JPS6060615A - Focus detector of camera - Google Patents

Abstract

PURPOSE:To prevent harmful reflected light by arranging a field lens on or near a surface conjugate to a film surface and providing a light shield cylinder between a submirror and the field lens. CONSTITUTION:When a main mirror holding frame 39 is elevated by the interlock with shutter release, a guide pin 46 abuts and slides on the cam part 43a of a submirror holding frame 43, which rotates in the opposite direction of a direction B as the main mirror holding frame 39 is further elevated. When the elevation of the main mirror holding frame 39 is completed, the submirror 40 is folded and photographic luminous flux reaches shutter curtains 37 without any eclipse and at this time, the submirror holding frame 43 prevents reverse incident light from a finder optical system into a mirror box. When a film is exposed, harmful reflected light of luminous flux passed through the photographic lens which is reflected by the field lens 54 to reach the film surface is cut off by the light shield cylinder 48a and never reaches the film surface.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a focus detection device used in a -eye reflex camera or the like.

A focus detection device in which a focus detection optical system and a photoelectric converter are placed at the bottom of a camera's mirror box has been proposed, but since the light beam incidence surface of the focus detection device is exposed at the bottom of the mirror box, the photographing lens cannot be used. It is known that the transmitted light is reflected by this light flux incident surface and has an adverse effect on the film surface.

In order to improve this drawback, some proposals have been made to provide a shielding member that shields the light beam incidence surface and to block the light beam incidence surface in conjunction with the vertical movement of the main mirror, but the shielding member is installed in the limited space at the bottom of the mirror box. Since the members must be arranged, the structure becomes complicated, making it difficult to manufacture and causing an increase in cost.

The purpose of the present invention is to prevent the harmful reflected light mentioned above.
The purpose is to provide a focus detection device for a camera that has a shielding tube with a simple configuration instead of a complicated shielding device. In a focus detection device that detects the focusing state of a photographing lens from a change in the position of the lens, a field lens is disposed on or near a plane conjugate to the film plane, and a light-shielding tube is provided between the submirror and the field lens. This is a characteristic feature.

Next, the present invention will be explained in detail based on the embodiments shown in FIG. 1 and below.

FIGS. 1 and 2 are cross-sectional views of the camera body. FIG. 1 shows the main mirror in a lowered state, and FIG. 2 shows it in a raised state. The camera body is composed of a bottom cover 22 surrounding a base 21 made of Guicast, for example, a back cover 23, an upper cover 24, a front cover 25, and a lens mount 26 to which a photographic lens is attached. A main mirror 27 is provided in the mirror box at the center to selectively guide the light beam that has passed through the photographic lens to the finder optical system and the photographic film surface above, and the center part is a half mirror. It becomes.

In the finder optical system, a focusing plate 28, a condenser lens 29, a pentaprism 30, and eyepiece lenses 31a and 31b are sequentially arranged along the optical path. Also,
Light receiving element 3 for measuring subject brightness for exposure 1'i)
2, and a Fresnel lens 33 for condensing the light diffused by the matte surface 28a of the focusing plate 28 onto the light receiving element 32, is fixed to the upper part of the eyepiece frame 34, and the peak of the distance measurement sensitivity is set on the photographing screen. Prism 3 to align with the center of
5 is a pentaprism 30 facing the Fresnel lens 33
The emission surface of the beam is investigated.

Further, a pressure bonding plate 36 for holding the photographic film in the focal plane, a shutter curtain 37 of the focal plane shutter, and an aperture frame 38 are arranged inwardly from the back cover 23.

The main mirror 27 at the center of the mirror box is attached to a main mirror holding frame 39, and the light beam that has passed through a part of the half mirror is attached to a sub-mirror 40 at the center of the holding frame 39.
It has an opening 39a for guiding light. Holding frame 3
9 is rotatably supported by a rotating shaft 41, and is urged to rotate in the direction of arrow A by a spring (not shown), but this rotation is prevented by a stopper slightly protruding inside the mirror box. 42 within a predetermined range. A rubber plate 39b is added at the position of the holding frame 39 that comes into contact with the stopper 42 to absorb shocks during lifting and lowering. Further, a sub-mirror 40 is arranged at the back of the main mirror holding frame 39 to guide the light beam that has passed through a part of the half-mirror to the focus detection optical system. is also adjusted to be larger. This sub-mirror 40 is fixed to a sub-mirror holding frame 43, rotatably supported on the main mirror holding frame 39 by a rotating shaft 44, and is urged to rotate in the direction of arrow B by a spring (not shown). . Stopper 4
Reference numeral 5 regulates the stopping position of the sub-mirror holding frame 43, and a cam portion 43a is provided at the end of the sub-mirror holding frame 43 on the rotating shaft 44 side. It is configured to move along the outer circumference of the guide pin 46.

A sensor block 47 serving as a secondary imaging optical system for focus detection is arranged below the main mirror 27 via a first mask 48 for preventing ghosts, and the light entrance part of this first mask 48 is arranged below the main mirror 27 . is a light-shielding tube 4 having a central axis along the optical path.
It is said to be 8a. A sensor package 49 having a CCD line sensor is attached to the lower surface of the sensor block 47. Further, below the sensor block 47, an operating lever 50 that interlocks with the automatic diaphragm lever on the photographing lens side and a base plate 51 that holds this are provided, and the operating lever 50 is rotatably supported by a caulking dowel 52. ing. Note that 53 is an LED for displaying the focus state;
It is attached to the lower surface of the pentaprism 30.

FIG. 3 shows a cross section of the sensor block 47 and its adjustment mechanism, which sequentially includes the field lens 54, reflection mirror 55, infrared cut filter 56, image separation prism 57, secondary imaging lenses 58a, 58b, 58c, and the like according to the incident optical path. A reflecting mirror 60 is arranged. Image separation prism 57
The secondary imaging lenses 58a, 58b, and 58c are molded, and the parts other than the effective parts of the image separation prism 57 are coated with light-shielding coating. A second mask 61 is provided in front of the field lens 54, and is located on the horizontal image plane. A spacer 62 for adjusting the position of the CCD line sensor in the optical axis direction and a third mask 63 for preventing stray light are installed between the sensor block 47 and the sensor bundle 49. The sensor block 47 is integrally held by a unit holding part 64, and a shaft part 64a integrally molded coaxially is provided at both ends of the unit holding part ffR64.
, 64b, one shaft portion 64a is rotatably supported by a bearing plate 65, and the other end shaft portion 64b has an angle 66 that restricts movement in a direction perpendicular to the drawing, and an angle 66 parallel to the drawing. It is rotatably held by a slide plate 67 that restricts directional movement. The angle 66 is screwed onto the base body 21 with screws 68, and a torsion spring 69 presses the sensor block 47 downward from the holding portion 64. By adjusting the positional relationship between the rotation adjustment plate 70 and the bearing plate 65, which are held in the unit holding part 64, the sensor block 47 can be adjusted by the shaft parts 64a and 64b.

In the mechanism shown in FIGS. 1 to 3, when the main mirror 27 is in the lowered state in FIG. It is divided into those who are guided and those who are guided. The light beam that has passed through a portion of the half mirror located at the center of the main mirror 27 is reflected by the submirror 40 and enters a focus detection optical system disposed at the bottom of the mirror box. The focus detection optical system includes a sensor block 47 as shown in FIG.
The light beam is transmitted from the first mask 48 to the second mask 48.
Mask 61 → Field lens 54 → Reflection mirror 55
→ Infrared cut filter 56 → Image separation prism 57 → Secondary imaging lenses 58a, 58b, 58c + reflection mirror 60
→ third mask 63 → sensor package 49, and detects the phase difference between the images on the two CCD line sensors of the sensor package 49 to detect the focusing state of the photographing lens. .

It should be noted that the angle of incidence of the light beam passing through the optical axis of the photographic lens on the sub-mirror 40 is set to be larger than 45 degrees, and that the light reflected on the surface of the field lens 54 is prevented from entering the photographic film. Since the first mask 48 having a light-shielding tube 48a for ghost prevention is attached, it is possible to arrange the opening of the focus detection optical system near the aperture frame 38 at the bottom of the mirror box, and the focus detection optical system An effective layout is planned.

When the main mirror holding frame 39 rises against the bias in the direction A shown in FIG. 3 in conjunction with a shirt release (not shown), the guide pin 46 and the cam portion 43a of the sub-mirror holding frame 43 come into contact and slide. However, as the main mirror holding frame 39 further rises, the sub mirror holding frame 43 moves to B in FIG.
rotate in the opposite direction. When the main mirror holding frame 39 is completely raised, the sub-mirror 40 is in the folded state shown in FIG. 4, and the photographing light beam reaches the shutter curtain 37 without being eclipsed. At this time, the sub mirror holding frame 43
closes the opening 39a of the main mirror holding frame 39 to prevent light from entering the mirror box from the finder optical system.

During film exposure in the state shown in FIG. 2, among the light beams that have passed through the photographic lens, harmful reflected light that is reflected by the field lens 54 and reaches the film surface is canted by the light-shielding tube 48a as shown by the arrow in FIG. and never reaches the film surface.

As explained above, according to the camera focus detection device according to the present invention, a light-shielding tube is arranged on the bottom of the mirror box between the sub-mirror and the field lens. It is possible to prevent harmful reflected light.

[Brief explanation of drawings]

The drawings show an embodiment of the camera focus detection device according to the present invention, in which FIG. 1 is a cross-sectional view of the camera body with the main mirror in a lowered state, FIG. 2 is a cross-sectional view of the camera body with the main mirror in a raised state, and FIG. The figure is a cross-sectional view of the sensor block. 27 is a main mirror, 40 is a submirror, 47 is a sensor block, 48 is a first mask for ghost prevention, 4
8a is a light-shielding tube, and 49 is a sensor package. Patent applicant Canon Co., Ltd.

Claims (1)

[Claims] 1. In a focus detection device that guides the light flux from the photographic lens to the bottom of the mirror box by a submirror and detects the in-focus state of the photographic lens from a change in the position of the image relative to the photoelectric conversion element, 1. A focus detection device for a camera, characterized in that a field lens is disposed on or near the sub-mirror, and a light-shielding tube is provided between the sub-mirror and the field lens. 2. The focus detection device for a camera according to claim 1, wherein the light-shielding tube is disposed at an opening on the surface of the mirror box 11. 3. The focus detection device for a camera according to claim 1, wherein the light-shielding tube is arranged at a position that blocks light reflected in the direction of the film surface by the field lens.