens. Is D2,
2 ≦ D1 / D2
It is characterized by satisfying the following conditions.

In particular,
The focus detection device detects a focus position of an objective lens corresponding to a predetermined position in a rectangular field, and the two pairs of light receiving elements are positioned side by side in the long side direction of the rectangular field. ,
The stop further includes a pair of apertures arranged in the short side direction of the rectangular field, and the secondary imaging system has a pair of two corresponding to the pair of apertures arranged in the short side direction of the rectangular field. The light-receiving means has a pair of secondary image-forming lenses corresponding to a pair of apertures arranged in the short side direction of the rectangular field of view and has a pair of light quantity distributions corresponding to the subject image. It further has a pair of light receiving elements to be formed.

  According to the present invention, it is possible to detect the focus of various subjects, and while increasing the focus detection accuracy of a bright objective lens, the focus detection device with a small increase in the light receiving area of the light receiving means and a better arrangement efficiency Is obtained.

  FIG. 1 is a configuration diagram of an embodiment in which the focus detection apparatus of the present invention is applied to a single-lens reflex camera. In FIG. 1, the inside of the paper is the vertical direction (vertical direction), and the direction perpendicular to the paper is the horizontal direction (horizontal direction).

  In FIG. 1, reference numeral 21 denotes an objective lens (photographing lens) that can be attached to and detached from the camera body CB, 8 denotes a pupil of the objective lens 21, and 1 denotes an optical axis of the objective lens 21. A light beam incident along the optical axis 1 reaches a quick return mirror 22 having a semi-transmissive portion, and is divided into two light beams of reflected light and transmitted light.

  On the reflection side, a focusing screen 23, a pentaprism 24, and an eyepiece lens 25 are disposed along the optical axis 1, and these members constitute a finder system for visualizing a finder image formed on the focusing screen 23.

  On the other hand, on the transmission side of the quick return mirror 22, a movable sub-mirror 26 along the optical axis 1, and then a phase difference type focus detection system (focus detection device) indicated by elements 2 to 7 in the figure. FD is arranged. At the time of automatic focus detection, based on the output from the focus detection system FD, the focus section of the objective lens 21 is driven by a drive mechanism (not shown) to adjust the focus state.

  Details of the focus detection system FD will be described. Reference numeral 2 denotes a field mask placed at or near the focal plane of the objective lens 21. 3 is a field lens, 4 is a reflecting mirror, 5 is an aperture stop (brightness stop), 6 is a re-imaging lens for forming a secondary image relating to the subject image, and 7 is a light quantity distribution of the secondary image relating to the subject image ( This is a light receiving sensor (light receiving means) for detecting (image shift). The light receiving sensor 7 is constituted by a photoelectric conversion element. Each element from the field mask 2 to the re-imaging lens 6 constitutes a secondary imaging optical system.

  In this embodiment, secondary optical systems 2 to 6 that form a plurality of pairs of quantity distributions including two or more pairs in the horizontal direction with respect to a subject image using light beams that have passed through different regions of the pupil 8 of the objective lens 21; And a light receiving means 7 including a plurality of pairs of light receiving element arrays for detecting the relative positional relationship between the plurality of pairs of light quantity distributions, and the focal position of the objective lens 21 is detected using a signal from the light receiving means 7. is doing.

  FIG. 2 is an explanatory diagram illustrating the optical path expanded from the elements 2 to 7 of the focus detection system FD of FIG.

  3 to 7 are explanatory views of a part of FIG. Next, the structure of each member of the focus detection apparatus of the present invention will be described with reference to FIGS.

  FIG. 3 is an explanatory diagram when the field mask 2 is viewed from the front (in the direction of the optical axis 1). It has a cross-shaped opening 2a, which has an opening 2H corresponding to the first focus detection area that is long in the horizontal direction (horizontal direction) and an opening 2V corresponding to the second focus detection area that is long in the vertical direction (vertical direction). It is configured.

  FIG. 4 shows the aperture stop 5 of the secondary imaging system as viewed from the front. Two pairs of openings 5a1 and 5a2 arranged in the horizontal direction corresponding to the horizontally long first focus detection area, and one pair of openings 5a3 arranged in the vertical direction corresponding to the vertically long second focus detection area. And have.

  In the two pairs of openings 5a1 and 5a2 arranged in the horizontal direction, the length of the wide combination of the center-of-gravity intervals of the openings is L1, and the length of the narrow center-of-gravity interval is L2. The opening 5a1 corresponds to a detection system corresponding to an objective lens having a smaller F number than the opening 5a2.

  FIG. 5 is a front view of the re-imaging lens 6, which has three pairs of lens portions 6 a 1 to 6 a 3 corresponding to the openings 5 a 1 to 5 a 3 of the diaphragm 5 and through the opening 2 a of the field mask 2 of FIG. The object image formed by the objective lens 21 is formed again on each light receiving element array of the light receiving sensor 7.

  FIG. 6 is an explanatory view of the light receiving sensor 7 as seen from the front. The light quantity distribution of the subject image formed by the re-imaging lens 6 is converted into an electric signal.

  1 and 2, the light beam that has passed through the aperture 2a of the field mask 2 passes through the aperture 6 and the re-imaging lens 6 of the field lens 3, and re-forms the secondary image of the subject image on the light receiving means 7. .

  On the surface of the light receiving means 7 in FIG. 6, a field mask 2 is provided in a region 2a ′ indicated by a dotted line surrounding a pixel row in a set of pixel rows (light receiving element rows) 7a1 and 7a2 made up of a large number of pixels for photoelectric conversion. A secondary image of the subject image cut out in the opening shape 2a is formed.

  The secondary image 2a ′ of the object is formed by the re-imaging lens 6 corresponding to the opening of one aperture 6 as shown by the dotted line in FIG. 6, and the secondary image 2a ′ is a light receiving element depending on the focus adjustment state of the objective lens 21. It moves in the longitudinal direction of the rows 7a1 to 7a3.

  The sets 7a1 to 7a3 of the light receiving element arrays respectively detect the relative intervals of the secondary images on the light receiving means 7 with respect to the images of the openings 2a of the field mask 2 corresponding to the sets 7a1 to 7a3, respectively. The focus adjustment state of the objective lens 21 is detected.

In this embodiment, as shown in FIG. 6, the distance between the centers of gravity of each pair of the two pairs of light receiving element rows 7a1 and 7a2 in the horizontal direction among the plurality of pairs of light receiving element rows 7a1 to 7a3 of the light receiving means 7 is D1, respectively. When D2
2 ≦ D1 / D2
Is satisfied.

Furthermore, the center-of-gravity intervals D1, D2 are
D1 / D2 ≦ 2.5
Is satisfied.

  This makes it possible to detect the focus of a variety of subjects, and while increasing the focus detection accuracy of a bright objective lens, achieves a focus detection device that suppresses an increase in the light receiving area of the light receiving means and has better arrangement efficiency. ing.

  Next, features of the configuration of the present invention will be described. In order to perform focus detection on various subjects that do not depend on the direction of the light amount distribution of the subject image, it corresponds from a small (bright) objective lens with a small F value (F number) to a large (dark) objective lens. It is essential to combine the focus detection system in a cross shape. As a result, focus detection can be performed on various subjects regardless of the F value.

  However, with the focus detection apparatus as it is, even with an objective lens having a small F value, which can perform focus detection with high accuracy, only a detection accuracy equivalent to that of an objective lens having a large F value can be obtained. Therefore, it is necessary to add a focus detection system corresponding to an objective lens having a small F value.

  Here, the detection optical system corresponding to the objective lens having a small F value as shown in FIG. 7 can also be arranged in a cross shape like the dark objective lens.

  However, considering the increase in the light receiving area of the light receiving means 7, when one optical system is added, the area becomes twice as large as the area of the cross-shaped arrangement of the dark focus detection system having the F value. Since the length of the light receiving means 7 is doubled in both the vertical direction and the horizontal direction due to the arrangement of the shapes, the area is increased four times. The manufacturing difficulty (cost) of the light receiving means is proportional to the area, so that the manufacturing difficulty (cost) is also quadrupled and should be avoided.

  In order to introduce an optical system corresponding to an objective lens having a small F value, the next problem is in which direction the opening of the diaphragm 5 is opened. Possibility is not limited to vertical and horizontal, and the diaphragm 5 can be arranged with an arbitrary oblique angle. However, when considering the accuracy of focus detection and avoiding an increase in cost, it is best to provide an opening in the lateral direction.

  First, accuracy issues are listed. In the single-lens reflex camera, the focus detection device FD is disposed after passing through the quick return mirror 22 in the camera CB as shown in FIG. At this time, the optical path passing through the quick return mirror 22 differs depending on the position where the light beam passes and the difference in angle.

  This causes an error of several μm on the light receiving sensor 7. In a focus detection apparatus that requires submicron accuracy as the accuracy on the light receiving sensor 7, the difference of several μm is large. However, in the light beam divided by opening the aperture of the diaphragm 5 up and down, the optical path length is different and the optical action is different. And the object image to be compared on the light receiving sensor 7 is not displaced.

  That is, it is best in focus detection performance to divide the aperture of the diaphragm 5 in the left-right direction (lateral direction).

  Next, an increase in the area of the light receiving means 7 when the aperture of the diaphragm 5 is provided in the vertical or horizontal direction will be described.

  2. Description of the Related Art In recent years, focus detection apparatuses in which a plurality of focus detection areas are arranged in the imaging plane of the objective lens 1 and focus on not only the center but also the peripheral part of the screen have been widely used.

  FIG. 8 shows an example of a field mask 2 having seven focus detection areas on the screen and a focus detection system having a cross opening 2a1 in the center, and FIG. 9 shows a light receiving sensor 7 corresponding thereto.

  The shape of the image sensor is horizontally long as represented by a silver salt film. For this reason, the focus detection area is arranged with a higher image height in the horizontal direction than in the vertical direction.

  Similarly, the arrangement of the light receiving element rows 7a of the light receiving sensor 7 is also arranged with a high image height in the vertical direction. At this time, it is considered that a focus detection system corresponding to an objective lens having a small F value is introduced in the central portion.

  FIG. 10 shows the arrangement of the light receiving element array 7a when the light receiving element array 7a of the light receiving sensor 7 is inserted in the horizontal direction, and FIG. 11 shows the arrangement of the light receiving element array 7a of the light receiving sensor 7 when inserted in the vertical direction. It is. When the sensor chip is cut from the silicon wafer, it is cut into a square shape.

  For this reason, in consideration of the restriction that the sensor shape must be square, the light receiving means increases when the array of the light receiving element rows 7a of the light receiving sensor 7 is inserted in the horizontal direction rather than when it is inserted in the vertical direction. It can be seen from comparison that the area change from FIG. 9 to FIG. 10 and from FIG. 9 to FIG.

  Therefore, an increase in the light receiving area of the light receiving sensor 7 can be suppressed by opening the diaphragm 5 of the focus detection system having a small F value in the horizontal direction instead of the vertical direction.

  Further, as shown in FIG. 10, the distance between the centers of gravity of the pair of light receiving element arrays 7a1 of the focus detection system having a small F value that opens in the horizontal direction is D1, and the pair of light receiving element arrays of the focus detection system having a large F value. When the distance between the centers of gravity of 7a2 is D2, D1 / D2 is preferably 2 or more. The light beam that has passed through the objective lens 1 has a very short distance from the diaphragm 5 to the light receiving sensor 7 compared to the distance from the pupil 8 to the field mask 2. Reach 7 up. On the light receiving sensor 7, an image similar to the opening shape of the field mask 2 and having almost the same area is projected as many as the numerical aperture of the diaphragm 5. For this reason, there is a high correlation between the arrangement of the diaphragm 5 and the arrangement of the image on the light receiving sensor 7.

  The subject images on the light receiving sensor 7 are not desirably overlapped. When an area where the subject images overlap appears, it is no longer possible to arrange the light receiving element array in the area, and it becomes a useless area, causing an increase in the light receiving area of the light receiving sensor, and where the subject images overlap, The possibility of detecting stray light other than a specific focus detection region that should not be incident on the light receiving sensor is also increased.

  Here, if D1 / D2 is less than 2, a useless increase in the light receiving area of the light receiving sensor is caused. As shown in FIG. 10, the focus detection system corresponding to the objective lens having a dark F value is arranged so that the subject images formed on the light receiving means 7 do not overlap each other, and the light receiving area of the light receiving sensor 7 is reduced. From the request, the center-of-gravity distance D2 of the subject image formed by the diaphragm for the objective lens having a large F value arranged in the horizontal direction is a value twice the size of the image.

  On the other hand, the center-of-gravity distance D1 of the subject image formed by the aperture for the objective lens having a small F value is 4 because the subject image is not overlapped and the light receiving area of the light receiving sensor 7 is minimized. Double the value.

  The fact that D1 / D2 is less than 2 means that the distance between the subject images due to the aperture having a large F value is more than twice the size of the subject image, resulting in a useless light receiving region in the center. This increases the light receiving area.

  On the other hand, when D1 / D2 exceeds 2, not only the accuracy of the focus detection system having a small F value increases, but also the distance between subject images increases, so that other focus detection areas that should not be incident on the light receiving sensor can be obtained. Since the risk of incident stray light entering the light receiving sensor is reduced, there is a margin between the subject image of the focus detection system with a small F value and the focus detection system with a large F value as a margin. Good.

  That is, the light receiving element has a “margin” that does not overlap images formed by a bright light beam (light beam that has passed through a diaphragm having a small F value) and a dark light beam (light beam that has passed through a diaphragm having a large F value). Is good.

  However, a larger margin is undesirable because it increases the light receiving area. For this reason, it is better that D1 / D2 ≦ 2.5.

  As described above, according to the present invention, in order to make it possible to detect a variety of subjects with a large number of objective lenses, the opening of the field mask in the focus detection system corresponding to a large F-number (dark) objective lens has a cross shape. By appropriately adding a focus detection system that is arranged and corresponds to a (bright) objective lens having a large F value, it is possible to obtain a focus detection device having a new configuration with high accuracy and a compact light receiving area.

1 is a schematic diagram of a main part of a first embodiment of a camera system of the present invention. 1 is an enlarged explanatory view of a part of FIG. Explanatory drawing of the field mask of FIG. Explanatory drawing of the aperture mask of FIG. Explanatory drawing of the re-imaging lens in FIG. Explanatory drawing of the photoelectric conversion element of FIG. Explanatory drawing of photoelectric conversion element corresponding to bright F-number objective lens Explanatory drawing of a visual field mask having a seven-point focus detection area having a cross-shaped focus area at the center Explanatory drawing of the photoelectric conversion element which has a seven-point focus detection area | region which has a cross-shaped focus area | region in the center Explanatory drawing of a light receiving sensor when a light receiving element corresponding to a bright objective lens is inserted laterally into a focus detection system having seven focus detection areas Explanatory drawing of a light receiving sensor when a light receiving element corresponding to a bright objective lens is inserted in a vertical direction into a focus detection system having seven focus detection areas.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Optical axis 2 Field mask 3 Field lens 4 Reflection mirror 5 Aperture mask 6 Re-imaging lens 7 Photoelectric conversion element 8 Pupil 21 Objective lens 22 Quick return mirror 23 Focusing screen 24 Penta prism 25 Eyepiece 26 Sub mirror

Claims (5)

A stop provided with two pairs of apertures through which two pairs of light beams having different heights from the optical axis pass on the pupil of the objective lens; and two pairs of secondary imaging lenses corresponding to the two pairs of apertures A secondary imaging system; and a light receiving means including two pairs of light receiving elements in which two pairs of light quantity distributions corresponding to the subject image are formed by the two pairs of secondary imaging lenses. A focus detection device that detects a focal position of the objective lens using a signal, and is one of the two pairs of light receiving elements of the light receiving means, which has a higher height from the optical axis on the pupil of the objective lens. The center-of-gravity interval of a pair of light-receiving elements that receive a pair of light beams is D1, and the center-of-gravity distance of a pair of light-receiving elements that receive a pair of light beams having a lower height from the optical axis on the pupil of the objective lens. When D2
2 ≦ D1 / D2
A focus detection device satisfying the following condition:   The focus detection device detects a focus position of an objective lens corresponding to a predetermined position in a rectangular field, and the two pairs of light receiving elements are arranged side by side in the long side direction of the rectangular field. The focus detection apparatus according to claim 1, characterized in that:   The stop further includes a pair of apertures arranged in the short side direction of the rectangular field, and the secondary imaging system has a pair of two corresponding to the pair of apertures arranged in the short side direction of the rectangular field. The light-receiving means has a pair of secondary image-forming lenses corresponding to a pair of apertures arranged in the short side direction of the rectangular field of view and has a pair of light quantity distributions corresponding to the subject image. The focus detection apparatus according to claim 1, further comprising a pair of light receiving elements formed. The center-of-gravity distances D1 and D2 further satisfy D1 / D2 ≦ 2.5.
The focus detection apparatus according to claim 1, 2 or 3, wherein:   A camera comprising the focus detection device according to any one of claims 1 to 4.