JP2013054288A - Focus detecting device and imaging apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To reduce vignetting of an imaging luminous flux leading to an image pickup element, that is caused by a focus detecting element.SOLUTION: An imaging apparatus 1 includes a quick return mirror 3 having: a main mirror 3a which reflects an imaging luminous flux passing through an imaging optical system 2 and leads the imaging luminous flux to a finder screen 5 side, while transmitting a portion of the luminous flux; and a sub-mirror 3b which reflects the luminous flux transmitted through the main mirror, the sub-mirror 3b being a convex mirror. The imaging apparatus 1 further includes: an image pickup element 4 for imaging by receiving the imaging luminous flux when the quick return mirror 3 is retreated from an optical path of the imaging luminous flux; and a focus detecting element 6 which receives the luminous flux reflected on the sub-mirror 3b when the quick return mirror 3 is on the optical path of the imaging luminous flux and outputs a focus detection signal.

Description

  The present invention relates to a focus detection device and an imaging device including the focus detection device.

  There is known an imaging apparatus including a quick return mirror that transmits a part of subject light and reflects others, and a sub mirror that guides a part of an imaging light beam transmitted through the quick return mirror to a focus detection element (for example, Patent Document 1). In such an imaging apparatus, a plane mirror is used as the sub-mirror. At this time, the focus detection element is disposed at a position physically equivalent to the imaging element.

JP 2008-304808 A

  However, in the conventional imaging apparatus, there is a possibility that vignetting of the imaging light beam guided to the imaging device may occur due to the focus detection element arranged at a position physically equivalent to the imaging device.

  A focus detection apparatus according to an embodiment of the present invention reflects an imaging light beam that has passed through an imaging optical system and guides it to a finder optical system, and transmits a main mirror that transmits a part of the light beam and a transmitted light beam of the main mirror. A quick return mirror having a reflecting sub-mirror, an image sensor for receiving and imaging the imaging light beam when the quick return mirror is retracted from the optical path of the imaging light beam, and a quick return mirror on the optical path of the imaging light beam And a focus detection element that receives a reflected light beam reflected by the sub mirror and outputs a focus detection signal, and the sub mirror is a convex mirror.

  The substantial focal length of the imaging optical system to the focus detection element can be extended by guiding a part of the imaging light beam that has passed through the imaging optical system to the focus detection element using the sub-mirror constituted by the convex mirror. For this reason, it is possible to reduce the vignetting of the imaging light beam guided to the image sensor generated by the focus detection element.

It is an example of sectional drawing of the imaging device by one embodiment of the present invention. It is a figure which shows the example of 1 structure of a focus detection element. It is a figure which shows an example of the focus detection mechanism by one embodiment of this invention. It is a figure which illustrates about the relationship between a mirror shape and interference of a reflected light beam.

  An imaging device including a focus detection device according to an embodiment of the present invention will be described below. This imaging apparatus performs focus adjustment of an imaging optical system by phase difference detection type autofocus (hereinafter referred to as phase difference detection AF). The phase difference detection AF detects the defocus amount of the photographing lens based on the phase difference between a pair of images by two light fluxes that have passed through different exit pupils of the imaging optical system, and performs focus adjustment based on the detection result. This is the autofocus method to be performed.

  FIG. 1 is a block diagram illustrating a configuration example of an imaging apparatus according to the present invention. An imaging apparatus 1 illustrated in FIG. 1 is a single-lens reflex camera, and includes a lens barrel 100 and a camera body 200. The lens barrel 100 is attached to the camera body 200 in a replaceable manner.

  Inside the lens barrel 100, an imaging optical system 2 including a plurality of photographing lenses 2a to 2c, a lens driving motor 11, and a diaphragm member 12 are provided. The photographing lens 2 b is a focus adjustment lens that is driven by a lens driving motor 11.

  Inside the camera body 200, there are a quick return mirror 3 composed of a main mirror 3a and a sub mirror 3b, an image sensor 4, a finder screen 5, a focus detector 6, a pentaprism 7, an eyepiece 8, and for photometry. A lens 9 and a photometric sensor 10 are provided.

  The quick return mirror 3 is a movable mirror, and is located on the optical path of the imaging light beam that has passed through the imaging optical system 2 or a position retracted from the optical path of the imaging light beam (for example, the lower side of the finder screen 5). ).

  A part of the main mirror 3a is a half mirror, and a part of the imaging light beam incident on the half mirror part is transmitted and incident on the sub mirror 3b, and the rest is reflected to the viewfinder screen 5 side. Further, the image forming light beam incident on the part other than the half mirror part of the main mirror 3a is also reflected to the viewfinder screen 5 side. The sub mirror 3b is formed of a convex mirror, and reflects the light beam transmitted through the half mirror portion of the main mirror 3a to the focus detection element 6.

  The image sensor 4 is composed of a CCD image sensor, a CMOS image sensor, or the like. The imaging element 4 receives the imaging light beam that has passed through the imaging optical system 2 when the quick return mirror 3 is at a position retracted from the optical path of the imaging light beam, and outputs an imaging signal.

  The finder screen 5 is provided at a position equivalent to the image sensor 4. The imaging light beam reflected by the main mirror 3 a forms an image on the finder screen 5. The subject image formed on the finder screen 5 is observed by the photographer's eyes through the pentaprism 7 and the eyepiece lens 8 and is also guided to the photometric sensor 10 through the pentaprism 7 and the photometric lens 9. . The imaging device 1 performs an exposure calculation based on a photometric signal for each photometric area output from the photometric sensor 10, and calculates a shutter speed and an aperture value of the aperture member 12 according to the luminance of the subject. When the manual exposure shooting mode is set, the shutter speed and aperture value set by the photographer are used.

  The focus detection element 6 receives the imaging light beam reflected by the sub-mirror 3 b and outputs a focus detection signal used for focus adjustment of the imaging optical system 2. The imaging device 1 drives the focus adjustment lens 2 b based on the focus detection signal output from the focus detection element 6 and performs focus adjustment of the imaging optical system 2.

  FIG. 2 is a diagram illustrating an example of the focus detection element 6. The focus detection element 6 illustrated in FIG. 2 outputs a focus detection signal in phase difference detection AF, and includes a microlens array 61, a focus detection sensor 62, and a focus detection calculation circuit 63. In the microlens array 61, a plurality of microlenses 610 are two-dimensionally arranged. In the focus detection sensor 62, a plurality of light receiving element arrays 620 are two-dimensionally arranged. Further, each of the plurality of light receiving element arrays 620 includes a plurality of light receiving elements that photoelectrically convert the received light flux.

  FIG. 3 is a diagram illustrating a configuration example of the focus detection mechanism in the imaging apparatus 1. A focus detection mechanism 300 illustrated in FIG. 3 includes the imaging optical system 2 of the lens barrel 100, the quick return mirror 3, the imaging element 4, and the focus detection element 6 of the camera body 200. As shown in FIG. 3, the focus detection element 6 is provided behind the position equivalent to the imaging element 4 by a predetermined distance L. The sub mirror 3b is formed of a convex mirror, and the actual focal length of the imaging optical system 2 via the sub mirror 3b is increased by a predetermined distance L. Therefore, the imaging light beam is imaged on the focus detection element 6.

  A microlens array 61 of the focus detection element 6 is provided at a position behind the position physically equivalent to the image sensor 4 by a predetermined distance L. The light beam that has passed through the exit pupil of the imaging optical system 2 is guided to each light receiving element of the light receiving element array 620 via the microlens 610. The light receiving elements of the light receiving element array 620 photoelectrically convert each received light beam and output an electrical signal to the focus detection arithmetic circuit 63. The focus detection calculation circuit 63 detects a defocus amount based on an output signal from each light receiving element of the light receiving element array 620, and outputs a focus detection signal based on the defocus amount.

  The focus detection calculation circuit 63 corrects a change in aberration that occurs when the sub mirror 3b is a convex mirror when calculating the defocus amount. The correction value used for correcting the aberration may be experimentally determined in advance at the manufacturing stage and stored as a lookup table in a predetermined storage device such as a memory provided in the camera body 200.

According to the embodiment described above, the following operational effects can be obtained.
The imaging apparatus 1 includes a main mirror 3a that reflects and guides the imaging light beam that has passed through the imaging optical system 2 to the viewfinder screen 5 side, and transmits a part of the light beam, and a sub mirror 3b that reflects the transmitted light beam of the main mirror 3a. Quick return mirror 3 having In addition, the imaging apparatus 1 includes an imaging element 4 that receives and images the imaging light beam when the quick return mirror 3 is retracted from the optical path of the imaging light beam, and the quick return mirror 3 uses the light of the imaging light beam. It has a focus detection element 6 that receives a reflected light beam reflected by the sub mirror 3b when it is on the road and outputs a focus detection signal. The sub mirror 3b is a convex mirror, and the focal length of the imaging light beam reflected by the sub mirror 3b is longer than the distance to a position physically equivalent to the image sensor 4. Therefore, the focus detection element 6 can be provided behind the position physically equivalent to the image sensor 4, and the focus detection element 6 can be moved away from the imaging light beam incident on the image sensor 4. Thereby, since the substantial focal distance of the imaging optical system 2 to the focus detection element 6 can be extended, the vignetting of the imaging light beam guided to the image sensor 4 by the focus detection element 6 can be reduced.

  Further, by making the sub mirror 3b a convex mirror and extending the substantial focal length of the photographing optical system up to the focus detection element 6, other operational effects can be obtained. For example, when the F value of the lens barrel 100 is brighter than the open F value of the microlens 610, it is possible to reduce the occurrence of interference between the light beams that have passed through the exit pupil of the imaging optical system 2 that occurs in the light receiving element array 620.

  FIG. 4A shows a situation in which the light beam that has passed through the exit pupil of the imaging optical system 2 causes interference 400 in the light receiving element array 620 when the sub-mirror is constituted by a plane mirror as in the prior art. Yes. In FIG. 4A, the microlens array 610 is in a position physically equivalent to the image sensor 4.

  FIG. 4B shows a case where the sub mirror is a convex mirror. In FIG. 4B, the microlens array 610 is arranged at a position that is a predetermined distance L behind the position physically equivalent to the image pickup device 4, and the incident angle of the light beam incident on the microlens array 610 is narrowed. Since the exit angle of the light beam that has passed through the microlens array 610 is also narrowed, the occurrence of interference due to the light beams that have passed through the exit pupil of the imaging optical system 2 is suppressed.

The embodiment described above can be implemented with the following modifications.
[1] In the above embodiment, the focus detection element 6 includes the microphone lens array 61, the focus detection sensor 62, and the focus detection calculation circuit 63. In the microlens array 61, the microlenses 610 are two-dimensionally arranged. However, the focus detection element 6 may be configured such that the imaging pixels are two-dimensionally arranged, and the focus detection pixels having the microlens 610 and the light receiving element array are arranged between the imaging pixels.

[2] In the above embodiment, the quick return mirror 3 is composed of the main mirror 3a and the sub mirror 3b, and the sub mirror 3b is a convex mirror, but instead of the quick return mirror 3, a convex pellicle mirror is arranged. May be. In this case, it is desirable that the photographer can observe the subject image received by the image sensor 4.

  The embodiment and various modifications described above are merely examples, and the present invention is not limited to these contents as long as the features of the invention are not impaired.

DESCRIPTION OF SYMBOLS 1 Imaging device 2 Imaging optical system 3 Quick return mirror 3a Main mirror 3b Sub mirror 4 Imaging element 5 Finder screen 6 Focus detection element 7 Penta prism 8 Eyepiece lens 9 Photometric lens 10 Photometric sensor 11 Lens drive motor 12 Aperture member 100 Lens barrel 200 Camera body 300 Focus detection mechanism

Claims (5)

A quick return mirror having a main mirror that reflects the imaging light beam that has passed through the imaging optical system and guides it to the finder optical system and transmits a part of the light beam; and a sub mirror that reflects the transmitted light beam of the main mirror;
An imaging device that receives and images the imaging light beam when the quick return mirror is retracted from the optical path of the imaging light beam;
A focus detection element that receives the reflected light beam reflected by the sub mirror when the quick return mirror is on the optical path of the imaging light beam and outputs a focus detection signal;
The focus detection apparatus, wherein the sub-mirror is a convex mirror. The focus detection apparatus according to claim 1,
The image sensor is at a first position on the optical path of the imaging light beam,
The focus detection device according to claim 1, wherein the focus detection element is on an optical path of the reflected light flux and is located a predetermined distance behind a second position equivalent to the first position. The focus detection apparatus according to claim 1 or 2,
The focus detection element is
A microlens array in which a plurality of microlenses are arranged; and
And a light receiving element array in which a plurality of light receiving elements are arranged corresponding to each microlens of the microlens array. The focus detection apparatus according to claim 3,
The focus detection device has a plurality of imaging pixels arranged two-dimensionally, and the microlens array and the light receiving element array are arranged between the plurality of imaging pixels. .   An imaging device comprising the focus detection device according to any one of claims 1 to 4.

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