JP2757373B2 - Focus detection device - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a focus detection device suitable for a photographic camera, a video camera, and the like, and in particular, divides a pupil of a photographing lens into a plurality of regions and passes through each region. BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a focus detection device that detects a focus state of a photographic lens by forming a light amount distribution for a plurality of subject images using a light beam and obtaining a relative positional relationship between the plurality of light amount distributions.

(Prior Art) As one type of a focus adjusting device conventionally used in a photographic camera or the like, an exit pupil of a photographing lens is divided into two by an optical system for focus detection and passes through each exit pupil region. The two subject images formed by the luminous flux are received by a photoelectric conversion element array (for example, a sensor array such as a CCD), the focus state of the imaging lens is detected from the output, and the imaging lens is driven based on the detection result. A so-called image shift detection method is well known.

FIG. 5 is a schematic view of an optical system of this type of conventional focus detection device. The photographing lens whose focus is to be detected in FIG.
The field lens FLD is arranged with the same optical axis as the LNS. Two secondary imaging lenses FCLA and FCLB are arranged at positions symmetrical with respect to the rear optical axis. Further behind the sensor arrays SAA and SAB are arranged. Stops DIA and DIB are provided near the secondary imaging lenses FCLA and FCLB. Field lens F
LD is the secondary imaging lens FCL with the exit pupil of the taking lens LNS
A, Image is almost formed on the pupil plane of FCLB. As a result, the light beams incident on the secondary imaging lenses FCLA and FCLB respectively become
Are emitted from the non-overlapping areas of equal area corresponding to the respective secondary imaging lenses FCLA and FCLB on the exit pupil plane of. When the aerial image formed near the field lens FLD is re-imaged on the surface of the sensor arrays SAS and SAB by the secondary imaging lenses FCLA and FCLB, based on the displacement of the aerial image position in the optical axis direction, The two images on the sensor arrays SAA and SAB change their positions. Therefore, if the amount of displacement (deviation) of the relative positions of the two images on the sensor array is detected, the photographing lens
You can know the focus state of LNS.

FIG. 6 shows an example of the photoelectric conversion output of two images formed on the sensor arrays SAA and SAB in FIG. The output image signal of the sensor array SAA is A (i), and the output signal of the sensor array SAB is B
(I). The number of pixels of the sensor is about 10 or more out of 5.

In FIG. 6, the image shift amount is calculated from the image signals A (i) and B (i).
As a signal processing method for detecting PR, for example, Japanese Patent Laid-Open No. 58-142
No. 306, JP-A-59-107313, JP-A-60-101513
And Japanese Patent Application No. 61-160824 are disclosed by the present applicant. The focus of the photographing lens is adjusted by adjusting the focus of the photographing lens based on the image shift amount of the two images by the methods disclosed in these publications.

A camera equipped with this type of focus detection device normally performs automatic focus adjustment on a distance measurement area located in the center of a shooting screen. For example, in a single-lens reflex camera using a 35 mm film, the distance measurement visual field length on the film equivalent surface is about 3 to 4 mm or more.

When photographing with a camera equipped with such an automatic focus adjustment device, accurate focus adjustment cannot be performed unless the main subject is located at a distance measuring point at the center of the viewfinder. That is, when the main subject goes out of the distance measurement area in the center of the viewfinder due to framing or the like, focus adjustment is performed once so that the main object enters the distance measurement area in the center of the viewfinder.
Using the focus lock function, etc., the framing is performed while maintaining the focus state at that time, and then shooting is performed. Such a photographing method is preferable when the main subject is stationary, but it is necessary to always adjust the focus when the main subject moves, and it is also difficult to perform framing.

As a means for solving such a problem, a focus detection system capable of measuring and focusing on a plurality of points in the viewfinder is used to manually or automatically select a ranging point in the viewfinder, and the selected ranging point is selected. There is a focus detection device that can adjust the focus of a subject located in the camera.

However, in a focus detection device capable of measuring a plurality of points, the number of distance measuring points, distance between the distance measuring points, an optical layout, and the like are severely restricted in design. And it becomes ghost light to reduce the distance measurement accuracy.

(Problems to be Solved by the Invention) In the present invention, in a focus detection device using an image shift method, a plurality of light-shielding members having a predetermined shape are arranged at an arbitrary position between a field mask and a light receiving surface. When performing focus detection in the focus detection area, a focus detection device capable of preventing harmful light beams from outside the focus detection area from entering the target light receiving element and performing high-precision multi-point ranging. For the purpose of providing.

(Means for Solving the Problems) The exit pupil of the photographing lens is divided into a plurality of different areas by a pupil dividing means arranged on the image plane side of the photographing lens, and a light beam passing through the plurality of areas is photographed. After passing through a field mask having a plurality of openings arranged on a predetermined imaging plane of the lens, a plurality of light amount distributions relating to the subject image are formed on a light receiving means comprising a light receiving element array by a secondary optical system. A focus detection device for determining a relative positional relationship of the light amount distribution of the second lens by the light receiving means, and determining an in-focus state of the photographing lens by an arithmetic means using an output signal from the light receiving means; The system has a plurality of secondary lenses arranged in one direction, and the secondary lenses form a light amount distribution of a subject image for a plurality of visual field regions. Is orthogonal to the one direction Providing a light shielding member having a shape with the optical axis direction as a longitudinal direction in a plane,
Light beams from openings other than the plurality of openings of the field mask targeted by the secondary lens are prevented from entering the secondary lens.

(Embodiment) FIG. 1 is a perspective view of a main part of an optical system according to an embodiment of the present invention. FIG. 2 is a plan view of a part of FIG.

In FIGS. 1 and 2, reference numeral 3 denotes a photographing lens, and reference numeral 10 denotes a visual field mask, which is arranged near a predetermined imaging plane of the photographing lens 3 and has five openings 11a to 11e. Reference numerals 18a to 18e are field lenses (omitted in FIG. 1).
The field mask 10 is arranged behind the openings 18a to 18e in correspondence with the openings 18a to 18e. Reference numeral 15 denotes a secondary optical system, which has five secondary lenses 15a to 15e arranged in a direction perpendicular to the optical axis L of the taking lens 3. 14 is a light receiving means, corresponding to the secondary lenses 15a to 15e, a pair of five light receiving element rows,
17a (17a '), 17b (17b'), 17c (17c '), 17d (17
d '), 17e (17e'). A stop 16 is arranged in front of the secondary optical system 15 (not shown in FIG. 1) and has five openings 16a to 16e corresponding to the five secondary lenses 15a to 15e. ing. Reference numeral 2 denotes an exit pupil of the taking lens 3.

The field lenses 18a to 18e each have an aperture 16a of the diaphragm 16.
16e is formed substantially in the vicinity of the exit pupil 2, whereby the exit pupil 2 is divided into a plurality of regions.

Reference numerals 12a to 12d denote light shielding members, respectively, which are provided between the field mask 10 and the secondary optical system 15, and in which the light beams from the openings 11a to 11e of the field mask 10 correspond to the corresponding light receiving element rows 17a.
To 17e (17a 'to 17e'), for example, a flat plate shape. By using the light shielding members 12a to 12d, for example, as shown by a dotted line in FIG. 2, after the light beam from the opening 11b of the field mask 10 passes through the field lens 18b, it becomes a harmful light beam other than the target secondary lens 15b. Incident on the secondary lens 15d, and the light receiving element array 17d (17d ')
To reach the ghost light.

This enables highly accurate focus detection in an arbitrary distance measurement area.

In this embodiment, the light amount distribution of the subject image based on the luminous flux passing through one of the five ranging areas corresponding to the positions of the openings 11a to 11e of the field mask 10 is represented by a pair of light receiving element arrays. The focus detection is performed in the distance measurement area selected by the calculation means (not shown) using the output signal from the light receiving element array at this time.

For example, when performing distance measurement at a position corresponding to the peripheral portion of the screen, an output signal from the light receiving element array 17a (17a ') based on a light beam passing through the opening 11a of the visual field mask 10 is calculated by the calculation means. .

The focus detection method in this embodiment is the same as that of the above-described image shift method. When the light quantity distributions of the formed object images are close to each other and the image forming point of the photographing lens 3 is behind the predetermined image forming plane, the light receiving element arrays 17a and 17a 'are respectively placed on the two light receiving element arrays 17a and 17a'. The light quantity distributions formed are separated from each other.
In addition, since the shift amount of the light amount distribution formed on each of the two light receiving element arrays 17a and 17a 'has a certain functional relationship with the defocus amount of the photographing lens 3, the shift amount is calculated by an appropriate arithmetic unit. The direction and amount of defocus of the photographing lens 3 at the position in the distance measurement area 11a can be detected.

In the embodiment shown in FIG. 1, even if the light shielding members 12a to 12d are arranged between the secondary optical system 15 and the light receiving means 14, the harmful light beam can be removed as described above.

Further, instead of arranging the light shielding members 12a to 12d in parallel with the optical axis as shown in FIG. 1, for example, as shown in FIG. 3, a slit or circular shape corresponding to each of the field lenses 18a to 18e is formed. Even if the light blocking member 31 having the openings 31a to 31e is arranged in a plane orthogonal to the optical axis, the same effect as described above can be obtained.

FIGS. 4A and 4B are a perspective view and a plan view of a main part of another embodiment of the present invention. In the figure, reference numeral 41 denotes a field mask having nine openings 41a to 41i, which are arranged in a plane orthogonal to an optical axis near a predetermined imaging plane of the photographing lens.

The nine openings 41a to 41i of the field mask 41 each correspond to a distance measurement area. Reference numeral 42 denotes a secondary optical system, which has three secondary lenses 42a, 42b, and 42c. Three secondary lenses 42a, 4
2b and 42c respectively correspond to three openings of the field mask 41. 43 is a light receiving means, and a pair of nine light receiving element arrays
43a (33a ') to 43i (33i'). 44a and 44b are light shielding members, respectively, which are arranged between the field mask 41 and the secondary optical system 42.

In this embodiment, for example, three openings 41a to 41c, one secondary lens 42a, and three pairs of light receiving element rows 44a (44
a ') to 44c (44c') correspond to each other, thereby forming one secondary imaging system. Then, three secondary imaging systems are juxtaposed. The light shielding members 44a and 44b are respectively arranged at positions for separating the secondary imaging system.

In the present embodiment, as shown in FIG. 4 (A), the secondary lenses 42a, 42b, 42c of the visual field are arranged in one direction orthogonal to the optical axis, and in a plane orthogonal to the one direction. Further, light shielding members 44a and 44b having a shape whose longitudinal direction is the optical axis direction are provided.

In the configuration shown in the figure, if the light shielding members 44a and 44b are not disposed, for example, the light beam passing through the opening 41a may pass through the secondary lens 42b and form an image as a harmful light beam near the non-target light receiving element array 43g. . Therefore, in order to block such harmful light beams, light shielding members 44a and 44b are provided so as to separate the respective secondary imaging systems as shown in FIG. For example, a light beam passing through the opening 41a and the secondary lens 42a forms an image only on the light receiving element row 43a, and does not enter the other light receiving element rows 43d to 43i.

Further, in the configuration of the present embodiment, no harmful light beams enter between the openings 31a to 31c even if the light shielding member is not disposed due to the configuration.

In this embodiment, even if the light shielding members 44a and 44b are arranged between the secondary optical system 42 and the light receiving means 43, the same effect as described above can be obtained.

In each of the above embodiments, the number of openings of the field mask may be set arbitrarily according to the number of distance measurement fields.

(Effect of the Invention) According to the present invention, in the focus detection device of the image shift detection method, by arranging the light shielding member as described above, any one of a plurality of ranging areas is selected to perform focus detection. When performing the above, it is possible to prevent a harmful light beam such as a ghost from being incident on the light receiving element from another secondary lens, thereby achieving a focus detection device capable of performing highly accurate focus detection.

In addition, since a harmful light beam can be easily removed, a high-precision focus detection device having an increased degree of freedom in assembling and designing each element when configuring the focus detection device can be achieved.

[Brief description of the drawings]

FIG. 1 is a perspective view of an essential part of an optical system according to an embodiment of the present invention, and FIG.
FIG. 3 is a plan view of a part of FIG. 1, FIG. 3 is a plan view of a part of FIG. 2 when modified, and FIGS. 4A and 4B are main parts of another embodiment of the present invention. Perspective view and plan view, FIG. 5, FIG.
FIG. 1 is an explanatory diagram of an optical system and output signals of a conventional image shift type focus detection device. In the figure, 3 is a photographing lens, 2 is an exit pupil, 10 is a field mask,
11a to 11e, 41a to 41i are openings, 18a to 18e are field lenses, 12a to 12d, 31a to 31e, 44a, 44b are light blocking members, and 15 is 2
The secondary optical system, 15a to 15e, 42a to 42c are secondary lenses, 14 is a light receiving means, 14a (14a ') to 14e (14e') are light receiving element arrays, and 16 is a stop.

──────────────────────────────────────────────────の Continued on the front page (72) Inventor Akira Ishizaki 770 Shimonoge, Takatsu-ku, Kawasaki, Kanagawa Prefecture Inside the Tamagawa Office of Canon Inc. (72) Kenji Suzuki 770 Shimonoge, Takatsu-ku, Kawasaki-shi, Kanagawa Tamagawa Business (56) References JP-A-1-216309 (JP, A) JP-A-63-289513 (JP, A) (58) Fields investigated (Int. Cl. ⁶ , DB name) G02B 7/00

Claims (1)

(57) [Claims] An exit pupil of the photographing lens is divided into a plurality of different regions by a pupil dividing means arranged on an image plane side of the photographing lens, and a light beam passing through the plurality of regions is formed into a predetermined image of the photographing lens. After passing through a field mask having a plurality of openings arranged on the surface, a plurality of light amount distributions relating to the subject image are formed on a light receiving means comprising a light receiving element array by a secondary optical system,
A focus detection device for obtaining a relative positional relationship between the plurality of light quantity distributions by the light receiving means and obtaining an in-focus state of the photographing lens by an arithmetic means using an output signal from the light receiving means; The secondary optical system has a plurality of secondary lenses arranged in one direction, and the secondary lenses form a light amount distribution of the subject image in a plurality of visual field regions. An aperture other than the plurality of apertures of the field mask targeted by the secondary lens is provided between the lens and a light-shielding member having a shape whose longitudinal direction is the optical axis direction in a plane orthogonal to the one direction. A focus detection device for preventing a light beam from the lens from being incident on the secondary lens.