JPH067220B2 - Camera focus detector - Google Patents

Description

The present invention relates to a focus detection device used in a single-lens reflex camera or the like.

Conventionally, a focus detection device in a single-lens reflex camera has been proposed in which a part of the subject light is bent by a sub-mirror integrally provided with the reflex mirror and introduced into the focus detection optical system. Since the exit surface of the secondary imaging optical system and the photoelectric conversion element surface are opposed to each other, stray light enters the photoelectric conversion element, and the output of the photoelectric conversion element cannot accurately represent the brightness distribution of the subject. It will be possible.

1 to 3 show an example of a conventional focus detection optical system,
1 is a perspective view of the focus detection device, FIG. 2 is a plan view, and FIG.
The figure is an illustration of arrangement in the camera. Here, the light flux transmitted through the taking lens 1 is transmitted through the main mirror 2 and is reflected by the sub mirror 3 obliquely downward and forward of the camera body.
It reaches the reflection mirror 5 through the field lens 4. Then, in the area A in FIG. 2, the light is reflected backward by the reflection mirror 5 to reach the light splitter 6, and the reflection surface 6 of the light splitter 6 is reflected.
Left and right are separated by a and 6b. The light reflected obliquely forward to the right by the reflecting surface 6a passes through the secondary imaging lens 7, is reflected backward by the reflecting mirror 8, and is further reflected by the reflecting mirror 9.
After being reflected to the left by the photoelectric conversion element 11 in the area B in FIG.
You will have an image on top. On the other hand, the light reflected to the left by the reflecting surface 6b is reflected to the front by the prism 12, is reflected to the right by the prism 14 after passing through the secondary imaging lens 13, and is reflected downward again to the prism 15. Then, an image is formed on the photoelectric conversion element 16.

Therefore, when the focus detection optical system and the photoelectric conversion element are arranged in the two areas A and B shown in FIG. 3 and the emission surface of the focus detection optical system and the photoelectric conversion element surface face each other,
A light ray emitted from the periphery of the emission surface, a light ray passing through the outside of the lens, or reflection on the lens surface may enter the photoelectric conversion element. When such stray light is incident, the output of the photoelectric conversion element does not accurately represent the brightness distribution of the subject, which causes erroneous distance measurement or inability to measure distance.

An object of the present invention is to provide a focus detection device for a camera which can prevent an erroneous distance measurement or an inability to measure a distance due to incident stray light generated from a focus detection optical system on a photoelectric conversion element, and can achieve accurate distance measurement. That is, the gist thereof is a re-imaging optical system disposed behind a predetermined image forming surface of the taking lens, and focus detecting means for performing focus detection of the taking lens by an object image formed on the focus detecting surface. In a focus detection device for a camera having a mask, a field lens is provided in the vicinity of the predetermined image forming surface, and a diaphragm having an opening is provided in the vicinity of the re-imaging optical system, and an exit surface of the re-imaging optical system is provided. Another mask for blocking an ineffective light beam is provided on the light incident side of the focus detection surface opposed to the above.

Next, the present invention will be described in detail based on the embodiments shown in FIG.

4 and 5 are sectional views of the camera body, FIG. 4 shows a state in which the main mirror is lowered, and FIG. 5 shows a state in which the main mirror is raised. The camera body is composed of a bottom cover 22, a back cover 23, an upper cover 24, a front cover 25, and a lens mount 26 for joining a photographing lens, which surrounds a base body 21 made of, for example, die casting. In the central mirror box, there is provided a main mirror 27 for selectively guiding the light flux passing through the taking lens to the upper finder optical system and the photographic film surface, and the central portion thereof is a half mirror section. Has become.

In the finder optical system, a focusing plate 28, a condenser lens 29, a pentaprism 30 and eyepieces 31a and 31b are sequentially arranged along the optical path thereof. Also,
A light receiving element 32 for measuring the subject brightness for exposure, and a Fresnel lens 33 for collecting the light diffused by the mat surface 28a of the focusing plate 28 on the light receiving element 32 are fixed to the upper portion of the eyepiece lens frame 34. A prism 35 for adjusting the peak of the distance measuring sensitivity to the center of the photographing screen is attached to the exit surface of the pentaprism 30 so as to face the Fresnel lens 33.

In addition, a pressure plate 36 for holding the photographic film on the focal plane from the back cover 23 inward, a shutter curtain 37 of a focal plane shutter, and an aperture frame 38 are arranged.

The main mirror 27 in the central part of the mirror box is attached to the main mirror holding frame 39, and in the central part of the holding frame 39, the light flux transmitted through the half mirror part is sub-mirror 40.
It has an opening 39a for guiding light to. Holding frame 3
9 is rotatably supported by a rotation shaft 41 and is urged by a spring (not shown) to rotate in the direction of arrow A. This rotation is a stopper slightly projected into the mirror box. 42 regulated within a predetermined range. At the position of the holding frame 39 that abuts the stopper 42, a rubber plate 39b is added to absorb the shock when moving up and down. Further, a sub mirror 40 for guiding the light flux transmitted through the half mirror portion to a focus detection optical system is arranged at the back of the main mirror holding frame 39, and the incident angle θ of the light ray passing through the optical axis of the photographing lens is 45 degrees or less. It has been adjusted to be larger. The sub-mirror 40 is fixed to the sub-mirror holding frame 43, is rotatably supported by the main mirror holding frame 39 by a rotation shaft 44, and is urged to rotate in the arrow B direction by a spring (not shown). . Stopper 4
Reference numeral 5 controls the stop position of the sub-mirror holding frame 43. A cam portion 43a is provided at the end of the sub-mirror holding frame 43 on the rotary shaft 44 side. As the main mirror 27 moves up, the cam portion 43a moves. The guide pin 46 is configured to move along the outer circumference of the guide pin 46.

Below the main mirror 27, a sensor block 47 serving as a secondary imaging optical system for focus detection is arranged via a first mask 48 for preventing ghosts, and a light incident portion of the first mask 48 is provided. Is a light-shielding tube 4 having a central axis along the optical path
8a. CCD on the bottom surface of the sensor block 47
A sensor package 49 having a line sensor is attached. Below the sensor block 47, an operating lever 50 interlocking with an automatic aperture lever on the side of the taking lens.
And a base plate 51 for holding the same are provided, and the operating lever 5
0 is rotatably supported by the caulking dowel 52.
Reference numeral 53 denotes an LED for displaying a focus state, which is attached to the lower surface of the pentaprism 30.

FIG. 6 shows a cross section of the sensor block 47 and its adjusting mechanism. The field lens 54, the reflection mirror 55, the infrared cut filter 56, the image separation prism 57, the secondary imaging lenses 58a, 58b, 58c and A reflection mirror 60 is arranged. Image separation prism 57
The secondary imaging lenses 58a, 58b, and 58c are molded, and light-shielding coating is applied to portions other than the effective portion of the image separation prism 57. A second mask 61 is provided on the front surface of the field lens 54, and is located substantially on the primary image plane. A spacer 62 for adjusting the position of the CCD line sensor in the optical axis direction and a third mask 6 for preventing stray light are provided between the sensor block 47 and the sensor package 49.
3 and 3 are attached. The sensor block 47 is integrally held by the unit holding portion 64, and the shaft portion 64 coaxially integrally formed at both ends of the unit holding portion 64.
a, 64b, one shaft portion 64a is rotatably supported by a bearing plate 65, and the other end shaft portion 64b is parallel to an angle 66 and a drawing for restricting movement in a direction perpendicular to the drawing. It is rotatably held by a slide plate 67 that restricts movement in various directions. The angle 66 is screwed to the base 21 by a screw 68, and the torsion spring 69 presses the sensor block 47 downward from the holding portion 64. Then, by adjusting the positional relationship between the rotation adjusting plate 70 attached to the unit holding portion 64 and the bearing plate 65, the sensor block 47 can be adjusted by the shaft portions 64a and 64b.

In the mechanism shown in FIGS. 4 to 6, in the lowered state of the main mirror 27 of FIG. 4, the speed of light transmitted through the taking lens is guided to the finder optical system by the main mirror 27 and the focus detection optical system. It is divided into what is guided and what is guided. The light flux that has passed through the half mirror portion in the center of the main mirror 27 is reflected by the sub mirror 40 and enters the focus detection optical system arranged at the bottom of the mirror box. The focus detection optical system has a sensor block 47 as shown in FIG.
Is unitized as a unit, and the luminous flux is changed from the first mask 48 to the second mask.
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 is configured to detect the phase difference between the images on the two CCD line sensors of the sensor package 49 to detect the in-focus state of the photographing lens. .

The angle of incidence of light rays passing through the optical axis of the photographing lens on the sub mirror 40 is set to be larger than 45 degrees, and the light reflected on the surface of the field lens 54 is prevented from entering the photographic film. Since the first mask 48 for preventing ghosts 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 to effectively arrange the focus detection optical system. There is.

When the main mirror holding frame 39 moves up against the bias in the direction A shown in FIG. 4 by interlocking with a shutter release (not shown), the guide pin 46 and the cam portion 43a of the sub mirror holding frame 43 abut and slide. As the main mirror holding frame 39 is further raised, the sub mirror holding frame 43 is
And rotate in the opposite direction. When the raising of the main mirror holding frame 39 is completed, the sub mirror 40 is in the folded state shown in FIG. 5, and the photographing light flux 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 holder 39 to prevent reverse light from entering into the mirror box from the finder optical system.

FIG. 7 is a perspective view in which only the components of the focus detection optical system are taken out, and an infrared cut filter 56, a molded image separation prism 57, a secondary imaging lens 58a, 5
8b and 58c are formed in a rectangular shape having an effective visual field portion in the center, and the upper side and the side edges orthogonal to the upper side are precisely finished in flatness and serve as built-in reference planes. Incidentally, 28a is a matte surface of the focusing plate 28, and 71 is a photographing screen on a photographic film.

FIG. 8 is a diagram for explaining the operation of this automatic focusing optical system, but it is different from the actual arrangement. A diaphragm 72 of a secondary imaging system is provided on the back of the image separation prism 57, and two rectangular openings 72a and 72b are opened at positions where the optical axis is narrowed. On the exit pupil 73 of the photographing lens, the aperture 72a when the diaphragm 72 is projected by the field lens 54,
There are images 74, 75 of 72b. In addition, the displacement image 7 in the case where the position of the diaphragm 72 is displaced, or the optical axis of the photographing lens and the optical axis of the focus detection optical system are parallelly decentered or tilted.
4'and 75 'are shown displaced. Aperture opening 72
The light flux that has passed through a forms a secondary image on the CCD line sensor 76, and the light flux that has passed through the other aperture opening 72b forms a secondary image on the CCD line sensor 77.
Then, the in-focus state is detected by detecting the phase difference between the output signals of the CCD line sensors 76 and 77.

The light fluxes that enter the aperture openings 72a and 72b are projected onto the exit pupil 73 of the projection lens by the images 74 of the respective aperture openings.
Since it passes through the range of 75, the illuminance levels of the CCD line sensors 76 and 77 are equal in this case, but the shift image 7
In the case of 4'and 75 ', the illuminance levels on the CCD line sensors 76 and 77 are different. If the levels of the two images are different, it becomes impossible to detect the phase difference, which may cause distance measurement failure or 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, and the processing accuracy of the components is also limited. Therefore, the adjustment mechanism is an essential condition. .

FIG. 9 is an exploded perspective view showing the adjusting mechanism of the sensor block 47. Metal wings 49a and 4a are provided on both sides of the sensor package 49 in which the CCD line sensors 76 and 77 are housed.
9b is provided, and notches 49c and 49d are provided based on the positions of the CCD line sensors 76 and 77, respectively. Sensor positioning pins 64c and 64d, which are integrally formed, are projected downward from the lower portion of the unit holding portion 64 located above the sensor package 49, and these, the cutout portions 62a and 62b of the spurser 62, and the third mask 63. The spacers 62, the third mask 63, and the CCD line sensors 76 and 77 are positioned relative to the unit holding portion 64 in the YZ axis directions by the notch portions 63a and 63b and the notch portions 49c and 49d of the sensor package 49. Further, by changing the plate thickness of the spacer 62, the focus direction of the CCD line sensors 76 and 77 can be adjusted.

Embossing 64e, 64 on both sides of the unit holding portion 64
f is provided, and by inserting the torsion spring 69 in the C direction, the coil portions 69a and 69b drop into the outer circumferences of the embosses 64e and 64f and are coupled. At this time, the connecting portion 69c of the torsion spring 69 is configured to enter the groove 64g of the unit holding portion 64. The slide plate 67 includes a shaft portion 6 of the unit holding portion 64.
4b is provided with a slanted long hole 67a which fits in a rotatable and slidable manner with respect to 4b and long holes 67b and 67c for screwing. The shaft portion 64b is inserted into the slot 67a and the notch 66a of the angle 66 and is held in a rotatable state, and the slide plate 67 is fixed to the base body 21 by fixing screws 78 and 79.

The rotation adjusting plate 70 to be inserted into the shaft portion 64a of the unit holding portion 64 has the unit holding portion 64 in the caulking holes 70a and 70b.
After passing through the caulking dowels 64h and 64i, the caulking dowels 64h and 64i are heat caulked to be fixed to the unit holding portion 64. The rotation adjusting plate 70 is made of a metal plate having a spring property, and the adjusting step portion 70c has an adjusting inclined long hole 70d and a locking hole 70c.
e is provided. The shaft portion 64 is formed by the adjusting elongated hole 65a of the bearing plate 65 and the adjusting elongated hole 70d of the rotation adjusting plate 70.
The rotation position around a is adjusted.

FIG. 10 shows the details of this portion, and is a drawing seen from the direction D in FIG. The shaft portion 64a of the unit holding portion 64 is rotatably inserted into a long hole 65b that is long in the longitudinal direction of the bearing plate 65, and the step portion 70c of the rotation adjusting plate 70 has the bearing plate 6 formed therein.
5 is in contact with the surface 65c. The bearing plate 65 has holes 65d and 65e for screw fixing, and is fixed to the base 21 by screws 82 and 83 via plate bodies 80 and 81 for focus adjustment, respectively.

The sensor block 47 is adjusted in three directions, that is, the X direction shown in FIG. 8, that is, the sensor block 47 in FIG.
Direction of incidence on the Y axis, rotation around the Y axis, that is, rotation around the shaft portions 64a and 64b of the unit holding portion 64 in FIG. 9, z
It is necessary to rotate about the shaft, that is, to move the shaft portion 64b in FIG. The adjustment in the X direction is performed by changing the plate thickness of the focus adjusting plates 80 and 81. Rotation adjustment around the Y-axis is performed by the mechanism shown in FIG.
By inserting the adjustment tool 84 into the maximum width portion of the slit formed by the adjustment long hole 70d of the rotation adjustment plate 70 and the adjustment inclined long hole 65a of the bearing plate 65, and moving in the E or F direction, the sensor The block 47 has shaft portions 64a, 6a.
Since it rotates about 4b, the screw 85 is inserted and fixed in the lock hole 65f of the bearing plate 65 and the lock hole 70e of the rotation adjusting plate 70 after the adjustment is completed. Rotational adjustment around the Z axis is performed by moving the slide plate 67, in which the shaft portion 64b is inserted into the inclined elongated hole 67a, in the G direction. At this time, the shaft portion 64b of the unit holding portion 64 has the angle 6
Since it is inserted in the notch 66a facing the H direction of 6,
Move only in the direction. Since the torsion spring 69 is in the charged state, the sensor block 47 is always pressed downward. Therefore, the long hole 65b provided to enable the movement of the shaft portion 64b in the H direction does not cause a backlash. Further, since the rotation adjustment plate 70 is a metal plate having a spring property, the rotation adjustment about the Y axis and the rotation adjustment about the Z axis can be independently performed without interfering with each other.

As described above, the focus detection device for a camera according to the present invention has a mask and a field lens near the predetermined image plane,
By providing a diaphragm with an aperture near the re-imaging optical system and a mask on the light incident side of the focus detection surface, light rays emitted from the periphery of the lens, light rays that have passed through the lens, or light reflected by the lens surface, etc. It is possible to prevent stray light from entering the photoelectric conversion element, and there is no risk of malfunction such as erroneous distance measurement or inability to measure distance.

[Brief description of drawings]

FIG. 1 is a perspective view showing a conventional focus detection optical system, FIG. 2 is a plan view, FIG. 3 is an explanatory view of an arrangement state in a camera, and FIG. 4 and the following are examples of a focus detection device for a camera according to the present invention. FIG. 4 is a cross-sectional view of the camera main body in the main mirror lowered state, FIG. 5 is a cross-sectional view of the camera main body in the main mirror raised state, FIG. 6 is a cross-sectional view of the sensor block, and FIG. FIG. 8 is a perspective view of the detection optical system, FIG. 8 is an operation explanatory view of the focus detection mechanism, FIG. 9 is an exploded perspective view of an adjustment mechanism of the sensor block, and FIG. 10 is a rear view of the sensor block. Reference numeral 27 is a main mirror, 40 is a sub-mirror, 47 is a sensor block, 49 is a sensor package, 54 is a field lens, 55 and 60 are reflection mirrors, 57 is an image separation prism, 58a, 58b and 58c are secondary imaging lenses, 6
3 is a stray light prevention mask.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Akira Hiramatsu 770 Shimonoge, Takatsu-ku, Kawasaki-shi, Kanagawa Canon Inc. Tamagawa Business Office (72) Keishi Otaka 770 Shimonoge, Takatsu-ku, Kawasaki-shi, Kanagawa Canon Inc. Company Tamagawa Plant (56) References Actually open Sho 58-38128 (JP, U) Actually open 60-36615 (JP, U)

Claims (1)

[Claims] 1. A camera having a re-imaging optical system arranged behind a predetermined image forming surface of a taking lens, and focus detecting means for detecting the focus of the taking lens based on a subject image formed on the focus detecting surface. In the focus detection device, a mask and a field lens are provided in the vicinity of the predetermined image forming surface, a diaphragm having an opening is provided in the vicinity of the re-imaging optical system, and the aperture is opposed to the exit surface of the re-imaging optical system. A focus detection device for a camera, wherein another mask for blocking an ineffective light beam is provided on the light incident side of the focus detection surface.