JPH01266503A - Focus detecting device - Google Patents

Abstract

PURPOSE:To improve the accuracy of focus detection for an object corresponding to the center of a screen and a position distant from it by arranging three photodetecting element arrays corresponding to at least secondary image-forming lenses, selecting two optional photodetecting element arrays according to the signal from an input means, and utilizing the output signals of those two photodetecting element arrays. CONSTITUTION:An optical means is provided with at least one field lens which is arranged nearby a plane equivalent to the image formation plane of an objective 1 and the three secondary image forming lenses 41-43 arranged at least linearly in a plane perpendicular to the optical axis of the objective 1. Then the optical axis of the center secondary image forming lens among the three secondary image forming lenses 41-43 is aligned nearly with the optical axis of the objective 1 and a photodetecting means is provided with the three photodetecting element arrays 51-53 corresponding to the three secondary image forming lenses 41-43. Two optical photodetecting element arrays are selected among those three photodetecting element arrays 51-53 by an input means and its output signal is used to perform focus detection at an optional position in the screen. Consequently, the focus detection for a position distant from the center of the screen is performed with high accuracy.

Description

DETAILED DESCRIPTION OF THE INVENTION (Industrial Application Field) The present invention relates to a focus detection device suitable for photographic cameras, video cameras, etc. In particular, the pupil of an objective lens is divided into a plurality of regions, and the focus detection device is configured to pass through each region. The present invention relates to a focus detection device that uses a light flux to form light intensity distributions for a plurality of subject images and detects the in-focus condition of an objective lens by determining the relative positional relationship of these plurality of light intensity distributions.

(Prior Art) Conventionally, there is a so-called image shift method as a light-receiving focus detection method that utilizes a light beam passing through an objective lens.

For example, as shown in FIG. 4, this image blurring method places a field lens 3 near the expected imaging plane 2 where the object image is formed by the objective lens 1. Behind the field lens 3, an aperture 6 and two secondary A secondary optical system 4 having lenses 4A and 4B is arranged, and a plurality of light receiving element rows 5A are arranged behind it.
, 5B.

Using the light beams that have passed through two different areas of the pupil of the objective lens 1 from the field lens 3 and the secondary optical system 4, light intensity distributions regarding the two subject images are formed on the respective light receiving element array surfaces. . At this time, the relative positional relationship between the two light quantity distributions formed on the light receiving element row surface, that is, the amount of deviation of the light quantity distributions, differs depending on the focusing state of the objective lens. For example, the amount of lateral shift appears in the direction in which the elements on the light receiving element array are arranged in accordance with the amount of defocus of the objective lens from the intended imaging plane.

FIG. 4(A) shows the case where the objective lens 1 is in focus,
A subject P, which is a point light source, is formed approximately at the center of the light receiving element array 5A, 58 surface. FIG. 5(A) shows the output signals from the light receiving element arrays 5A and 5B at this time, and the light receiving element array 5A of the point light source P.

The spacing on the 5B plane is offset by 1°.

FIG. 4(B) shows a flying state in which the objective lens 1 is extended toward the object side, and at this time, the interval between the focal lights fiP formed on the surfaces of the light receiving element rows 5A and 5B is as shown in FIG. 5(B). As shown in (A), it becomes narrower than in the figure (A).

FIG. 4(C) shows the objective lens 1 in a focused state after being retracted to the film surface side, and at this time, the light receiving element arrays 5A, 5B
The interval between the focal beams d'I P formed on the surface is shifted, and as shown in FIG. 5(C), it becomes wider than that in FIG. 5(A).

Generally, at this time, the relative lateral shift amount δ of the light quantity distribution on the two light receiving element arrays and the defocus amount d of the objective lens have a constant functional relationship.

The in-focus state of the objective lens, that is, the amount of defocus at this time, is 2
This is done by detecting the relative positional relationship between the two light quantity distributions, that is, the amount of lateral deviation of the light quantity distributions using a light receiving means.

In the focus detection device shown in FIG. 4, the aperture of the diaphragm 6 is set to be relatively small so that the light beam passing through the aperture is not eclipsed within the objective lens 1.

In addition, the focus detection device shown in the same figure measures the distance at the center of the screen, and when measuring the distance of a subject at a position other than the center of the screen, the aperture diameter of the diaphragm 6 is made smaller, or secondary imaging is performed. It was necessary to narrow the distance between the apertures of the lens 4 and the corresponding aperture 6.

For this reason, there is a problem in that the amount of light decreases or the amount of deviation in the light amount distribution of the object image decreases, resulting in a decrease in the ability and performance of detecting the brightness of the object.

On the other hand, it is conceivable to measure the distance at a point other than the center of the screen by using a pair of secondary imaging lenses and a pair of light-receiving element rows, but this method would complicate the entire device. There were also problems in that the size of the device increased.

(Problems to be Solved by the Invention) The present invention provides an image shift type focus detection device, in which a screen is An object of the present invention is to provide a focus detection device that can perform focus detection at a position away from the center with high precision while reducing the size of the entire device.

(Means for Solving the Problem) A plurality of light intensity distributions regarding a subject image are formed using a light flux that has passed through different regions of the pupil of the objective lens by an optical means disposed on the image plane side of the objective lens, and In the focus detection device, the optical means determines the relative positional relationship of the light quantity distribution by a light receiving means, and uses the signal from the light receiving means to determine the in-focus state of the objective lens by a calculating means. at least one field lens disposed near a plane equivalent to the imaging plane; and three secondary imaging lenses arranged (ξ) in at least one dimension in a plane perpendicular to the optical axis of the objective lens. The optical axis of the central secondary imaging lens among the three secondary imaging lenses is arranged to substantially coincide with the optical axis of the objective lens, and the light receiving means It has three light-receiving element rows corresponding to the imaging lens, and any two light-receiving element rows are selected by input means from the three light-receiving element rows, and the output 3 from the two light-receiving element rows is The focus was detected at any position on the screen using the

(Embodiment) FIGS. 1A and 1B are schematic diagrams of an embodiment of the present invention. FIG. 5A shows a case where focus detection is performed at the center of the screen, and FIG. 1B shows a case where focus pressure detection is performed at the periphery of the screen, both of which are shown with the optical system in an expanded state.

In Fig. 1 (A) and (B), 1 is the objective lens "
Also called a photographic lens. ), 2 is the intended image-forming plane of the objective lens 1, 3 is a field lens placed near the intended image-forming plane 2, and 4 is a secondary optical system, which is arranged so as to coincide with the optical axis of the objective lens 1. It is constructed by one-dimensionally arranging three lenses: a secondary imaging lens 42 and two secondary imaging lenses 41 and 43 arranged symmetrically with respect to the optical axis of the objective lens 1. 5 is a light receiving means, and the three lenses 4
It is composed of three light-receiving element rows 51, 52, and 53 arranged one-dimensionally behind it corresponding to 1°42.43. 6 is the aperture, and the three lenses 41, 4
2. Three openings 61, 62 arranged corresponding to 43
．． 63. Reference numeral 7 denotes an exit pupil of the objective lens l, which is divided into a plurality of parts (three in this embodiment) by a field lens 3 and the like, as will be described later.

8 is a calculation means, which has three light receiving element arrays 51°52.5
2 based on the instruction signal from the input means 9 that specifies the focus detection position among the light amount distribution signals regarding the subject image from 3 to 2.
The relative positional relationship of the light amount distributions for the two subject images, that is, the amount of shift δ, is determined, and the out-of-focus ff1d of the objective lens 1 at the designated screen position is calculated based on this.

In this embodiment, the field lens 3, secondary imaging lenses 41, 42, 43, diaphragm 6, etc. constitute a part of the optical means.

The field lens 3 has the function of forming an image of the apertures 61, 62° 63 near the area 71° 72.73 of the exit @ 7 of the objective lens 1, and the light transmitted through each area 71, 72.73 The light flux forms a light amount distribution regarding the subject image on each of the light receiving element arrays 51, 52, and 53.

In FIG. 1(A), a subject P on the optical axis of the photographic lens 1
The object light emitted from 0 is converged by the photographing lens 1,
Point P on film equivalent surface 2. ′.

Point P. The aerial image formed at ′ is further transmitted to field lens 3
, passes through the aperture 6 and is imaged onto each light receiving element array 51, 52° 53 by the secondary imaging lens 41° 42, 43. 3
The two secondary imaging lenses 41, 42, and 43 are arranged one-dimensionally in a plane perpendicular to the optical axis of the photographing lens 1, and the optical axis of the secondary imaging lens 42 located at the center and the photographing lens 1 are arranged one-dimensionally. coincides with the optical axis of In addition, the optical axis of the secondary imaging lens 42 located at the center and the secondary imaging lenses 4 located above and below in the figure
Since the optical axis of 1.43 is separated by a distance fiL,
The aerial image of the point 20' is formed at the corresponding position of the light receiving element array 51, 52, 53. When the object P0 to be detected is selected by the signal from the input means 9 specifying the focus detection position, the calculation means 8 selects the outputs of the light receiving element arrays 51 and 53, and calculates the correlation between the respective light quantity output distributions. Performs focus detection at the center of the screen.

FIG. 1(B) shows a case where a subject P, which is viewed from the optical axis of the photographic lens 1, is selected based on a signal from the input means 9 instructing the focus detection position. Subject P.

The object light emitted from the camera is converged by the photographing lens 1 and focused on a point P1' on the film equivalent surface 2. The aerial image formed at the point P1' further passes through the field lens 3 and the diaphragm 6, and is imaged onto each light-receiving element array 51, 52 by the secondary imaging lens 41.42.

Here, the field lens 3 is designed so that the pupil 7 of the S3 lens 1 and the aperture 6 almost satisfy the imaging relationship, and the thickness of the lens is limited due to the space etc. when mounting it on the camera body. Since there is a limit to how thick the lens can be, its refractive power cannot be increased very much.

As a result, when the F value of the photographic lens 1 is large, the subject P
1 is far from the optical axis of the photographic lens 1, the effective luminous flux of the subject P to the secondary imaging lens 53 is eclipsed by the exit pupil 7 or the effective diameter of the lenses constituting the photographic lens 1. A condition arises. When a portion of the light beam reaching the light-receiving element array is eclipsed, the focus detection particle size by the correlation method decreases.

The calculation means 8 performs calculation processing based on the information inputted from the input means 9 specifying the focus detection position, the position of the exit pupil 7 of the photographic lens 1, and the F value. At this time, outputs from the light-receiving element array are selected and focus detection is performed using the outputs from the light-receiving element array that do not cause vignetting in the light beam reaching the light-receiving element array.

In addition, in FIGS. 1(A) and 1(B), the light receiving element array 51
The luminous fluxes of the subject 20 and P are simultaneously incident on ゜52, but since the position of incidence on the light receiving element array differs depending on the subject position, it is not possible to limit the range of output from the light receiving element array that is actually subjected to arithmetic processing. It is done. Also, film equivalent surface 2
A viewing mask made of a liquid crystal element, an electrochromic element, etc. may be placed nearby.

FIG. 2 is a schematic diagram of an embodiment of the diaphragm 6 shown in FIG. 1. The solid circle indicates the opening of the diaphragm 6 according to the present invention. The dotted circle indicates the aperture of a conventional diaphragm.

As shown in the figure, in the conventional aperture, the range of the aperture is limited in order to accommodate off-axis subjects. On the other hand, since the center-of-gravity spacing of the apertures of the aperture 6 according to the present invention satisfies the relationship 2L >L' to L with respect to the center-of-gravity distance L' of the conventional aperture apertures, off-axis objects can be detected. The accuracy is almost the same as before, and it is possible to improve the accuracy of detecting on-axis objects compared to before.

In the above embodiment, three 2
Although an example in which the secondary imaging lens is arranged has been shown, a configuration may also be adopted in which two secondary imaging lenses are arranged symmetrically with respect to the secondary imaging lens 42 in the direction perpendicular to the plane of the paper. At this time, the light receiving means corresponding to the secondary imaging lens 42 may be constituted by a cross-shaped or area sensor.

FIG. 3 is a schematic diagram of essential parts of an optical system according to another embodiment of the present invention. In this embodiment, the field lens is made to correspond to the three secondary imaging lenses 41, 42, and 43, and the three lenses 21
, 22, and 23 is different from the embodiment shown in FIG. 1, and the rest of the structure is the same as the embodiment shown in FIG.

In this embodiment, the subject light from the subject off the optical axis of the photographing lens (not shown) forms an image at a point P1' on the film equivalent surface 2, and then passes through the field lens 21 and the aperture 61 of the diaphragm 6. Next, the light receiving element array 51.
52. Field lens 21, 22.2
3 is composed of a plano-convex lens with a convex surface facing the object side, and the apex of the convex surface of each lens is set to match the scheduled detection position on the film equivalent surface 2.

The planes on one side of the field lenses 21 and 23 form a wedge with respect to the film equivalent surface 2, and function to guide the subject light to the secondary imaging lens.

(Effects of the Invention) As described above, according to the present invention, at least three secondary imaging lenses and three light-receiving element arrays are arranged as described above, and two light-receiving elements are selected at any given time based on the signal from the input means. By selecting an element array and using the output signals from the two light-receiving element arrays, it is possible to easily and efficiently detect the focus of subjects at the center of the screen and positions further away from the center of the screen. A focus detection device can be achieved.

[Brief explanation of the drawing]

731 (A) and (B) are schematic diagrams of 36 examples of part of the present invention, FIG. 2 is a schematic diagram of one embodiment of the aperture shown in FIG.
FIG. 4 is a schematic diagram of main parts of another embodiment of the present invention. FIG. 5 is a schematic diagram of a conventional image shift type focus detection device and an explanatory diagram of the light amount distribution. In the figure, 1 is the objective lens, 2 is the intended imaging plane, 3°31.3
2.33 is a field lens, 4 is a secondary imaging system, 41,
42. 43 is a secondary imaging lens, 5 is a light receiving means, 51, 5
2.53 is a light receiving element array, 6 is an aperture, 7 is an exit pupil, 8 is a calculation means, and 9 is an input means. Isamu 2 Kuchi Isamu 4 A Figure 5

Claims (1)

[Claims] (1) Forming a plurality of light intensity distributions regarding the subject image using an optical means disposed on the image plane side of the objective lens using light fluxes that have passed through different areas of the pupil of the objective lens, and comparing the relative light intensity distributions of the plurality of light intensity distributions. In the focus detection device, the positional relationship is determined by a light receiving means, and the in-focus state of the objective lens is determined by a calculation means using a signal from the light receiving means, wherein the optical means is located near a plane equivalent to the image forming plane of the objective lens. at least one field lens arranged, and three secondary imaging lenses arranged in at least one dimension in a plane perpendicular to the optical axis of the objective lens; The optical axis of the central secondary imaging lens among the lenses is arranged so as to substantially coincide with the optical axis of the objective lens, and the light receiving means includes three light receiving elements corresponding to the three secondary imaging lenses. Out of the three light-receiving element rows, any two light-receiving element rows are selected by the input means, and the output signals from the two light-receiving element rows are used to display the image at any position on the screen. A focus detection device characterized by performing focus detection.