JPH01282513A - Focus detecting device - Google Patents

Abstract

PURPOSE:To enable high-accuracy focus detection by providing light shielding members which prevent light from opening parts except object opening parts of a visual field mask for respective light receiving element arrays from being incident at optional positions between the visual field mask and the surface of a light receiving means. CONSTITUTION:The light shielding members 12a-12d are provided between the visual field mask 10 and a secondary optical system 15 and are formed in, for example, a flat plate shape so that pieces of luminous flux from respective opening parts 11a-11e of the visual field mask 10 are incident on only corresponding light receiving element arrays 17a-17e (17a'-17e'). Thus, the light shielding members 12a-12d are used to prevent luminous flux from the opening part 11b of the visual field mask 10 from entering a secondary lens 15d other than an object secondary lens 15b as harmful luminous flux after passing through a field lens 18b and then reaching the light receiving element array 17d (17d') to become ghost light. Consequently, the high-accuracy focus detection is enabled in an optical distance measurement area.

Description

Detailed Description of the Invention (Field of Industrial Application) The present invention relates to a focus detection device suitable for photographic cameras, video cameras, etc. In particular, the pupil of a photographic lens is divided into a plurality of regions, and the pupil of the photographic lens is divided into a plurality of regions, and the focus detection device is The present invention relates to a focus detection device that detects the in-focus state of a photographic lens by forming light intensity distributions regarding a plurality of subject images using a light flux and determining the relative positional relationship of these plurality of light intensity distributions.

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

FIG. 5 is a schematic diagram of an optical system of a conventional focus detection device of this type. In the figure, the photographing lens L whose focus should be detected
A field lens FLED is placed on the same optical axis as the NS. Behind it, two secondary imaging lenses FCLA and FCLB are arranged at symmetrical positions with respect to the optical axis. Furthermore, sensor arrays SAA and SAB are arranged behind it. An aperture DIA is located near the secondary imaging lenses FCLA and FCLB.

A DIB is provided. The field lens FLD focuses the exit pupil of the photographing lens LNS into two secondary imaging lenses FCLA,
The image is almost formed on the pupil plane of FCLB. As a result, the ray bundles incident on the secondary imaging lenses FCLA and FCLB are transmitted from areas of equal area that do not overlap each other and correspond to the respective secondary imaging lenses FCLA and FCLB on the exit pupil plane of the photographing lens LNS. It becomes something that has been ejected. The aerial image formed near the field lens FLD is sent to sensor arrays SAA and SAB by secondary imaging lenses FCLA and FCLB.
When reimaged onto the plane of the sensor array SAA, based on the displacement of the aerial image position in the optical axis direction.

The two images on the SAB will change their positions.

Therefore, by detecting the amount of displacement (deviation) in the relative positions of the two images on the sensor array, it is possible to know the focal state of the photographing lens LNS.

FIG. 6 shows the sensor array SAA in FIG. 5.

An example of photoelectric conversion output of two images formed on the SAB is shown.

The output image signal of the sensor array SAA is A(i).

Let B(i) be the output signal of sensor array SAB.

Note that the number of pixels of the sensor used is about 5 to 10 or more.

In FIG. 6, as a signal processing method for detecting the image shift amount PR from the image signals A(i) and B(i), for example, Japanese Patent Laid-Open No. 58
-142306, JP-A-59-10731:1, JP-A-60-101513, Japanese Patent Publication No. 61-160824, etc. are disclosed by the present applicant. The methods disclosed in these documents focus the photographic lens by adjusting the focus of the photographic lens based on the amount of image shift between the two images.

A camera equipped with this type of focus detection device normally performs automatic focus adjustment on a distance measurement area placed spot-wise in the center of the photographic screen. For example, in a single-lens reflex camera using 35 mm film, the field of view for distance measurement in the film equivalent plane 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 the distance measurement point in the center of the finder. In other words, if the main subject is outside the focus area in the center of the viewfinder due to framing, etc., adjust the focus so that the main subject is within the focus area in the center of the viewfinder, and use the focus lock function etc. I used the camera to frame the subject while maintaining the 1 o'clock focus state, and then took the picture. Such a photographing method is suitable when the main subject is stationary, but when the main subject is moving, it is necessary to constantly adjust the focus, and furthermore, it is difficult to perform framing.

As a means to solve such problems, a focus detection system that can measure and adjust focus at multiple points in the finder manually or automatically selects the distance measurement point in the finder, and then A focus detection device that can adjust the focus for a subject is considered.

However, in a focus detection device capable of multi-point distance measurement, there are severe design constraints such as the number of distance measurement points, distance measurement point spacing, and optical layout, and in terms of performance, light flux from outside the target distance measurement area is There were problems such as ghost light mixed into the light and reducing distance measurement accuracy.

(Problems to be Solved by the Invention) The present invention provides a focus detection device using an image shift method.
By placing a light-shielding member of a predetermined shape at any position between the field mask and the light receiving means surface, harmful light flux from outside the target distance measurement area is targeted when performing focus detection in multiple distance measurement areas. It is an object of the present invention to provide a focus detection device capable of highly accurate multi-point distance measurement while preventing the light from being mixed into a light-receiving element.

(Means for solving the problem) The J&
The exit pupil of the i-shade lens is divided into a plurality of different regions, and the light flux that has passed through the plurality of regions is caused to pass through a field mask having a plurality of openings arranged near the planned imaging plane of the Jul-shade lens. After that, a secondary optical system forms a plurality of light quantity distributions regarding the subject image on a light receiving means surface consisting of a plurality of light receiving element arrays, and the relative positional relationship of the plurality of light quantity distributions is determined by the light receiving means. In the focus detection device, the secondary optical system has at least two secondary lenses, and the secondary optical system has at least two secondary lenses, and the secondary optical system has at least two secondary lenses. A light-shielding member is provided at any position between the light-receiving means surface and the light-shielding member to prevent light from entering from openings other than the openings of the field mask targeted by each light-receiving element array.

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

1st. In FIG. 2, reference numeral 3 denotes a photographing lens, and numeral 10 denotes a field mask, which is disposed near the intended imaging plane of the photographic lens 3 and has five openings 11a to 11lie. 18a
˜18e are field lenses (omitted in FIG. 1). Each opening 18a˜1 of the field mask 10
It corresponds to 8e and is arranged behind it. 15 is 2
It is a secondary optical system and has five secondary lenses 15a to 15e arranged perpendicularly to the optical axis of the photographic lens 3. 14 is a light receiving means and secondary lenses 15a to 15e.
Corresponding to
a'), 17b (17b'), +7c(
+7c'), 17d (17d'), 17c
(17e'). Reference numeral 16 denotes a diaphragm, which is arranged in front of the secondary optical system 15 (omitted in FIG. 1).
It has two openings 16a to 16e. 2 is jH55
'Z is the exit pupil of lens 3.

The field lenses 18a to 18e each have the function of forming an image of the apertures 16a to 16e of the diaphragm 16 approximately in the vicinity of the exit pupil 2, thereby dividing the exit pupil 2 into a plurality of regions.

12a to 12d are light shielding members, and the visual field mask 10
and the secondary optical system 15, and the light beams from the respective apertures 11a-lie of the field mask 10 are connected to the corresponding light-receiving element rows +7a''-17e (17a'-Be').
It has a shape, for example, a flat plate, so that it is incident only on the beam. By using the light shielding members 12a to 12d, the opening 1 of the field mask 10 can be closed, for example, as shown by the dotted line in FIG.
After the luminous flux from 1b passes through the field lens 18b, it becomes a harmful luminous flux and is transmitted to the secondary lens 15b other than the target secondary lens 15b.
Next, the light enters the lens 15d, and the light receiving element array +7d (+7d'
) and prevents it from becoming ghost light.

This enables highly accurate focus detection in any distance measurement area.

In this embodiment, the light amount distribution of the subject image based on the light flux passing through one of the five distance measurement areas corresponding to the positions of the openings 11a to 11ie of the field mask 10 is set to 1.
Detection is performed using a pair of light-receiving element arrays, and the output signal from the light-receiving element array at this time is used to perform focus detection in a distance measurement area selected by an arithmetic means (not shown).

For example, when performing distance measurement at a position corresponding to the periphery of the screen, the output chi 3 from the light receiving element array +7a (17a') due to the light beam passing through the aperture 11a of the field mask 10 is calculated and determined by the calculation means. ing.

The focus detection method in this embodiment is the same as the image shift method described above, and when the imaging point of the photographing lens 3 is in front of the intended imaging plane, two light receiving element rows +7a and +7d are used.
When the light intensity distributions of the object images formed on the respective planes become close to each other and the image forming point of the photographic lens 3 is located behind the intended image forming plane, the two light receiving element arrays 17a
, 17a', the light quantity distributions formed on the surfaces are separated from each other. Moreover, two light receiving element rows +7a
, +7a' and +7a' and the amount of deviation in the light intensity distribution formed respectively has a certain functional relationship with the amount of defocus of the photographing lens 3, so
When the amount of deviation is calculated using an appropriate calculation means, the distance measurement area 1
It is possible to detect the direction and amount of defocus of the i-shadow lens 3 at the position 1a.

In the embodiment shown in FIG. 1, the light shielding members 12a to 12
Even if the lens d is placed between the secondary optical system 15 and the light receiving means 14, harmful light flux can be removed in the same way as described above.

Also, instead of arranging the light shielding members 12a to 12d in a stacked manner parallel to the optical axis as shown in FIG. 1, for example, as shown in FIG. Even if the light shielding member 31 having the openings 31a to 31e is arranged in a plane perpendicular to the optical axis, the same effect as described above can be obtained.

FIGS. 4(A) and 4(B) are a perspective view and a plan view of main parts of another embodiment of the present invention. In the figure, reference numeral 41 denotes a field mask, which has nine openings 41a to 41i, and is arranged in a plane perpendicular to the optical axis in the vicinity of the intended imaging plane of the photographing lens.

The nine openings 41a to 41i of the field mask 41 each correspond to a distance measurement area. A secondary optical system 42 includes three secondary lenses 42a and 42b.

42c. Three secondary lenses 42a.

42b and 42c each indicate three openings of the field mask 41;
It corresponds to part 1. 43 is a light receiving means, and nine 1
Paired light receiving element rows 43a (33a ”) to 43i (:
)3i'). 44a and 44b are light shielding members, respectively, and are arranged between the field mask 41 and the secondary optical system 42.

In this embodiment, for example, three openings 41a to 41c and one
One secondary lens 42a1 and three pairs of light receiving element arrays 44a (44a') to 44c (44c') correspond to each other, thereby configuring one secondary imaging system. Three secondary imaging systems are arranged side by side. The light shielding members 44a and 44b are arranged at positions that separate the secondary imaging systems.

In the configuration shown in the figure, if the light shielding members 44a and 44b are not provided, the light flux passing through the opening 41a will not pass through the secondary lens 42.
b, and may form an image as a harmful 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 to separate each secondary imaging system as shown in the same figure, and thereby, as shown in FIG. 4(B), For example, openings 41a and 2
The light beam passing through the next lens 42a forms an image only on the light-receiving element array 43a, and is prevented from being incident on the surfaces of the other light-receiving element arrays 43d to 43i.

Further, according to the configuration of this embodiment, each of the openings 31a to 31
Regarding the space between c and c, harmful light beams will not be incident on each other even if no light shielding member is disposed due to the structure.

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 in the field mask may be arbitrarily set depending on the number of distance measurement fields.

(Effects of the Invention) According to the present invention, in the focus detection device using the image shift detection method, by arranging the light shielding member as described above, focus detection is performed by selecting any one of a plurality of distance measurement areas. When performing this, it is possible to prevent harmful light beams such as ghosts from entering the light receiving element from other secondary lenses, thereby achieving a focus detection device capable of highly accurate focus detection.

Furthermore, since the harmful light flux can be easily removed, a highly accurate focus detection device can be achieved which increases the degree of freedom in designing the assembly of each element when configuring the focus detection device.

[Brief explanation of the drawing]

FIG. 1 is a perspective view of the main parts of an optical system according to an embodiment of the present invention, and FIG.
The figure is a plan view of a portion of FIG. 1; FIG. 3 is a plan view of a portion of FIG. 2 after being changed; FIGS. Perspective view and plan view, Figure 5,
FIG. 6 is an explanatory diagram of the 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 11a, 41a to 41i are openings, and 18a to 41i are openings.
18e is a field lens, 12a-l 2d, 31
a-31e, 44a. 44b is a light shielding member, 15 is a secondary optical system, 15a to 15e
, 42a to 42c are secondary lenses, 14 is a light receiving means, 1
4a (14a') to 14e (14e') are light receiving element arrays, and 16 is an aperture. Figure 2 Figure 3 Figure 4 (A) Figure 4 (B)

Claims (1)

[Claims] (1) The exit pupil of the photographic lens is divided into a plurality of different regions by a pupil dividing means placed on the image plane side of the photographic lens, and the light flux that has passed through the plurality of regions is distributed near the planned imaging plane of the photographic lens. After passing through a field mask having a plurality of apertures arranged in a field, a secondary optical system forms a plurality of light quantity distributions regarding the subject image on a light receiving means surface consisting of a plurality of light receiving element arrays, and the plurality of light quantity distributions are In the focus detection device, the secondary optical system includes at least two It has a secondary lens, and prevents light from entering any position between the field mask and the light-receiving means surface from openings of the field mask other than the openings of the field mask targeted by each light-receiving element array. A focus detection device characterized by being provided with a light shielding member.