JPS6075813A - Automatic focus detector - Google Patents

Abstract

PURPOSE:To enable easy mounting of a device having good accuracy to a camera by disposing a light projecting and photodetecting optical system in places on both sides of a photographing lens where there are allowances in space. CONSTITUTION:A projecting luminous flux L1 emitted from a light emitting element 10 is reflected via a projecting lens 11 by the reflecting surfaces 16a, 16b of a prism member 16 and the reflecting surface 17a in a parallel flat plate member 17 and is primarily imaged near a primary imaging plane F. The light is thereafter projected via a photographing lens 3 onto a subject S by the reflection at a quick return mirror 6. The reflected luminous flux L2 from the subject S traces backward the route roughly similar to the route of the flux L1 and is primarily imaged near the primary imaging plane F and thereafter the light is deflected by the reflecting surface 17a in the member 17 and the reflecting surfaces 18a, 18b of a prism member 18. The deflected light is secondarily imaged near a sensor 14 via a photodetecting lens 13.

Description

[Detailed Description of the Invention] The present invention relates to a so-called active type automatic focus detection device that projects light from the camera side toward a subject and detects the subject distance Nh by receiving the reflected light. It is.

Conventionally, various methods have been considered as this type of active automatic focus detection device, but one method is one that both emits and receives light, as shown in Figures 1 (a) to (C). Some are done through a photographic lens. In this method, as shown in FIG. 1(a), a projection lens 2 for projecting light from a light source 1 has an optical axis o1 eccentrically parallel to the optical axis 0 of a photographing lens 3. Further, the optical axis o2 of the light receiving lens 4 is similarly arranged eccentrically parallel to the optical axis 0. A projected light beam L1 emitted from a light source I is primarily imaged by a projecting lens 2 onto a plane F that is conjugate with the film surface, and then projected onto a subject S via a photographic lens 3. The reflected light beam L2 reflected by the subject S is firstly imaged in the vicinity of a plane F that is conjugate with the film surface via the photographing lens 3, and then a second image is formed in the vicinity of the sensor 5 by the light receiving lens 4. be done.

In such a configuration, when the photographing lens 3 is in focus on the subject S, the projected light flux Llr'r is projected onto the center of the subject S, as shown in FIG. 1(b). The reflected light beam L2 is formed into a secondary image at the center of the sensor 5 by the photographing lens 3 and the light receiving lens 4. On the other hand, in the out-of-focus state, the projected light flux Ll deviates from the center of the subject S, as shown in FIGS. 1(a) and (c), depending on the rear focus and front focus states. to move upward or downward.

Therefore, the offending light flux L2 is transferred to the photographing lens 3 and the light receiving lens 4.
When light is received by the sensor 5, the light receiving position similarly moves up and down. Therefore, for example, a differential type sensor consisting of two light receiving elements 5a and 5b is used as the sensor 5, and the amount of light between the two is compared to determine the reflected light flux L2. By detecting the position of the camera, the in-focus, rear-focus, and front-focus states are determined.

The automatic focus detection device according to the above method emits and receives light both through the photographing lens 3, so there is no parallax and lenses can be replaced, and furthermore, it operates effectively even when the brightness of the subject S is low. It has the following advantages.

However, according to this method, it is necessary to provide both the light emitting means and the light receiving means on the camera side, and it is difficult to miniaturize these due to optical performance and manufacturing issues, so the arrangement requires a considerable amount of space. There is a problem in that it requires space, which is a particular problem when it is used in a -eye reflex camera. The reason for this is that it is difficult to secure a large space for accommodating mechanical, electrical, or optical components within the body of the eye reflex camera.

An object of the present invention is to improve the above-mentioned problems, and to provide an automatic focus detection device in which the projection/reception optical system is arranged so as not to interfere with the various components constituting the camera, and also to avoid deterioration of the focus detection performance. The gist thereof is to provide an automatic focus detection device that projects light onto a subject using a light projecting means, receives the reflected light using a light receiving means, and detects the imaging state of a photographic lens, The light projecting means and the light receiving means are arranged on both sides of the eyepiece, a first reflecting member is below the light projecting means, a second reflecting member is below the pentaprism that guides the photographing light to the eyepiece, A third reflecting member is installed below the light receiving means, and the light emitted from the light projecting means follows an optical path to the subject via the first reflecting member, the second reflecting member, and the photographic lens. The reflected light is characterized by having an optical path in which the reflected light reaches the light receiving means via the photographing lens, the second reflecting member, and the third reflecting member.

The present invention will be explained below based on the embodiments shown in FIG. 2 and below.

Fig. 2 is a side sectional view of an embodiment in which the present invention is applied to a single-lens reflex camera, and Fig. 3 is a perspective view showing the main parts thereof, where 3 is a photographing lens, and 6 is a single-lens reflex camera. Camera fink return mirror, 7 is pentaprism,
8 indicates an eyepiece.

In this embodiment, light emitting elements 1 are provided on both sides of the eyepiece 8.
A light projecting means 12 constituted by a light transmitting lens 11 and a light receiving means 15 constituted by a light receiving lens 13 and a sensor 14 comprising a photoelectric conversion element are respectively arranged. Further, a prism member 16 as a first reflecting member is arranged below the light projecting means 12, and a parallel plate member 17 having a reflective surface 17a inside is arranged below the pentagonal prism 7 as a second reflecting member. A prism member 18, which is a third reflecting member, is arranged below the light receiving means 15. Prism members 16 and 18 each have a reflective surface 16
a, 16b and 18a, 18b. The light emitting element 1o emits light in the infrared region, for example, which is different from the wavelength range that mainly contributes to photographing, in order to distinguish it from the photographing light beam, and correspondingly, the reflective surface 17a inside the parallel plate member 17 emits light. It is a half mirror that reflects only the light in a specific wavelength range emitted by the element lo, and transmits the light beam that mainly contributes to photographing.

Further, a pentaprism 7, an eyepiece lens 8, and a light projecting means 12
, the light receiving means 15, the prism wing 16, 18, and the parallel plate member 17 are housed in a common protective cover 19 to form a single unit, and this unit is structured to be detachable from the camera body. There is.

In the above-described configuration, the projected light flux L1 emitted from the light emitting element 10 passes through the projected lens 11, and is emitted from the prism member 1.
It is reflected by the reflecting surfaces 16a, 16b of 6 and the deviating surface 17a of the parallel plate member 7, and is primarily imaged near the -order imaging plane F. Thereafter, the light is reflected by the tight return mirror 6 and is projected onto the subject S via the photographing lens 3. Then, the reflected light beam L2 reflected from the subject S reversely traces almost the same path as the projected light beam L1 in FIG. 1
7 a and reflective surfaces 18 a and 18 b of the prism member 18 , and passes through the light receiving lens 13 to form a secondary image near the sensor 14 . However, the projected light flux L1 in the photographic lens 3. The reflected light flux L2 passes through different areas 3a and 3b of the photographic lens 3, as shown in FIG.
Prism member 16.18, reflective surface 1 of parallel plate member 17
The angle and shape of 7a and the optical axes of the projecting/receiving lenses 11 and 13 are set.

By arranging the projection/reception optical systems 12.15 on both sides of the eyepiece 8, the area around the eyepiece 8 of the eye reflex camera can be spatially controlled by mechanical, electrical, or optical members. Because it is an area that is not subject to many restrictions, it is possible to secure a relatively large amount of space.
It becomes possible to easily arrange the light emitting/receiving optical systems 12 and 15 here. Also, the projection and reception optical system 12.15
The outer diameter of the light-receiving lenses 11 and 13 can also be made as large as possible, and manufacturing becomes easy. Furthermore, in such an arrangement, the distance between the -order imaging plane F and the light emitting element IO or the sensor 14 can be increased, and the distance between the light emitting and receiving lens 11.1 can be increased.
It becomes possible to lengthen the focal length of 3, and good optical performance can be obtained.

On the other hand, the projection/reception optical system 12.15 is placed around the eyepiece 8.
By centrally arranging the prism members 16, 18, parallel plate member 17, etc., they can be housed together with the pentaprism 7 and the eyepiece 8 in the same protective cover 19 to form a unit. If it is detachably attached to the camera body, it becomes possible to autofocus even a camera that does not have an autofocus function by simply converting only the unit.

As explained above, the automatic focus detection device according to the present invention is
Since the projecting/receiving optical system is arranged in a relatively spacious area on both sides of the photographic lens, a highly accurate device can be easily mounted on the camera.

[Brief explanation of the drawing]

FIGS. 1(a), (b)'t(c) are principle diagrams of an active type automatic focus detection device, FIGS. 21A and below show an embodiment of the automatic focus detection device according to the present invention, and FIG. 3 is a side sectional view thereof, FIG. 3 is a perspective view, and FIG. 4 is an optical path of the projection/reception optical system. Code 3 is a photographing lens, 6 is a quick return mirror, 7
is a pentaprism, 8 is an eyepiece, 10 is a light emitting element,
11 is a light projecting lens, 12 is a light projecting means, 13 is a light receiving lens, 14 is a sensor, 15 is a light receiving means, 16, 18 is a prism member, 17 is a parallel plate member, and 19 is a protective cover. Patent applicant Canon Co., Ltd.

Claims (1)

[Scope of Claims] 1. An automatic focus detection device for projecting light onto a subject using a light projecting means, and detecting the image formation state of a photographic lens by receiving the reflected light by a light receiving means, which The means and light receiving means are placed on both sides of the eyepiece! A first reflecting member is provided below the light projecting means, and a second reflecting member is provided below the pentaprism that guides the W-shaped light to the eyepiece. Jll material, a third reflecting member is installed below the light receiving means,
The light emitted from the light projecting means has an optical path that passes through the first reflecting member, the second reflecting member, and the photographing lens to reach the subject, and the reflected light passes through the photographing lens, the second reflecting member,
An automatic focus detection device characterized by having an optical path that passes through a third reflecting member and reaches a light receiving means. 2. The automatic focus detection device according to claim 1, wherein the light emitted from the light projecting means has a specific wavelength range different from a wavelength range that mainly contributes to photographing. 3. The automatic focus detection device according to claim 2, wherein the second reflecting member mainly reflects only light in the specific wavelength range. 4, the light projecting means, the light receiving means, the first. Automatic focus detection according to claim 1, wherein the second and third reflecting members are housed in a common protective member together with the pentaprism and the eyepiece to form a unit, and are detachable from the camera body. Device.