JP2971889B2 - Focus detection optical system - Google Patents

Description

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a focus detection optical system of a camera, and more specifically, focus detection for multi-point distance measurement having a distance measurement zone at a position away from the optical axis. Optical system.

"Prior art and its problems" In recent auto-focus single-lens reflex cameras, a so-called multi-point distance measuring device has been developed that can measure the distance of a subject in a plurality of distance measuring zones in order to prevent so-called centering. (For example, JP-A-63-278012).

FIG. 3 shows an outline of the conventional auto-focus single-lens reflex camera equipped with the multi-point distance measuring apparatus, FIG. 4 shows a distance measuring zone in the finder field, and FIG. 5 shows a focus detecting optical system.

Most of the luminous flux of the subject entering the photographing lens 10 and exiting from the final imaging lens L is reflected upward by the main mirror 12 and guided to the finder optical system 14. Main mirror
The central part of 12 is a half mirror, and a part of the subject light beam passes through this half mirror part, is reflected downward by a sub mirror 16 arranged behind it, and from an opening 19 formed in a light shielding plate 18. It is led to the distance measuring module 40.

The viewfinder optical system 14 has three distance measurement zones 15A, 15B, and 15 indicating the range of the object to be focused within a field frame 15 thereof.
C is provided.

The distance measuring module 40 includes a field mask 42 disposed near an equivalent surface of the film surface F, and a condenser lens 44, a prism 46, a separator lens 48, and a distance sensor 50 disposed in this order behind the field mask 42. It is the main component. The distance measuring sensor 50 has three CCD line sensors 50A, 50B, 5
0C, each line sensor 50A, 50B, 50C is disposed at a position and an orientation corresponding to the distance measuring zones 15A, 15B, 15C, and the light receiving surface thereof is located on an equivalent surface with the film surface F. ing.

The field of view mask 42 has openings 42A, 42B, and 42C that allow only the subject light flux forming the distance measuring zones 15A, 15B, and 15C, and the prism 46 has a distance measuring zone that passes through the respective peripheral openings 42A and 42C. Prisms 46A and 46C are formed to deflect the luminous fluxes of 15A and 15C in a direction approaching the luminous flux of the distance measuring zone 15B passing through the central opening 42B.

The separator lens 48 has a split lens 4 for splitting the subject light beam passing through the openings 42A, 42B, and 42C into two, and forming an image on the distance measurement sensors (line sensors) 50A, 50B, and 50C.
8A, 48A, 48B, 48B, 48C, 48C are formed. Further, on the front surface of the separator lens 48, each of the split lenses 48
A,..., A mask 52 for cutting a harmful light beam that does not pass through 48C is provided.

Therefore, the subject light beams passing through the openings 42A, 42B, and 42C are condensed by the condenser lens 44, the peripheral light beam is deflected in the central light beam direction by the prism 46, and is divided into two by the separator lens 48, and the corresponding lines. Sensor 50
Imaged on A, 50B, 50C.

In the configuration without the above prism, the surrounding distance measurement zone 15
The farther A and 15B are from the optical axis (the central ranging zone 15B), the farther the imaging position on the light receiving surface of the ranging sensor is from the optical axis x. Therefore, in the distance measuring module 40, a prism 46 is provided to deflect the peripheral light beam in the direction of the optical axis x (central light beam).

However, since the prism 46 must be formed separately from the condenser lens 44, the number of members increases, and the number of manufacturing steps and assembly steps increases.

Instead of the prism 46, a peripheral condenser lens 44
A, A means to decenter the 44C sphere has also been developed. That is, the spheres of the condenser lenses 44A and 44C through which the luminous flux of the peripheral ranging zones 15A and 15C pass are decentered toward the sphere of the condenser lens 44B through which the central luminous flux passes, and the peripheral luminous flux is deflected toward the optical axis x. Things.

However, in the deflection due to the eccentricity of the spherical center, the aberration due to the eccentric optical system increases when the eccentricity is increased, so that a large deflection angle cannot be set. Therefore, when the surrounding distance measurement zones 15A and 15C are provided away from the optical axis x,
The distance between the line sensors 50A, 50B, and 50C must also be increased, which causes a problem that the distance measuring sensor 50 becomes large and the distance measuring module 40 becomes large.

In view of this, there has been proposed an arrangement in which a single plane mirror is disposed below the openings 42A, 42B, and 42C, and the optical path is reflected in parallel with the optical axis X of the photographing lens (Japanese Patent Laid-Open No. 63-11906).
issue).

However, also in this conventional example, since the peripheral light beam and the central light beam are both reflected in the same direction, it is necessary to decenter the prism or the spherical center in order to bring the imaging position closer to the sensor surface. Had occurred.

"Object of the Invention" The present invention has been made in view of the problems of the above-described conventional multi-point distance measuring apparatus, and has a light beam in a distance measuring zone away from the optical axis.
Provided is a focus detection optical system that forms an image near an image of a light beam in a center distance measurement zone on a sensor surface to enable downsizing of a sensor and a distance measurement module, and also facilitates manufacture thereof. The purpose is to:

"Summary of the Invention" The present invention that achieves the above object transmits through an imaging optical system,
A focus detection optical system for connecting subject images in different areas of the subject light beams transmitted through the plurality of distance measurement zones on the distance measurement sensors corresponding to the respective distance measurement zones, behind a final imaging lens of the photographing optical system; And a mirror that reflects the subject light beam emitted from the final imaging lens toward the outside of the optical path of the imaging optical system, and which corresponds to the center ranging zone of the subject light beam reflected by the mirror. A central opening through which the subject light beam passes and a peripheral opening through which the subject light beam corresponding to the surrounding ranging zone is provided, and each of the openings is provided between the opening and each of the distance measuring sensors, and passes through each of the openings. An optical path turning mirror that reflects the subject light flux in the corresponding distance measuring sensor direction, and a case that houses the distance measuring sensor, wherein the opening is formed in the case;
An optical path turning mirror that reflects the object light beam that has passed through the peripheral opening is arranged in a direction that causes the reflected object light beam to approach the object light beam that has passed through the central opening, and each optical path turning mirror is formed integrally with the case. It is characterized in that.

According to the above configuration, the subject luminous flux that has passed through the plurality of openings is reflected by the optical path turning mirror, and the subject luminous flux that has passed through the peripheral opening approaches the subject luminous flux that has passed through the central opening. Since it is possible to dispose it on a small area, and since the opening and the optical path turning mirror are integrally provided in the case accommodating the distance measuring sensor, it is possible to reduce the size of this case.

"Examples of the Invention" The present invention will be described below with reference to illustrated examples. FIG. 1 is a perspective view showing an internal structure of a distance measuring module to which the focus detection optical system of the present invention is applied, and FIG. 2 is a perspective view showing a schematic optical path when the distance measuring module is mounted on a camera. Since this embodiment is applied to the conventional single-lens reflex camera shown in FIG. 3, the camera will be described with reference to FIG.

A part of the subject light flux that enters the photographing lens 10 as an imaging optical system and exits from the final imaging lens L passes through the main mirror 12 and is reflected downward by the sub-mirror 14 to form a light shielding plate.
It is guided to the distance measuring module 20 from the opening 19 of 18.

On the upper surface of the resin case 22 of the distance measuring module 20, openings 22A, 22B, and 22C corresponding to the distance measuring zones 15A, 15B, and 15C in the finder field of view 15 are opened.
The subject luminous flux measured from 2A, 22B and 22C enters the inside of the distance measuring module 20.

Optical path turning mirrors 24A, 24B, and 24C are provided below the openings 22A, 22B, and 22C, respectively. Each of the optical path turning mirrors 24A, 24B, and 24C reflects the incident light beam toward the distance measuring sensor 26. The distance measuring sensor 26 is composed of three CCD line sensors 26A, 26B, 26C formed on one chip. Each of the line sensors 26A, 26B, 26C has a light receiving surface equivalent to the film surface F, Each ranging zone 15A, 15B,
It is arranged in the position and orientation corresponding to 15C.

The central optical path turning mirror 24B reflects the incident light beam toward the line sensor 26B in parallel with the optical axis, and the peripheral optical path turning mirrors 24A and 24C transmit the incident light beam to the central apertures, respectively.
The light is reflected and deflected in the direction approaching the subject light beam passing through 22B, that is, toward the peripheral line sensors 26A and 26C.

In the optical path turning mirrors 24A, 24B, and 24C, the substrate is molded integrally with the resin case 22 of the distance measuring module 20, and the reflection surface is formed by vapor deposition of metal.

A separator lens 28 (28A, 28A, 28B, 28B, 28B) is provided between the optical path refracting mirror 24 and the line sensors 26A, 26B, 26C.
C, 28C). Each ranging zone 15A, 15B, 15
The subject luminous flux of C is divided into two by the separator lens 28, and the corresponding line sensors 26A, 26B, 26
Imaged on C. Although not shown, a mask for cutting harmful light flux is provided on the front surface of the separator lens 28.

In the single-lens reflex camera equipped with the distance measuring module 20, the luminous flux in the distance measuring zones 15A, 15B, 15C proceeds as follows. Most of the luminous flux incident from the taking lens 10 is reflected upward by the main mirror 12 and
Is partially transmitted through the half mirror portion. The subject light flux transmitted through the half mirror is reflected downward by the sub-mirror 16 and passes through the aperture 19 of the light-shielding plate 18 to the distance measuring module.
Guided to 20.

Of the luminous fluxes guided to the distance measuring module 20, the luminous fluxes in the ranging zones 15A, 15B, and 15C respectively have apertures 22.
Enter the distance measurement module 20 from A, 22B and 22C. And
The luminous flux of the subject in the central ranging zone 15B entered from the central aperture 22B is reflected by the optical path turning mirror 24B at a substantially right angle in parallel (horizontal direction) with the optical axis X. The subject luminous fluxes in the peripheral distance measuring zones 15A and 15C entering from the peripheral apertures 22A and 22C are deflected in a substantially horizontal direction by the optical path turning mirrors 24A and 24C, respectively, and in a direction approaching the object luminous flux in the central distance measuring zone 15B. Reflected.

The subject luminous flux in the ranging zones 15A, 15B, 15C reflected by the optical path turning mirrors 24A, 24B, 24C is divided into two by a separator lens 28, respectively, and the line sensors 26A, 26B, 26
Imaged on C. The electric charges stored in the line sensors 26A, 26B, 26C are read out by predetermined control means. Then, it is A / D converted and subjected to predetermined arithmetic processing,
A defocus value is determined.

As described above, in the present embodiment, the subject light flux in the surrounding distance measurement zones 15A and 15C is deflected in the optical axis direction by the reflection of the optical path turning mirrors 24A and 24C, and the image forming positions on the distance measurement sensor 26 are mutually shifted. Since they are close to each other, optical problems such as aberration do not occur even if the deflection angle is increased. Therefore, it is possible to collect the luminous fluxes of the peripheral distance measuring zones 15A and 15C in a small range on a short optical path, and it is possible to form the line sensors 26A, 26B and 26C on one chip. That is, the distance measuring sensor 26 can be made smaller, and the optical path length in the distance measuring module 20 can be shortened, so that the distance measuring module 20 can be made more compact.

In addition, the optical path turning mirrors 24A, 24B, and 24C are
If it is molded integrally with 2, the manufacture becomes easy and the assembly becomes easy.

Furthermore, if the optical path turning mirror is a concave mirror, the conventional condenser lens functions, so that the condenser lens becomes unnecessary and the distance measuring module can be made more compact.

The number, size, and arrangement of the distance measurement zones are arbitrary, and the optical path turning mirror is changed according to the distance measurement zones.

[Effects of the Invention] As is clear from the above description, according to the focus detection optical system of the first aspect of the present invention, the subject light flux transmitted through the plurality of apertures is reflected by the optical path turning mirror and passes through the peripheral aperture. The measured light flux approaches the light flux passing through the central opening, so that each distance measurement sensor can be placed on a small area, and the opening and the optical path turning mirror are integrated into the case that houses the distance measurement sensor. Because of the provision, the case can be reduced in size.

According to the second aspect of the present invention, the concave mirror functions as a condenser lens, and the condenser lens which has been required conventionally becomes unnecessary, which contributes to a reduction in the number of parts and a reduction in size.

[Brief description of the drawings]

FIG. 1 is a perspective view showing an outline of the internal structure of a distance measuring module to which the distance measuring optical system of the present invention is applied, and FIG. 2 shows a schematic optical path when the distance measuring module is mounted on a single-lens reflex camera. FIG. 3 is a perspective view, FIG. 3 is a diagram showing an outline of a distance measuring optical system of the autofocus single-lens reflex camera, which is taken along an optical axis, FIG. 4 is a diagram showing a positional relationship of a distance measuring zone in a finder visual field, and FIG. FIG. 5 is a plan view showing an optical path of a distance measuring module to which a conventional distance measuring optical system is applied. 10 Photographic lens, 12 Main mirror, 15A, 15B, 15C Distance measuring zone, 16 Submirror, 20 Distance measuring module, 22A, 22B, 22C Opening, 24A, 24B, 24C … Optical path bending mirror, 26A, 26B, 26C …… Line sensor, 28A, 28B, 28C …… separator lens.

──────────────────────────────────────────────────続 き Continued on the front page (58) Fields surveyed (Int.Cl. ⁶ , DB name) G02B 7/28-7/40 G03B 3/00-3/12

Claims (2)

(57) [Claims] 1. A focus detection optical system for transmitting subject images in regions where subject light beams transmitted through a photographing optical system and transmitted through a plurality of distance measuring zones are respectively different from each other on distance measuring sensors corresponding to the respective distance measuring zones. A mirror provided behind the final imaging lens of the imaging optical system, for reflecting a subject light beam emitted from the final imaging lens toward outside the optical path of the imaging optical system; and a subject reflected by the mirror. Of the luminous flux, a central opening through which the subject luminous flux corresponding to the central ranging zone and a peripheral aperture through which the subject luminous flux corresponding to the surrounding ranging zone passes, and each of the above apertures and each of the above ranging sensors A light path turning mirror that reflects the subject light flux passing through each of the openings in the direction of the corresponding distance measurement sensor, and a case that houses the distance measurement sensor. An optical path turning mirror formed on the case and reflecting the object light beam passing through the peripheral opening is arranged in a direction to make the reflected object light beam approach the object light beam passing through the central opening, and each optical path turning mirror is A focus detection optical system, which is formed integrally with the case. 2. The focus detecting optical system according to claim 1, wherein
Each of the optical path turning mirrors formed integrally with the case is a concave mirror.