JPH01140108A - Focus detector - Google Patents

Abstract

PURPOSE:To detect a focusing state by the use of output by arranging a grating member around the expected image forming plane of a photographing lens and a fine lens array behind the member, providing each of some fine lenses with a pair of photodetectors, obtaining two light quantity distributions, and selectively line-connecting the photodetectors. CONSTITUTION:The fine lenses 40 of distributed index type are closely arranged to attain a plane, and the photodetectors 13a and 13b are provided on the emitting surface side of some lens in a group 7b to create a light receiving area 30. The lens group 7b is made thinner than a lens group 7a, and the elements are placed slightly closer to an object side than the image forming point P1 of an image forming lens. An image is re-formed in a point P2 on a focus glass plane. Gratings 31a-31g are placed on the face 5a of a concave lens 5 to form a space filter. The elements receiving fluxes from an eye area the same as the photographing lens are connected to use their output. When the gratings are vibrated perpendicular to the optical axis, front and back pins have reverse phases because fluxes incident on the photodetectors 13a and 13b have prescribed angles. Together with the defocus of the photographing lens, the phase difference increases, so that a focal point can be detected.

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., and in particular, a focus detection device that divides the pupil of a photographic lens into a plurality of regions, for example, two regions, The present invention relates to a focus detection device that obtains a light 11 distribution regarding two subject images from a light flux passing through each area, and detects the in-focus state of a photographic lens using the light intensity distribution regarding the two subject images.

(Prior Art) Various types of focus detection devices have been proposed as devices for detecting the in-focus state of a photographic lens.

For example, in Japanese Patent Application Laid-Open No. 55-118019, a part of the main movable mirror that guides the photographing light flux to the finder system is made into a half-mirror surface, and a sub-mirror is provided behind it to guide the light flux for focus detection to the bottom of the mirror box. ing. As a result, a distance measuring field mask made of an opaque member, a CCD, etc. are optically disposed on and in the vicinity of the expected image formation plane of the photographic lens, and the in-focus state of the photographic lens is detected. This focus detection device has problems such as the focus detection area being affected by the position of the secondary mirror, and the size of the secondary mirror being limited by the main movable mirror, making it difficult to expand and move the distance measurement field of view. was there.

Also, JP-A-58-108506, JP-A-58-1
11910, Utility Model Application Publication No. 57-40919, etc., a part of the focus glass of the finder system is transparent,
A beam splitter separates the light beam passing through the lens into a finder system and a focus detection system, and a transparent distance measuring element is formed on the surface of the focusing plate to detect the in-focus state.

In this method, the distance measurement field is a transparent focusing plate, so it is impossible to check the image formation state by the photographing lens, and the beam splitter must be larger in order to expand and move the distance measurement field. There was a problem.

In addition, a focus detection device has also been proposed in which a charge conversion element such as CdS is formed on the surface of a focus plate and the contrast of an object image is detected to detect the in-focus state.

With this method, the CdS blocks the photographing light, making it impossible to confirm the subject within the distance measurement field of view, and since it is a contrast-based focus detection method, the amount of day focus is lower than that of the phase-difference focus detection method. There were problems such as poor detection ability.

(Problems to be Solved by the Invention) The present invention utilizes a drivable grating member and a lens array as a spatial frequency filter to function as a focusing plate for observing an object image and to reduce the size of the finder system. It can be placed in a part of the viewfinder system without sacrificing this point, and it is also suitable for focusing on an arbitrary field of view from a wide range within the viewfinder's field of view.It is particularly suitable for eye reflex cameras. The purpose of this invention is to provide a focus detection device.

(Means for solving the problem) A lens array having a grating member as a spatial frequency filter and a plurality of microlenses behind the grating member as a spatial frequency filter is arranged near the planned image forming plane of the photographing lens, and a part of the lens array is A pair of light-receiving elements is provided for each microlens in the optical path of the microlens, and two light intensity distributions related to the subject image are obtained from the light fluxes passing through different areas of the pupil of the photographing lens from these plurality of light-receiving elements. A connection means is provided for electrically connecting the plurality of light receiving elements that receive light beams from the same pupil area of the photographing lens, and the output signal from the light receiving element is used to connect the light receiving elements that receive light from the same pupil region of the photographing lens. This means that the in-focus state has been detected.

(Embodiment) FIG. 1 is a schematic diagram of an embodiment in which the present invention is applied to a single-lens reflex camera.

In the figure, 1 is the camera body, 2 is the photographing lens, and 3 is a movable mirror, which can reflect all the light flux or reflect 50% of it, for example.
It has transmission-reflection characteristics such that it transmits an amount of light and reflects the rest. 4 is a convex lens, and 5 is a concave lens, which are coupled to a grating drive mechanism 6 and controlled to drive in a fixed direction.

Reference numeral 7 denotes a lens array having a plurality of minute lenses of a refractive index distribution type, and is used to make the subject image on the primary imaging plane of the photographing lens 2 erect and equal to the same magnification on the matte surface 8a of the focusing glass 8. It is being re-imaged. 8b is a Fresnel lens that condenses the light beam from the subject image on the matte surface 8a of the focusing glass 8. 8C is a split prism for checking the imaging state, and is provided in a part of the focusing glass 8.

9 is a pentaprism, and 10 is an eyepiece lens, through which the subject image on the matte surface 8a of the focusing glass 8 is observed.

FIG. 2 is an enlarged explanatory diagram showing the imaging state near the lens array 7 in FIG. 1. In the figure, the light rays advance from left to right and are incident on the concave lens 5. The concave lens 5 is for correcting field curvature caused by the convex lens 4. Further, each element is set so that the lens surface 5a of the concave lens 5 substantially coincides with the expected image formation surface of the photographing lens 2.

Here, taking as an example the light ray A that forms an image on the lens surface 5a, the light ray emitted from the concave lens 5 enters the front micro lens group 7b of the refractive index distribution type micro lens 40, and then enters the rear micro lens group 7a. The image is formed at a point P1 inside the .

After that, it moves in a undulating manner through the microlens and is placed at a point P2 on the matte surface 8a on the glass 8.
The image is re-imaged. At this time, various factors such as the refractive index distribution and length of the microlens 40 are specified as described later so that the subject image formed on the lens surface 5a becomes an erect, equal-magnification image on the matte surface 8a. are doing.

In this way, in this embodiment, a large number of microlenses 40 are arranged,
The entire microlens group constitutes a lens array 7, and one continuous erect real image of equal magnification is obtained.

For reference, the conditions for obtaining an erect, life-sized real image using a minute lens in this example are as follows.

become that way. The refractive index on the central axis of the microlens is No.
When A is the refractive index distribution constant and γ is the distance from the central axis, the refractive index distribution N(γ) is N(γ)=No (1--
Ar1) becomes. And when the length of the microlens is closed by 2 degrees, rt/, rT <Zo< 2rt/f
If the configuration satisfies the following inequality, an erect, equal-sized real image can be obtained.

Incidentally, the refractive index gradient lens array 7 shown in FIG. 2 has two microlens groups, a front microlens group 7b and a rear microlens group 7a.
A pair of light receiving elements 13a and 13b are provided on the exit surface side of b,
Both parts are joined together using a translucent adhesive.

FIGS. 3 to 7 are explanatory views of one embodiment of the lens array 7 according to the present invention.

FIG. 3 shows the front microlens group 7b and the fourth lens array 7.
The figure is an explanatory diagram when viewed from the exit surface side of the rear microlens group 7a of the lens array 7.

As shown in FIGS. 3 and 4, a minute lens group 7b.

7a is composed of a flat plate in which a plurality of microlenses 40 of a refractive index distribution type are arranged closely. A pair of light receiving elements 1, such as an amorphous silicon charge conversion element, are provided on the exit surface side of a portion of the microlenses 40 in the front microlens group 7b.
3a and 13b are formed.

These plurality of light receiving elements constitute one light receiving region 30a.

In this embodiment, two microlens groups 7 are used as shown in FIG.
Of a and 7b, the front microlens group 7b is made shorter than the rear microlens group 7a, and the positions of the light receiving elements 13a and 13b are set to be located somewhat in front (on the subject side) of the imaging point P1. ing.

FIG. 5 is an explanatory diagram showing an embodiment in which a light receiving area consisting of a plurality of light receiving elements 13a and 13b is arranged within the finder visual field 50 in this embodiment. In the figure, 30a to 30i are a plurality of light receiving elements 13a and 13b.
The light receiving area is shown. Focus detection is performed by selecting any of these light receiving areas 30a to 30i as will be described later.

FIG. 6 is a perspective view showing a pillar for connecting each light receiving element 13a, 13b in one light receiving area 30a of FIG. 5. FIG. Light-receiving elements located in the same direction with respect to the optical axis of the microlens are connected to each other, and their outputs are output from output pads 15a, 15b,
16a and 16b are connected to the outside.

Note that the connections of the light receiving elements in the other light receiving areas 30b to 30i are also similar to those shown in FIG. 6.

FIG. 7 is an explanatory diagram showing the structure of an embodiment when an amorphous silicon photoelectric conversion element is used as a light receiving element. In the figure, the transparent substrate 1 on the front microlens group 7b is
A charge conversion section 19 made of amorphous silicon is constructed between the light-shielding electrode 18 and the light-shielding electrode 18 . The light incident from below in the figure is photoelectrically converted.

Since the amorphous silicon photoelectric conversion element can be formed on a glass substrate in this way, it is easy to increase the area. In the figure, 20 is an insulator, and 21 is a light shielding electrode for interrupting the transparent electrode 17 and the pad 16a.

FIGS. 8 to 11 are explanatory diagrams showing each element of the light flux passing through the photographing lens 2 and reaching the eyepiece 10 in FIG. 1 in an expanded manner.

In this figure, the same elements as those shown in FIG. 1 are given the same reference numerals.

FIG. 8 shows a light beam passing through the optical axis of the microlens 40 in the lens array 7, and FIG. 9 shows a light beam that forms an erect, equal-magnification image from one point on the optical axis of the microlens 40, and the light receiving element. 1
It shows the light rays passing through the center of gravity of 3a and 13b.

As shown in FIGS. 8 and 9, a light receiving element 13a.

The surface 7C on which the lens 13b is formed is set to be projected onto the surface A near the exit pupil of the photographic lens 2 by the convex lens 4 and the concave lens 5. Therefore, the light receiving elements 13a, 1
On the surface A, the light beam incident on the beam 3b falls into two areas 14a as shown in FIG.

The light beams pass through the respective light beams 14b. That is, if the areas 14a and 14b on the surface A are not eclipsed by the effective diameter of the photographing lens 2, the light receiving elements 13a and 13b
The light beam incident on all the light receiving elements 13a, without vignetting,
The light flux is uniformly incident on the light beam 13b.

Further, since the surface A is configured to be near the exit pupil of the photographing lens 2, the light receiving elements 13a and 13b do not form an image on the focusing glass 8.

FIG. 11 is an explanatory diagram showing the imaging state of the light beam of a predetermined F number at this time. 8th. 5a shown in FIG. 9 corresponds to the planned imaging planes F and P in FIG. 11, and the distance from there! The position far away corresponds to point A within the projection lens 2.

Further, in FIG. 11, 26 is a light beam with an F number of 5.6 that enters the center of the screen, TI and T2 are light receiving elements 13a,
This is the imaging point with the maximum angle of view among the light beams incident on the beam 13b, and corresponds to when the F number of the focus detection system is set to F5.6.

Further, the effective luminous flux range of the focus detection system when corresponding to F5.6, which is the outer periphery of areas 14a and 14b in FIG. 10, is indicated by diagonal lines. According to FIG. 11, if the aperture of the photographing lens 2 or the image in the image space of the edge of the lens, that is, the exit pupil, is outside the diagonal lines, the light beam for focus detection will not be eclipsed and good focus detection will be possible. It shows what will happen.

Next, the principle of focus detection according to the present invention will be explained with reference to FIGS. 12 to 15.

Reference numerals 31a to 31b in FIG. 12 each indicate a grating formed on the lens surface Sa of the concave lens 5, and the lattices 31a to 31b in FIG.
located on the predetermined image plane of the image plane and acts as a spatial frequency filter. In the figure, gratings 31a to 31i are provided at nine locations within the finder screen, and are composed of a large number of rectangular light shielding parts. This arrangement is similar to the light receiving area 30a shown in FIG.
It corresponds to the arrangement of ~30i. Furthermore, the concave lens 5 is the first
The grating drive mechanism 6 shown in the figure reciprocates in the direction perpendicular to the finder optical axis (in the direction of arrow B), and its amplitude is approximately 1/2 the grating period. By performing this reciprocating motion at high speed, the grating is not visible in the finder system, and good viewfinder image observation is maintained.

FIGS. 13(A), (B), and (C) show the light receiving elements 13a and 13b when the grating shown in FIG. 12 moves back and forth.
2 is an explanatory diagram showing the relationship between fluctuations in the output signal from the camera and the imaging state of the photographing lens 2. FIG.

(A) shows the focused state, (B) shows the front bin state, and (C) shows the rear bin state. In the figure, reference numeral 32 indicates one light-receiving region of the lens array 7 that includes the light-receiving elements 13a and 13b described above. In the figure, for simplicity, only the light beam incident on the central part of the screen corresponding to the grating 31i is shown.

In such a configuration, specific spatial frequency components included in the subject image captured by the photographing lens 2 are extracted by scanning the grating. When the grating is driven in a sinusoidal manner, the output signal from the light receiving element is expressed as a time change. Furthermore, the light receiving element 1
The luminous flux incident on 3a and 13b is 34.3 in the figure, respectively.
3, and since they have a predetermined angle to each other, when the photographing lens 2 is in the front bin state or the back bin state, the two light fluxes that formed the subject image have different lattice vibrations. The grid will be blocked at the right time. As a result, the output changes from the light receiving elements 13a and 13b have opposite phase differences between the front bin state and the rear bin state, and this phase difference becomes larger as the day focus amount of the photographing lens 2 increases. .

Focus detection becomes possible by controlling the position of the photographing lens 2 on the optical axis based on this.

Note that a known treatment method, for example, the treatment method disclosed in Japanese Patent Publication No. 60-32846, etc., can be applied to the output signal obtained at this time.

The above explains the principle of distance measurement at the center of the shooting screen, but
Next, operations other than the center of the photographic screen and day focus detection calculation will be explained based on FIGS. 14 and 15.

FIG. 14 shows the front bin state shown in FIG. 13(B) represented by a light ray passing through the center of gravity of the optical image. That is,
Region 14a shown in FIG.

14b center of gravity P4. A light ray passing through P3 and a point R on the optical axis that is day focused by a distance DF is shown. Further, FIG. 15 similarly shows a ray passing through an off-axis point S defocused by a distance DF. Here, day focus detection using lattice vibration is nothing but detection of the relative positional shift of the subject image on the planned imaging planes F and P by the two light beams 33 and 34 shown in FIG. 13, as explained earlier. So,
The relationship between the day focus amount and the positional deviation of the image is as follows.

First, in FIGS. 14 and 15, ΔP3P4Rco ΔT4T3R ΔP3P4S C/3 ΔT6T5S Therefore, from this, the distance measurement field of view is the light receiving area 30a to 30 in FIG.
As shown in i, it is possible to calculate the day focus amount from the image shift amount using the same calculation formula even at various positions within the screen.

In this embodiment, the convex lens 4 does not need to be particularly provided, and the same effect can be obtained even if a simple parallel plane plate is used instead of the concave lens 5.

(Effects of the Invention) According to the present invention, a focus detection device having the following effects can be achieved.

(b) The focus detection system can be placed directly in the camera's finder system, eliminating the need for a secondary mirror and reducing the number of parts.
The mechanism can be simplified, and at the same time, the focus detection accuracy is not affected by the positional accuracy of the sub-mirror.

(b) There is no need to pass through the position corresponding to the range-finding field of the focusing glass, and a matte surface or a split prism can be formed, making it possible to confirm the imaging state of the subject image.

(c) Since it can be laid out in the finder system, it is possible to select a distance measurement field from a wide range within the finder screen, or to create a wide distance measurement field.

(d) By using a refractive index gradient microlens,
The focus detection optical system can be easily made compact.

(E) Since the light-receiving element is projected near the exit pupil plane of the photographic lens, its image does not appear on the focusing glass, and the object image is not blocked by the light-receiving element. Furthermore, by reciprocating the grating on the intended image plane at high speed, it is possible to observe a good finder image without being visually recognized by the finder system.

(f) It is advantageous in terms of light quantity because it does not require light division between a focus detection system and a finder system using a half mirror or the like.

(g) Even when the light-receiving element is formed on a glass substrate, the number of wiring lines can be reduced, which facilitates miniaturization.

[Brief explanation of the drawing]

Fig. 1 is a schematic diagram of an embodiment of the present invention applied to a single-lens reflex camera, Fig. 2 is an enlarged explanatory diagram showing the imaging state near the lens array in Fig. 1, Figs. is an explanatory diagram of the lens array in Fig. 1, Fig. 5 and Fig. 6 are explanatory diagrams showing the arrangement of the light receiving elements included in the lens array of Fig. 1, and Fig. 7 is an explanatory diagram showing the arrangement of the light receiving elements included in the lens array of Fig. 1. Schematic diagram when used, No. 8. Figure 9 is an explanatory diagram showing the imaging state of the light flux when the optical system in Figure 1 is expanded, Figure 1O is an explanatory diagram of the light flux passing through the photographing lens in Figure 1, and Figure 11 is for focus detection. FIG. 12 is an explanatory diagram showing the arrangement of the grating on the concave lens, FIG. 13 is an explanatory diagram showing the relationship between the imaging state and the output signal from the light receiving element, and FIG. 14 is an explanatory diagram showing the relationship between the imaging state and the output signal from the light receiving element. 1st
FIG. 5 is an explanatory diagram showing the relationship between the day focus amount and the relative shift. In the figure, 2 is a photographing lens, 3 is a movable mirror, 4 is a convex lens, 5 is a concave lens, 6 is a grating drive mechanism, 7 is a lens array, 8 is a focusing glass, 9 is a pentaprism, 10 is an eyepiece, 13a, 13b is a light receiving element, and 40 is a microlens. 1st solid 2nd zuko 3 M 4th father's 5 to 6th zunu (Kaya 10 Kuchi Ryo 11 Zumen 12 Kuchi 13 times

Claims (2)

[Claims] (1) A lens array having a grating member as a spatial frequency filter and a plurality of microlenses behind it is arranged near the planned imaging plane of the photographing lens, and a microlens is placed in the optical path of a part of the microlenses in the lens array. A pair of light-receiving elements is provided for each lens, and two light intensity distributions related to the subject image are obtained from the light beams passing through different areas of the pupil of the photographing lens from these plurality of light-receiving elements. A connection means is provided for electrically connecting light receiving elements that receive light beams from the same pupil area of the lens, and the in-focus state of the photographing lens is detected using an output signal from the light receiving element. Features a focus detection device. (2) The focus detection device according to claim 1, wherein the lens array re-images the subject image formed by the photographing lens on a predetermined plane in an erect, same-size image.