JPS6060611A - Focus detector of camera - Google Patents

Abstract

PURPOSE:To facilitate assembling and adjustment by arranging a field lens in the optical path between a submirror and the 1st reflecting mirror, and a secondary image forming lens in the optical path between the 1st reflecting mirror and the 2nd reflecting mirror. CONSTITUTION:The 1st reflecting mirror 55 reflects light reflected from the submirror 40 in the optical axis direction of a photographic lens, and the 2nd reflecting mirror 60 reflects light reflected from the 1st reflecting mirror 55 in an upward and a downward direction of a camera. Then, the field lens 54 is arranged in the optical path from the submirror 40 to the 1st reflecting mirror 55 on or near the expected focal plane of the photographic lens, and the secondary image forming lens 58c is arranged in the optical path from the 1st reflecting mirror 55 to the 2nd reflecting mirror 60, so that the elements are arranged effectively in the limited space at the bottom of a mirror box.

Description

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

Conventionally, a focus detection device in a -eye reflex camera converges a light beam that has passed through a photographic lens and then re-images it using a secondary imaging lens. A device has been proposed in which a photoelectric converter is placed in the lens to detect the imaging state of the photographic lens, but both the secondary imaging lens and the photoelectric converter are placed near the pentaprism, which increases the size of the camera. is inviting. In addition, each component is separated and placed independently, making it easy to assemble.
Another disadvantage was that the adjustment was complicated.

SUMMARY OF THE INVENTION In order to eliminate the above-mentioned drawbacks, it is an object of the present invention to provide a camera focus detection device that can be easily and effectively recorded on the bottom of a camera body. The light beam is guided to the bottom of the mirror box by a sub-mirror, and the optical path is formed by a first reflecting mirror that reflects the light beam in the optical axis direction of the photographing lens, and a second reflecting mirror that reflects the light beam in the vertical direction of the mirror box. The direction is changed and the field lens is placed on the photoelectric conversion element, and a field lens is placed at or near the planned focal plane of the photographing lens in the optical path from the sub-mirror to the first reflecting mirror, and the field lens is placed on the first reflecting mirror. The present invention is characterized in that secondary imaging lenses are disposed in each optical path from the mirror to the second reflecting mirror.

Next, the present invention will be explained in detail based on illustrated embodiments.

FIG. 1 is a sectional view of the camera body with the main mirror lowered. The camera body is composed of a bottom cover 22, a back cover 23, a top cover 24, a front cover 25, and a lens mount 26 to which a photographic lens is attached, surrounding a base 21 made of Guicast, for example. 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,
A light receiving element 32 for measuring subject brightness for exposure and a Fresnel lens 33 for focusing light diffused by the matte surface 28a of the focusing plate 28 onto the light receiving element 32 are fixed to the upper part of the eyepiece frame 34. A prism 35 for aligning the peak of distance measurement sensitivity with the center of the photographic screen is attached to the exit surface of the pentaprism 30, facing the Fresnel lens 33.

Further, a pressure bonding plate 36 for holding the photographic filter on 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 a position of the holding frame 39 that comes into contact with the stopper 4z 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. The light incident portion of the sensor block 47 and the first mask 48 is a light-shielding tube 48a having a central axis along the optical path. Sensor block 47 C on the bottom surface
A sensor package 49 with a CD line sensor is attached. Further, below the sensor block 47 is an operating lever 5 that is linked to the automatic aperture lever on the photographing lens side.
0 and a base plate 51 to hold it, and the 8-
50 is rotatably supported by a caulked dowel 52; and 53 is an LED for displaying the focusing state, which is attached to the lower surface of the pentaprism 30.

FIG. 2 shows a cross section of the sensor block 47 and its adjustment mechanism, which sequentially follow the incident optical path: field lens 54, first reflection mirror 55, infrared cut filter 56, image separation prism 57, secondary imaging lenses 58a, 58b. , 58
c and a second reflecting mirror 60 are arranged. Image separation prism 57 and secondary imaging lenses 58a, 58b, 58c
The image separating prism 57 is molded, and the parts other than the effective part of the image separating prism 57 are coated with a 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 package 49. The sensor block 47 is integrally held by a unit holding part 64, and has shaft parts 64a and 64b integrally molded coaxially at both ends of the unit holding part 64, and one shaft part 64a is attached to a bearing plate 65.
The shaft portion 64b at the other end is rotatably supported by the shaft portion 64b.
is rotatably held by an angle 66 that restricts movement in a direction perpendicular to the drawing and a slide plate 67 that restricts movement in a direction parallel to the drawing. Angle 66 is screw 68
The torsion spring 69 is screwed onto the base body 21 by
This presses the sensor block 47 downward from the holding portion 64. By adjusting the positional relationship between the rotation adjusting plate 70 attached to the unit holding part 64 and the bearing plate 65, the sensor block 47 can be adjusted by the shaft parts 64a and 64b.

In the mechanism shown in FIGS. 1 and 2, 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 luminous flux is -y7 of if. ri48→
Second mask 61 → field lens 54 → first reflection mirror 55 → infrared cut filter 56 → image separation prism 57 → secondary imaging lenses 58a, 58b, 58c + second
The structure extends from the reflecting mirror 60 to the third mask 63 to the sensor package 49, and the in-focus state of the photographing lens is detected by detecting the phase difference between the images on the two CCD line sensors of the sensor package 49. I have a lot of power.

Note that the angle of incidence of the light beam passing through the optical axis of the photographic lens onto the sub-mirror 40 is set to be larger than 45 degrees, and in order to prevent the light reflected from the surface of the field lens 54 from entering the photographic film. The first one for ghost prevention.
Since the mask 48 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 it is possible to effectively utilize the space at the bottom of the mirror box. .

FIG. 3 is a perspective view showing only the components of the focus detection optical system, including an infrared cut filter 56, a molded image separation prism 57, and secondary imaging lenses 58a and 58.
8b and 58c are formed into rectangles having an effective field of view in the center, and their upper sides and sides perpendicular to the upper sides are precisely finished in flatness and serve as built-in reference surfaces. Note that 28a is a matte surface of the focusing plate 28, and 71 is a photographic screen on the photographic film. 11. FIG. 4 is an explanatory diagram of the operation of this autofocus optical system, but it differs from the actual arrangement. A diaphragm 72 of a secondary imaging system is provided at the back of the image separation prism 57, and two rectangular openings 72a and 72b are opened at positions narrowing the optical axis. Images 74 and 75 of the apertures 72a and 72b when the aperture 72 is projected by the field lens 54 are present on the exit pupil 73 of the photographing lens. In addition, a shift in the position of the aperture 72,
Alternatively, shifted images 74' and 75' are shown displaced when there is parallel eccentricity or inclination of the optical axis of the photographic lens and the optical axis of the focus detection optical system. The light flux that has passed through the aperture aperture 72a forms a secondary image on the CCD line sensor 76,
The light beam passing through the other diaphragm opening 72b forms a secondary image on the CCD line sensor 77. And this CC
The in-focus state is detected by detecting the phase difference between the output signals of the D-line sensors 76 and 77.

The light beams incident on the aperture apertures 72a and 72b form images 74, .
75, the illuminance levels of the CCD line sensors 76 and 77 will be the same in any case, but in the case of shifted images 74' and 75', the illuminance levels of the CCD line sensors 76 and 77 will be the same.
The illumination level above will be different. If the levels of the two images are different, it becomes impossible to detect a phase difference, which causes distance measurement to be impossible or to cause a distance measurement error. Therefore, the projection position of the entrance pupil of the secondary imaging optical system onto the photographing lens exit pupil 73 needs to be accurate.

As explained above, the camera focus detection device according to the present invention includes a first reflecting mirror that reflects the reflected light from the sub-mirror in the direction of the optical axis of the photographing lens, and a second reflecting mirror that reflects the reflected light from the first reflecting mirror up and down the camera body. It has a second reflecting mirror that reflects in the direction, and a secondary imaging lens is arranged in the optical path between the first and second reflecting mirrors. This allows for efficient placement of the camera body without increasing the size of the camera body. Furthermore, it becomes possible to arrange the sensor and the optical system close to each other, which also has the effect of simplifying assembly and adjustment.

[Brief explanation of the drawing]

The drawings show an embodiment of the camera focus detection device according to the present invention, in which FIG. 1 is a sectional view of the camera body with the main mirror in a lowered state, FIG. 2 is a sectional view of the sensor block, and FIG. 3 is a focus detection optical system. A perspective view of the system, FIG. 954, is an explanatory diagram of the operation of the focus detection mechanism. 27 is a main mirror, 40 is a submirror, 47 is a sensor block, 48 is a first mask for ghost prevention, 4
9 is a sensor package, 54 is a field lens, 55
is a first reflecting mirror, 60 is a second reflecting mirror, 58a
, 58b and 58c are secondary imaging lenses. Continuing from page 1 ■Inventor Keishi Otaka 77 Hata, Shimonoge, Takatsu-ku, Kawasaki City, Canon Co., Ltd. Tamagawa Office

Claims (1)

[Claims] l. A first reflecting mirror that guides the light flux from the photographic lens to the bottom of the mirror box by a submirror and reflects the light flux in the optical axis direction of the photographic lens; The direction of the optical path is changed by the second reflecting mirror to reach the photoelectric conversion element, and the optical path from the sub-mirror to the first reflecting mirror is photographed! ,! A field lens is placed at or near the predetermined focal plane of the solar lens, and
A focus detection device for a camera, characterized in that secondary imaging lenses are arranged in each optical path leading to a reflecting mirror. 2. The focus detection device for a camera according to claim f51, wherein the angle of incidence of the light beam passing through the optical axis of the photographing lens on the submirror is set to be larger than 45 degrees.