JPH11149036A - Autofocusing camera - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an autofocusing camera by which excellent autofocusing accuracy is obtained by a simple constitution. SOLUTION: This autofocusing camera possesses a light emitting element member 1 radiating an object with irradiating light, a focal state detecting element 5 detecting the focal state of the image of the object on a film surface based on reflected light from the object and a diffraction optical element 4 to diffract the reflected light from the object in the direction of the focal state detecting element.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a camera having an autofocus (hereinafter, referred to as "AF") module for focusing, and more particularly to a focal plane shutter camera.

[0002]

2. Description of the Related Art Conventionally, in a range finder camera or the like, a so-called external light type AF module is used, and an absolute distance from a camera to a subject is calculated based on a principle of triangulation. Then, the focusing lens is driven to a predetermined position based on the calculated absolute distance,
A method for performing AF is adopted.

[0003]

However, in an external light AF module used in a conventional focal plane shutter camera such as a range finder, the in-focus state of a subject image on a surface corresponding to a film surface is directly determined. It does not detect. Therefore, AF accuracy is low,
There is a problem that a so-called focus is likely to be a slightly blurred photograph.

In order to guide light from a subject transmitted through a photographic lens to an AF module, it is necessary to provide a mirror like a single-lens reflex camera. Therefore, a mechanical problem such as securing a space for a mirror also occurs.

SUMMARY OF THE INVENTION The present invention has been made in view of the above-described problems, and it is possible to obtain a high AF accuracy by directly detecting an in-focus state on a surface corresponding to a film surface. It is an object of the present invention to provide a camera that can guide light from a subject through a lens to an AF module with a configuration.

[0006]

In order to achieve the above object, an autofocus camera according to the present invention comprises a light emitting element member for irradiating a subject with irradiation light, and the subject on a film surface based on reflected light from the subject. And a diffractive optical element for diffracting the reflected light from the subject in the direction of the focused state detecting element.

With this configuration, in the autofocus camera of the present invention, light is first emitted from a light emitting element member such as a laser diode to the subject. Then, the reflected light that hits the subject and returns in the direction of the camera enters the diffractive optical element in the camera, and is diffracted in the direction of a focus state detecting element such as a line sensor. The focus state detecting element detects the focus state of the subject image on the film surface based on the reflected light from the subject.

Therefore, even in a focal plane shutter camera, for example, by using a diffractive optical element, an external light type AF module for measuring an absolute distance to a subject based on conventional triangulation is not required, and a film surface is not required. The focused state on the corresponding surface can be directly detected. Therefore, highly accurate AF can be realized with a simple configuration.

Further, since a diffractive optical element is used to guide the light from the subject through the photographing lens to the AF module, a mirror such as a single-lens reflex camera is not required, and a high-precision AF is realized by a simple mechanism. You can get a camera to do.

[0010]

Embodiments of the present invention will be described below with reference to the accompanying drawings. FIG. 1 is a diagram showing a configuration of an autofocus camera according to a first embodiment of the present invention.

A light emitting element 1 such as a light emitting diode (LED) or a laser diode irradiates a subject (not shown) with light necessary for distance measurement (AF). The wavelength of the irradiation light is arbitrary, but infrared light is preferable in consideration of the output and the sensitivity of the light receiving element. Light reflected by a subject (not shown) (indicated by a broken line) passes through a photographing lens and passes through a shutter curtain 3.
The light is incident on the diffraction grating 4 provided on the upper photographing lens side.
The reflected light is diffracted in the direction of the distance measuring element 5 by the diffraction grating. Here, it is desirable that the grating interval of the diffraction grating 4 is set so that the wavelength of the light emitted from the light emitting element 1 is efficiently diffracted to the distance measuring element 5. When a diffraction grating is provided on the shutter curtain, the diffraction grating moves together with the shutter curtain at the time of photographing.

FIG. 2 is a conceptual diagram showing the principle of distance measurement (AF). This is a distance measurement method using a so-called shift method, in which light from the subject O that has passed through the photographing lens 2 is pupil-divided and received by the line sensor LS.

In FIG. 2, an optical path which is reflected by the object O, passes through the taking lens 2, and is further diffracted by the diffraction grating 4 is shown on one plane by folding back on a diffraction surface (line).
Here, in the diffraction by the diffraction grating 4, a component for obtaining distance measurement information (in the figure, the density of the reflected light in the vertical direction) is not affected, so that it is similar to the reflection by the mirror of the conventional single-lens reflex camera. You can think.

FIG. 2 shows a "focused" state in which the film surface-equivalent surface F is in focus. When the focus state is deviated, the distance between the subject images on the line sensor LS becomes narrower or wider. Therefore, the driving direction and the driving amount of the focusing lens required for focusing can be calculated based on the interval.

In the case where, for example, infrared light is used as the wavelength of the light emitted from the light emitting element, if there is an object emitting infrared light between the camera and the object, the infrared light reflected from the object and the infrared light Both infrared light from the object will be received. For this reason, a ranging error may occur. In order to reduce the influence of light having the same wavelength as that of the light emitting element, the value obtained when the light emitting element emits light is subtracted from the value obtained when the light emitting element emits light, and this is subtracted. It is preferable to calculate the amount of focus on the basis of this, since an accurate value can be obtained. This calculation method can be similarly applied to a case where the subject itself emits infrared light.

Further, the light emitting element is repeatedly turned on and off,
More accurate distance measurement can be performed by a method of adding the differences of several measurements. However, increasing the number of measurements increases the time required for ranging. Therefore, this method is more suitable when the subject is stationary than when the subject is moving (that is, when the subject is moving).

FIG. 3 is a diagram showing an autofocus camera according to a second embodiment of the present invention. Light emitting element 1
Is disposed in the camera so that the irradiation light is emitted through the photographing lens 2. By passing the irradiation light through the photographing lens 2, the irradiation light can be efficiently applied to the subject without being influenced by the focal length of the lens 2. Also,
If irradiation is performed without passing through the lens 2, there is a problem that irradiation light does not efficiently enter the AF module depending on the distance to the subject. However, by passing the irradiation light through the lens 2, this problem is solved, and the distance can be accurately measured to a distant place.

In the autofocus camera according to the present embodiment, the light from the light emitting element 1 is diffracted by a single diffractive optical element (diffraction grating) such as a hologram, and is guided toward the photographing lens 2, and the light is emitted from the subject. The reflected light is diffracted and guided to the distance measuring element 5. Therefore, of the irradiation light from the light emitting element 1, the zero-order light that is not diffracted in the direction of the taking lens 2
The light directly enters the distance measuring element 5. Therefore, the ranging element 5 receives not only the light reflected from the subject but also the light coming directly from the light emitting element 1. Therefore, it is conceivable that the contrast of the image on the line sensor in the distance measuring element 5 decreases, and the accuracy of AF decreases. The camera according to the third embodiment of the present invention has been made in view of the problem of the zero-order light, and FIG. 4 shows its configuration.

As shown in FIG. 4, in the autofocus camera according to the third embodiment, two diffraction gratings 4 of a diffraction optical element for irradiation light and a diffraction optical element for reflected light are used.
4 'is provided. Therefore, the diffraction angle of the irradiation light from the light emitting element 1 and the diffraction angle of the light reflected from the subject can be set independently. For this reason, the light diffracted by the irradiation light diffraction grating is not diffracted in the direction of the distance measuring element 5, so that the influence of the zero-order light can be removed, and more accurate distance measurement can be performed. .

[0020]

As described above, according to the present invention, since the in-focus state on the surface corresponding to the film surface can be detected, the present invention is applied to a conventional focal plane shutter camera such as a range finder. Unlike a conventional external light type AF module, high AF accuracy can be obtained. In addition, since a diffractive optical element is used to guide the light from the subject through the photographing lens to the AF module, a mirror such as a single-lens reflex camera is not required, and a camera that performs high-precision AF with a simple mechanism. Can be obtained.

[Brief description of the drawings]

FIG. 1 is a diagram showing a configuration of an autofocus camera according to a first embodiment of the present invention.

FIG. 2 is a diagram illustrating an AF method.

FIG. 3 is a diagram illustrating a configuration of an autofocus camera according to a second embodiment of the present invention.

FIG. 4 is a diagram illustrating a configuration of an autofocus camera according to a third embodiment of the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Light-emitting element 2 Photographing lens 3 Shutter 4, 4 'Diffractive optical element 5 Distance measuring element F Film equivalent surface FL Field lens CL Condenser lens

Claims (6)

[Claims] 1. A light emitting element member for irradiating a subject with irradiation light; a focus state detection element for detecting a focus state of an image of the subject on a film surface based on reflected light from the subject; And a diffractive optical element for diffracting the reflected light in the direction of the in-focus state detecting element. 2. The auto-focus camera according to claim 1, wherein the irradiating light is transmitted through a photographic lens of the auto-focus camera to irradiate the subject. 3. The autofocus camera according to claim 1, further comprising another diffractive optical element for diffracting irradiation light from the light emitting element member toward the subject. 4. The autofocus camera according to claim 1, wherein said diffractive optical element is a hologram. 5. The autofocus according to claim 1, wherein the autofocus camera has a focal plane shutter, and wherein the diffractive optical element is disposed on the focal plane shutter. camera. 6. The in-focus state detecting element according to claim 1, wherein the in-focus state detecting element detects the in-focus state based on a light flux of the reflected light that has passed through the taking lens of the autofocus camera. The autofocus camera according to 3, 4, or 5.