JPH06160703A - Focus detector - Google Patents

Abstract

PURPOSE:To improve the detecting accuracy of a focus by providing an optical element having a light diffusing characteristic near a scheduled focusing surface with respect to a focus detection optical system corresponding to a focus detection area at the peripheral part of a photographic picture. CONSTITUTION:The plural focus detection areas are set at the center and the peripheral part of the photographic picture provided on the scheduled focusing surface of a photographing optical system 3. Every focus detection area, the focus detection optical systems 10b and 30b and a pair of photoelectric conversion means 26 and 36 are provided. Then, a pair of luminous flux passed through the areas of the photographing optical system 3 whose exit pupils are different is guided to a pair of conversion means 26 and 36 and a pair of object images is formed again. Then, the focusing state of the optical system 3 of every focus detection area is detected. Besides, the optical element 350 having the light diffusing characteristic is provided near the scheduled focusing surface of the optical system 3 with respect to the optical system 30b. By the element 350, a pair of focus detection luminous flux made incident on the focus detection area at the peripheral part of the photographic picture from the exit pupil of the optical system 3 is diffused.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a focus detection device such as a camera.

[0002]

2. Description of the Related Art A plurality of focus detection areas are set at the center of a photographing screen provided on a planned focal plane of a photographing optical system and its peripheral portion, and the focus adjustment state of the photographing optical system is detected for each focus detection area. There are known focus detection devices. In this type of device, each focus detection area has a focus detection optical system and a pair of photoelectric converters, and a pair of light fluxes that have passed through different areas of the exit pupil of the photographing optical system by the focus detection optical system are converted into a pair of photoelectric converters. The pair of subject images are re-imaged by being guided to the converter, the relative image shift amount of the pair of subject images is detected by the output signals of the pair of photoelectric converters, and the photographing optical system is based on the image shift amount. The focus adjustment state, that is, the defocus amount between the image plane of the photographing optical system and the film surface is detected. In the following, the above focus detection optical system is referred to as a pupil division type focus detection optical system.

[0003]

However, in the conventional focus detection apparatus, when the open F-number of the photographing optical system is large, vignetting of the focus detection light beam by the photographing optical system occurs in the focus detection area in the peripheral portion of the photographing screen. However, there is a problem in that the focus detection accuracy decreases.

FIG. 22 is an explanatory view of vignetting of a focus detection light beam by the photographing optical system, and a pupil division type focus detection optical system corresponding to a focus detection area which is elongated in the radial direction from the center of the photographing screen in the central portion of the photographing screen. The diaphragm mask 134 to the photographing optical system 3 are shown. One opening 1 of the diaphragm mask 134
35 is a visual field mask 1 due to the condenser lens 133.
31 is projected on the area 45 on the pupil set at a predetermined distance from 31, and the point A of the opening 132 of the visual field mask 131,
The light fluxes passing through B and C respectively pass through the optical paths shown in the figure. On the other hand, the photographic optical system 3 is provided with the diaphragm 137, and if the diaphragm diameter is small, that is, if the open F number is large, a part of the light flux passing through the points A, B and C is blocked by the diaphragm 137 as shown in the figure. That is, vignetting occurs.

FIG. 23 shows areas 41, 42 and 43 where the light fluxes passing through the points A, B and C pass through the diaphragm 137, respectively.
Indicates. As shown in the figure, the region 41 of the light flux passing through the point A has the largest vignetting, and the vignetting decreases as it approaches the point C. With respect to the other opening 136 of the aperture mask 134, it becomes symmetrical with the case of the above-mentioned opening 135, and the region 43 of the light flux passing through the point C has the largest vignetting, and the vignetting decreases as it approaches the point A. .

FIG. 24 shows a light intensity distribution of a pair of subject images formed on a pair of photoelectric converters (not shown) by the focus detection optical system shown in FIG. 22 when the subject has a uniform luminance. The horizontal axis represents the arrangement direction of the plurality of light receiving elements of the photoelectric converter, and the vertical axis represents the light intensity detected by each light receiving element.
In the figure, the solid line shows the light intensity distribution of the subject image due to the light flux passing through the opening 135 of the aperture mask 134, and the broken line shows the light intensity distribution of the subject image due to the light flux passing through the opening 136. Object image (solid line) by light flux passing through the opening 135
Indicates that the light intensity of the light flux passing through the point A with large vignetting is the lowest, and the light intensity increases toward the point C with less vignetting. On the other hand, in the subject image (broken line) formed by the light flux passing through the opening 136, the light intensity of the light flux passing through the point C with large vignetting is the lowest, and the light intensity increases toward the point A with less vignetting. The focus detection detects the light intensity distribution of the pair of subject images by the pair of light fluxes passing through the openings 135 and 136, and detects the focus adjustment state of the photographing optical system 3 based on the relative shift amount of the pair of subject images. Therefore, if the degree of coincidence of the light intensity distributions of the pair of subject images is low as shown in FIG. 24, focus detection becomes difficult. Although the above description is for the case where the focus detection area is arranged in the center, vignetting is more likely to occur as the position of the focus detection area is farther from the optical axis, that is, closer to the peripheral portion.

It is an object of the present invention to provide a focus detecting device which reduces the influence of vignetting of the focus detecting light beam by the photographing optical system and improves the focus detecting accuracy in the focus detecting area in the peripheral portion of the photographing screen. .

[0008]

FIG. 1 showing a first embodiment.
The present invention will be described in association with No. 2. In the invention of claim 1, a plurality of focus detection areas are set in the center of the photographing screen provided on the planned focal plane of the photographing optical system 3 and its peripheral portion. The focus detection optical system 20b, 30b and the pair of photoelectric conversion means 26, 36 are provided for each focus detection area, and the focus detection optical system 2 is provided.
A pair of light fluxes that have passed through different regions of the exit pupil of the photographic optical system 3 by 0b and 30b, a pair of photoelectric conversion means 26 and 36.
The present invention is applied to a focus detection device that guides the image upward to re-image a pair of subject images and detects the focus adjustment state of the photographing optical system 3 for each focus detection area. The above object is achieved by providing the optical element 350 having the light diffusion characteristic in the vicinity of the planned focal plane of the photographing optical system 3 with respect to the focus detection optical system 30b corresponding to the focus detection area in the peripheral portion of the photographing screen. To do.
The focus detection area in the peripheral part of the photographing screen of the focus detecting device according to the second aspect is a strip-shaped area extending in the radial direction from the center of the photographing screen.

[0009]

The optical element 350 diffuses a pair of focus detection light fluxes which are incident from the exit pupil of the photographing optical system 3 to the focus detection area in the peripheral portion of the photographing screen. That is, the passing area of the focus detection light beam on the exit pupil is enlarged to reduce the influence of vignetting and aberration by the photographing optical system.

Incidentally, in the section of means and action for solving the above problems for explaining the constitution of the present invention, the drawings of the embodiments are used for the purpose of making the present invention easy to understand. It is not limited to.

[0011]

【Example】

First Embodiment FIG. 1 is a sectional view taken along the optical axis of a photographing optical system of a camera equipped with the focus detection device of the first embodiment. A replaceable lens barrel 2 is attached to the camera body 1, and a photographing optical system 3 is provided in the lens barrel 2. The light flux from the subject passes through the photographing optical system 3 and is guided to the main mirror 4 which is a half mirror. Part of the light flux passes through the main mirror 4, reaches the sub-mirror 5, and part of the light is reflected by the main mirror 4. Is guided to a finder 9 including a screen 6, a pentaprism 7, an eyepiece lens 8 and the like. The light flux that has reached the sub-mirror 5 is further deflected from the direction of the shutter 10 toward the bottom of the body, and the plurality of pupil division type re-imaging type focus detection modules 20, 30, which are installed on the planned focal plane of the photographing optical system 3. You are led to 40. The focus detection modules 30 and 40 are arranged on the left and right of the focus detection module 20 when viewed from the front of the camera (in FIG. 1, above and below the plane of the drawing), and near the planned focal plane of the photographing optical system 3 as shown in FIG. The diffuser plates 350 and 450 are provided, respectively.

FIG. 3 shows each focus detection module 20, 3
The focus detection areas of 0 and 40 are shown. In the center of the photographing screen M provided on the planned focal plane of the photographing optical system 3 and its peripheral portion,
Three cross-shaped focus detection areas 20a, 30a, 40a are set. The focus detection module 20 corresponds to the central focus detection area 20a, and the peripheral focus detection areas 30a and 40a.
a corresponds to the focus detection modules 30 and 40, respectively. The focus detection areas 30a and 40a in the peripheral portions are band-shaped areas 301 and 40 extending in the radial direction from the center of the photographing screen M.
1 (hereinafter, referred to as a radial area), the shooting screen M
Band-shaped regions 302 and 402 (hereinafter, referred to as tangential direction regions) extending in the tangential direction of a concentric circle having the center of the circle as the center of the circle.

FIG. 4 is an exploded perspective view showing the positional relationship between the focus detection module 20 and the exit pupil 12 of the photographing optical system 3. The focus detection module 20 is arranged on the optical axis of the photographing optical system 3, and has a focus detection optical system 20b and a sensor 26 such as a CCD. The focus detection optical system 20b includes a field mask 21 having a cross-shaped opening 211, a condenser lens 22, and two pairs of aperture openings 241, 242, and 2.
The sensor 26 is composed of a diaphragm mask 24 having 43, 244, two pairs of re-imaging lenses 251, 252, 253, 254, etc.
3,264. The light receiving portion 26 of the sensor 26
Each of 1 to 264 is composed of a plurality of pixels. Further, the center of the opening 211 of the field mask 21 is installed on the optical axis near the planned focal plane, whereby the photographing screen M is displayed.
The focus detection position is set at the center of.

FIG. 5 shows two pairs of diaphragm openings 24 of the diaphragm 24.
It is the figure which looked at 1,242,243,244 from the front.
These two pairs of aperture openings 241, 242, 243, 2
The condenser lens 44 is projected by the condenser lens 22 onto two pairs of regions 121, 122, 123 and 124 which are symmetrical with respect to the optical axis of the exit pupil 12 of the photographing optical system 3, as shown in FIG. The photographing optical system 3 forms a primary image of the subject on the optical axis near the planned focal plane, that is, near the field mask 21 by the light flux passing through these areas 121 to 124. The primary image formed in the opening 211 of the visual field mask 21 is formed by the condenser lens 22 and the two pairs of aperture openings 241, 242, 2 and 2.
43, 244 and two pairs of re-imaging lenses 251, 25
2, 253, 254 re-images as two pairs of secondary images on the two pairs of light receiving portions 261, 262, 263, 264 of the sensor 26.

Two pairs of light receiving parts 261, 262, 263, 2
The two pairs of secondary images formed on 64 are photoelectrically converted by the respective light receiving portions according to the light intensity distribution, and an electrical subject image signal is generated. As is well known, the focus adjustment state of the photographing optical system 3, that is, the focus adjustment state of the photographing optical system 3 The defocus amount between the image plane and the planned focal plane can be detected. In this way, the focus detection module 20 accurately detects the defocus amount in the cross-shaped focus detection area set in the center of the shooting screen M.

FIG. 7 is an exploded perspective view showing the positional relationship between the focus detection module 30 and the exit pupil 12 of the photographing optical system 3. The focus detection module 30 is arranged outside the optical axis of the photographing optical system 3, and has a focus detection optical system 30b and a sensor 36 such as a CCD. The focus detection optical system 30b includes a diffusion plate 350, a field mask 31 having a cross-shaped opening 311, a condenser lens 32, and two pairs of aperture openings 34.
A diaphragm mask 34 having 1,342, 343, 344,
The sensor 36 is composed of two pairs of re-imaging lenses 351, 352, 353, 354, etc.
362, 363, 364. The diffusion plate 350 is arranged near the field mask 31, that is, near the planned focal plane of the photographing optical system 3, and has the diffusion characteristics shown in FIG. The light receiving units 361 to 364 of the sensor 36 are each composed of a plurality of pixels. Further, the opening 311 of the visual field mask is provided outside the optical axis in the vicinity of the planned focal plane, whereby the focus detection position is set in the peripheral portion of the photographing screen M.

Two pairs of aperture openings 341, 342, 34
3, 344 are the condenser lens 32 and the diffusion plate 3
The image is projected onto two pairs of regions 125, 126, 127, 128 which are symmetric with respect to the optical axis of the exit pupil 12 of the photographing optical system 3 by 50. These areas 125, 126, 127, 128
As shown in FIG. 9, due to the diffusion action of the diffusion plate 350, the regions 121, 122, 12 without the diffusion plate 350 are formed.
Greater than 3,124. The condenser lens 32
The arrangement of the two pairs of aperture openings 341, 342, 343, 344 is the same as that of the focus detection module 20 due to the condenser lens 32 in the two pairs of aperture openings 341, 342, 343, 344 when the diffusion plate 350 is not provided. Area 121,
It is determined that the images are projected on 122, 123, and 124.

FIG. 10 is a sectional view of the focus detection optical system 30b showing the areas of the openings 343 and 344 of the aperture mask 34 projected on the exit pupil 12 of the photographing optical system 3. Diffuser 3
Due to the diffusing action of 50, a region 12 larger than the regions 123 and 124 on the exit pupil 12 in the absence of the diffuser plate 350.
The light flux that has passed through 7,128 is the aperture mask opening 34
It is incident on 3,344. Further, although not shown in the drawing, due to the diffusing action of the diffusing plate 350, the light flux that has passed through the regions 125 and 126 larger than the regions 121 and 122 on the exit pupil 12 in the case where the diffusing plate 350 is not provided is used as the aperture mask opening 3.
It is incident on 41 and 342. That is, due to the diffusing action of the diffusing plate 350, the contours of the regions 121 to 124 on the exit pupil 12 are blurred and enlarged, and the shapes of the regions 125 to 128 are formed.

The photographing optical system 3 includes an area 12 on the exit pupil 12.
Off the optical axis near the planned focal plane due to the light flux passing through 5 to 128,
That is, a primary image of the subject is formed near the field mask 31. The primary image formed in the opening 311 of the visual field mask 31 includes a condenser lens 32 and two pairs of aperture openings 34.
1, 342, 343, 344, and two pairs of re-imaging lenses 351, 352, 353, 354 for sensor 36.
Are re-imaged as two pairs of secondary images on the two pairs of light receiving portions 361, 362, 363, 364.

Two pairs of light receiving parts 361, 362, 363, 3
The two pairs of secondary images formed on 64 are photoelectrically converted by the respective light receiving portions according to the light intensity distribution, and an electrical subject image signal is generated. The defocus amount of the photographing optical system 3 is detected by detecting the relative positional relationship between the pair of secondary images on the sensor 36 in the alignment direction of the light receiving units based on the subject image signal. In this way, the focus detection module 30 accurately detects the defocus amount in the cross-shaped focus detection area 30a set around the shooting screen M. Note that the focus detection module 40 is arranged at a position symmetrical to the focus detection module 30 with respect to the optical axis, and the configuration and operation thereof are the same as those of the focus detection module 30, so description thereof will be omitted.

FIG. 11 is a perspective view showing the positional relationship between the photographing optical system 3 and the focus detection modules 20 and 30, and FIG.
Shows the sectional view. As shown in the figure, the focus detection module 20 having no diffusion plate is arranged on the optical axis 11 of the photographing optical system 3, and the focus detection module 30 having the diffusion plate 350 is arranged at a position apart from the optical axis. To be done.
Although the focus detection module 40 is not shown in this figure, it is arranged at a position symmetrical to the focus detection module 30 with respect to the optical axis 11.

22 and 23, when a diffusion plate is provided outside the optical axis in the vicinity of the planned focal plane of the photographing optical system 3 with respect to the focus detection optical system corresponding to the focus detection area in the peripheral portion of the photographing screen M, it is shown in FIGS. Areas 41, 42, 43 where the light flux passing through the points A, B, C pass through the diaphragm 137 are expanded to areas 51, 52, 53 shown in FIG. 25 by the diffusion action of the diffusion plate. As a result, the degree of vignetting of the light flux passing through the point A or the point C is reduced, and the light intensity distribution of the pair of subject images is shown in FIG.
24, the degree of coincidence is improved as compared with the case where the diffuser plate shown in FIG. 24 is not used. In the light intensity distributions of the pair of subject images shown in FIG. 26, the degree of coincidence is further increased by removing the inconsistency of low frequency components with a high pass filter or the like, and focus detection can be sufficiently performed.

Next, how the problem of the vignetting of the focus detecting light flux is solved by the focus detecting apparatus of the embodiment will be described in more detail. Focus detection module 3
0 and 40 are areas 301 and 401 in the radial direction and an area 30 in the tangential direction with respect to the center of the screen, in the peripheral portion of the photographing screen M.
Cross-shaped focus detection areas 30a and 40 having 2,402
a. When performing focus detection around the screen,
In addition to the problem of vignetting of the focus detection light flux described above, there is a problem of mismatch between the photographic image plane and the focus detection image plane due to the aberration of the photographic optical system 3. These problems are more prominent in the radial focus detection area than in the tangential focus detection area.

FIG. 13 shows a case where the diffuser plate 350 is not installed in the focus detection optical system 30b of the focus detection area 30a in the peripheral portion of the photographing screen M, and the focus detection area 301 in the radial direction from the areas 123 and 124 of the exit pupil 12. FIG. 6 is a cross-sectional view in the radiation direction showing a pair of focus detection light beams incident on In addition, FIG.
When a diffuser plate 350 is not installed in the focus detection optical system 30b of the focus detection area 30a in the peripheral part of the photographic screen M, a pair of incident light enters the focus detection area 302 in the tangential direction from the areas 121 and 122 of the exit pupil 12. FIG. 4 is a tangential sectional view showing a light beam for focus detection. As you can see from these figures,
A light beam incident on the focus detection area 301 in the radial direction passes through a portion that is asymmetric with respect to the optical axis 11 when passing through the photographing optical system 3. As a result, the pair of focus detection light beams are affected by different aberrations of the photographing optical system 3. On the other hand, the light flux incident on the focus detection area 302 in the tangential direction is
When passing through the photographic optical system 3, the pair of focus detection light beams pass through a portion symmetrical with respect to the optical axis 11, and are affected by aberrations of the photographic optical system 3 that are substantially the same.

That is, the focus detection area, which is set in a band shape along the radial direction from the center of the screen on the peripheral portion of the shooting screen M, is easily affected by the aberration of the shooting optical system, and conversely is set in a band shape along the tangential direction. The formed focus detection area is not easily affected by the aberration of the photographing optical system. Therefore, as shown in the above-described embodiment, a diffuser plate is installed in the focus detection area in the peripheral portion of the shooting screen M in the vicinity of the planned focal plane of the shooting optical system of the focus detection optical system. As a result, the shape of the pupil region of the pair of light beams incident on the focus detection region is expanded, the degree of coincidence of the pair of focus detection light beams passing through the two regions is increased, and the influence of aberration is mitigated. Accurate focus detection is possible. In particular, it is effective for a strip-shaped focus detection area that is set in the radial direction from the center of the photographing screen in the peripheral portion of the photographing screen.

FIG. 15 shows the photographic optical system 3 viewed from the focus detection area 30a of the photographic screen M when the diffuser plate 350 is not installed in the focus detection optical system 30b of the focus detection area 30a in the peripheral portion of the photographic screen M. Exit pupil 220 and the exit pupil 220
It is a figure which shows the relationship with the passage areas 121-124 of the light beam for focus detection which passes through. The shape of the exit pupil 220 of the photographing optical system 3 viewed from the peripheral portion of the photographing screen M is such that the width in the arrangement direction of the pupil regions 123 and 124 corresponding to the focus detection region 301 in the radial direction is the focus detection region 302 in the tangential direction. Narrower than the width of the corresponding pupil regions 121 and 122 in the arrangement direction,
In addition to the diaphragm of the photographing optical system 3, the shape of the exit pupil 220 is regulated by the diameter of the lens itself arranged before and after the diaphragm, so that as shown in the figure, it is asymmetric with respect to the arrangement direction of the regions 123 and 124. Becomes

FIG. 16 shows a state in which the open F number of the photographing optical system 3 is larger than the state shown in FIG. In this state, vignetting has occurred in the pupil area 123. As described above, the area on the exit pupil corresponding to the focus detection area that is set in a strip shape along the radial direction from the center of the screen in the peripheral portion of the photographing screen M is easily vignetted, and conversely is set in a strip shape along the tangential direction. The area on the exit pupil corresponding to the focus detection area is hard to be vignetted. Therefore, as shown in the above-described embodiment, a diffuser plate is installed in the focus detection area in the peripheral portion of the shooting screen M in the vicinity of the planned focal plane of the shooting optical system of the focus detection optical system. Thereby, the shape of the pupil region of the pair of light beams incident on the focus detection region is enlarged, the difference in the light amount due to vignetting of the pair of focus detection light beams is reduced, and the effect of vignetting is mitigated.
Accurate focus detection is possible even in the peripheral area of the screen. In particular, it is effective for a strip-shaped focus detection area that is set in the radial direction from the center of the photographing screen in the peripheral portion of the photographing screen.

On the other hand, the focus detection area 2 at the center of the photographing screen M
0a, since the focus detection module 20 is provided on the optical axis of the photographing optical system 3, whether the focus detection area is radial or tangential, the focus detection area 2
When passing through the photographic optical system 3, the light beam incident on 0a passes through a portion symmetrical with respect to its optical axis 11. Therefore, the focus detection area 20a at the center of the photographic screen M is not affected by the above-mentioned aberration, and vignetting is less likely to occur than the focus detection area in the peripheral portion even if the open F number is large.

By providing a diffusing plate in the focus detection optical system, the above-mentioned problems of aberration and vignetting can be solved, but there are the following problems. 17 to 19 are diagrams showing the light intensity distribution in the direction in which the light receiving elements are arranged for the secondary image of the subject formed on the sensor by the focus detection optical system.
FIG. 17 shows a light intensity distribution in a focused state, which has a high contrast regardless of the presence or absence of a diffusion plate, and enables accurate focus detection. FIG. 18 shows the light intensity distribution in the defocused state from the in-focus state when the diffuser plate is not installed. In this state, the contrast is lowered but the focus can be detected sufficiently. FIG. 19 shows a case where the diffuser plate is installed, and a state in which the same amount as in FIG. 18 is defocused from the focused state. Due to the diffusing action of the diffusing plate, the contrast is lower than that of the light intensity distribution shown in FIG. 18, and focus detection cannot be performed with such a light intensity distribution.

As described above, when the diffuser plate is installed in the focus detecting optical system, there is a demerit that the maximum defocus amount that can be detected by the focus is reduced as compared with the case where the diffuser plate is not installed, and the focus at the center of the screen without problems of aberration and vignetting. No diffuser plate is installed in the detection area.

Second Embodiment Next, in the peripheral portion of the photographing screen, focus detection is performed only in the strip-shaped focus detection area extending from the center of the screen in the radial direction.
An example will be described. FIG. 20 is a diagram showing the focus detection area set on the shooting screen. The above-described cross-shaped focus detection area 20 is set in the center of the photographing screen M, and radial focus detection areas 50a and 60a are set in the peripheral portion. For the central focus detection area 20a, as described above, the focus detection module 20 shown in FIG. 4 is installed on the optical axis near the planned focal plane of the photographing optical system 3. On the other hand, for the focus detection area 50a in the peripheral portion, the focus detection module 50 shown in FIG. 21 is installed outside the optical axis in the vicinity of the planned focal plane of the photographing optical system 3. Further, for the focus detection area 60a in the peripheral portion, a focus detection module 60 having the same configuration as the focus detection module 50 shown in FIG. 21 is provided outside the optical axis near the planned focal plane of the photographing optical system 3 to detect the focus. 50 and the optical axis are installed symmetrically.

In FIG. 21, the focus detection module 50
Is arranged outside the optical axis of the photographing optical system 3, and has a focus detection optical system 50b and a sensor 56 such as a CCD. The focus detection optical system 50b includes a diffusion plate 550 and a one-dimensional opening 511.
A field mask 51 having an aperture, a condenser lens 52, and an aperture mask 5 having a pair of aperture openings 543 and 544.
4, a pair of re-imaging lenses 553, 554, etc., and the sensor 56 has a pair of light receiving portions 563, 564. The diffusing plate 550 is arranged in the vicinity of the field mask 51, that is, in the vicinity of the planned focal plane of the photographing optical system 3, as shown in FIG.
It has the diffusion characteristics shown in. The light receiving portions 563 and 564 of the sensor 56 each include a plurality of pixels. Further, the opening 511 of the field mask 51 is installed outside the optical axis near the planned focal plane, whereby the photographing screen M is displayed.
The focus detection position is set in the peripheral portion of the.

The pair of aperture openings 543 and 544 are formed by the condenser lens 52 and the diffusion plate 550 and are symmetrical with respect to the optical axis of the exit pupil 12 of the photographing optical system 3.
Projected on 7,128. These areas 127 and 128
Is larger than the regions 123 and 124 when the diffusion plate 550 is not provided due to the diffusion action of the diffusion plate 550 as described above.
The condenser lens 52 and the pair of aperture openings 54
When the diffuser plate 550 is not provided, the pair of aperture openings 543 and 544 are arranged so that the condenser lens 52 is not disposed.
The same areas 123, 12 as the focus detection module 20
4 so that it is projected.

The photographing optical system 3 includes an area 12 on the exit pupil 12.
By the light flux passing through 7,128, off the optical axis near the planned focal plane,
That is, a primary image of the subject is formed near the field mask 51. The primary image formed in the opening 511 of the visual field mask 51 has a condenser lens 52 and a pair of aperture openings 54.
Through a pair of re-imaging lenses 553,554
Thus, a pair of secondary images are re-imaged on the pair of light receiving portions 563 and 564 of the sensor 56.

The pair of secondary images formed on the pair of light receiving portions 563 and 564 are photoelectrically converted by the respective light receiving portions in accordance with the light intensity distribution to generate an electrical object image signal. The defocus amount of the photographing optical system 3 is detected by detecting the relative positional relationship between the pair of secondary images on the sensor 56 in the arrangement direction of the light receiving units based on the subject image signal. In this way, the focus detection module 50 accurately detects the defocus amount in the one-dimensional focus detection area 50a set in the radial direction of the peripheral portion of the photographing screen M.
It should be noted that the focus detection module 60 is simply arranged at a position symmetrical to the focus detection module 50 with respect to the optical axis,
The structure and operation are the same as those of the focus detection module 50, and thus the description thereof will be omitted.

As described above, the focus detection module of the pupil division type re-imaging method for performing focus detection in the center of the photographing screen is arranged on the optical axis near the planned focal plane of the photographing optical system, and the peripheral portion of the photographing screen is provided. A focus detection module of the pupil division type re-imaging method that performs focus detection at least in a band-shaped area extending in the radial direction from the center of the screen is arranged outside the optical axis in the vicinity of the planned focal plane, and the latter focus detection module in the peripheral area of the screen On the other hand, since a diffuser plate is installed near the planned focal plane of the shooting optical system, focus detection can be performed up to a large defocus amount in the center of the screen as in the conventional case, and aberrations of the shooting optical system in the peripheral part of the screen The effect of vignetting is reduced and focus detection accuracy can be improved.

If the diffusion characteristic of the diffuser plate does not extremely reduce the contrast of the focus detection image,
A liquid crystal, a phase type focusing screen, a sand screen, etc. can be used.

In the structure of the above embodiment, the focus detection optical system 20b and the sensor 26 correspond to the center focus detection area of the photographic screen and the photoelectric conversion means, and the focus detection optical systems 30b and 50b and the sensor. Three
Reference numerals 6 and 56 denote a focus detection optical system and a photoelectric conversion unit corresponding to a focus detection area in the peripheral portion of the photographing screen, a diffusion plate 350,
450 and 550 form optical elements, respectively.

[0039]

As described above, according to the present invention, only in the focus detection optical system corresponding to the focus detection area in the peripheral portion of the photographing screen, the optical system having the light diffusion characteristic near the planned focal plane of the photographing optical system. Since elements are provided, focus detection can be performed up to a large defocus amount in the center of the screen as in the conventional case, and the effects of aberration and vignetting of the imaging optical system are reduced in the peripheral part of the screen to improve focus detection accuracy. It is possible,
The focus detection accuracy and the defocus detection ability can be optimally balanced in the entire system.

[Brief description of drawings]

FIG. 1 is a cross-sectional view taken along the optical axis of a photographing optical system of a camera including a focus detection device according to a first embodiment.

FIG. 2 is a diagram showing a focus detection module of a focus detection area set in a peripheral portion of a shooting screen.

FIG. 3 is a diagram showing a focus detection area of the first embodiment set within a shooting screen.

FIG. 4 is a diagram showing a focus detection module in a focus detection area in the center of a shooting screen.

FIG. 5 is a front view of a diaphragm showing two pairs of diaphragm openings.

FIG. 6 is a diagram showing a region where a focus detection light beam passes on an exit pupil of a photographing optical system.

FIG. 7 is a diagram showing a focus detection module in a focus detection area in the peripheral portion of a shooting screen.

FIG. 8 is a diagram showing diffusion characteristics of a diffusion plate.

FIG. 9 is a diagram illustrating a state in which a region on the exit pupil where a focus detection light flux passes is enlarged by a diffusion action of a diffusion plate.

FIG. 10 is a diagram showing a relationship between an aperture of a diaphragm mask and a region on an exit pupil of a photographing optical system.

FIG. 11 is a diagram showing a positional relationship between a focus detection module corresponding to a focus detection area at the center of a shooting screen and a focus detection module corresponding to a focus detection area at a peripheral portion of the shooting screen.

FIG. 12 is a layout view of the focus detection modules at the center and the periphery of the screen.

FIG. 13 is a diagram showing a light beam for focus detection that is incident on a focus detection region in the radial direction on the periphery of the image capturing screen.

FIG. 14 is a diagram showing a light beam for focus detection incident on a focus detection region in the tangential direction in the peripheral portion of the shooting screen.

FIG. 15 is a diagram showing an exit pupil of a photographic optical system viewed from a focus detection area in the periphery of a photographic screen and a focus detection light flux passing area on the exit pupil.

16 is a diagram showing an exit pupil and a focus detection light flux passing region in a state where the diaphragm of the photographing optical system is narrowed down from the state shown in FIG.

FIG. 17 is a diagram showing a light intensity distribution of a secondary image of a subject in the alignment direction of light receiving elements when focusing.

FIG. 18 is a diagram showing a light intensity distribution of a secondary image of a subject in a direction in which light receiving elements are arranged when defocused from a focused state.

FIG. 19 shows a state in which a diffusion plate is provided in the focus detection optical system.
8 is a diagram showing a light intensity distribution of a secondary image of a subject in a direction in which light receiving elements are arranged when defocused from the focused state by the same amount as 8. FIG.

FIG. 20 is a diagram showing a focus detection area of the second embodiment set within a shooting screen.

FIG. 21 is a diagram showing a focus detection module provided in a radial focus detection region in the peripheral portion of the screen according to the second embodiment.

FIG. 22 is a diagram illustrating vignetting of a focus detection light beam by a photographing optical system.

FIG. 23 is a diagram showing a region in which a light flux passing through an opening of a field mask of a focus detection optical system passes through a diaphragm of a photographing optical system.

24 is a diagram showing the light intensity distributions of a pair of subject images formed on a pair of photoelectric converters by the focus detection optical system shown in FIG.

25 is a diagram showing a region where a light beam passing through an opening of a field mask of the focus detection optical system passes through a diaphragm of the photographing optical system in the case where the focus detection optical system shown in FIG. 22 is provided with a diffusion plate.

FIG. 26 is a diagram showing a light intensity distribution of a pair of subject images formed on a pair of photoelectric converters when a diffuser plate is provided in the focus detection optical system shown in FIG. 22.

[Explanation of symbols]

1 camera body 2 lens barrel 3 photographing optical system 4 main mirror 5 sub-mirror 6 screen 7 pentaprism 8 eyepiece 9 viewfinder 10 shutter 11 optical axis 12,220 exit pupil 20, 30, 40, 50 focus detection module 20a, 30a, 40a, 50a, 60a, 301, 3
02, 401, 402 Focus detection area 20b, 30b Focus detection optical system 21, 31, 51, 131 Field-of-view mask 22, 32, 52, 133 Condenser lens 24, 34, 54, 134 Aperture mask 26, 36, 56 Sensor 41 to 41 43, 45, 51-53, 121-124, 12
5 to 128 regions 132, 135, 136, 211, 241-244, 3
11, 341 to 344, 511, 543, 544 Aperture 137 Aperture 251 to 254, 351 to 354, 553, 554 Re-imaging lens 261 to 264, 361 to 364, 563, 564 Light receiving part 350, 450, 550 Diffusion plate

Claims (2)

[Claims] 1. A plurality of focus detection areas are set at the center and its periphery of a shooting screen provided on a planned focal plane of the shooting optical system, and each focus detection area has a focus detection optical system and a pair of photoelectric conversion regions. A pair of light fluxes that have passed through different areas of the exit pupil of the photographing optical system by the focus detection optical system and are directed onto the pair of photoelectric conversion means to re-image a pair of subject images. In a focus detection device for detecting a focus adjustment state of the photographing optical system for each focus detection region, a planned focal plane of the photographing optical system with respect to a focus detection optical system corresponding to a focus detection region in a peripheral portion of the photographing screen. A focus detection device characterized in that an optical element having a light diffusion characteristic is provided in the vicinity thereof. 2. The focus detection device according to claim 1, wherein the focus detection area in the peripheral portion of the photographing screen is a strip-shaped area extending in the radial direction from the center of the photographing screen. apparatus.