JPS6278517A - Focus detecting device - Google Patents

Abstract

PURPOSE:To detect a focus at high accuracy even if a defocused range is expanded by using a reflecting member with a reflection plane in the prescribed shape for an image reforming system. CONSTITUTION:A luminous flux from an object passing through a photographing lens 1 forms a primary object image in the vicinity of an expected image forming plane 3. Among luminous fluxes forming primary object images, the luminous flux L1 passing through one area 2a of the emitting pupil 2 of the photographing lens 1 makes incident on an image reforming lens 6-11, is reflected on two reflection planes 6-121 and 6-122 of the reflecting member 6-12, and forms a secondary object image on a photodetecting element train 8-1. The luminous flux L2 passing through the other area 2b of the emitting pupil 2 makes incident on an image reforming lens 6-21, passes through an optical block 6-22 without being reflected and forms a secondary object image on a photodetecting element train 8-2. For detecting a focus, a light receiving means 8 detects the relative position relation-ship between two secondary images. Thus a highly accurate focus detection becomes possible.

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 focal state of a photographic lens by forming a plurality of secondary object images from a light beam and detecting the relative positional relationship of the plurality of secondary object images.

(Prior Art) Conventionally, there is a so-called image shift method as a relatively high-precision light-receiving focus detection method.

This image shift method is proposed, for example, in Japanese Patent Laid-Open No. 52-95221, in which one or two re-imaging lenses are installed behind the expected imaging plane where the primary object image is formed by the taking lens. A re-imaging system having a light receiving element and a light receiving means having two light receiving element rows are arranged. The re-imaging system forms two secondary object images from the primary object image on each of the light-receiving element array surfaces using the light flux that has passed through the two pupil regions of the photographing lens. The relative positions of the two secondary object images on the plane of the light-receiving element array appear as a lateral shift in the direction in which the elements of the light-receiving element array are arranged, depending on the focusing state of the photographing lens. The focus of the photographing lens is detected by detecting the relative positional relationship between the two secondary object images using a light receiving means.

For this reason, in focus detection devices using the image shift method, the second
The optical performance of the next object image on the light-receiving means surface greatly influences focus detection accuracy.

A conventional focus detection device using an image shift method uses a prism body in which two prisms are arranged so that their wedge angles are opposite to each other, or a part of two re-imaging lenses is used so that the refraction directions are opposite to each other. A prism is attached to divide the pupil of the photographic lens into two. Two secondary object images are separated in a direction perpendicular to the pupil division direction, and two light receiving element rows are arranged in parallel in the vertical direction. This increases the length of the light-receiving element array, prevents two secondary object images from overlapping each other even if there is a large amount of defocus, and expands the focus detection range.

However, since conventionally a prism was used to separate the two secondary object images, various aberrations such as distortion and chromatic aberration were generated by the prism, which significantly degraded the optical performance of the secondary object image. Ta.

As a result, the degree of detection of the relative positional relationship between the two secondary object images is reduced, which is a major cause of reduction in focus detection accuracy.

(Problems to be Solved by the Invention) The present invention provides a focus detection device using an image shift method that enables highly accurate focus detection while maintaining good optical performance of a secondary object image. With the goal.

(Means for solving the problem) The pupil of the photographic lens is divided into two regions on the image plane side of the photographic lens, and a secondary object image is formed from the light flux passing through the two divided pupil regions. A re-imaging system is arranged, a light receiving means consisting of two light receiving element rows is arranged near the image plane of the re-imaging system, and the relative positional relationship of the two secondary object images is detected by the light receiving means. In the focus detection device that detects the focus state of the photographing lens by
After passing through a pair of re-imaging lenses and a reflecting member having at least two reflective surfaces that reflect one of the light beams passing through the pair of re-imaging lenses in a direction perpendicular to the pupil division direction, The other light beam is provided with a reflecting member that guides the other light beam to each of the two light-receiving element arrays without directly reflecting it.

Other features of the invention are described in the Examples.

(Embodiment) FIGS. 1A and 1B are schematic diagrams of an optical system according to an embodiment of the present invention. The same figure (A) is a top view, and the same figure (B) is a front view. In the figure, 1 is a photographic lens, 2 is an exit pupil of the photographic lens 1, 3 is a planned imaging plane of the photographic lens 1, 4 is a field lens, 5 is a field mask, and 6 is a re-imaging system, which is shown in perspective in Figure 2. Show the diagram. The re-imaging system 6 includes a pair of re-imaging lenses 6-
11, 6-21 and a reflective member 6- having two reflective surfaces
12 and an optical block 6-22 provided as necessary. 7 is a diaphragm having two apertures arranged in front of the re-imaging lenses 6-11 and 6-21, and 8 is a light receiving means having two light receiving element arrays 8-1 and 8-2 on the same plane. There is. The two light receiving element rows 8-1 and 8-2 are shown in Figure 1 (C
), it is configured to be separated into two parts in the vertical direction with respect to the Y axis.

In this embodiment, the re-imaging lens 6 is formed by the field lens 4.
-11, pupil of 6-21 and exit aperture ψ of 1-most shadow lens 1,
2 have a substantially conjugate relationship, and the exit pupil 2 of the photographic lens 1 is divided into two regions 2a and 2b.

The light beam from the subject that has passed through the photographic lens 1 forms a primary object image near the intended image formation plane 3. The light flux L1 that has passed through one region 2a of the exit pupil 2 of the photographing lens 1 in the primary object image enters the re-imaging lens 6-11, and is reflected by the reflecting member 6-1.
12 two reflective surfaces 6-121.6-122,
A secondary object image is formed on the light receiving element array 8-1. The light beam L2 that has passed through the other region 2b of the exit pupil 2 enters the re-imaging lens 6-21 and is not reflected by the optical block 6.
-22 as it is, and forms a secondary object image on the light receiving element array 8-2.

The relative positions of the two secondary object images on the light-receiving element row are determined by the arrows on the light-receiving element row 8-1 and 8-2 depending on the focusing state of the photographing lens 1 such as the front focus or rear focus and the magnitude of the defocus amount. C
This appears as a lateral shift amount in the directions indicated by -1 and C-2.

Focus detection is performed by detecting the relative positional relationship between the two secondary object images using the light receiving means 8 at this time.

In this embodiment, by appropriately setting the angle of the reflecting surface of the reflecting member 6-12 of the re-imaging system 6, two secondary object images are formed in a direction perpendicular to the dividing direction of the exit pupil 2, that is, in an up-down direction. The light is divided and re-imaged onto each of the light receiving element rows 8-1 and 8-2.

In this embodiment, each reflecting surface is set so that the principal rays incident on the light receiving element rows 8-1, 8-2 are substantially parallel to simplify the configuration.

Then, it passes through the re-imaging lens 6-11 and then passes through the reflecting member 6-12.
After being reflected by the two reflecting surfaces, the optical path length reaches the light receiving element array 8-1 and the optical path passes through the re-imaging lens 6-21 and reaches the light receiving element array 8-2 via the optical block 22. The reflecting member 6-12 and the optical block 6-2 are arranged so that their lengths are approximately equal.
The length of 2 is set.

Note that in this embodiment, the optical block 6-22 does not need to be provided.

As described above, in this embodiment, instead of using a prism as a means for vertically separating the light beam in the re-imaging system as in the past, a reflective member is used to eliminate the influence of aberrations generated from the prism, and the image quality is improved. A secondary object image having optical performance is formed on the surface of the light receiving means. This enables highly accurate focus detection at all times.

In this embodiment, two light receiving element rows 8-1 and 8
-2 has the dimensions shown by the solid line in Figure 1 (C), but since the two light-receiving element rows are arranged vertically parallel to each other, it is extended in the horizontal direction shown by the dotted line in the same figure. It may also be configured by dimensions. By extending the length of the light-receiving element array, it is possible to detect a large amount of defocus, and the focus detection range can be expanded.

The reflecting member 6-12 may be composed of two reflecting mirrors instead of a glass block. Further, the reflecting member 6-12 and the optical block 6-22 are connected to re-imaging lenses 6-11 and 6-, respectively.
21 may be integrated.

In this embodiment, a case is shown in which two re-imaging lenses are used, but the exit pupil 2 of the photographic lens 1 is configured to include one re-imaging lens and include two apertures of the diaphragm 7. It may be divided into two areas.

(Effects of the Invention) According to the present invention, by using a reflecting member having a reflecting surface of a predetermined shape in the re-imaging system, two secondary object images are separated in the vertical direction, and are placed on the light-receiving element array. A focus detection device capable of highly accurate focus detection with an expanded defocus range can be achieved.

[Brief explanation of drawings]

1(A) and 1(B) are respectively a plan view and a front view of an optical system according to an embodiment of the present invention, FIG. 1(C) is an explanatory diagram of a portion of the light receiving means in FIG. 1(A), FIG. 2 is a perspective view of an embodiment of the reimaging system of the present invention. In the figure, 1 is a photographing lens, 2 is an exit pupil, 3 is a planned imaging plane, 4 is a field lens, 5 is a field mask, 6 is a reimaging system, 7 is an aperture, 6-11.6-
21 is a re-imaging lens, 8-1 and 8-2 are light receiving element arrays, 8 is a light receiving means, and 6 to 12 are reflecting members.

Claims (1)

[Claims] A re-imaging system that divides the pupil of the photographic lens into two regions and forms a secondary object image from each of the light beams passing through the two divided pupil regions is disposed on the image plane side of the photographic lens. A light receiving means consisting of two light receiving element arrays is arranged near the image plane of the imaging system, and the focus state of the photographing lens is determined by detecting the relative positional relationship between the two secondary object images using the light receiving means. In the focus detection device for detection, the two light-receiving element arrays are arranged on substantially the same plane, and the re-imaging system has one
After passing through a pair of re-imaging lenses and a reflecting member having at least two reflective surfaces that reflect one of the light beams passing through the pair of re-imaging lenses in a direction perpendicular to the pupil division direction, A focus detection device comprising a reflecting member configured to guide the other light beam to each of the two light-receiving element arrays without being directly reflected.